Patent Grant
7742010
The present invention relates to an antenna arrangement and an RF communication terminal incorporating the arrangement.
User terminals for use in mobile communications, e.g. portable radios or telephones or radios carried in vehicles, conventionally support operation in a single RF (radio frequency) band, i.e. the operational band of the system. Such terminals employ an antenna to transform RF signals in an operational frequency band between a bound (conductor guided) form and a radiated form for over-the-air transmission. The antenna comprises a resonator designed to provide electrical resonance in the operational frequency band. Typically, a conventional resonator has a monopole or quarter wavelength linear conductor form.
Different mobile communication systems typically operate in different RF bands. Often the RF bands are in significantly different parts of the frequency spectrum. Some advanced terminals are being designed to provide operation in different systems and/or frequency bands and to provide continuous mobile connectivity whilst switching from one system/frequency band to another. Thus, antenna arrangements are required for use in such terminals which can operate in different frequency bands in one or more communication systems. Such arrangements are required to have a shape and size which is suitably compact and lightweight for user satisfaction.
Antenna arrangements employing resonators of conventional form have been found to be unsuitable for use in supporting communications in multiple systems/frequency bands owing to lack of satisfactory bandwidth. Resonators of unconventional form are known which provide multiple resonances but such resonators do not show sufficient bandwidth and operational efficiency when operated in widely different frequency bands. Furthermore, such resonators generally have a shape and size which does not easily fit into the terminal in a sufficiently compact manner.
According to the present invention in a first aspect there is provided an antenna arrangement as defined in claim 1 of the accompanying claims.
According to the present invention in a second aspect there is provided a terminal for a method of operation in a terminal for radio frequency communications.
Further features of the invention are as defined in the accompanying dependent claims and are disclosed in the embodiments of the invention to be described.
Embodiments of the present invention will now be described by way of example with reference to the accompanying drawings, in which:
In embodiments of the invention to be described, an antenna arrangement for use in an RF communication terminal includes a plurality of resonators formed from a plurality of conducting wires, the resonators being operable to provide radio frequency resonances in at least two different operational frequency bands, the wires being mutually adjacent and at least three of the wires having different lengths, and a plurality of radio frequency feed channels each being operably connected to an associated one of the resonators to deliver an RF signal between that resonator and an associated radio.
A controller 111 controls selection of the radios 103 to 109 that are to be operational. Thus, the controller 111 may select any one or more of the radios 103 to 109 to be operational at any one time. Furthermore, the controller 111 selects whether each of the radios 103 to 109 is in a transmit mode, a receive mode or optionally a standby mode.
The radio 103 is operably connected via an RF feed channel 113 optionally including a control device 114 (whose operation is described later) to an associated resonator (antenna) 123. The radio 103, the channel 113 and the resonator 123 provide operation in a first frequency band B1. Similarly, the radio 105 is operably connected via an RF feed channel 115 optionally including a control device 116 (whose operation is described later) to an associated resonator 125. The radio 105, the channel 115 and the resonator 125 provide operation in a second frequency band B2. Similarly, the radio 107 is operably connected via an RF feed channel 117 optionally including a control device 118 (whose operation is described later) to an associated resonator 127. The radio 107, the channel 117 and the resonator 127 provide operation in a third frequency band B3. Similarly, the radio 109 is operably connected via an RF feed channel 119 optionally including a control device 120 (whose operation is described later) to an associated resonator 129. The radio 109, the channel 119 and the resonator 129 provide operation in a fourth frequency band B4. Thus, each of the resonators 123 to 129 is designed to resonate in one of the operational frequency bands B1 to B4. The resonators 123 to 129 are formed from wires and have physical properties which differ to give resonance in these required frequency bands. Examples of suitable forms of the resonators 123 to 129 and of antenna arrangements including the resonators 123 to 129 are described later.
Each of the resonators 123 to 129 when connected to an associated one of the radios 103 to 109 which is in a transmit mode converts a bound RF signal produced by the associated one of the radios 103 to 109 and delivered by an associated one of the feed channels 113 to 119 to a radiated RF form for over-the-air transmission to another terminal (not shown). Each of the resonators 123 to 129 when connected to an associated one of the radios 103 to 109 which is in a receive mode converts a received RF signal in radiated form to bound RF form for delivery via an associated one of the feed channels 113 to 119 to its associated one of the radios 103 to 109 for down-conversion and demodulation by the associated radio.
Examples of typical commercially significant frequency ranges which may be included in the operational frequency bands B1 to B4 are given in Table 1 as follows:
Where the radio 109 and the resonator 129 operate in the GPS frequency range, the radio 109 may operate in a receive mode only, to receive GPS (Global Positioning System) signals.
In alternative terminals embodying the invention, it may be necessary to employ only two or three of the radios 103 to 109 and their associated feed channels and resonators to provide operation in all of the frequency ranges specified in Table 1. Illustrative embodiments of the invention described later to provide operation in the ranges specified employ variously four, three and two radios.
As noted earlier, each of the feed channels 113 to 119 in the terminal 100 of
The selected impedance applied by each of the control devices 114 to 120 for out of band frequencies may be an impedance which is one of two types. A first type of impedance which may be selected and applied is equivalent to an open circuit of the feed channel (in which the particular control device is included) as seen from the one of the resonators 123 to 129 associated with that feed channel. Alternatively, a second type of impedance which may be selected and applied may be an impedance equivalent to a short circuit to ground of the feed channel (in which the particular control device is included) as seen from the one of the resonators 123 to 129 associated with that feed channel.
RF systems, generally, are designed to have a target impedance, e.g. fifty (50) ohms, in their operating range. Thus all components used in such a system, including band pass filters, are designed to have the target impedance in their operating frequency band or range. However, in general, the characteristic impedance of a band pass filter is not constant with frequency. Often the impedance is not specified for out of band operation of a band pass filter. However, in the case of the terminal 100, the out of band impedance provided by each of the control devices 114 to 120 is selected to be an impedance of the first or second type referred to above.
Thus, for a given frequency which is within the operating band of one particular resonator of the resonators 123 to 129, but not of the other resonators, the control device which is associated with that one resonator provides a band pass filter to pass frequencies in the operating frequency band of that one particular resonator. At the same time, each of the control devices of the feed channels associated with the other resonators, which are out of band relative to the operational band of the one particular resonator, applies at the given frequency one of the selected impedances described above. The particular impedance selected, i.e. of the first or second type, depends on how the wires of the resonators are selected to interact for a given operational frequency band. Examples of the use of selected impedances of the first and second types are given later.
Whilst the one particular resonator is operational in its own frequency band, any one or more of the other resonators which has at that frequency band an impedance of the first or second type for out of band frequencies can also be operational at the same time in its own frequency band, so the control device associated with that other resonator provides a filter which passes frequencies in the operational band of that other resonator.
As illustrated later, where the selected impedance of a feed channel comprises a short circuit to ground when the associated resonator is not used as a main operational resonator, the short circuit to ground may be employed beneficially to enhance the bandwidth of another resonator which is operational.
An illustrative schematic generic form 200 of control device for use as each of the control devices 114 to 120 is shown in
Each of the control devices 114 to 120 may additionally include a tuning circuit (not shown) which may be employed in a known way to tune the (resonance of the) resonator 123 to 129 connected to the control device.
Although each of the control devices 114 to 120 have been described as passive devices they could be active devices programmed to give the required operation described above. In this case, the control devices could be combined as a single control device programmed to give the required operation described above.
The resonators 123 to 129 (or at least two of them) of the terminal 100, are formed from a plurality of adjacent conducting wires in which at least three of the wires have different sizes. Examples of antenna arrangements embodying the invention including multiple resonators formed from multiple wires having different sizes will be described later. Examples of individual resonators formed from conducting wires which may be used in such arrangements will first be described as follows.
A first form (example) 300 of resonator suitable for use in embodiments of the invention is shown in
In
In
In
In
In
In
An antenna arrangement 1000 embodying the invention is shown in
An alternative antenna arrangement 1100 embodying the invention is shown in
In
The effective electrical length of the resonator 1105 is determined by the length of the longer straight wire portion 1112 which is greater than the length of the straight wire 1107 of the resonator 1109. The effective electrical length of the resonator 1103 is determined by the sum of the lengths of the straight wire portions 1102, 1104 and 1110 and the folds 1106 and 1108. That sum is greater than the length of the longer straight wire portion 1112 of the resonator 1103. A specific example, ‘Example 2’, of the antenna arrangement 1100 is described later.
An alternative antenna arrangement 1200 embodying the invention is shown in
In
The resonator 1203 includes a straight conducting wire 1202 which is connected to the feed channel 113 by the feed point 301 and is similar to the monopole form 300 of resonator shown in
The wires (excluding folds and connections) of the resonators in each of the arrangements 1000, 1100 and 1200 may extend parallel to a common axis. They may be mutually configured to be in a single plane in a comb like structure as illustrated in
In
In
The wires 1303 to 1309 forming resonators in the configuration 1300 may be considered to be in the form of a bundle extending respectively from the base 1304, and the wires 1403 to 1413 in the configuration 1400 may be considered to be in the form of a bundle extending from the base 1404. In each case, the wires and the resonators formed by them may be enclosed in an insulating casing (as illustrated later with reference to
The resonators employed in the embodiments of the invention described above may be formed from conducting wires which have a selected wire gauge (diameter) and a selected mutual separation between individual wires. In general, the gauge and the separation are selected according to the operational frequency bands of the radios 103 to 109 associated with the resonators which need to be covered in operation. For operation in the frequency ranges defined in Table 1 earlier, a suitable common gauge for the wires employed in all of the resonators, e.g. resonators 123 to 129, has been found to be in the range 0.5 mm (millimetres) to 1.5 mm, especially 0.8 mm to 1.2 mm, e.g. 1.0 mm. For operation in the frequency ranges defined in Table 1, a suitable minimum separation between the wires of the resonators, e.g. the resonators 123 to 129, has been found to be in the range 2d to 6d, especially 3d to 5d, e.g. 4d, where d is the gauge of the wire used to provide the resonators.
The ends of the wires 1501 which in operation are to connect to the feed channels 113 to 119 (
The circuit board 1505 may carry all of the active operational components of the terminal 100 including radio circuits of the radios 103 to 109 shown in
It is to be noted that enclosure of the wires 1501 forming the resonators in the arrangement 1500 in the insulating casing 1503 attached to the base 1502 gives mechanical and physical protection to the wires and the resonators formed by them. Beneficially, the shape and size of the casing 1503 together with the base 1502 can be similar to that of a conventional single antenna in a mobile station. Thus, the antenna arrangement 1500 including the resonators formed by the bundle of wires 1501 can be compact and does not need to occupy a space greater than that of a single antenna operating at the in the lowest frequency range to be covered.
Terminals and antenna arrangements which are specific examples of embodiments of the invention described above will now be described.
In this example of the terminal 100 shown in
In this example, the impedance of the feed channels is selected in the following way to obtain the combinations listed in Table 2. Resonators which are not operational, i.e. not ON, are normally connected to a feed channel in which the control device 114 to 120 provides an impedance equivalent to an open circuit, i.e. the feed channel is in the OPEN state, unless the resonator has an electrical length which is less than that of an adjacent resonator which is operational, i.e. ON, in which case the feed channel of the resonator which is not operational is in the SHORT state.
When a resonator adjacent to another resonator in the ON state has a shorter electrical length and is in the OPEN state it has only a minor influence on the resonator in the ON state and has no detrimental effect on the operation of that resonator. However, when the same resonator in the OPEN state is adjacent to a longer resonator also in the OPEN state, it is unable to perform properly. By providing a short circuit connection to the longer resonator, the resonator in the ON state is not affected and performs adequately.
Furthermore, in this Example, the following conditions are provided for operation in the VHF range and in the UHF range. In these cases, the feed channel 117 connected to the radio 107 and the resonator 127 is in the SHORT state to beneficially enhance bandwidth in the VHF and UHF ranges. The resonator 127 is connected to ground permanently. This arrangement provides improved resonance frequency bandwidth for both of the UHF and 700/800 frequency ranges.
In Example 1, the geometrical antenna lengths specified in Table 3 as follows have been found to be suitable to give resonances in the frequency ranges specified:
Using the configuration of Example 1, a resonance frequency bandwidth obtained for the VHF frequency range was about 38 MHz. In contrast, prior art antennas typically give a bandwidth of about 15 MHz for the same range. Using the configuration of Example 1, a resonance frequency bandwidth obtained for the UHF frequency range was about 147 MHz. In contrast, prior art antennas typically give a bandwidth of about 50 MHz for the same range. Using the configuration of Example 1, a resonance frequency bandwidth obtained for the 700/800 frequency range was about 124 MHz. In contrast, prior art antennas typically give a bandwidth of about 70 MHz for the same range.
In this example, the radios 103, 105 and 109 of the terminal 100 are employed but the radio 107, the resonator 107 and the feed channel 117 are not employed. The frequency ranges specified in Table 1 are again covered in operation, but the radio 105, feed channel 115 and resonator 125 operate in a single wide band that covers both of the UHF and 700/800 MHz ranges. The resonators 123, 125 and 129 are in an arrangement of the form 1100 shown in
The respective associated control devices 114, 116 and 120 of the feed channels 113, 115 and 119 (
In this Example, only the radio 103, together with its associated feed channel 113 and its associated resonator 123, and the radio 109 together with its associated feed channel 119 and its associated resonator 129, are employed. The radios 105, 107, the feed channels 115 and 117 and the resonators 125 and 127 are not employed. The resonators 123 and 129 are in an arrangement of the form 1200 of
The wire 1202 together with the wire 1211 of the form 1200 provides in this case resonances in the UHF and 700/800 ranges, and the wires 1202, 1207, 1201, and 1205 provide resonance in the VHF range. Beneficially, using the arrangement 1200 in this way reduces the number of active resonator/radio feed channel connections required.
Use of the form 1200 in the configuration of Example 3 has given the following resonances: an operational resonance frequency band of 136 MHz to 165 MHz for the VHF range; an operational resonance frequency band of 380 MHz to 550 MHz for the UHF range; and an operational resonance frequency band of 800 MHz to 870 MHz for the 700/800 range.
The antenna arrangements embodying the invention which have been described above beneficially can provide operation in any or all of the frequency ranges specified in Table 1 (as selected) whilst providing unusually wide band operation in the lower of those ranges, especially the specified VHF range. Such an antenna arrangement may be produced in a compact form which need not be substantially bulkier than a single antenna operating at the VHF range. Furthermore, the arrangement can simplify circuit constructions within a communication terminal in which the arrangement is used, since use of multiplexers to provide RF feeds between multiple radios and a single resonator can be avoided.
Although operation of antenna arrangements embodying the invention has been illustrated by reference to the frequency ranges specified in Table 1 earlier, operation is not limited to such ranges. For example, operation at 2.4 gigahertz (GHz) and/or 4.9 GHz can be provided for use in Bluetooth or WLAN (Wireless Local Area Network) communication systems by using one or more suitably sized resonators as will be apparent to those familiar with the art.
Although the present invention has been described in terms of the embodiments described above, especially with reference to the accompanying drawings, it is not intended to be limited to the specific form described in such embodiments. Rather, the scope of the present invention is limited only by the accompanying claims. In the claims, the terms ‘comprising’ or ‘including’ do not exclude the presence of other integers or steps. Furthermore, although individually listed, a plurality of means, elements or method steps may be implemented by, for example, a single unit or processor. Additionally, although individual features may be included in different claims, these may possibly be advantageously combined, and the inclusion in different claims does not imply that a combination of features is not feasible and/or advantageous. In addition, singular references do not exclude a plurality. Thus references to “a”, “an”, “first”, “second” etc do not preclude a plurality.
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