Patent Application
20130201070
The present invention relates to the field of communications, and more particularly, to loop type antennas, circular polarization, dual polarization and related methods.
The use of satellite communications has increased the demand for circularly polarized antennas and for dual polarization antennas. For instance, many of the satellite transponders in use today carry two programs on the same frequency by using separate polarizations. Thus, single antenna structure may be called upon to simultaneously receive two polarizations, or perhaps to transmit in one polarization and receive in another. The single antenna structure should therefore separate the two polarization channels, to a high degree of isolation.
It is possible to have dual linear or dual circular polarization channel diversity. That is, a frequency may be reused if one channel is vertically polarized and the other horizontally polarized. Or, a frequency can also be reused if one channel uses right hand circular polarization (RHCP) and the other left hand circular polarization (LHCP). Polarization refers to the orientation of the E field in the radiated wave, and if the E field vector rotates in time, the wave is then said to be rotationally or circularly polarized.
An electromagnetic wave has an electric field that varies as a sine wave within a plane coincident with the line of propagation, and the same is true for the magnetic field. The electric and magnetic planes are perpendicular and their intersection is in the line of propagation of the wave. If the electric-field plane does not rotate (about the line of propagation) then the polarization is linear. If, as a function of time, the electric field plane (and therefore the magnetic field plane) rotates, then the polarization is rotational. Rotational polarization is in general elliptical, and if the rotation rate is constant at one complete cycle every wavelength, then the polarization is circular.
The polarization of a transmitted radio wave is determined in general by the antennas shape and the type of current flowing on that shape. In general, antenna types may be classified as to dipoles and loops, based on the divergence or curl of current. The canonical forms of the dipole and loop antennas are the line and circle. Of course there can be hybrid antennas that use both divergence and curl. Preferred antenna shapes are often Euclidian, being simple geometric shapes known for optimization through the ages.
For example, the monopole antenna and the dipole antenna are two common examples of divergence antennas with linear polarization. A helix antenna is a common example of a hybrid divergence and curl antenna with circular polarization. Another example of a circularly polarized antenna is a crossed array of dipoles fed in phase quadrature, e.g. the “Turnstile”. Linear polarization is usually further characterized as either Vertical or Horizontal. Circular Polarization is usually further classified as either Right Hand or Left Hand.
The dipole antenna has been perhaps the most widely used of all the antenna types. It is of course possible however to radiate from a conductor which is not constructed in a straight line. Approaches to circular polarization in loop antennas appear lesser known, or perhaps even unknown in the purest forms. In spite of the higher gain of the full wave loop vs. the half wave dipole (3.6 dBi vs. 2.1 dBi), dipoles are commonly used for circular polarization needs, as for instance in turnstile arrays. A circle antenna structure can be more suited for circular polarization than an X antenna. Both the dipole turnstile and a single loop antenna are planar, in that their thin structure lies nearly in a single plane.
Many structures are described as loop antennas, but the circle shape best provides the curling motion, and a circle advantageously provides the most area for the least circumference. The resonant loop is a full wave circumference circular conductor, often called a “full wave loop”. The typical prior art full wave loop is linearly polarized, having a radiation pattern that is a two petal rose, with two opposed lobes normal to the loop plane, and a gain of about 3.6 dBi. Reflectors are often used with the full wave loop antenna to obtain a unidirectional pattern.
Dual linear polarization (simultaneous vertical and horizontal polarization from the same antenna) has commonly been obtained from crossed dipole antennas. For instance, U.S. Pat. No. 1,392,221 to Runge, proposes a crossed dipole system. Polarization diversity was recited. The embodiment shown in FIG. 3 and described on page 2 lines 20-29 also provided circular polarized reception.
U.S. Pat. No. 5,977,921 to Niccolai et al. is directed to an antenna for transmitting and receiving circularly polarized electromagnetic radiation which is configurable to either right-hand or left-hand circular polarization. The antenna has a conductive ground plane and a circular closed conductive loop spaced from the plane, i.e., no discontinuities exist in the circular loop structure. A signal transmission line is electrically coupled to the loop at a first point and a probe is electrically coupled to the loop at a spaced-apart second point. This antenna requires a ground plane and includes a parallel feed structure, such that the RF potentials are applied between the loop and the ground plane. The “loop” and the ground plane are actually dipole half elements to each other, and the invention is related to microstrip antennas.
U.S. Pat. No. 5,838,283 to Nakano is directed to a loop antenna for a circularly polarized wave. Driving power fed may be conveyed to a feeding point via an internal coaxial line and a feeder conductor is transmitted through an I-shape conductor to a C-type loop element disposed in spaced facing relation to a ground plane. By the action of a cutoff part formed on the C-type loop element, the C-type loop element radiates a circularly polarized wave. Dual linear, or dual circular polarization are not however provided.
U.S. Pat. No. 6,522,302 to Iwasaki is directed to a circularly polarized antenna array rather than a single circularly polarized loop element. A circle is among the most elemental of antenna structures, and it is a fundamental single geometry capable of circular polarization.
U.S. Pat. Pub. No. 2008/0136720 to Parsche, the inventor of the present application, discloses a multiple polarization loop antenna which includes a circularly polarized loop antenna. The circularly polarized loop antenna utilizes a loop electrical conductor and two signal feedpoints along the loop electrical conductor separated by one quarter of the length of the loop circumference for a signal feedpoint phase angle input difference of 90 degrees. Each of the signal feedpoints includes a loop discontinuity, so that at least one signal source coupled thereto provides circular polarization from the loop electrical conductor. The circularly polarized loop antenna provides an increase in gain and decrease in size relative to the dipole turnstile. It can provide two orthogonal polarizations from two isolated ports, and the polarizations may be dual linear or dual circular.
While U.S. Pat. Pub. No. 2008/0136720 represents an exemplary advance in the field of circularly polarized loop antennas, further advances are still desirable. For example, improvement to the degree of circularity of the polarization can help improve antenna performance, and a single antenna structure capable of both circular and linear polarization would be useful in some applications.
In view of the foregoing background, it is therefore an object of the present invention to provide a wireless device having a waveguide transducer that can be configured for different polarizations.
This and other objects, features, and advantages in accordance with the present invention are provided by a wireless communications device that includes wireless communications circuitry, and a waveguide transducer coupled to the wireless communications circuitry. The waveguide transducer includes a loop electrical conductor having a plurality of spaced apart gaps therein defining a plurality of respective spaced apart coupling points. The waveguide transducer also includes a feed assembly that includes at least one waveguide feed, and a feed network coupled between the at least one waveguide feed and the plurality of coupling points. The waveguide transducer includes a waveguide surrounding the loop electrical conductor and extending outwardly therefrom. The waveguide includes a tubular body having an open end and an opposing closed end carrying the loop electrical conductor. Accordingly, the waveguide transducer allows operation using both linear and circular polarization, for example, and provides robust performance.
A method aspect is directed to a method of making a waveguide transducer for use in a wireless communications device. The method includes forming a loop electrical conductor having a plurality of spaced apart gaps therein defining a plurality of respective spaced apart coupling points. The method also includes forming a feed assembly by forming a feed network and coupling the feed network between at least one waveguide feed and the plurality of coupling points, and positioning a waveguide to surround the loop electrical conductor and extend outwardly therefrom.
a illustrates the waveguide transducer of
b-13d are radiation patterns for the waveguide transducer of
a-14c are field rotation graphs for the waveguide transducer of
The present invention will now be described more fully hereinafter with reference to the accompanying drawings, in which preferred embodiments of the invention are shown. This invention may, however, be embodied in many different forms and should not be construed as limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Like numbers refer to like elements throughout, and prime notation is used to indicate similar elements in alternative embodiments.
Referring initially to
The antenna 12 comprises a loop electrical conductor 13, which is preferably circularly shaped. The loop electrical conductor 13 may be a metallic ring, circular wire, tubing hoop, a conductive trace, or may be a hole defined in a metallic surface, as will be appreciated by those of skill in the art. Approximations the circle shape may also be used, such as polygons. The loop electrical conductor 13 has four spaced apart gaps therein which define four respective spaced apart coupling points 14a, 14b, 14c, 14d. Each of the spaced apart gaps may create a pair of terminals on either side of the gap. The spaced apart coupling points 14a, 14b, 14c, 14d may comprise ports.
The spaced apart coupling points 14a, 14b, 14c, 14d are separated by one quarter of a length of the circumference of the loop electrical conductor 13, and the length of the loop electrical conductor itself corresponds to an operating wavelength of the antenna 12. In particular, good results may be obtained with the circumference of the loop electrical conductor 13 being equal to the operating wavelength of the antenna 12, although it should be noted that the loop electrical conductor 13 circumference may also be multiples and/or fractions of the operating wavelength.
The antenna 12 includes a feed assembly 15, to relay signals to and from the wireless communications circuitry 20, as well as to configure the antenna for different modes of operation, as will be explained in detail below. The feed assembly 15, in turn, includes an antenna feed 18 which is coupled to the wireless communications circuitry 20. The antenna feed 15 in turn is coupled to each of four signal feed lines 16a, 16b, 16c, 16d at a common node 19. The signal feed lines 16a, 16b, 16c, 16d are illustratively delay lines, but it should be understood that they need not be. Each delay line 16a, 16b, 16c, 16c is coupled to a respective one of the coupling points 14a, 14b, 14c, 14d. The feed assembly 15 divides radio frequency power four ways and delivers the divided power at different relative phases. Baluns 17a, 17b, 17c, 17d may be provided suppress common mode currents on feed assembly 15, such as ferrite beads. Baluns 15 may also be balun transformers to the match coupling point 14a, 14b, 14c, 14d impedances to the feed assembly 15, if desired.
As can be appreciated by those in the art,
Since the length of each delay line 16a, 16b, 16c, 16d is illustratively different, each delay line will refer a fraction of the transmit signal to the coupling points 14a, 14b, 14c, 14d at different relative phase, or in the receive case refer the fractions of the receive signal to antenna feed 18 in a reciprocal fashion to the transmit case. Here, the phases shifted versions of the transmit signal are referred to the coupling points 14a, 14b, 14c, 14c, or the phase shifted versions of the receive signal are referred to the antenna feed 18, at 0°, 90°, 180°, and 270° relative phase respectively. The feed assembly 15 may provide equal amplitude excitations in phase quadrature (0, 90, 180, 270 degrees) at the coupling points 14a, 14b, 14c, 14d. For example, if the wireless communications circuitry 20 provides 1 watt of RF power, then the feed assembly 15 provides watt of RF power to each of the coupling points 14a, 14b, 14c, 14d at relative phases of 0, 90, 180 and 270 degrees. This arrangement of phase differences results in a signal being transmitted with circular polarization, in particular right hand circular polarization is produced out of the page. This is because the equal amplitude quadrature phase excitations at the spaced apart coupling points 14a, 14b, 14c, 14d imparts a traveling wave current distribution on the loop electrical conductor 13.
The traveling wave current distribution will be further explained. A traveling wave current distribution means that the loop electrical conductor 13 has a sine wave current distribution which is moving around the circumference of the loop circumference at an angular velocity of ω=2πf. So to speak then, two “lumps of current” rotate around the loop electrical conductor 13 circumference. The two current maxima are opposite each other at all times. Since the flow of RF electric currents cause radio waves, and the RF currents are themselves rotating around the loop, then the transmitted wave must spin around its axis, which is circular polarization.
As background, prior art linearly polarized full wave loop antennas have an electrical current distributions on the loop conductor that does not spin around the loop circumference. Rather, the two current maxima stand still in space.
A theory of operation for a circular loop electrical conductor 13 will now be provided. The four equal amplitude quadrature phase excitations would if summed together in an ordinary fashion cancel and become zero, e.g. the vector sum of 10°+1
90°+1
180°+1
270°=0 The structure of the circular loop electrical conductor 13 however has dual properties of: 1) a radiating antenna and 2) a hybrid ring power combiner. So, the circular loop electrical conductor 13 can hybrid combine the RF powers at the coupling points 14a, 14b, 14c, 14d without cancellation, and this produces a traveling wave current distribution. The hybrid power combining properties of the circular loop electrical conductor 13 are as follows: port 14a is uncoupled from port 14b, port 14b is uncoupled from port 14c, port 14c is uncoupled from port 14d, and port 14d is uncoupled from port 14a, or stated as scattering parameters S14a14b=0, S14b14c=0, S14c14d=0. The quadrature excitation and hybrid combining in the loop electrical conductor 13 results in the superposition of sines and cosines in an extension of the Pythagorean Identity:
I
loop=(sin θ)2+(cos θ)2+(−sin θ)2+(−cos θ)2
Where Iloop is the current on the loop conductor 13. The sine term corresponds to the 0 degree excitation at coupling point 14a, the cosine to the 90 degree excitation at 14b, the −sine term to the 180 degree excitation at 14c, and the −cosine term to the 270 degree excitation at 14d. The traveling wave current distribution transduces a circularly polarized wave as it is moving in a circle.
If the delay lines 16a, 16b, 16c, 16c are sized such that the phase delay increases in the opposite sense as shown, the circular polarization will be left handed circular polarization produced into the page. So, increasing phase delay (such as more cable length) is introduced in a sense opposite that of the desired circular polarization sense. In addition, as will be appreciated by those of skill in the art, the delay lines 16a, 16b, 16c, 16c need not cause the delay due to a mere function of their length, and need not have different lengths, but may include suitable phase shifting elements therein so as to produce the desired phase shift. Examples include coaxial cables having different permittivity dielectrics or ferrites, and ladder networks of inductors and capacitors.
Regarding the choice of circular polarization sense, right handed circular polarization may be preferential in the northern hemisphere, and left handed circular polarization may be preferable in the southern hemisphere, due to electron rotation (gyro resonance) in the ionosphere (see also “Ionospheric Radio Propagation”, K. Davies. National Bureau of Standards, Apr. 1, 1965).
The far field radiation pattern is the Fourier transform of the current distribution on the loop conductor 13, so the radiated field of the antenna 12 in the Z direction (normal to the loop plane) has a constant magnitude over time which is described by
E=(cos2 ωt+sin2 ωt)1/2=1,
which is the condition for circular polarization. ω is the orientation of the E field about the wave axis, e.g. the polarization angle, and t is time.
If a large plane reflector (not shown) is spaced one quarter wavelength (λ/4) from the antenna 12 a single radiation pattern lobe is formed with 82 degrees beamwidth. When efficiently matched and tuned, the realized gain is 8.2 dBic. If a plane reflector is spaced relatively close to the antenna 12 a “patch antenna” may be formed.
The degree of polarization circularity produced by the
The
Fewer than four or more than four coupling points 14 may be used in antenna 12 but the combination of a loop electrical conductor 13 circumference near one wavelength with four equally spaced coupling points 14 is very effective.
Now described with reference to
Here, a quadrature hybrid unit 26′ drives the antenna 12′ at the coupling points 14a′, 14b′, 14c′, 14d′, providing 0 and 90 degree phasing at its outputs. In addition, here, there are two antenna feeds 18a′, 18b′, each of which feeds a power divider 22′, 24′, respectively. The power dividers are each coupled to two opposite coupling points (i.e. 14a′ and 14c′, and 14b′ and 14d′) by respective delay lines (i.e. 16a′ and 16c′, 16b′ and 16d′). Here, the delay lines 16a′, 16b′, 16c′, 16d′ are configured to provide phase delays of 0°, 90°, 180°, and 270°, respectively.
As explained, this design provides for transmission or reception of dual circularly polarized signals, allowing for simultaneous transmission of two separate signals. In addition, this design may be used for full duplex communications, where a transmitter may simultaneously be operated at coupling points 14a′ and 14c′, and a receiver at coupling points 14b′ and 14d′, without mutual interference.
This antenna 12′ provides a very high axial ratio which may approach 1.0. Such a high axial ratio means that there is little to no interference of the right hand circularly polarized signal caused by the left hand circularly polarized signal, or vice versa. This is highly desirable in satellite communications, for example for frequency reuse. In addition, this embodiment may be advantageous at high (HF) frequencies for NVIS (near vertical incidence skywave) communications.
With reference to
This phase configuration results in linear polarization, rather than circular polarization. In particular, this antenna 32 produces horizontal linear polarization into and out of the page. If the phases at the coupling points were 34a, 34b, 34c, 34d reversed, the antenna 32 would produce vertical linear polarization into the page.
The radiation patterns for the
Now, an embodiment of the antenna 30′ that is configured for simultaneous operation using both horizontal and linear polarization, e.g. dual linear polarization or duplexed linear polarization is described with reference to
The ability to operate using both horizontal and vertical polarization simultaneously can provide polarization diversity, and may have the effect of producing greater penetration into buildings and difficult reception areas than a signal with just one plane of polarization. In the antenna 30′, the vertical polarized coupling points 34a′, 34c′ and horizontal polarized coupling points 34b′, 34d′ are isolated from one another, and may also be used as independent communication channels, or for duplex communications. For instance, a transmitter may be included at one of the signal feedpoints, and a receiver used at the other.
The embodiments of the present inventions are not so limited as to require gaps in the loop electrical conductor 13 to form the coupling points 14a, 14b, 14c, 14d. Other approaches may be utilized such as gamma matches, Y matches, or delta matches as are common for dipole and yagi-uda antenna driven elements. In this regard, the textbook “Antennas For All Applications”, John Kraus, Ronald J. Marhefka, 3rd edition, Tata McGraw-Hill, 2002 is identified as a reference in its entirety and the FIG. 23-19 page 822 is referenced in specific.
Table 1 provides a comparison between the antenna 12 and the circularly polarized half wave dipole turnstile antenna:
A full wave circularly polarized loop antenna 12 therefore provides many advantages over the prior art half wave dipole turnstile: more gain, a symmetric beam, reduced size. The bandwidth for size is greater with the loop 12. The antenna 12 provides circular polarization of exceptional circularity: unlike the turnstile it is not easily upset by tolerances. So, the antenna 12 may replace the turnstile in many applications such as satellite communications and ionospheric communications.
Referring now to
The feed assembly includes two waveguide feeds 118a, 118b, or feed points, and a feed network in the form of two delay lines 116a, 116b coupled between the two waveguide feeds, and the two coupling points 114a, 114b. In other embodiments, the feed network may alternatively or additionally include digital delay processing circuitry configured to provide a delay. In other words, the digital delay processing circuitry may execute computer-executable instructions to provide phase delays. Since there are two coupling points 114a, 114b, and two delay lines 116a, 116b, the 180° power dividers are not used.
The waveguide transducer 112 also includes a waveguide 140 surrounding the loop electrical conductor 113. The loop electrical conductor 113, two delay lines 116a, 116b, the waveguide feeds 118a, 118b, and the waveguide 140 advantageously cooperate to function as a waveguide transducer.
The waveguide 140 extends outwardly from the loop electrical conductor 113, and includes a cylindrical body 141, having an open end 142 and an opposing closed end 143. The closed end 143 carries the loop electrical conductor 113. The body 141 of the waveguide 140 may be another shape.
The reflector 140 may be electrically conductive, for example, and may be metallic. The cylindrically shaped body 141 of the waveguide 140 is sized so that it extends outwardly beyond the loop electrical conductor 113. In other words, the loop electrical conductor 113 is carried below the open end 142 of the cylindrically shaped body 141.
The loop electrical conductor 113 is carried by closed end 143 of cylindrically shaped body 141 in spaced apart relation therefrom. More particularly, the loop electrical conductor 113 is spaced above the closed end 143 by the two delay lines 116a, 116b. A typical spacing of the loop electrical conductor 113 above the closed end 143 by a distance of λg/4 or a quarter of a wavelength. The cylindrical body 141 may also be 2λ or two wavelengths long from the closed end 143 to the open end 142. Of course, the cylindrical body 141 may be another length, and the loop electrical conductor 113 may be spaced differently.
The waveguide transducer 112 also includes a horn 150 coupled to the open end 142 of the waveguide 140. More particularly, the horn 150 includes a frusto-conical body 151 having a smaller opening 152 coupled to the open end 142 of the waveguide 140 and a larger opening 152 opposing the smaller opening 151. The horn 150 advantageously focuses RF waves from the loop electrical conductor 113 and provides increased gain. The loop electrical conductor 113 excites the waveguide 140 and the horn 150 in the TE11 mode, which is used for satellite communications, for example.
The horn 150 may further include impedance elements 154 carried by an interior of the conical body 151. The impedance elements 154 are illustratively in the form of rings defining a choke. The impedance elements 154 cooperate with the frusto-conical body 151 to reduce current on the interior of the frusta-conical body. As will be appreciated by those skilled in the art, current has a tendency to “walk back” along the frusto-conical body 151.
Referring now to
The digital delay processing circuitry 146′ may execute computer-executable instructions and cooperate with the delay lines to provide phase delays of 0°, 90°, 180°, 270°, respectively. In some embodiments, the digital delay processing circuitry 146′ may be used without the four delay lines 116a′, 116b′, 116c′, 116d′. The digital delay processing circuitry 146′ may also be configured to perform additional functions, for example, that of the power dividers 122′, 124′, 126′.
Referring now to
Referring now to
Referring to the graphs in
Referring now to the graph in
A method aspect is directed to a method of making a waveguide transducer 112 for use in a wireless communications device 110. The method includes forming a loop electrical conductor 113 having a plurality of spaced apart gaps therein defining a plurality of respective spaced apart coupling points 114a, 114b, and forming a feed assembly by forming a feed network 116a, 116b and coupling the feed network between the waveguide feeds 118a, 118b and the plurality of coupling points 114a, 114b. The method also includes positioning a waveguide 140 to surround the loop electrical conductor 113 and extend outwardly therefrom. The waveguide 140 includes a tubular body 141 having an open end 142 and an opposing closed end 143 carrying the loop electrical conductor 113.
The embodiments described herein may provide a circular waveguide transducer for the TE11 and other waveguide modes, and a coax to waveguide transition. A circular loop electric conductor may generate electromagnetic fields and may provide one or more of linear polarization, circular polarization, and dual polarization. The embodiments, including the waveguide transducer 112 may simplify reflector antenna feeds by reducing rectangular waveguide components, such as, for example, the magic T hybrid and rectangular to circular waveguide transducers.
Additional details of a wireless communications device including a related antenna may be found in related application attorney docket Nos. GCSD-2490 and GCSD-2491, and U.S. Patent Application Publication No. 2008/0136720 to Parsche et al, all of which are assigned to the present assignee, and the entire contents of each of which are herein incorporated by reference. Many modifications and other embodiments of the invention will come to the mind of one skilled in the art having the benefit of the teachings presented in the foregoing descriptions and the associated drawings. Therefore, it is understood that the invention is not to be limited to the specific embodiments disclosed, and that modifications and embodiments are intended to be included within the scope of the appended claims.
