Patent Grant
6914558
This invention relates to a variable directivity antenna apparatus having directivity which is variable, and to a receiver system using such variable directivity antenna apparatus.
A variable directivity antenna is used to selectively receive radio waves coming from different directions. An example of such variable directivity antennas is disclosed in Japanese Utility Model Publication No. SHO 63-38574 (Y2) published on Oct. 12, 1988, assigned to the same assignee of the present application.
According to the technique disclosed in this UM publication, first and second antennas are disposed at right angles to each other in the same horizontal plane. The first and second antennas may be dipole antennas or folded-dipole antennas. A signal received by the first antenna is coupled through a first variable attenuator to a combiner, to which a signal received by the second antenna is also coupled through a second variable attenuator. The amounts of attenuation provided by the first and second variable attenuators are varied to change the directivity of the variable directivity antenna.
Because the directivity can be rotated, the variable directivity antenna of the Japanese UM publication can select and receive only a desired one of radio waves coming to the antenna from various directions. This antenna, however, has an 8-shaped directivity pattern, it also receives a radio wave coming to it from the direction opposite to the direction of the desired radio wave, and, therefore, its F/B ratio is low.
Therefore, an object of the present invention is to provide a small-sized antenna apparatus with an improved F/B ratio, which can selectively and satisfactorily receive radio waves coming to the antenna apparatus from different, two directions. Another object of the present invention is to provide a receiver system with a variable directivity antenna apparatus which can selectively and satisfactorily receive radio waves coming to the antenna from various directions.
A variable directivity antenna apparatus according to the present invention includes first and second antennas, which are adapted to receive radio waves in a first frequency band, e.g. a UHF band. Each of the first and second antennas exhibits an 8-shaped directivity pattern extending along a line perpendicular to the length of the antenna. The first and second antennas are disposed in parallel with each other with a spacing therebetween is approximately equal to or smaller than a quarter wavelength of the first frequency band. The variable directivity antenna apparatus also includes third and fourth antennas for receiving radio waves in the first frequency band. Each of the third and fourth antennas, too, exhibits an 8-chaped directivity pattern extending along a line perpendicular to the length of the antenna. The third and fourth antennas are disposed in parallel with each other with the same spacing therebetween as the one between the first and second antennas and perpendicularly to the first and second antennas. The first through fourth antennas may be, for example, dipole antennas or folded-dipole antennas.
Because of the spacing therebetween, the signal resulting from reception by the first antenna (hereinafter referred to the reception signal from the first antenna) of a radio wave coming from a first direction perpendicular to the first and second antennas, in which the radio wave arrives at the second antenna earlier than the first antenna, is provided with a phase delay relative to the reception signal resulting from reception by the second antenna (hereinafter referred to as the reception signal from the second antenna) of the radio wave coming from the first direction. On the other hand, the reception signal from the second antenna of a radio wave coming from an opposite, second direction perpendicular to the first and second antennas, in which the radio wave arrives at the first antenna earlier than the second antenna, is provided with a phase delay relative to the reception signal from the first antenna of the radio wave coming from the second direction. Similarly, the signal resulting from reception by the third antenna (hereinafter referred to as the reception signal from the third antenna) of a radio wave coming from a third direction perpendicular to the third and fourth antennas, in which the radio wave arrives at the fourth antenna earlier than the third antenna, is provided with a phase delay relative to the signal resulting from reception by the fourth antenna (hereinafter referred to as the reception signal from the fourth antenna) of the radio wave coming from the third direction. On the other hand, the reception signal from the fourth antenna of a radio wave coming from an opposite, fourth direction perpendicular to the third and fourth antennas, in which the radio wave arrives at the third antenna earlier than the fourth antenna, is provided with a phase delay relative to the reception signal from the third antenna of the radio wave coming from the fourth direction.
First phase adjusting means adjusts the phases of the reception signals from the first and second antennas and combines them into a combined signal having a selected one of a first directivity state corresponding to a directivity oriented to the first direction and a second directivity state corresponding to a directivity oriented to the second direction. For example, if the phase of one of the reception signals from the first and second antennas in the first frequency band coming from the second direction is adjusted such that the signals can be in substantially opposite phase, the combined signal can have the first directivity state because the reception signals resulting from receiving a radio wave from the second direction, when combined, are cancelled out, while the reception signals resulting from receiving a radio wave from the first direction, when combined, provide a resultant component. On the other hand, if the phase of one of the reception signals from the first and second antennas in the first frequency band coming from the first direction is adjusted such that the signals can be in substantially opposite phase, the combined signal can have the second directivity state because the reception signals resulting from receiving a radio wave from the first direction, when combined, are cancelled out, while the reception signals resulting from receiving a radio wave from the second direction, when combined, provide a resultant component.
Second phase adjusting means adjusts the phases of the reception signals from the third and fourth antennas and combines them into a combined signal having a selected one of a third directivity state corresponding to a directivity oriented to the third direction and a fourth directivity state corresponding to a directivity oriented to the fourth direction. For example, if the phase of one of the reception signals from the third and fourth antennas in the first frequency band coming from the fourth direction is adjusted such that the signals can be in substantially opposite phase, the combined signal can have the third directivity state because the reception signals resulting from receiving a radio wave from the fourth direction, when combined, are cancelled out, while the reception signals resulting from receiving a radio wave from the third direction, when combined, produce a resultant component. On the other hand, if the phase of one of the reception signals from the third and fourth antennas in the first frequency band coming from the third direction is adjusted such that the signals can be in substantially opposite phase, the combined signal can have the fourth directivity state because the reception signals resulting from receiving a radio wave from the third direction, when combined, are cancelled out, while the reception signals resulting from receiving a radio wave from the fourth direction, when combined, produce a resultant component.
Signal combining means adjusts the level of the first phase adjusting means output signal in the first or second directivity state and the level of the second phase adjusting means output signal in the third or fourth directivity state, and, then, combines the level-adjusted signals, so that the resulting output signal from the signal combining means can have directivity oriented to a selected one of the first through fourth directions and directions between adjacent ones of the first through fourth directions. The variable directivity antenna can exhibit directivity oriented to a selected one of sixteen (16) directions, for example.
The first phase adjusting means may operate to shift the phase of one of the reception signals from the first and second antennas by a predetermined amount in order to provide the combined, output signal with the first directivity state, and to shift the phase of the other one of the reception signals of the first and second antennas by the predetermined amount in order to provide the combined, output signal with the second directivity state. The second phase adjusting means may operate to shift the phase of one of the reception signals from the third and fourth antennas by a predetermined amount in order to provide the combined, output signal with the third directivity state, and to shift the phase of the other one of the reception signals from the third and fourth antennas by the predetermined amount in order to provide the combined, output signal with the fourth directivity state.
With the above-described arrangement of a variable directivity antenna apparatus according to the present invention, reception signals from the first and second antennas, which essentially exhibit an 8-shaped directivity pattern, are combined in the first phase adjusting means to exhibit directivity oriented to the first or second direction, before it is combined, in the signal combining means, with reception signals from the third and fourth antennas, which essentially exhibit an 8-shaped directivity pattern, combined in the second phase adjusting means to exhibit directivity oriented to the third or fourth direction. In this manner, the directivity of the variable directivity antenna apparatus is directed to a desired direction. Accordingly, the antenna apparatus can have an improved F/B ratio over a wide frequency band. One of the reception signals from the first and second antennas is phase-shifted by the first phase adjusting means, and one of the reception signals of the third and fourth antennas is phase-shifted by the second phase adjusting means. Since the amounts of phase shift provided by the first and second phase adjusting means are equal, the combining of the signals in the signal combining means is not affected by any phase difference, which leads no disturbance in directivity when the antenna directivity is directed in any directions other than the first through fourth directions.
The first phase adjusting means may include first combining means for combining reception signals from the first and second antennas, a first phase shifter, and first switching means for coupling the reception signal from the second antenna through the first phase shifter to the first combining means when the reception signal from the first antenna is being coupled to the first combining means and for coupling the reception signal from the first antenna through the first phase shifter to the first combining means when the reception signal from the second antenna is being coupled to the first combining means. In this case, the second phase adjusting means includes second combining means for combining reception signals of the third and fourth antennas, a second phase shifter providing the same amount of phase-shift as the first phase shifter, and second switching means for coupling the reception signal from the fourth antenna through the second phase shifter to the second combining means when the reception signal from the third antenna is being coupled to the second combining means and for coupling the reception signal from the third antenna through the second phase shifter to the second combining means when the reception signal from the fourth antenna is being coupled to the second combining means.
Alternatively, the first phase adjusting means may include third and fourth combining means having their outputs selectively outputted, the first phase shifter, and third switching means. The third switching means operates to cause the reception signal from the first antenna to be coupled to the third combining means and to cause the reception signal from the second antenna to be coupled to the third combining means through the first phase shifter when the output signal of the third combining means is selected. When the output signal of the fourth combining means is selected, the third switching means operates to cause the reception signal from the second antenna to be coupled to the fourth combining means and to cause the reception signal from the first antenna to be coupled through the first phase shifter to the fourth combining means. When the first phase adjusting means has such arrangement, the second phase adjusting means includes fifth and sixth combining means having their outputs selectively outputted, the second phase shifter providing the same amount of phase shift as the first phase shifter, and fourth switching means. The fourth switching means operates to cause the reception signal from the third antenna to be coupled to the fifth combining means and to cause the reception signal from the fourth antenna to be coupled to the fifth combining means through the second phase shifter when the output signal of the fifth combining means is selected. When the output signal of the sixth combining means is selected, the fourth switching means operates to cause the reception signal from the fourth antenna to be coupled to the sixth combining means and to cause the reception signal from the fifth antenna to be coupled through the second phase shifter to the sixth combining means.
With the above-described arrangement, the same, first phase shift means can be used for placing the antenna apparatus in either of the first and second directivity states, and, similarly, the same, second phase shift means can be used for placing the antenna apparatus in either third and fourth directivity states, which results in reduction of manufacturing costs.
The reception signals of the first and second antennas may be amplified by first and second amplifiers before being applied to the first phase adjusting means, with the reception signals of the third and fourth antennas amplified by third and fourth amplifiers before being applied to the second phase adjusting means. With this arrangement, the amplified signals are level-adjusted in the signal combining means, which results in improvement of the S/N ratio of the signal outputted from the signal combining means.
The first, second, third and fourth antennas may be dipole antennas. In this case, first and second extension elements are adapted to be connected to respective opposite outer ends of the first antenna through first and second switch elements, respectively. Third and fourth extension elements are adapted to be connected to respective opposite outer ends of the second antenna through third and fourth switch elements, respectively. Also, fifth and sixth extension elements are adapted to be connected to respective opposite outer ends of the third antenna through fifth and sixth switch elements, respectively, and seventh and eighth extension elements are adapted to be connected to respective opposite outer ends of the fourth antenna through seventh and eighth switch elements, respectively. The first and third switch elements are located on corresponding outer sides of the first and second antennas. For example, the first switch element is disposed at the outer end of one of the two dipole antenna elements of the first antenna corresponding to the outer end of the dipole element of the second antenna at which the third switch element is disposed. Similarly, the second and fourth switch elements are located on the corresponding, other outer sides of the first and second antennas. The fifth and seventh switch elements are located on corresponding outer sides of the third and fourth antennas, and the sixth and eighth switch elements are located on the corresponding, other outer sides of the third and fourth antennas. When the output signal of the signal combining means exhibits directivity oriented to a direction other than the first through fourth directions, either the first and third switch elements or the second and fourth switch elements, of the first and second antennas, are closed, and either the fifth and seventh switch elements or the sixth and eighth switch elements, of the third and fourth antennas, are closed.
With this arrangement, there is no disturbance in the directional characteristic of the variable directivity antenna apparatus when it exhibits directivity in a direction other than the first through fourth directions. Because the first and second antennas are spaced from each other by a distance smaller than a quarter of the wavelength of the first frequency band, the directivity exhibited is sharp in the first or second direction. For the same reason, the directivity exhibited by the third and fourth antennas is sharp in the third or fourth direction. Because of such sharp directivities, disturbances tend to occur in composite directivity in a direction other than the first through fourth directions, which results from combining the reception signals from the first and second antennas with the reception signals from the third and fourth antennas. In order to eliminate or reduce such disadvantage, desired one or more pairs of the extension elements located on the same sides of the respective antenna pairs are connected to the corresponding one or more pairs of the antennas. This causes the composite directivity of the first and second antennas to deviate from the first or second direction and causes the composite directivity of the third and fourth antennas to deviate from the third or fourth direction. After that the deviated composite directivity providing signals are further combined to reduce disturbance in the directivity.
The first antenna and the first and second extension elements, when connected, may be adapted to be capable of receiving radio waves in a second frequency band lower than the first frequency band, with the second antenna and the third and fourth extension elements, when connected, being adapted to be capable of receiving radio waves in the second frequency band. Also, when the fifth and sixth extension elements are connected to the third antenna, the third antenna can receive radio waves in the second frequency band. Similarly, the fourth antenna and the seventh and eighth extension elements, when connected, are adapted to be capable of receiving radio waves in the second frequency band. With this arrangement, the antenna apparatus can exhibit variable directivity for radio waves in the second frequency band.
Fifth and sixth antennas exhibiting an 8-shaped directivity may be additionally disposed in parallel between the first and second antennas and between the third and fourth antennas, respectively, for receiving radio waves in a third frequency band lower than the second frequency band. When receiving a radio wave in the third frequency band, reception signals of the fifth and sixth antennas are coupled to the signal combining means. With this arrangement, radio waves in the third frequency band, too, can be received with variable directivity.
The signal combining means may include first level adjusting means to which the output signal of the first phase adjusting means is applied, second level adjusting means to which the output of the second phase adjusting means is applied, and means for combing output signals of the first and second level adjusting means. In this case, each of the first and second level adjusting means is arranged to selectively assume a first factor state, a second factor state and a blocking state. In the first factor state, the signal inputted to each level adjusting means is outputted at a level proportional to a first factor. In the second factor state, the input signal is outputted at a level proportional to a second factor smaller than the first factor. In the blocking state, the input signal is blocked. The first and second level adjusting means are selectively placed in a first state in which the first level adjusting means is in the first factor state and the second level adjusting means is in the blocking state, in a second state in which the first level adjusting means is in the first factor state and the second level adjusting means is in the second factor state, in a third state in which both the first and second level adjusting means are in the second factor state, in a fourth state in which the first level adjusting means is in the second factor state and the second level adjusting means is in the first factor state, and in a fifth state in which the first level adjusting means is in the blocking state and the second level adjusting means is in the first factor state. This enables the antenna apparatus to exhibit directivity selectively in the sixteen directions.
The control in the first and second phase adjusting means may be provided in response to a control signal, and the level control in the signal combining means is also provided in response to the control signal. The variable directivity antenna apparatus is provided with control means, which provides the control signals. The control means prepares the control signals by demodulating a modulation signal, which is provided by a modulator through a transmission line through which the output signal of the signal combining means is transmitted to the receiver. The modulator produces the modulation signal by modulating a carrier with the control signal provided by predetermined control signal generating means. The modulator may employ any one of various modulating systems, including, but not limited to, phase-shift keying modulation, frequency-shift keying modulation, and amplitude-shift keying modulation, but the amplitude-shift keying modulation is desirous in view of simplicity of circuit arrangement.
A signal from another antenna may be combined with the output signal of the signal combining means. The composite signal is transmitted to the receiver through the transmission line.
The receiver may include a generator generating the control signals, reception state detecting means for detecting the reception state of a desired radio wave, and receiver control means for varying, when the reception state becomes unacceptable, the control signals to be supplied to the modulator from the control signal generator until the reception state as detected by the reception state detecting means becomes acceptable and supplies the control signals providing such acceptable reception state to the modulator.
Referring to
The variable directivity antenna apparatus 500 has a main body 1, as shown in
Referring also to
The first dipole antenna 4a includes dipole antenna elements 8a and 10a disposed on the same straight line. The antenna elements 8a and 10a have the same length, which may be equal to, for example, about a quarter of a predetermined wavelength λ in the UHF band. The antenna element 8a includes two conductors 12a and 14a disposed in parallel with each other as shown in FIG. 3. Although not shown, a plurality of capacitors are disposed and connected between the conductors 12a and 14a at predetermined intervals to place the conductors 12a and 14a at the same potential in terms of high frequency. The dipole antenna element 10a, too, has two parallel conductors 18a and 20a, which are connected to each other by a plurality of capacitors (not shown) disposed between them at predetermined intervals so that they can be at the same potential in terms of high frequency. The total length of the first dipole antenna 4a including the dipole antenna elements 8a and 10a is about a half of the wavelength λ.
A first extension element 24a is disposed outward of the outer end of the dipole antenna element 8a, being aligned with the dipole antenna element 8a. Similarly a second extension element 26a is disposed outward of the outer end of the dipole antenna element 10a, being aligned with the dipole antenna element 10a. The sum of the length of the dipole antenna element 8a and the length of the extension element 24a is smaller than about a quarter of a predetermined wavelength in the VHF band, e.g. about a quarter of a predetermined wavelength λ in the VHFH band, and is not so long that the outer end of the extension element 24a would extend out of the main body 1. The sum length of the dipole antenna element 10a and the length of the extension element 26a is similarly selected. The dipole antenna elements 8a and 10a and the extension elements 24a and 26a may be formed on a single printed circuit board.
A switch element, for example, a PIN diode 28a is connected between the conductor 14a of the dipole antenna element 8a and the extension element 24a (FIG. 3). In the illustrated example, the anode of the PIN diode 28a is connected to the extension element 24a, while the cathode is connected to the conductor 14a. A DC path and switch element, e.g. a coil 30a, is connected between the conductor 12a and the extension element 24a. When a DC voltage is applied between the conductors 12a and 14a in such a polarity that the conductor 12a is positive and the conductor 14a is negative, the PIN diode 28a is rendered conductive. Then, the extension element 24aand the conductors 12a and 14a are electrically connected together. The conductors 12a and 14a are connected together in terms of high frequency. Thus, a parallel combination of the conductors 12a and 14a connected in parallel in terms of high frequency is connected in series with the extension element 24a. Without the DC voltage, the PIN diode 28a is nonconductive, the extension element 24a is disconnected in terms of high frequency from the parallel combination of the conductors 12a and 14a.
The value of the coil 30a is selected such that it can make the extension element 24a substantially decoupled from the conductors 12a and 14a at frequencies in the UHF band, make the extension element 24asubstantially coupled to the conductors 12a and 14a at frequencies in the VHF band, and make the electrical sum length of the dipole antenna element 8a and the extension element 24a become about one quarter of the predetermined length λ of the VHF band. Then, even when the PIN diode 28a is nonconductive at frequencies of the VHF band, the extension element 24a and the conductors 12a and 14a are substantially connected together. The coil 30a functions as a loading coil in the VHFH band, which can make the sum length of the extension element 24a and the conductors 12a, 14a shorter than would be required if the coil 30a were not used.
Similarly, a PIN diode 34a and a coil 38a are connected between the extension element 26a and the conductors 18a and 20a of the dipole antenna element 10a. The length of the extension element 26a is selected in the same manner as the extension element 24a, and the value of the coil 30a is selected in the same manner as the coil 30a.
The second dipole antenna 6a is constructed similar to the first dipole antenna 4a, and includes dipole antenna elements 42a and 44a. The dipole elements 42a and 44a include a conductor pair 46a and 48a and a conductor pair 50a and 52a, respectively. The conductors 46a and 48a are connected together in terms of high frequency by means of a plurality of capacitors (not shown), and, also, the conductors 50a and 52a are connected together in terms of high frequency by means of a plurality of capacitors (not shown). Disposed outward of the outer ends of the dipole antenna elements 42a and 44a are extension elements 58a and 60a, respectively. A PIN diode 62a and a coil 66a are connected between the dipole antenna element 42a and the extension element 58a. Similarly, a PIN diode 70a and a coil 74a are connected between the dipole antenna element 44a and the extension element 60a. The lengths of the extension elements 58a and 60a are determined in the same manner as the extension elements 24a and 26a. The values of the coils 66a and 74a are selected in the same manner as the coils 30a and 38a.
The second dipole antenna 6a is disposed in the main body 1 and in parallel with the first dipole antenna 4a with a spacing therebetween smaller than a quarter of the wavelength λ of the UHF band.
The inner ends of the dipole antenna elements 8a and 10a of the first dipole antenna 4a are used as feed points. The inner ends of the conductors 14a and 20a are connected to a matching device, e.g. a balun 78a(FIG. 3). Similarly, the inner ends of the dipole antenna elements 42a and 44a of the second dipole antenna 6a are used as feed points, and the inner ends of the conductors 46a and 50a are connected to a matching device, e.g. a balun 80a. The baluns 78a and 80a are arranged such that the output of the balun 78a is 180°-out-of-phase with the output of the balun 80a.
High-frequency blocking coils 82a and 84a are connected in series between the conductors 12a and 48a, and a parallel combination of capacitors 86a and 88a is connected between the junction of the coils 82a and 84a and a point of reference potential, e.g. a point of ground potential. To the junction between the coils 82a and 84a, also connected is a voltage supply terminal 90ato which a positive voltage for rendering the PIN diodes 28a and 62a conductive is applied. Similarly, a series combination of high-frequency blocking coils 92a and 94a is connected between the conductors 18a and 52a, and a parallel combination of capacitors 96a and 98a is connected between the junction of the coils 92a and 94a and a point of ground potential. A voltage supply terminal 100a is connected at the junction of the coils 92a and 94a, for application of a positive voltage thereto for rendering the PIN diodes 34a and 70a conductive. The baluns 78a and 80a has grounded portions, and, therefore, when the positive voltage is applied to the voltage supply terminal 90a or 100a, current will flow from the baluns 78a and 80a to the ground potential point, and, the PIN diodes 28a and 62a or the PIN diodes 34a and 70a are made conductive.
A second antenna device 2b for receiving both radio waves in the first frequency band and radio waves in the second frequency band has substantially the same configuration as the first antenna device 2a. Therefore, the same reference numerals are used for components similar to the components of the first antenna device 2a, with a suffix “b” substituted for the suffix “a”, and no detailed description is given. The second first and second frequency receiving antenna device 2b is disposed within the main body 1. The second antenna device 2b is spaced vertically from the first antenna device 2a, as shown in
As shown in
The dipole antenna elements 402a includes plural elements, e.g. three elements 406a, 408a and 410a, which are disposed on a straight line with a minute spacing disposed between each other. The lengths of the elements 406a, 408a and 410a are so selected that any of them function as none of a director, a reflector or a radiator for the UHF band receiving dipole antennas 4a and 6a when they receive UHF band waves. The lengths may be, for example, from about 0.15 λ to about 0.3 λ. The outer end of the element 410a extends out of the main body 1. For that purpose, the element 410a is a metal sheet housed in a plastic case, but it may be in the form of pipe formed of aluminum or stainless steel. The other elements 406a and 408a are located within the main body 1, and, therefore, they can be formed on a printed circuit board, but they may be in the form of metal sheet.
The elements 406a and 408a are connected to each other by a coil 412a, and the elements 408a and 410a are connected together by a coil 414a. The coils 412a and 414a have such inductance that they can function as extension coils to make the sum length of the elements closer to a quarter of the wavelength of a radio wave at a predetermined frequency in the VHFL band, and can exhibit such high impedance in the UHF and VHFH bands as to electrically separate the elements 406a, 408a and 410a from each other.
The dipole antenna element 404a also includes elements 416a, 418a and 420a, which are equivalent to the elements of the dipole antenna element 402a. Coils 422a and 424a are connected between the elements 416a and 418a and between the elements 418a and 420a, respectively. The inductance values of the coils 422a and 424a are equal to those of the coils 412a and 414a, respectively.
A VHFL band receiving dipole antenna 400b is disposed between the first and second dipole antennas 4b and 6b of the first and second frequency band receiving antenna device 2b (FIG. 1). The configuration and arrangement of the dipole antenna 400b is the same as that of the dipole antenna 400a except that it is disposed orthogonal to the dipole antenna 400a with its center coinciding with that of the dipole antenna 400a. Accordingly, the same reference numerals with a suffix “b” substituted for the suffix “a” as used for the components of the dipole antenna 400a are used for the same or equivalent components of the dipole antenna 400b, and no detailed description is made.
The inner ends of the dipole antenna elements 402a an 404a are used as feed points, and coupled to a matching device, e.g. a balun 426a. Similarly, the inner ends of the dipole antenna elements 402b and 404b, acting as feed points, are coupled to a matching device, e.g. a balun 426b.
The VHFL band receiving dipole antenna 400a exhibits an 8-shaped directivity pattern extending in a direction perpendicular to its length direction. Let four directions, forward, backward, leftward and right ward directions, be considered such that the side of the antenna apparatus 500 to which the dipole antenna 4a is located nearer is the forward side, the side to which the dipole antenna 6a is located nearer is the backward side, the side to which the dipole antenna 4b is located nearer is the right side, and the side to which the dipole antenna 6b is located nearer is the left side of the antenna. Then, the VHFL band dipole antenna 400a exhibits an 8-shaped directivity along the forward-backward direction, while the VHFL band dipole antenna 400b exhibits an 8-shaped directivity along the left-right direction.
Referring to
Similarly, the output signal of the high-pass filter 102a is either amplified or not amplified in the variable amplifier 108a before being applied to the phase adjusting circuit 104a. The circuit arrangement of the variable amplifier 108a is the same as that of the variable amplifier 106a. Therefore the same suffixed reference numerals used for the components of the amplifier 106a is attached to the components equivalent to those of the amplifier 108a with an additional suffix “a” attached, and no further detailed description about them is given.
When the reception level of a UHF or VHFH band radio wave to be received by the variable directivity antenna apparatus described above is low, the output signals of the high-pass filters 101a and 102a are amplified in the variable amplifiers 106a and 108a, respectively. Changeover switches and combiners in the stage succeeding the variable amplifiers 106a and 108a may give attenuation to signals, but the amplification by the amplifiers 106a and 108a can improve the S/N ratio of the antenna apparatus.
The phase adjusting circuit 104a includes first combining means, e.g. a combiner 128a. A first input of the combiner 128a is connected to switching means, e.g. one contact 132a of a changeover switch 130a, which has a movable arm 134a connected to the output of the variable amplifier 106a. The first input of the combiner 128a is also connected to switching means, e.g. to a contact 138a of a changeover switch 136a having its movable arm connected to the output of the variable amplifier 108a.
The other, second input of the combiner 128a is connected to a movable arm 144a of a changeover switch 142a. The switch 142a has a contact 146a connected to a contact 166a of the changeover switch 130a. The switch 142a has another contact 148a connected to a contact 150a of the changeover switch 136a.
A phase shifter, e.g. a fixed phase shifter (FPS) 152a, is connected between the contacts 146a and 148a of the changeover switch 142a. The fixed phase shifter 152a may be formed of, for example, a delay line, more specifically, a coaxial cable or a microstrip line.
The changeover switches 130a, 136a and 142a are formed of semiconductor switches, such as PIN diodes, like band switching sections 464a and 464b which will be described later, and include voltage supply terminals 154a, 156a, 158a, 160a, 162a and 164a, to which a positive voltage may be applied as a control signal.
When a positive voltage is applied to the voltage supply terminal 154a and a positive voltage is not applied to the voltage supply terminal 156a, the movable arm 134a of the changeover switch 130a is connected to the contact 166a, and, when a positive voltage is not applied to the voltage supply terminal 154a and a positive voltage is applied to the voltage supply terminal 156a, the movable arm 134a of the changeover switch 130a is connected to the contact 132a.
When a positive voltage is applied to the voltage supply terminal 158a and a positive voltage is not applied to the voltage supply terminal 160a, the movable arm 140a of the changeover switch 136a is connected to the contact 138a, and, when a positive voltage is not applied to the voltage supply terminal 158a and a positive voltage is applied to the voltage supply terminal 160a, the movable arm 140a of the changeover switch 136a is connected to the contact 150a.
When a positive voltage is applied to the voltage supply terminal 162a and a positive voltage is not applied to the voltage supply terminal 164a, the movable arm 144a of the changeover switch 142a is connected to the contact 146a, and, when a positive voltage is not applied to the voltage supply terminal 162a and a positive voltage is applied to the voltage supply terminal 164a, the movable arm 144a of the changeover switch 142a is connected to the contact 148a.
A voltage A is synchronously applied to the voltage supply terminals 154a, 158a and 164a, and a voltage a is synchronously applied to the voltage supply terminals 156a, 160a and 162a. When the voltage A is positive, the voltage a is not positive, and vice versa.
Thus, when the voltage A is not positive and the voltage a is positive, the movable arm 134a of the changeover switch 130a is connected to the contact 132a, the movable contact 140a of the changeover switch 136a is connected to the contact 150a, and the movable contact 144a of the changeover switch 142a is connected to the contact 146a, as illustrated in FIG. 4. When the voltage A is positive and the voltage a is not positive, the movable arm 134a of the changeover switch 130a is connected to the contact 166a, the movable contact 140a of the changeover switch 136a is connected to the contact 138a, and the movable contact 144a of the changeover switch 142a is connected to the contact 148a.
When the voltage a is positive, the combiner 128a receives an unmodified version of the output signal of the balun 78a, and receives the output signal of the balun 80a through the fixed phase shifter 152a. On the other hand, when the voltage A is positive, the combiner 128a receives the output signal of the balun 78a through the fixed phase shifter 152a and receives an unmodified version of the output signal of the balun 80a.
Now, let it be assumed that the dipole antenna 4a is facing forward of the antenna apparatus 500, while the dipole antenna 6a is facing backward, and that all of the switches are opened. A UHF band radio wave coming to the antenna apparatus from the backward direction is received by the dipole antennas 4a and 6a and causes an output to be developed at each of the baluns 78a and 80a. The reception signal resulting from reception of the radio wave by the forward dipole antenna 4a is delayed by an amount D due to the spacing (less than a quarter of λ) between the dipole antennas 4a and 6a, relative to the reception signal resulting from the reception of the radio wave by the backward dipole antenna 6a. Further, the balun 78a is configured to invert the phase of the signal from the antenna 4a by 180°. More specifically, the output signal of the balun 78a has a phase difference equal to (−λ/2)−D relative to the output signal of the balun 80a. When the voltage a is made positive, the states of the changeover switches 130a, 136a and 142a are switched into the states shown in
The output signal of the balun 80a corresponding to the reception signal from the dipole antenna 6a resulting from receiving a UHF radio wave coming from the forward direction is delayed by D from the reception signal from the dipole antenna 4a of the same radio wave. Due to the arrangement of the balun 78a, the output signal of the balun 78a is in 180°-out-of-phase with the reception signal from the dipole antenna 4a. Thus, the output signal of the balun 78a has a phase difference equal to −λ/2 relative to the reception signal from the dipole antenna 4a, and the output signal of the balun 80a has a phase difference equal to −D relative to the reception signal from the dipole antenna 4a.
When the voltage A is made positive, the movable arm 134a of the switch 130a is brought into contact with the contact 166a, the movable arm 140a of the switch 136a is brought into contact with the contact 138a, and the movable arm 144a of the switch 142a is brought into contact with the contact 148a, so that the output signal of the balun 78a is applied to the combiner 128aafter being delayed by the fixed phase shifter 152a, while the output signal of the balun 80a is applied, as it is, to the combiner 128a. Since the output signal of the balun 78a is delayed by the amount D in the fixed phase shifter 152a, the phase of the output signal of the balun 78a at the combiner 128a is (−λ/2)−D, resulting in a phase difference of −λ/2 relative to the phase −D of the output signal of the balun 80a. This means that the first antenna device 2a has a backward directivity, but not a forward directivity.
As described above, by making the voltage a positive, the antenna device can exhibit a forward directivity, and by making the voltage A positive, the antenna device 2a can exhibit a backward directivity.
As described above, the same fixed phase shifter 152a is used in the phase adjusting circuit 104a for causing the antenna device 2a to exhibit either of a forward directivity and a backward directivity.
The reception signals of the antenna device 2b are processed in the phase adjusting circuit 104b in a manner similar to the one described above for the antenna device 2a so that the antenna device 2b can exhibit either a rightward directivity or a leftward directivity. The structure of the phase adjusting circuit 104b is the same as that of the phase adjusting circuit 104a, the components of the phase adjusting circuit 104b are given the same reference numerals as the ones attached to the corresponding components of the phase adjusting circuit 104a, with a suffix “b” substituted for the suffix “a”, and no further detailed description is made. It should be noted, however, the output signal of the balun 80b is applied to the high-pass filter 101b, and the output signal of the balun 78b is applied to the high-pass filter 102b. The amount of delay provided by the fixed phase shifter 152b is equal to the delay amount provided by the fixed phase shifter 152a.
As shown in
The polarity switching section 430a includes also an inverting circuit, which includes a balun 444a connected through the DC blocking capacitor 434a to the input terminal 432a. The polarity of the signal at the output of the balun 444a is inverted before being applied to another balun 446a. The output of the balun 446a is connected through switching devices, e.g. PIN diodes 448a and 450a, and the DC blocking capacitor 440a, to the output terminal 442a. More specifically, the PIN diode 448a has its cathode connected to the output of the balun 446a and has its anode connected to the anode of the PIN diode 450a, of which the cathode connected to the DC blocking capacitor 440a. Thus, when the PIN diodes 448a and 450a are rendered conductive, the signal applied to the input terminal 432a from the amplifier 428a is inverted in polarity by the baluns 444a and 446a and outputted through the PIN diodes 448a and 450a to the output terminal 442a.
In order to control the PIN diodes 436a and 438a, the junction of their anodes is connected through a resistor 452a to a voltage supply terminal 454a, and, in order to control the PIN diodes 448a and 450a, the junction of their anodes is connected through a resistor 456a to a voltage supply terminal 458a. Also, high-frequency blocking coils 460a and 462a are used so that the PIN diodes 436a, 438a, 448a and 450a become conductive when voltages are supplied to the voltage supply terminals 454a and 458a.
As shown in
When the PIN diodes 472a and 474a are conductive, the VHFH or UHF signal supplied from the combiner 128a to the input terminal 466a appears at the output terminal 470a, whereas, when the PIN diodes 480a and 482a are conductive, the VHFL signal supplied from the band switching section 430a to the input terminal 468a appears at the output terminal 470a.
In the variable directivity antenna 500, as shown in
When the variable bandpass filters 465a and 465b are developing UHF or VHFH signals with forward or backward directivity, a signal with a desired directivity can be obtained by appropriately selecting the directivity of the UHF or VHFH signals provided by the variable bandpass filters 465a and 465b, appropriately adjusting the levels of these signals in the variable attenuators 1136a and 1136b, respectively, and combining them. Similarly, when the band switching sections 464a and 464b are developing VHFL signals with an 8-shaped directivity, the 8-shaped directivity can be oriented in a desired direction by appropriately selecting the polarities of these signals, appropriately adjusting the levels of these signals in the variable attenuators 1136a and 1136b, and combining them.
For that purpose, the variable attenuators 1136a and 1136b are configured such as to provide an amount of attenuation selectable from plural amounts, e.g. three values, namely, 0 dB, 7 dB and infinity (∞). The directivity of the resultant signal can be adjusted to directions at predetermined intervals from the forward direction (0°), for example, in sixteen (16) directions angularly spaced by 22.5°, by adjustment of directivities of the signals, and the adjustment of the amounts of attenuation in the variable attenuators 1136a and 1136b, for the UHF or VHFH band signal, and by the adjustment of polarities and the adjustment of the amounts of attenuation in the variable attenuators 1136a and 1136b for the VHFL band signal.
For that purpose, the variable attenuator 1136a has a series combination of switching devices, e.g. PIN diodes 1140a and 1142a connected between the variable bandpass filter 465a and a combiner 1138 as shown in FIG. 7. The PIN diode 1140a has its cathode connected to the output of the band switching section 464a, and has its anode connected to the anode of the PIN diode 1142a, which has its cathode connected to an input of the combiner 1138. The junction of the anodes of the PIN diodes 1140a and 1142a is connected through a resistor 1144a to a voltage supply terminal 1146a. The cathodes of the PIN diodes 1140a and 1142a are connected respectively through high-frequency blocking coils 1148a and 1150a to a point of reference potential. Accordingly, when a positive voltage is applied to the voltage supply terminal 1146a, the PIN diodes 1140a and 1142a become conductive, so that the signal from the variable filter 465a is coupled to the combiner 1138 without being attenuated.
The variable attenuator 1136a also includes a fixed amount attenuator, e.g. a T-type attenuator 1154a. The attenuator 1154a includes three resistors 1152a and provides an amount of attenuation of 7 dB. A switching device is connected to the input of the attenuator 1154a. For example, the anode of a PIN diode 1156a is connected to the input of the attenuator 1154a. The cathode of the PIN diode 1156a is connected to the cathode of the PIN diode 1140a. A switching device is connected to the output of the attenuator 1154a. More specifically, the anode of a PIN diode 1158a, for example, is connected to the output of the attenuator 1154a. The cathode of the PIN diode 1158a is connected to the cathode of the PIN diode 1142a. The junction of the three resistors 1152a of the T-type attenuator 1154a is connected through a resistor 1160a to a voltage supply terminal 1162a. With this arrangement, when a positive voltage is applied to the voltage supply terminal 1162a, the PIN diodes 1156a and 1158a are rendered conductive, causing the T-type attenuator 1154a to be connected between the variable filter 465a and the combiner 1138, so that the signal from the variable filter 465a is provided with an attenuation of 7 dB.
The variable attenuator 1136a further includes a matching resistor 1164a having an impedance equal to the impedance of the first antenna device 2a. The resistor 1164a has its one end connected to a point of reference potential and has its other end connected through a DC blocking capacitor 1170a to a switching device, e.g. a PIN diode 1166a. The anode of the PIN diode 1166a is connected to the DC blocking capacitor 1170a. The cathode of the PIN diode 1166a is connected to the cathode of the PIN diode 1140a. The anode of the PIN diode 1166a is also connected through a resistor 1172a to a voltage supply terminal 1174a. With this arrangement, when a positive voltage is applied to the voltage supply terminal 1174a, the PIN diode 1166a is rendered conductive, causing the output of the variable filter 465a to be connected through the matching resistor 1164a to a point of reference potential, so that the signal from the variable filter 465a is given attenuation of infinite magnitude.
The variable attenuator 1136b is configured similar to the variable attenuator 1136a, and, therefore, its detailed description is not given. The components of the attenuator 1136b corresponding to those of the attenuator 1136a are given the same reference numerals as given to those of the attenuator 1136a, with an exception that a suffix “b” is substituted for the suffix “a”.
In order to vary the directivity of the variable directivity antenna 500, a control unit 180 is provided as shown in FIG. 7. The control unit 180 operates to produce a control signal by demodulating a modulation signal supplied by a receiver apparatus 518, which will be described later. In accordance with the demodulated control signal, the control unit 180 provides respective voltages, as shown in
Although not shown in
Although not shown in
In receiving any of the UHF, VHFH and VHFL bands, for the azimuth angle of 0°, 22.5° and 45°, the amount of attenuation given by the variable attenuator 1136a is 0 dB, it increases to 7 dB for 67.5° and infinity for 90°, and then decreases to 7 dB and to 0 dB for the angles of 112.5° and 135°. The amount of attenuation given by the attenuator 1136a is maintained to be 0 dB for 157.5°, 180°, 202.5° and 225°. It increases to 7 dB and infinity for 247.5° and 270°, respectively, then, decreases to 7 dB and 0 dB for 292.5° and 315°, respectively, and maintains to be 0 dB for the angle of 337.5°.
On the other hand, the amount of attenuation given by the variable attenuator 1136b is infinity, 7 dB and 0 dB for the azimuth angles of 0°, 22.5° and 45°, respectively. It is 0 db for the angles of 67.5°, 90°, 112.5° and 135°. For the azimuth angles of 157.5° and 180°, the amount of attenuation given by the variable attenuator 1136b is 7 dB and infinity. It is 7 dB and 0 dB for the angles of 202.5° and 225°, and maintains to be 0 dB for the angles of 247.5°, 270°, 292.5°, and 315°. The amount of attenuation for the azimuth angle of 337.5° given by the variable attenuator 1136b is 7 dB. Like this, when the amount of attenuation given by one of the variable attenuators 1136a and 1136b is 0 dB, the amount of attenuation given by the other attenuator increases or decreases.
When receiving VHFH and UHF band signals, the band switching sections 464a and 464b output VHFH or UHF signals, as shown in
Because the spacing between the dipole antennas 4a and 6a of the antenna device 2a and the spacing between the dipole antenna 4b and 6b of the antenna device 2b are smaller than a quarter of λ, in the UHF band, the directivities are shaper than when the spacings are equal to a quarter of λ. It has been found that this causes the antenna directivity is distorted at angular positions other than 0°, 90°, 180 and 270°, if the signals are combined in the above-described manner.
In order to solve this problem, when receiving the UHF band, only one of the two extension elements for each of the dipole antennas 4a and 6a is used to cause the dipole antennas to act as so-called asymmetrically fed dipole antennas exhibiting tilted directivities, which are combined. For that purpose, the voltages I, J, K and L shown in
As described previously, the phase adjusting circuit 104a uses the fixed phase shifter 152a when the combined directivity of the dipole antennas 4a and 6a is oriented forward or backward, and the phase adjusting circuit 104buses the fixed phase shifter 152b when the combined directivity of the dipole antennas 4b and 6b is oriented leftward or rightward. The amounts of phase shift provided by the fixed phase shifters 152a and 152b are equal. Accordingly, the phase shift of the signal resulting from combining the signals from the dipole antennas 4a and 6a in the combiner 1138, and the phase shift of the signal resulting from combining the signals from the dipole antennas 4b and 6b in the combiner 1138 are equal. Accordingly, this also improves distortion of the directivity at angles other than 0°, 90°, 180° and 270°.
The voltages P and Q shown in
As described above, the variable directivity antenna apparatus according to the present invention includes VHFL band dipole antennas 400aand 400b, and, therefore, it can give a sufficiently usable gain in the VHFL region, namely, a region of from 54 MHz to 88 MHz.
As shown in
The satellite broadcast intermediate frequency signal applied to a satellite broadcast intermediate frequency signal input terminal 518a is coupled to a satellite receiver 520, where it is demodulated, and demodulated signal is applied to a television receiver (not shown). The VHF or UHF television broadcast signal applied to a UHF/VHF television broadcast signal input terminal 518b is converted, in a tuner 521, to a television broadcast intermediate frequency signal and demodulated in a demodulating unit 522. Regardless whether the VHF or UHF television broadcast signal is analog or digital, demodulation of the signal is done in the demodulating unit 522, and the signal resulting from the demodulation is applied to the television receiver.
The television broadcast intermediate frequency signal is also applied to a reception state detecting section, e.g. a C/N ratio detecting unit 524, a bit error rate detecting unit 526 and a level detecting unit 528. The C/N ratio detecting unit 524 detects a C/N ratio of the VHF or UHF television broadcast signal, and applies its detection result to receiver apparatus control means, e.g. a CPU 530. The bit error rate detecting unit 526 detects a bit error rate of the VHF or UHF television broadcast signal when it is a digital broadcast signal, and applies the detection result to the CPU 530. The level detecting unit 528 detects a level of the VHF or UHF television broadcast signal and applies the detection result to the CPU 530.
The CPU 530 has a memory 532, and, when it receives an external command to receive a VHF or UHF channel, reads out antenna control data for that channel from the memory 532 and applies it to the antenna control commander 534, which causes the antenna apparatus 500 to exhibit directivity oriented to the direction from which the radio wave for that channel comes to the antenna apparatus 500.
The antenna control data is converted to a PSK (Phase Shift Keying) signal, a FSK (Frequency Shift Keying) signal, or an ASK (Amplitude Shift Keying) signal in the antenna control commander 534.
For example, when converting the antenna control data into an ASK signal, a carrier signal generator 534a in the antenna control commander 534 generates a carrier signal at a frequency different from the reception signal from the variable directivity antenna apparatus 500. The frequency of the carrier signal may be, for example, 10.7 MHz, and is applied to an ASK modulator 534b, to which applied also is the antenna control data from the memory 532 through the CPU 530 and a buffer 534c. The carrier signal is ASK modulated with the antenna control data, and the ASK signal is outputted from the modulator 534b. The ASK signal is outputted through a bandpass filter 534d, which removes undesired signal components, and through the mixer 514 and the DC blocking capacitor 512. It should be noted that for converting the antenna control data to a PSK or FSK signal, the modulator 534b is replaced by a modulator for PSK or FSK modulating the carrier signal with the antenna control data.
The PSK, FSK or ASK signal from the modulator is applied through the mixer 514, the DC blocking capacitor 512, the transmission path 510, the output terminal 500b of the variable directivity antenna apparatus 500, the mixer 509 and a high-frequency blocking coil 542 to the control unit 180, which provides the various controls described above.
If the currently received channel is a digital broadcast channel, the CPU 530 causes the directivity of the variable directivity antenna apparatus 500 to be varied when a selected one of the C/N ratio, the bit error rate and the level, e.g. the C/N ratio, is below a predetermined reference value associated therewith, i.e. when the reception state is unacceptable, and selects the direction where the C/N ratio above the reference value is achieved. The CPU 530, then, substitutes new antenna control data corresponding to that direction for the current antenna control data for receiving the channel being currently received. The renewed antenna control data is stored in the memory 532. Accordingly, the antenna control data to be subsequently used for receiving that channel is the renewed data. If the bit error rate is selected, the renewal of the antenna control data is done when the bit error rate decreases below the associated reference value, and if the signal level is selected the antenna control data renewal is done when the level is below the associated reference value.
If the currently received channel is an analog broadcast channel, the CPU 530 causes the directivity of the antenna apparatus 500 to be adjusted in a manner similar to the above-stated one when a selected one of the C/N ratio and the signal level is below a reference value predetermined therefor, and the antenna control data renewal is done.
A DC voltage, e.g. DC 12 V, is applied from a DC voltage supply 536 in the receiver apparatus 518 to the transmission path 510 via a high-frequency blocking coil 538 in the antenna control commander 534, and from which it is applied to the UHF/VHF band television broadcast signal output terminal 500b of the antenna apparatus 500. This voltage is then applied through the mixer 509 and the high-frequency blocking coil 542 to a voltage supply 540, from which power is supplied to the control unit 180 etc., as shown in FIG. 7.
A variable directivity antenna according to a second embodiment of the present invention has a configuration similar to the antenna apparatus 500 according to the first embodiment, except that phase adjusting circuits 4000a and 4000b shown in
The phase adjusting circuit 4000a includes two mixers 4002a and 4004a, and their outputs are selectively coupled to the band switching section 464a through a changeover switch 4006a.
The changeover switch 4006a has its movable arm 4008a connected to the band switching section 464a, has its contact 4010a connected to the output of the mixer 4002a, and has its another contact 4012a connected to the output of the mixer 4004a.
One input of the mixer 4002a is connected to a contact 4016a of a changeover switch 4014a, which has its movable arm 4018a connected to the variable amplifier 106a. Another contact 4020a of the switch 4014a is connected to a contact 4024a of a changeover switch 4022a. Another contact 4026a of the switch 4022a is connected to another input of the mixer 4002a.
Similarly, a contact 4030a of a changeover switch 4028a is connected to one input of the mixer 4004a. The changeover switch 4028a has its movable arm 4032a connected to the variable amplifier 108a. Another contact 4034a of the switch 4028a is connected to a contact 4038a of a changeover switch 4036a, which has its contact 4040a connected to the other input of the mixer 4004a.
A fixed phase shifter 4046a is connected between a movable arm 4042a of the switch 4022a and a movable arm 4044a of the switch 4036a. The amount of phase shift provided by the fixed phase shifter 4046a is determined in the same manner as the one for the fixed phase shifter 152a of the antenna apparatus according to the first embodiment.
The control unit 180 performs such control that, when the movable arm 4008a of the changeover switch 4006a is in contact with the contact 4010a, the movable arm 4018a of the changeover switch 4014a is in contact with the contact 4016a, the movable arm 4042a of the changeover switch 4022a is in contact with the contact 4026a, the movable arm 4032a of the changeover switch 4028 is in contact with the contact 4034a, and the movable arm 4044a of the changeover switch 4036a is in contact with the contact 4038a. In this state, the output signal of the variable amplifier 106a, i.e. the reception signal form the antenna 4a, is applied, as it is, to the mixer 4002a, whereas the output signal of the variable amplifier 108a, i.e. the reception signal from the antenna 6a, is phase shifted in the fixed phase shifter 4046a before being applied to the mixer 4002a. This causes the combined directivity of the antennas 4a and 6a to be oriented toward the forward direction, as in the first embodiment.
When the movable arm 4008a of the switch 4006a is in contact with the contact 4012a, such control is provided that the movable arm 4018a of the switch 4014a contacts the contact 4020a, the movable arm 4042a of the switch 4022a is in contact with the contact 4024a, the movable contact 4032a of the switch 4028a is in contact with the contact 4030a, and the movable arm 4044a of the switch 4036a is in contact with the contact 4040a. In this state, the output signal of the variable amplifier 106a, i.e. the reception signal from the antenna 4a, is phase shifted in the fixed phase shifter 4046a before it is applied to the mixer 4004a, whereas the output signal of the variable amplifier 108a, i.e. the reception signal from the antenna 6a is applied, as it is, to the mixer 4004a. This causes the combined directivity of the antennas 4a and 6a to be oriented toward the backward direction, as in the first embodiment.
The phase adjusting circuit 4000b has the same configuration as the phase adjusting circuit 4000a, and the combined directivity of the antennas 4b and 6b is oriented toward the leftward or rightward direction. The components of the phase adjusting circuit 4000b same as or similar to those of the phase adjusting circuit 4000a are given the same reference numerals with a suffix “b” substituted for the suffix “a”, and their detailed description is no given.
| Number | Date | Country | Kind |
|---|---|---|---|
| 2004-074448 | Mar 2004 | JP | national |
| Number | Name | Date | Kind |
|---|---|---|---|
| 3806930 | Gobert | Apr 1974 | A |
| 5585803 | Miura et al. | Dec 1996 | A |
| 6809691 | Yamamoto et al. | Oct 2004 | B2 |
| 20040196202 | Shirosaka et al. | Oct 2004 | A1 |
| Number | Date | Country |
|---|---|---|
| SHO63-38574 | Oct 1988 | JP |
