Examples and embodiments of the invention are in the field of communications including satellite communications and antennas. More particularly, examples and embodiments of the invention are related to directional coupler feeds for flat panel antennas.
Satellite communications involve transmission of electromagnetic waves. Electromagnetic waves can have small wavelengths and be transmitted at high frequencies in the gigahertz (GHz) range. Satellite antennas can produce focused beams of high-frequency electromagnetic radiation that allow for point-to-point communications having broad bandwidth and high transmission rates. One type of satellite antenna is a flat panel antenna. This type of antenna includes a number of panels or segments having dipoles or other radiating elements to receive and transmit electromagnetic waves. If the antenna elements are fed in series or if the antenna elements are distributed along the length of the feeding waveguide, as with a periodic leaky wave antenna, the feeding wave propagates along the aperture or area of a flat panel antenna and the power density distribution decays along the aperture as a result of radiation by the antenna elements. The power density distribution across the aperture of the antenna is desired to be as uniform as possible in order to maximize the aperture efficiency of the antenna.
Antennas such as flat panel, leaky wave antennas with directional coupler feeds and waveguides are disclosed. In one example, an antenna includes a surface having antenna elements, a guided wave transmission line, and a coupling surface. The guided wave transmission line provides a guided feed wave. The coupling surface is between and separates the guided wave transmission line and the surface having antenna elements. The coupling surface is to control coupling of the guided feed wave to the antenna elements. The coupling surface can control vertical coupling or lateral coupling of the guided feed wave to the antenna elements. The coupling surface can also spatially filter the guided feed wave to provide a more uniform power density and, thus, a more uniform excitation to the antenna elements. The guided feed wave can be a high-power-density electromagnetic wave or a high-power-density, radially decaying electromagnetic wave.
In one example, the antenna elements can be scattering antenna elements and the surface can be a scattering surface for the antenna. In one example, the guided wave transmission line can be part of an edge-fed cylindrical waveguide, a center-fed cylindrical waveguide, a linear waveguide, or a stripline transmission line. The waveguides can include a top waveguide and a bottom waveguide. In one example, a power density in the bottom waveguide can feed into the top waveguide through the coupling surface to compensate for power decay in the top guide.
Other antennas, methods, systems and coupler feeds are described.
The present invention will be understood more fully from the detailed description given below and from the accompanying drawings of various examples and examples which, however, should not be taken to the limit the invention to the specific examples and examples, but are for explanation and understanding only.
Examples and embodiments are disclosed for antennas such as flat panel, leaky wave antennas with directional coupler feeds and waveguides. In one example, an antenna includes a surface having antenna elements, a guided wave transmission line, and a coupling surface. The guided wave transmission line provides a guided feed wave. The coupling surface is between and separates the guided wave transmission line and the surface having antenna elements. The coupling surface is configured to control coupling of the guided feed wave to the antenna elements. In one example, the coupling surface can control vertical coupling or lateral coupling of the guided feed wave to the antenna elements. The coupling surface can spatially filter the guided feed wave to provide a more uniform power density and, thus, a more uniform excitation to the antenna elements. The guided feed wave can be a high-power-density electromagnetic wave or a high-power-density, radially decaying electromagnetic wave.
In one example, the antenna elements can be scattering antenna elements and the surface can be a scattering surface for the antenna. In various embodiments, the guided wave transmission line can be part of an edge-fed cylindrical waveguide, a center-fed cylindrical waveguide, a linear waveguide, or a stripline transmission line. The waveguides can include a top waveguide and a bottom waveguide. In one example, an electromagnetic wave in the bottom waveguide can feed into the top waveguide through the coupling surface to compensate for power decay in the top guide.
In the following description, numerous details are set forth to provide a more thorough explanation of the present invention. It will be apparent, however, that the present invention may be practiced without these specific details. In other instances, well-known structures and devices are shown in block diagram form, rather than in detail, in order to avoid obscuring the present invention.
Some portions of the detailed description that follow are presented in terms of algorithms and symbolic representations of operations on data bits within a computer memory. These algorithmic descriptions and representations are the means used by those skilled in the data processing arts to most effectively convey the substance of their work to others skilled in the art. An algorithm is here, and generally, conceived to be a self-consistent sequence of steps leading to a desired result. The steps are those requiring physical manipulations of physical quantities. Usually, though not necessarily, these quantities take the form of electrical or magnetic signals capable of being stored, transferred, combined, compared, and otherwise manipulated. It has proven convenient at times, principally for reasons of common usage, to refer to these signals as bits, values, elements, symbols, characters, terms, numbers, or the like.
In the following examples and embodiments, antennas are disclosed for improved and more uniform aperture distribution having a directional coupler with a coupling surface. In the following examples, a coupling surface can control coupling of a guided feed wave in a transmission line or waveguide to antenna elements for vertical coupling or lateral coupling, and filter the guided feed wave to provide a more uniform power density for the antenna elements. The directional coupler with a coupling surface can be used with any type of waveguide such as an edge-fed cylindrical waveguide, a center-fed cylindrical waveguide, a linear waveguide, or a strip transmission line feed waveguide and not limited to any particular type of waveguide system for an antenna.
Referring to
For the coupling surface 207 example in
For example, coupling surface 207 (directional coupler) filters the high power density electromagnetic wave 204 in bottom guide 203 and presents that power density as a coupled wave 208 that feeds into top guide 201 to provide a more uniform top guide electric magnetic wave 202. In one example, a coupling surface 207 can include a ground plane with periodic coupling rings. The ground plane can be electro-deposited onto a plastic such as Rexolite or made of a large printed circuit board (PCB). In another example, coupling surface 107 can be a perforated grounded surface having openings. In one example, coupling surface 207 can replace an intermediate guide plate in existing antennas and can be a broadband coupler in which aperture distribution is not dependent on frequency. In one example, a coupling surface 207 (or directional coupler) can be configured to compensate for the reduction in power density caused by the spreading of the electromagnetic wave 204 while propagating in the radial direction. This effect is common to cylindrical waveguides.
In one example, coupled wave 208 of bottom guide 203 couples to top guide electromagnetic wave 202 thereby increasing power density along the length of the top guide 201. Likewise, coupling surface 207 allows bottom guide electromagnetic wave 204, moving radially from the center feed point 205, to couple into top guide 201 thus compensating the power density of the electromagnetic wave so that it is no longer inversely proportional to the radius of the guide.
Referring to
Exemplary coupling surfaces or directional coupler as described in
The equations for the field ampllitudes um(z)=am+(z)e−jβ
which have, simple solutions:
The above ODEs provide a theoretical basis in coupled mode theory for the improved distribution. This coupled mode theory relates to optical co-directional couplers. In one example, the directional coupler disclosed herein involves solving a system of differential equations as disclosed in A. Yariv, “Coupled-Mode Theory for Guided-Wave Optics,” IEEE Journal of Quantum Electronics, vol. QE-9, No. 9, September 1973 and Robert R McLeod, University of Colorado, ECE 4006/5166 Guided Wave Optics, chapter on Coupled Modes—Derivation.
In one example, designing the directional coupler disclosed herein involves reformulating the ordinary differential equations (ODEs) and solving them for a different answer due to the presence of radiation in one of the waveguides in the center fed antenna. The resulting solution is different than for the optical directional couplers and is unique to this invention. The directional coupler as designed herein can be useful for both cylindrical leaky wave antennas as well as linear antennas. The desired aperture distribution is a result of the solution of the system of equations and can be a uniform or tapered distribution.
Regarding the system of the center fed antenna as disclosed in
dE
1
/dx−αE
2=0
dE
2
/dx+jkE
3
+αE
2=0
dE
3
/dx+jkE
2=0
The ODE equations for the antenna system can be reduced to two regions as shown in
dE
2
/dx+jkE
e
+αE
2=0
dE
3
/dx+jkE
2=0
The equations yield solutions for E3 and E2 and inputs include coupling and radiation rates. In one example, designing the coupling surface (directional coupler) assumes a constant radiation rate, and a variable coupling rate. The aperture distribution can then be calculated from the solution of the ODEs, as described below:
P
top_guide
=E
2
E
2
*/Z P
bottom guide
=E
3
E
3
*/Z
P
radiated=1−Ptop guide−Pbottom guide
|A(z)|2=d/dz Pradiated
The coupling surface can be designed to achieve a desired coupling rate or optimizing coupling curves for the system using the above ODEs in order to provide for a more uniform aperture distribution |A(z)|2. Such a directional coupler can provide for more uniform and improved illumination control of wave propagating along the aperture of the antenna.
By using such a directional coupler to improve aperture distribution, the system can provide a number of improvements. Examples of improvements can include aperture efficiency improvement and improved feed loss providing higher antenna gain aperture size can increase without drastically reducing aperture efficiency. Other advantages of using the directional coupler include simple mechanical implementation and lower building costs. Optimizing the directional coupler to provide different aperture distributions that are not uniform, but still desirable is possible. For example, targeting a Taylor or Chebychev distribution is possible for lowered radiation pattern sidelobes.
The above directional coupler feed examples and embodiments as described in
In one example, the antenna system uses surface scattering metamaterial technology to form and steer transmit and receive beams through separate antennas. In one example, the antenna systems are analog systems, in contrast to antenna systems that employ digital signal processing to electrically form and steer beams (such as phased array antennas).
In one example, the antenna system is comprised of three functional subsystems: (1) a wave guiding structure consisting of a cylindrical wave feed architecture; (2) an array of wave scattering metamaterial unit cells that are part of antenna elements; and (3) a control structure to command formation of an adjustable radiation field (beam) from the metamaterial scattering elements using holographic principles.
In one example, the antenna elements comprise a group of patch and slot antennas (unit cells). This group of unit cells comprises an array of scattering metamaterial elements. In one example, each scattering element in the antenna system is part of a unit cell that consists of a lower conductor, a dielectric substrate and an upper conductor that embeds a complementary electric inductive-capacitive resonator (“complementary electric LC” or “CELC”) that is etched in or deposited onto the upper conductor. LC in the context of CELC refers to inductance-capacitance, as opposed to liquid crystal.
In one example, a liquid crystal (LC) is disposed in the gap around the scattering element. Liquid crystal is encapsulated in each unit cell and separates the lower conductor associated with a slot from an upper conductor associated with its patch. Liquid crystal has a permittivity that is a function of the orientation of the molecules comprising the liquid crystal, and the orientation of the molecules (and thus the permittivity) can be controlled by adjusting the bias voltage across the liquid crystal. Using this property, in one example, the liquid crystal integrates an on/off switch and intermediate states between on and off for the transmission of energy from the guided wave to the CELC. When switched on, the CELC emits an electromagnetic wave like an electrically small dipole antenna. The teachings and techniques described herein are not limited to having a liquid crystal that operates in a binary fashion with respect to energy transmission.
In one example, the feed geometry of this antenna system allows the antenna elements to be positioned at forty-five degree (45°) angles to the vector of the wave in the wave feed. Note that other positions may be used (e.g., at 40° angles). This position of the elements enables control of the free space wave received by or transmitted/radiated from the elements. In one example, the antenna elements are arranged with an inter-element spacing that is less than a free-space wavelength of the operating frequency of the antenna. For example, if there are four scattering elements per wavelength, the elements in the 30 GHz transmit antenna will be approximately 2.5 mm (i.e., ¼th the 10 mm free-space wavelength of 30 GHz).
In one example, the two sets of elements are perpendicular to each other and simultaneously have equal amplitude excitation if controlled to the same tuning state. Rotating them +/−45 degrees relative to the feed wave excitation achieves both desired features at once. Rotating one set 0 degrees and the other 90 degrees would achieve the perpendicular goal, but not the equal amplitude excitation goal. Note that 0 and 90 degrees may be used to achieve isolation when feeding the array of antenna elements in a single structure from two sides as described above.
The amount of radiated power from each unit cell is controlled by applying a voltage to the patch (potential across the LC channel) using a controller. Traces to each patch are used to provide the voltage to the patch antenna. The voltage is used to tune or detune the capacitance and thus the resonance frequency of individual elements to effectuate beam forming. The voltage required is dependent on the liquid crystal mixture being used. The voltage tuning characteristic of liquid crystal mixtures is mainly described by a threshold voltage at which the liquid crystal starts to be affected by the voltage and the saturation voltage, above which an increase of the voltage does not cause major tuning in liquid crystal. These two characteristic parameters can change for different liquid crystal mixtures.
In one example, a matrix drive is used to apply voltage to the patches in order to drive each cell separately from all the other cells without having a separate connection for each cell (direct drive). Because of the high density of elements, the matrix drive is the most efficient way to address each cell individually.
In one example, the control structure for the antenna system has 2 main components: the controller, which includes drive electronics for the antenna system, is below the wave scattering structure, while the matrix drive switching array is interspersed throughout the radiating RF array in such a way as to not interfere with the radiation. In one example, the drive electronics for the antenna system comprise commercial off-the-shelf LCD controls used in commercial television appliances that adjust the bias voltage for each scattering element by adjusting the amplitude of an AC bias signal to that element.
In one example, the controller also contains a microprocessor executing software. The control structure may also incorporate sensors (e.g., a GPS receiver, a three-axis compass, a 3-axis accelerometer, 3-axis gyro, 3-axis magnetometer, etc.) to provide location and orientation information to the processor. The location and orientation information may be provided to the processor by other systems in the earth station and/or may not be part of the antenna system.
More specifically, the controller controls which elements are turned off and which elements are turned on and at which phase and amplitude level at the frequency of operation. The elements are selectively detuned for frequency operation by voltage application.
For transmission, a controller supplies an array of voltage signals to the RF patches to create a modulation, or control pattern. The control pattern causes the elements to be turned to different states. In one example, multistate control is used in which various elements are turned on and off to varying levels, further approximating a sinusoidal control pattern, as opposed to a square wave (i.e., a sinusoid gray shade modulation pattern). In one example, some elements radiate more strongly than others, rather than some elements radiate and some do not. Variable radiation is achieved by applying specific voltage levels, which adjusts the liquid crystal permittivity to varying amounts, thereby detuning elements variably and causing some elements to radiate more than others.
The generation of a focused beam by the metamaterial array of elements can be explained by the phenomenon of constructive and destructive interference. Individual electromagnetic waves sum up (constructive interference) if they have the same phase when they meet in free space and waves cancel each other (destructive interference) if they are in opposite phase when they meet in free space. If the slots in a slotted antenna are positioned so that each successive slot is positioned at a different distance from the excitation point of the guided wave, the scattered wave from that element will have a different phase than the scattered wave of the previous slot. If the slots are spaced one quarter of a guided wavelength apart, each slot will scatter a wave with a one fourth phase delay from the previous slot.
Using the array, the number of patterns of constructive and destructive interference that can be produced can be increased so that beams can be pointed theoretically in any direction plus or minus ninety degrees (90°) from the bore sight of the antenna array, using the principles of holography. Thus, by controlling which metamaterial unit cells are turned on or off (i.e., by changing the pattern of which cells are turned on and which cells are turned off), a different pattern of constructive and destructive interference can be produced, and the antenna can change the direction of the main beam. The time required to turn the unit cells on and off dictates the speed at which the beam can be switched from one location to another location.
In one example, the antenna system produces one steerable beam for the uplink antenna and one steerable beam for the downlink antenna. In one example, the antenna system uses metamaterial technology to receive beams and to decode signals from the satellite and to form transmit beams that are directed toward the satellite. In one example, the antenna systems are analog systems, in contrast to antenna systems that employ digital signal processing to electrically form and steer beams (such as phased array antennas). In one example, the antenna system is considered a “surface” antenna that is planar and relatively low profile, especially when compared to conventional satellite dish receivers.
Control module 680 is coupled to reconfigurable resonator layer 630 to modulate the array of tunable slots 610 by varying the voltage across the liquid crystal in
Radio Frequency (“RF”) holography is also possible using analogous techniques where a desired RF beam can be generated when an RF reference beam encounters an RF holographic diffraction pattern. In the case of satellite communications, the reference beam is in the form of a feed wave, such as feed wave 605 (approximately 20 GHz in some examples). To transform a feed wave into a radiated beam (either for transmitting or receiving purposes), an interference pattern is calculated between the desired RF beam (the object beam) and the feed wave (the reference beam). The interference pattern is driven onto the array of tunable slots 610 as a diffraction pattern so that the feed wave is “steered” into the desired RF beam (having the desired shape and direction). In other words, the feed wave encountering the holographic diffraction pattern “reconstructs” the object beam, which is formed according to design requirements of the communication system. The holographic diffraction pattern contains the excitation of each element and is calculated by whologram=win*wout, with win as the wave equation in the waveguide and wont the wave equation on the outgoing wave.
Reconfigurable resonator layer 630 also includes gasket layer 632 and patch layer 631. Gasket layer 632 is disposed between patch layer 631 and iris layer 633. In one example, a spacer could replace gasket layer 632. In one example, Iris layer 633 is a printed circuit board (“PCB”) that includes a copper layer as metal layer 636. In one example, iris layer 633 is glass. Iris layer 633 may be other types of substrates.
Openings may be etched in the copper layer to form slots 612. In one example, iris layer 633 is conductively coupled by a conductive bonding layer to another structure (e.g., a waveguide) in
Patch layer 631 may also be a PCB that includes metal as radiating patches 611. In one example, gasket layer 632 includes spacers 639 that provide a mechanical standoff to define the dimension between metal layer 636 and patch 611. In one example, the spacers are 75 microns, but other sizes may be used (e.g., 3-200 mm). As mentioned above, in one example, the antenna aperture of
A voltage between patch layer 631 and iris layer 633 can be modulated to tune the liquid crystal in the gap between the patch and the slots (e.g., tunable resonator/slot 610). Adjusting the voltage across liquid crystal 613 varies the capacitance of a slot (e.g., tunable resonator/slot 610). Accordingly, the reactance of a slot (e.g., tunable resonator/slot 610) can be varied by changing the capacitance. Resonant frequency of slot 610 also changes according to the equation
where f is the resonant frequency of slot 610 and L and C are the inductance and capacitance of slot 610, respectively. The resonant frequency of slot 610 affects the energy radiated from feed wave 605 propagating through the waveguide. As an example, if feed wave 605 is 20 GHz, the resonant frequency of a slot 610 may be adjusted (by varying the capacitance) to 17 GHz so that the slot 610 couples substantially no energy from feed wave 605. Or, the resonant frequency of a slot 610 may be adjusted to 20 GHz so that the slot 610 couples energy from feed wave 605 and radiates that energy into free space. Although the examples given are binary (fully radiating or not radiating at all), full grey scale control of the reactance, and therefore the resonant frequency of slot 610 is possible with voltage variance over a multi-valued range. Hence, the energy radiated from each slot 610 can be finely controlled so that detailed holographic diffraction patterns can be formed by the array of tunable slots.
In one example, tunable slots in a row are spaced from each other by λ/5. Other types of spacing may be used. In one example, each tunable slot in a row is spaced from the closest tunable slot in an adjacent row by λ/2, and, thus, commonly oriented tunable slots in different rows are spaced by λ/4, though other spacing are possible (e.g., λ/5, λ/6.3). In another example, each tunable slot in a row is spaced from the closest tunable slot in an adjacent row by λ/3.
Examples of the invention use reconfigurable metamaterial technology, such as described in U.S. patent application Ser. No. 14/550,178, entitled “Dynamic Polarization and Coupling Control from a Steerable Cylindrically Fed Holographic Antenna”, filed Nov. 21, 2014 and U.S. patent application Ser. No. 14/610,502, entitled “Ridged Waveguide Feed Structures for Reconfigurable Antenna”, filed Jan. 30, 2015, to the multi-aperture needs of the marketplace.
Referring to
Separate from conducting ground plane 1002 is interstitial conductor 1003, which is an internal conductor. In one example, conducting ground plane 1002 and interstitial conductor 1003 are parallel to each other. In one example, the distance between ground plane 1002 and interstitial conductor 1003 is 0.1-0.15″. In another example, this distance may be λ/2, where λ is the wavelength of the travelling wave at the frequency of operation.
Ground plane 1002 is separated from interstitial conductor 1003 via a spacer 1004. In one example, spacer 1004 is a foam or air-like spacer. In one example, spacer 1004 comprises a plastic spacer.
On top of interstitial conductor 1003 is dielectric layer 1005. In one example, dielectric layer 1005 is plastic. The purpose of dielectric layer 1005 is to slow the travelling wave relative to free space velocity. In one example, dielectric layer 1005 slows the travelling wave by 30% relative to free space. In one example, the range of indices of refraction that are suitable for beam forming are 1.2-1.8, where free space has by definition an index of refraction equal to 1. Other dielectric spacer materials, such as, for example, plastic, may be used to achieve this effect. Note that materials other than plastic may be used as long as they achieve the desired wave slowing effect. Alternatively, a material with distributed structures may be used as dielectric 1005, such as periodic sub-wavelength metallic structures that can be machined or lithographically defined, for example.
An RF-array 1006 is on top of dielectric 1005. In one example, the distance between interstitial conductor 1003 and RF-array 1006 is 0.1-0.15″. In another example, this distance may be λeff/2, where λeff is the effective wavelength in the medium at the design frequency.
The antenna includes sides 1007 and 1008. Sides 1007 and 1008 are angled to cause a travelling wave feed from coax pin 1001 to be propagated from the area below interstitial conductor 1003 (the spacer layer) to the area above interstitial conductor 1003 (the dielectric layer) via reflection. In one example, the angle of sides 1007 and 1008 are at 45° angles. In an alternative example, sides 1007 and 1008 could be replaced with a continuous radius to achieve the reflection. While
In operation, when a feed wave is fed in from coaxial pin 1001, the wave travels outward concentrically oriented from coaxial pin 1001 in the area between ground plane 1002 and interstitial conductor 1003. The concentrically outgoing waves are reflected by sides 1007 and 1008 and travel inwardly in the area between interstitial conductor 1003 and RF array 1006. The reflection from the edge of the circular perimeter causes the wave to remain in phase (i.e., it is an in-phase reflection). The travelling wave is slowed by dielectric layer 1005. At this point, the travelling wave starts interacting and exciting with elements in RF array 1006 to obtain the desired scattering.
To terminate the travelling wave, a termination 1009 is included in the antenna at the geometric center of the antenna. In one example, termination 1009 comprises a pin termination (e.g., a 50Ω pin). In another example, termination 1009 comprises an RF absorber that terminates unused energy to prevent reflections of that unused energy back through the feed structure of the antenna. These could be used at the top of RF array 1006.
In operation, a feed wave is fed through coaxial pin 1015 and travels concentrically outward and interacts with the elements of RF array 1016.
The cylindrical feed in both the antennas of
Examples of the antenna having a cylindrical feed solve one or more problems. These include dramatically simplifying the feed structure compared to antennas fed with a corporate divider network and therefore reducing total required antenna and antenna feed volume; decreasing sensitivity to manufacturing and control errors by maintaining high beam performance with coarser controls (extending all the way to simple binary control); giving a more advantageous side lobe pattern compared to rectilinear feeds because the cylindrically oriented feed waves result in spatially diverse side lobes in the far field; and allowing polarization to be dynamic, including allowing left-hand circular, right-hand circular, and linear polarizations, while not requiring a polarizer.
RF array 1006 of
In one example, each scattering element in the antenna system is part of a unit cell that consists of a lower conductor, a dielectric substrate and an upper conductor that embeds a complementary electric inductive-capacitive resonator (“complementary electric LC” or “CELC”) that is etched in or deposited onto the upper conductor.
In one example, a liquid crystal (LC) is injected in the gap around the scattering element. Liquid crystal is encapsulated in each unit cell and separates the lower conductor associated with a slot from an upper conductor associated with its patch. Liquid crystal has a permittivity that is a function of the orientation of the molecules comprising the liquid crystal, and the orientation of the molecules (and thus the permittivity) can be controlled by adjusting the bias voltage across the liquid crystal. Using this property, the liquid crystal acts as an on/off switch for the transmission of energy from the guided wave to the CELC. When switched on, the CELC emits an electromagnetic wave like an electrically small dipole antenna.
Controlling the thickness of the LC increases the beam switching speed. A fifty percent (50%) reduction in the gap between the lower and the upper conductor (the thickness of the liquid crystal) results in a fourfold increase in speed. In another example, the thickness of the liquid crystal results in a beam switching speed of approximately fourteen milliseconds (14 ms). In one example, the LC is doped in a manner well-known in the art to improve responsiveness so that a seven millisecond (7 ms) requirement can be met.
The CELC element is responsive to a magnetic field that is applied parallel to the plane of the CELC element and perpendicular to the CELC gap complement. When a voltage is applied to the liquid crystal in the metamaterial scattering unit cell, the magnetic field component of the guided wave induces a magnetic excitation of the CELC, which, in turn, produces an electromagnetic wave in the same frequency as the guided wave.
The phase of the electromagnetic wave generated by a single CELC can be selected by the position of the CELC on the vector of the guided wave. Each cell generates a wave in phase with the guided wave parallel to the CELC. Because the CELCs are smaller than the wave length, the output wave has the same phase as the phase of the guided wave as it passes beneath the CELC.
In one example, the cylindrical feed geometry of this antenna system allows the CELC elements to be positioned at forty-five degree (45°) angles to the vector of the wave in the wave feed. This position of the elements enables control of the polarization of the free space wave generated from or received by the elements. In one example, the CELCs are arranged with an inter-element spacing that is less than a free-space wavelength of the operating frequency of the antenna. For example, if there are four scattering elements per wavelength, the elements in the 30 GHz transmit antenna will be approximately 2.5 mm (i.e., ¼th the 10 mm free-space wavelength of 30 GHz).
In one example, the CELCs are implemented with patch antennas that include a patch co-located over a slot with liquid crystal between the two. In this respect, the metamaterial antenna acts like a slotted (scattering) wave guide. With a slotted wave guide, the phase of the output wave depends on the location of the slot in relation to the guided wave.
In one example, the antenna elements are placed on the cylindrical feed antenna aperture in a way that allows for a systematic matrix drive circuit. The placement of the cells includes placement of the transistors for the matrix drive.
In an initial approach to realize matrix drive circuitry on the cylindrical feed antenna with unit cells placed in a non-regular grid, two steps are performed. In the first step, the cells are placed on concentric rings and each of the cells is connected to a transistor that is placed beside the cell and acts as a switch to drive each cell separately. In the second step, the matrix drive circuitry is built in order to connect every transistor with a unique address as the matrix drive approach requires. Because the matrix drive circuit is built by row and column traces (similar to LCDs) but the cells are placed on rings, there is no systematic way to assign a unique address to each transistor. This mapping problem results in very complex circuitry to cover all the transistors and leads to a significant increase in the number of physical traces to accomplish the routing. Because of the high density of cells, those traces disturb the RF performance of the antenna due to coupling effect. Also, due to the complexity of traces and high packing density, the routing of the traces cannot be accomplished by commercial available layout tools.
In one example, the matrix drive circuitry is predefined before the cells and transistors are placed. This ensures a minimum number of traces that are necessary to drive all the cells, each with a unique address. This strategy reduces the complexity of the drive circuitry and simplifies the routing, which subsequently improves the RF performance of the antenna.
More specifically, in one approach, in the first step, the cells are placed on a regular rectangular grid composed of rows and columns that describe the unique address of each cell. In the second step, the cells are grouped and transformed to concentric circles while maintaining their address and connection to the rows and columns as defined in the first step. A goal of this transformation is not only to put the cells on rings but also to keep the distance between cells and the distance between rings constant over the entire aperture. In order to accomplish this goal, there are several ways to group the cells.
The density of the cells after the transformation is determined by the number of cells that the next larger square contains in addition to the previous square. In one example, using squares results in the number of additional antenna elements, ΔN, to be 8 additional cells on the next larger square. In one example, this number is constant for the entire aperture. In one example, the ratio of cellpitch1 (CP1: ring to ring distance) to cellpitch2 (CP2: distance cell to cell along a ring) is given by:
Thus, CP2 is a function of CP1 (and vice versa). The cell pitch ratio for the example in
which means that the CP1 is larger than CP2.
In one example, to perform the transformation, a starting point on each square, such as starting point 1121 on square 1101, is selected and the antenna element associated with that starting point is placed on one position of its corresponding ring, such as starting point 1131 on ring 1111. For example, the x-axis or y-axis may be used as the starting point. Thereafter, the next element on the square proceeding in one direction (clockwise or counterclockwise) from the starting point is selected and that element placed on the next location on the ring going in the same direction (clockwise or counterclockwise) that was used in the square. This process is repeated until the locations of all the antenna elements have been assigned positions on the ring. This entire square to ring transformation process is repeated for all squares.
However, according to analytical studies and routing constraints, it is preferred to apply a CP2 larger than CP1. To accomplish this, a second strategy shown in
which results in CP2>CP1. The transformation from octagon to concentric rings for cell placement according to
In one example, the cell placements disclosed with respect to
In other examples, while two shapes are given, any shapes may be used. Other increments are also possible (e.g., 6 increments).
In one example, a TFT package is used to enable placement and unique addressing in the matrix drive.
Another feature of the proposed cell placement shown in
In another example, the matrix drive circuitry and cell placement on the cylindrical feed antenna is accomplished in a different manner. To realize matrix drive circuitry on the cylindrical feed antenna, a layout is realized by repeating a subsection of the array rotation-wise. This example also allows the cell density that can be used for illumination tapering to be varied to improve the RF performance.
In this alternative approach, the placement of cells and transistors on a cylindrical feed antenna aperture is based on a lattice formed by spiral shaped traces.
Unlike the approaches for cell placement on the cylindrical feed antenna aperture discussed above, the approach discussed above in relation to
Due to the size of the cells and the required space between them for traces, the cell density cannot exceed a certain number. In one example, the distance is ⅕ based on the frequency of operation. As described above, other distances may be used. In order to avoid an overpopulated density close to the center, or in other words to avoid an under-population close to the edge, additional spirals can be added to the initial spirals as the radius of the successive concentric rings increases.
Another advantage of the use of spirals for cell placement is the rotational symmetry and the repeatable pattern which can simplify the routing efforts and reducing fabrication costs.
In one example, the cell placements disclosed with respect to
In one example, the antenna aperture is created by combining multiple segments of antenna elements together. This requires that the array of antenna elements be segmented and the segmentation ideally requires a repeatable footprint pattern of the antenna. In one example, the segmentation of a cylindrical feed antenna array occurs such that the antenna footprint does not provide a repeatable pattern in a straight and inline fashion due to the different rotation angles of each radiating element. One goal of the segmentation approach disclosed herein is to provide segmentation without compromising the radiation performance of the antenna.
While segmentation techniques described herein focuses improving, and potentially maximizing, the surface utilization of industry standard substrates with rectangular shapes, the segmentation approach is not limited to such substrate shapes.
In one example, segmentation of a cylindrical feed antenna is performed in a way that the combination of four segments realize a pattern in which the antenna elements are placed on concentric and closed rings. This aspect is important to maintain the RF performance. Furthermore, in one example, each segment requires a separate matrix drive circuitry.
As the result of this segmentation method illustrated in
As shown in
As is evident from
The antenna feed is coupled to the rest of the segments when the open area exists because the feed comes from the bottom, and the open area can be closed by a piece of metal to prevent radiation from the open area. A termination pin may also be used.
The use of substrates in this fashion allows use of the available surface area more efficiently and results in an increased aperture diameter.
Similar to the example shown in
For both approaches described above, the cell placement may be performed based on a recently disclosed approach which allows the generation of matrix drive circuitry in a systematic and predefined lattice, as described above.
While the segmentations of the antenna arrays above are into four segments, this is not a requirement. The arrays may be divided into an odd number of segments, such as, for example, three segments or five segments.
Whereas many alterations and modifications of the present invention will no doubt become apparent to a person of ordinary skill in the art after having read the foregoing description, it is to be understood that any particular example shown and described by way of illustration is in no way intended to be considered limiting. Therefore, references to details of various examples are not intended to limit the scope of the claims which in themselves recite only those features regarded as essential to the invention.
This application is a continuation of U.S. patent application Ser. No. 15/802,320, entitled Directional Coupler Feed for Flat Panel Antennas,” filed on Nov. 2, 2017, which claims priority and the benefit of U.S. Provisional Patent Application No. 62/416,907, entitled “DIRECTIONAL COUPLER FEED,” filed on Nov. 3, 2016, both of which are hereby incorporated by reference and commonly assigned.
Number | Date | Country | |
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62416907 | Nov 2016 | US |
Number | Date | Country | |
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Parent | 15802320 | Nov 2017 | US |
Child | 16859810 | US |