FIELD OF THE INVENTION
This invention relates to antennas, and more particularly to phased array antennas.
BACKGROUND OF THE INVENTION
Antennas generally fall into two classes—omnidirectional antennas and steerable antennas. Omnidirectional antennas transmit and receive signals omnidirectionally, i.e., transmit signals to and receive signals from all directions. A single dipole antenna is an example of an omnidirectional antenna. While omnidirectional antennas are inexpensive and widely used in environments where the direction of signal transmission and/or reception is unknown or varies (due, for example, to the need to receive signals from and/or transmit signals to multiple locations), omnidirectional antennas have a significant disadvantage. Because of their omnidirectional nature, the power signal requirements of omnidirectional antennas are relatively high. Transmission power requirements are high because transmitted signals are transmitted omnidirectionally, rather than toward a specific location. Because signal reception is omnidirectional, the power requirements of the transmitting signal source must be relatively high in order for the signal to be detected.
Steerable antennas overcome the power requirement problems of omnidirectional antennas. However, in the past, steerable antennas have been expensive. More specifically, steerable antennas are “pointed” toward the source of a signal being received or the location of the receiver of a signal being transmitted. Steerable antennas generally fall into two categories, mechanically steerable antennas and electronically steerable antennas. Mechanically steerable antennas use a mechanical system to steer an antenna structure. Most antenna structures steered by mechanical systems include a parabolic reflector element and a transmit and/or receive element located at the focal point of the parabola. Electronically steerable antennas employ a plurality of antenna elements and are “steered” by controlling the phase of the signals transmitted and/or received by the antenna elements. Electronically steerable antennas are commonly referred to as phased array antennas. If the plurality of antenna elements lie along a line, the antenna is referred to as a linear phased array antenna.
While phased array antennas have become widely used in many environments, particularly high value military, aerospace, and cellular phone environments, in the past phased array antennas have had one major disadvantage. They have been costly to manufacture. The high manufacturing cost has primarily been due to the need for a large number of variable time delay elements, also known as phase shifters, in the antenna element feed paths. In the past, the time delay or phase shift created by each element has been independently controlled according to some predictable schedule. In general, independent time delay or phase shift control requires the precision control of the capacitance and/or inductance of a resonant circuit. While mechanical devices can be used to control capacitance and inductance, most contemporary time delay or phase shifting circuits employ an electronic controllable device, such as a varactor to control the time delay or phase shift produced by the circuit. While the cost of phased array antennas can be reduced by sector pointing and switching phased array antennas, the pointing capability of such antennas is relatively coarse. Sector pointing and switching phased array antennas frequently use microwave switching techniques employing pin diodes to switch between phase delays to create switching between sectors. Because sector pointing and switching phased array antennas point at sectors rather than at precise locations, like omnidirectional antennas, they require higher power signals than location pointing phased array antennas.
Because of their expense, in the past, phased array antennas have not been employed in low-cost wireless network environments. For example, phased array antennas in the past have not been used in wireless fidelity (WiFi) networks. As a result, the significant advantages of phased array antennas have not been available in low-cost wireless network environments. Consequently, a need exists for a low-cost, steerable, phased array antenna having the ability to be relatively precisely pointed. This invention is directed to providing such an antenna.
SUMMARY OF THE INVENTION
The present invention is directed to a low-cost, steerable, phased array antenna suitable for use in wireless fidelity (WiFi) and other wireless communication network environments. Embodiments of the invention are ideally suited for use in multi-hop ad hoc wireless signal transmission networks.
A phased array antenna formed in accordance with the invention includes a plurality of antenna elements fed by a corporate feed. The corporate feed is implemented as a wire transmission line. Selected branches of the corporate feed are positioned and sized so as to allow the permittivity of a high-permittivity dielectric element to control branch phase shifting in a related manner. Thus, the corporate feed forms a phase shifting antenna feed, i.e., an antenna feed with selected branches that are phase shift controllable in a related manner.
In accordance with additional aspects of this invention, the selected branches of the corporate feed, i.e., the phase shift controllable branches, are parallel to each other and close together.
In accordance with other aspects of this invention, the antenna elements are linearly arrayed.
In accordance with still further aspects of this invention, phase shifting is electromechanically controlled by controlling the space between the high-permittivity dielectric element and the phase shifting branches of the corporate feed.
In accordance with other further aspects of this invention, the high-permittivity dielectric element has a planar shape and phase shifting is controlled by moving the plane of the element toward and away from the phase shifting branches of the corporate feed.
In accordance with alternative aspects of this invention, the high-permittivity dielectric element is in the form of a cylinder having an axis of rotation that is offset from the axis of the cylinder. Phase shifting is controlled by rotating the cylindrical element such that the space between the element and the phase shifting branches of the corporate feed changes.
In accordance with other alternative aspects of the invention, phase shifting is electronically controlled by electrically controlling the permittivity of the high-permittivity dielectric element.
In accordance with still further aspects of this invention, the steerable phased array antenna is an assembly that includes four separate linear phased array antennas; each antenna is positioned so as to point outwardly from one side of one arm of an L-shaped housing and cover a 90° quadrant. Because each of the antennas covers a different 90° quadrant and because the quadrants do not overlap, the antenna assembly encompasses an arc of 360°. Thus, the antenna assembly can be “pointed” in any direction by choosing the antenna covering the quadrant in which the location being pointed to is positioned and causing the chosen antenna to point at the location.
In accordance with yet further aspects of this invention, the linear phased array antenna elements and the corporate feed are implemented in printed circuit board form.
In accordance with yet still other aspects of this invention, the antenna elements and the corporate feed are printed on a sheet of dielectric material using conventional printed circuit board techniques.
In accordance with still further aspects of this invention, the antenna elements and the corporate feed are located on opposite surfaces of the sheet of dielectric material.
In accordance with other alternative aspects of the invention, the antenna elements and the corporate feed are located on the same surface of the sheet of dielectric material.
In accordance with yet other alternative aspects of this invention, a first set of antenna elements and a first corporate feed are located on one surface of the sheet of dielectric material and a second set of antenna elements and a second corporate feed are located on the other surface of the sheet of dielectric material.
As will be readily appreciated from the foregoing summary, the invention provides a low-cost, steerable, phased array antenna. The phased array antenna is low cost because a common high-permittivity dielectric element is employed to control the phase shift produced by the selected branches of a corporate feed that feeds the elements of the antenna. Rather than requiring precise, expensive, electronic phase shifting circuitry, a phased array antenna formed in accordance with the invention employs a low-cost high-permittivity dielectric element. Time delay (phase shift) control is provided by electromechanically controlling the interaction of the permittivity of the high-permittivity dielectric element on the selected branches of the corporate feed. The permittivity interaction is controlled by controlling the position of the high-permittivity dielectric element with respect to the selected branches using a low-cost electromechanical device, such as a low-cost servo-controlled motor, a voice coil motor, etc., or by electrically controlling the permittivity of the high-permittivity dielectric element. Phased array antennas formed in accordance with the invention are also low cost because such antennas are ideally suited for implementation in low-cost printed circuit board form.
In addition to providing a low-cost, steerable, phased array antenna, it will be readily appreciated from the foregoing description that the invention also provides a new and improved corporate feed with phase shift branches that can be simultaneously controlled.
BRIEF DESCRIPTION OF THE DRAWINGS
The foregoing aspects and many of the attendant advantages of this invention will become more readily appreciated as the same become better understood by reference to the following detailed description, when taken in conjunction with the accompanying drawings, where like reference numerals in different drawings refer to like elements throughout the drawings and wherein:
FIG. 1 is a partial isometric view of a microstrip transmission line;
FIG. 2 is a partial isometric view of a coplanar waveguide transmission line;
FIG. 3 is a pictorial view of a corporate feed for an eight element phased array antenna;
FIG. 4 is a corporate feed of the type illustrated in FIG. 3, including transmission line phase shift branches sized and positioned in accordance with the invention;
FIG. 5 is a reorientation of the corporate feed illustrated in FIG. 4 in accordance with the invention;
FIG. 6 is an isometric view, partially in section, of a first embodiment of a low-cost, steerable, phased array antenna formed in accordance with the invention;
FIG. 7 is a top cross-sectional view of FIG. 6;
FIG. 8 is an end elevational view of a portion of the phased array antenna illustrated in FIG. 6;
FIG. 9 is an isometric view, partially in section, of a second embodiment of a low-cost, steerable, phased array antenna formed in accordance with the invention;
FIG. 10 is a top cross-sectional view of FIG. 9;
FIG. 11 is an end elevational view of a portion of the phased array antenna illustrated in FIG. 9;
FIG. 12 is an isometric view of an alternative embodiment of a planar dielectric element suitable for use in the embodiments of the invention illustrated in FIGS. 6–8 and 9–11;
FIG. 13 is an isometric view, partially in section, of a third embodiment of a low-cost, steerable, phased array antenna formed in accordance with the invention;
FIG. 14 is a top cross-sectional view of FIG. 13;
FIG. 15 is an end elevational view of a portion of the phased array antenna illustrated in FIG. 13;
FIG. 16 is an isometric view, partially in section, of a fourth embodiment of a low-cost, steerable, phased array antenna formed in accordance with the invention;
FIG. 17 is a top cross-sectional view of FIG. 16;
FIG. 18 is an end elevational view of a portion of the phased array antenna illustrated in FIG. 16;
FIG. 19 is a top cross-sectional view of a fifth embodiment of a low-cost, steerable, phased array antenna formed in accordance with the invention;
FIG. 20 is an end elevational view of a portion of the phased array antenna illustrated in FIG. 19;
FIG. 21 is a top cross-sectional view of a sixth embodiment of a low-cost, steerable, phased array antenna formed in accordance with the invention;
FIG. 22 is an end elevational view of a portion of the phased array antenna illustrated in FIG. 21;
FIG. 23 is a block diagram of a control system for controlling the steering of the embodiments of the invention illustrated in FIGS. 6–22;
FIG. 24 is a pictorial view of a conventional communication network employing phased array antennas formed in accordance with the invention; and
FIG. 25 is a pictorial view of a mesh communication network employing phased array antennas formed in accordance with the invention.
DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT
As will be better understood from the following description, the corporate feed of a phased array antenna formed in accordance with this invention employs transmission line phase shifters. More specifically, phased array antenna elements typically receive signals to be transmitted from, and apply received signals to, microwave feeds. Typical microwave feeds include coaxial, stripline, microstrip, and coplanar waveguide (CPW) transmission lines. The propagation of signal waves down such transmission lines can be characterized by an effective permittivity that summarizes the detailed electromagnetic phenomenon created by such propagation. In this regard, the velocity of propagation (c) of a signal along a parallel wire transmission line is given by:
where ε is the relative permittivity and μ is the relative permeability of the dielectric materials in the region between the wires of the transmission line. Since all practical dielectrics have a μ of approximately 1, it is readily apparent that the velocity of propagation is proportional to the inverse square root of the permittivity value, i.e., the inverse square root of ε.
FIGS. 1 and 2 are partial isometric views that illustrate two types of microwave feed transmission lines—microstrip and CPW transmission lines, respectively. Both transmission lines have an effective permittivity given by complex formulas that can be developed by experimental or numerical simulations. Because approximate formulas can be found in many textbooks and papers and are not needed to understand the present invention, such formulas are not reproduced here. It is, however, important to understand that the effective permittivity of a transmission line depends on the thickness and permittivity values of the different dielectric layers included in the structure of the transmission line. It is also important to understand that varying the parameters of the different dielectric layers can be used to vary the velocity of transmission line signal propagation and, thus, used to shift the phase of signals propagating along the transmission line. Control of signal velocity controls signal time delay and, thus, controls phase shift.
As noted above, FIG. 1 illustrates a microstrip transmission line 21. The illustrated microstrip transmission line 21 comprises a ground plane 23 formed of a conductive material, a first dielectric layer 25, a signal conductor 27 also formed of a conductive material, and a second dielectric layer 29. The ground plane 23 is located on one surface of the first dielectric layer 25, and the signal conductor 27 is located on the other surface of the first dielectric layer 25. The first dielectric layer 25 may be a conventional dielectric sheet of the type used to create printed circuit boards (PCBs) and the ground plane 23 and signal conductor 27 printed circuits located on opposite surfaces of the dielectric sheet. The second dielectric layer 29 is spaced from the surface of the first dielectric layer containing the signal conductor 27. The effective permittivity of the microstrip transmission line illustrated in FIG. 1 depends on the thickness and permittivity values of the first and second dielectric layers 25 and 29 and by the air gap 31 between the first and second dielectric layers, since air is also a dielectric.
The coplanar wave guide (CPW) transmission line 41 illustrated in FIG. 2 comprises a first dielectric layer 43, a signal conductor 45, two ground conductors 47a and 47b, and a second dielectric layer 49. The signal conductor 45 and the ground conductors 47a and 47b are located on one surface of the first dielectric layer 43. The first and second ground conductors 47a and 47b lie on opposite sides of, and run parallel to, the signal conductor 45. The spacing between the signal conductor and each of the ground conductors is the same, i.e., the ground conductors are equally spaced from the signal conductor. The first dielectric layer 43, the signal conductor 45 and the first and second ground conductors 47a and 47b may take the form of a printed circuit board wherein the conductors are deposited on one surface of a dielectric sheet using conventional printed circuit board manufacturing techniques. The second dielectric layer 49 is spaced from the surface of the first dielectric layer 43 that contains the signal conductor 45 and the first and second ground conductors 47a and 47b. As with the microstrip transmission line illustrated in FIG. 1, the effective permittivity of the CPW transmission line illustrated in FIG. 2 is dependent on the thickness and permittivity values of the first and second dielectric layers 43 and 49 and the air gap 51 between the first and second dielectric layers.
As will be better understood from the following description, the invention is based on the understanding that the velocity of a signal propagating along a microwave feed type of transmission line, such as the microstrip and CPW transmission lines illustrated in FIGS. 1 and 2, is dependent on the effective permittivity of the transmission line. Because the velocity of signal propagation is determined by the effective permittivity of a transmission line, the time delay and, thus, the phase shift created by a transmission line can be controlled by controlling the effective permittivity of the transmission line. Further, several embodiments of the invention are based on the understanding that the effective permittivity of a transmission line can be controlled by controlling the thickness of the air gap defined by a pair of dielectric layers through which the signal conductor of the microwave feed transmission line passes. More specifically, these embodiments of the invention are based on controlling the thickness of the air layer immediately above the transmission line, i.e., the signal conductor. While either the first or second dielectric layer could be moved with respect to the other dielectric layer, preferably the second dielectric layer is moved with respect to the first dielectric layer, the first dielectric layer remaining stationary. Also, preferably, the second dielectric layer is formed of a low-cost, high-permittivity material, such as Rutile (Titanium Dioxide or TiO2), or compounds of Rutile containing alkali earth metals such as Barium or Strontium.
An alternative to mechanically controlling the thickness of the air gap between the first and second dielectric layers in order to control time delay and, thus, phase shift is to control the permittivity of the second dielectric layer and leave the thickness of the air gap constant. The permittivity of ferroelectric materials varies under the influence of an electric field. Rutile and Rutile compounds that contain alkalite earth metals such as Barium or Strontium exhibit ferroelectric properties.
As will be readily appreciated by those skilled in the art and others from FIGS. 1 and 2 and the foregoing description, transmission line phase shifters differ from conventional phase shifters in that they are distributed phase shifters, i.e., they include no lumped elements. As a result, no separate electrical components are needed to create transmission line phase shifters. Since there are no limitations on the physical size of transmission line phase shifters, such phase shifters can be used for high-power, low-frequency applications.
Phased array antennas are based on a simple principle of operation; the transmission or reception angle, i.e., the Bragg angle θ, of a linear phased array antenna is determined by the spacing, a, between the elements of the antenna array, the wavelength of the applied wave and the phase of the applied wave at each antenna element. More specifically,
where a equals the spacing between the elements of the antenna array, c equals the frequency (γ) divided by the wavelength (λ), Δ equals the time delay, φ equals the phase delay. Each antenna element (n) receives the wave at a time delay of:
Advancing the signals from each antenna element by the equation (3) amount results in the signals interfering in a constructive manner and gain being achieved.
As will be better understood from the following description, embodiments of the invention employ transmission line phase shifters of the type described above in the branches of a corporate feed connected to the antenna elements of a phased array antenna. FIG. 3 illustrates a conventional corporate feed, connected to the elements 61a, 61b, 61c, 61d, 61e, 61f, 61g, 61h of an eight-element phased array antenna. A conventional corporate feed is a tree-shaped arrangement having transformers placed at each of the vertices where the tree branches. The transformers are impedance matching transformers that match the impedances of the branches that join at the vertices. Impedance matching is customarily accomplished with transmission line resonant transformers. The signal input/output terminal 62 of the corporate feed illustrated in FIG. 3 terminates at a first level vertice 63a that splits into two branches each of which ends at a second level vertice 63b, 63c. The second level vertices 63b, 63c, in turn, each split into branches that end at a third level vertice 63d, 63e, 63f, 63g. The third level vertices split into branches that end at the antenna elements 61a, 61b, 61c, 61d, 61e, 61f, 61g, 61h.
The present invention recognizes that a phased array antenna can be steered by appropriately phase shifting the signals applied to the branches on one side of a corporate tree. Such an arrangement is illustrated in FIG. 4. More specifically, FIG. 4 illustrates a phased array antenna comprising eight elements 71a, 71b, 71c, 71d, 71e, 71f, 71g, 71h fed by a corporate feed similar to the corporate feed illustrated in FIG. 3, except the right-hand side of every branch of the corporate feed tree includes a transmission line phase shifter. More specifically, the corporate feed includes an input/output terminal 72 connected to the right-hand side 73a and the left-hand side 73b of the first branches of the corporate feed. The right-hand side 73a of the first branch of the corporate feed tree includes a transmission line phase shifter and the left side branch 73b does not include a phase shifter. The right side branches of 75a and 75c of the next level of the corporate feed tree also include transmission line phase shifters, whereas the left side branches 75b and 75d do not include phase shifters. Likewise, the right side branches 77a, 77c, 77e, 77g of the next (final) level of the corporate feed tree include transmission line phase shifters, whereas the left side branches 77b, 77d, 77f, and 77h do not include phase shifters.
As illustrated by different line lengths in FIG. 4, the amount of phase shift is different in each level branch. If the amount of phase shift that occurs in first level right side branch 73a is expressed as Δ, the phase shift of the right side branches 75a and 75c of the second level is Δ/2, and the phase shift of the right side branches 77a, 77c, 77e, and 77g of the third level is Δ/4. If additional branches were included, the delay of the right side branches of the next level would be Δ/8, etc. Thus, each antenna element 71a, 71b, 71c, 71d, 71e, 71f, 71g, 71h receives a uniform delay increment over its neighbor. In the case of an eight element linear array, if the leftmost element 71h has a 0 delay, the next element 71g has a delay of Δ/4, the next element 71f has a delay of Δ/2, the next element 71e has a delay of 3Δ/4, the next element 71d has a delay of Δ, the next element 71c has a delay of 5Δ/4, the next element 71b has a delay of 3Δ/2, and the final element 71c has a delay of 7Δ/4. Since each antenna receives a uniform delay increment over its neighbor, the antenna array is steered to the left by the Bragg angle θ.
As pictorially illustrated in FIG. 4, the foregoing phase shift scheme is easily effected by halving the length of the transmission line, forming the phase shifting branches of the levels of the corporate tree proceeding from the lower branch levels to the upper branch levels. A feature of this arrangement is that all of the phase shifting side (right) branches of the corporate feed tree can be “ganged” together so that a single mechanism can be used to simultaneously control the effective permittivity of all of the phase shifting side branches. Thus, only a single mechanical spacing control device, or a single value of electric field, is required to steer a phased array antenna incorporating a corporate feed of the type illustrated in FIG. 4. It is to be understood that while FIG. 4 depicts a corporate feed wherein the right side branches of the various levels of the corporate feed all include transmission line phase shifters, the same effect can be achieved by placing transmission line phase shifters instead in the left side branches.
While a single control system can be developed to control the phase shifting of the phase shifting branches of a corporate feed of the type illustrated in FIG. 4, in accordance with the invention, the complexity and size of such a control system can be reduced by changing the geometry of the corporate feed in the manner illustrated in FIG. 5. FIG. 5 illustrates an arrangement wherein all of phase shifting side branches of a corporate feed are closely packed in a single area. More specifically, FIG. 5 illustrates a corporate feed wherein the input/output terminal 82 of the corporate feed is connected to a first phase shift transmission line 83a that performs the function of the right side branch 73a of the first level of the corporate feed shown in FIG. 4. The first phase transmission line 83a is connected to a second phase shift transmission line 85a that, in turn, is connected to a third phase shift transmission line 87a. The second and third phase shift transmission lines 85a and 87a perform the functions of the rightmost side branches 75a and 77a of the next two levels of the corporate feed shown in FIG. 4. The third phase shift transmission line 87a is connected to the first antenna element 81a.
In addition to being connected to the third phase shift transmission line 87a, the second phase shift transmission line 85a is connected to the second antenna element 81b. In addition to being connected to the second phase shift transmission line 85a, the first phase shift transmission line 83a is connected to a fourth phase shift transmission line 87c. The fourth phase shift transmission line 87c performs the function of right side branch 77c of the corporate feed shown in FIG. 4. The fourth phase shift transmission line 87c is connected to the third antenna element 81c. The first phase shift transmission line 85a is also connected to the fourth antenna element 81d.
The input/output terminal 82 is also connected to a fifth phase shift transmission line 85c. The fifth phase shift transmission line 85c performs the function of right side branch 75c of the corporate feed shown in FIG. 4. The fifth phase shift transmission line 85c is connected to a sixth phase shift transmission line 87e. The sixth phase shift transmission line 87e performs the function of the right side branch 77e of the corporate feed shown in FIG. 4. The sixth phase shift transmission line 87e is connected to the fifth antenna element 81e. The fifth phase shift transmission line 85c is also connected to the sixth antenna element 81f.
The input/output terminal is also connected to a seventh phase shift transmission line 87g. The seventh phase shift transmission line 87g performs the function of the right side branch 77g of the corporate feed shown in FIG. 4. The seventh phase shift transmission line 87g is connected to the seventh antenna element 81g. The input/output terminal 82 is also directly connected to the eighth antenna element 81h.
The length of the third, fourth, sixth, and seventh phase shift transmission lines 87a, 87c, 87e, and 87g is equal to one-half the length of the second and fifth phase shift transmission lines 85a and 85c. Further, the length of the second and fifth phase shift transmission lines 85a and 85c is equal to one-half the length of the first phase shift transmission line 83a. Further, the third, fourth, sixth, and seventh phase shift transmission lines 87a, 87c, 87e, and 87g, while spaced apart, are coaxial, as are the second and fifth phase shift transmission lines 85a and 85c. Finally, the axis of the third, fourth, sixth, and seventh phase shift transmission lines 87a, 87c, 87e, and 87g, the axis of the second and fifth phase shift transmission lines 85a and 85c and the axis of the first phase shift transmission line 83A all lie parallel to one another and close together.
A comparison of FIGS. 4 and 5 reveals that the line delays or phase shift amounts applied to the signals applied to or received by each of the antenna elements is the same in both figures, the difference being that the geometry of the corporate feed in FIG. 5 is more closely packed into a single area than is the geometry of the corporate feed illustrated in FIG. 4. As will be better understood from the following description of the preferred embodiments of the invention, closely packing phase shift transmission lines into a single area allows a smaller high-permittivity element to be used to simultaneously control the phase shifting of each of the phase shift transmission lines. More specifically, as will be better understood from the following description, this arrangement allows a high-permittivity dielectric rectangular plate or cylinder whose position is controlled by a suitable electromechanical device, to be used to control the phase shift produced by the phase shift transmission lines. Alternatively, a permittivity controllable element can be used.
FIGS. 6–22 illustrate several embodiments of a low-cost, steerable, phased array antenna formed in accordance with the present invention based on the previously discussed phase shift concepts. While the phased array antennas illustrated in FIGS. 6–22 and described herein are all linear phased array antennas, it is to be understood that other antenna element arrays can be used in combination with corporate feeds of the type described herein to create other versions and embodiments of the invention. Hence, it is to be understood that the invention is not limited to the embodiments that are hereinafter described in detail.
FIGS. 6–8 illustrate a first embodiment of a 360° phased array antenna assembly formed in accordance with the present invention. The phased array antenna assembly includes an L-shaped housing 91. Located in each leg of the L-shaped housing are two back-to-back phased array antennas 93a, 93b, 93c, and 93d, each comprising eight linearly arrayed antenna elements and a corporate feed of the type illustrated in FIG. 5 and described above. More specifically, each of the phased array antennas includes a sheet of dielectric material 94, such as a printed circuit board (PCB) sheet. One of the PCB sheets 94 lies adjacent each of the four outer faces of the L-shaped housing 91. The outer surface of each of the PCB sheets includes a linear array of antenna elements, eight in the illustrated embodiment of the invention 95a, 95b, 95c, 95d, 95e, 95f, 95g, 95h. Located on the inner surface of each of the PCB sheets 94 is a corporate feed 96 having the geometric layout illustrated in FIG. 5 and described above. Overlying each of the corporate feeds 96 is a high dielectric layer 97, i.e., a dielectric layer formed of a high-permittivity material. A suitable low-cost, high-permittivity material is Rutile (Titanium Dioxide, or TiO2) or a Rutile compound containing alkali earth metals such as Barium or Strontium. The high-permittivity dielectric layer may be supported by another dielectric sheet or layer or, if sufficiently strong, may be self-supporting. In any event, each of the high-permittivity dielectric layers 97 is mounted and supported such that the gap between the layer and the underlying corporate feed is controllable by a suitable electromechanical positioning means such as an electric motor 99 operating a jack screw mechanism 98. The electric motor can be an AC or DC motor, servomotor, or any other suitable motor. Alternatively, the position of the high-permittivity layer can be controlled by a voice coil motor. For ease of illustration, support mechanisms for supporting the PCB sheets 94, the high-permittivity dielectric layers, and the electric motors 99 are not illustrated in FIGS. 6–8.
As will be readily appreciated from the foregoing description, controlling the position of the high-permittivity dielectric layers 97 controls the air gap between the layers and the phase shift transmission lines of the corporate feed, thereby steering, i.e., controlling, the pointing of the linear array of antenna elements 93a, 93b, 93c, 93d, 93e, 93f, 93g, 93h. As shown by the arcs in FIG. 7, each of the phased array antennas 93a, 93b, 93c, and 93d points in a different direction. In accordance with the invention, preferably each of the antennas covers an arc of 90°, i.e., a quadrant. As illustrated in FIG. 7, when the quadrants are combined, the quadrants do not overlap and the antenna assembly illustrated in FIGS. 6–8 covers 360°. As a result, the antenna assembly can be “pointed” in any direction by controlling which antenna is employed and the pointing of that antenna, as described below with respect to FIG. 23.
FIGS. 9–11 illustrate a second embodiment of a low-cost, steerable, phased array antenna assembly formed in accordance with the invention that is somewhat similar to, but different from, the embodiment of the invention illustrated in FIGS. 6–8. Like the embodiment of the invention illustrated in FIGS. 6–8, the embodiment of the invention illustrated in FIGS. 9–11 includes an L-shaped housing 101. Each leg of the housing includes two linear phased array antennas pointing in opposite directions. However, rather than the phased array antennas being mounted on the outer facing side of a different PCB sheet and the corporate feed mounted on the inner facing side of the same PCB sheet, the embodiment of the invention illustrated in FIGS. 9–11 includes a single PCB sheet 102 in each of the legs, mounted such that both surfaces face outwardly. The elements 103a, 103b, 103c, 103d, 103e, 103f, 103g, 103h of one of the linear phase array antennas are located on one face of the PCB sheet 102, and the elements 105a, 105b, 105c, 105d, 105e, 105f, 105g, 105h of the other phased array antenna are located on the other facing of the PCB sheet. Further, the corporate feeds 106 of the related antennas are located on the same side of the PCB sheet 102 as their related antenna elements. In addition, rather than high-permittivity dielectric layers being located inboard or between the PCB sheets supporting the antenna elements, as in the FIGS. 6–8 embodiment, the high-permittivity dielectric layers 107 of the FIGS. 9–11 embodiment are located outboard of the PCB sheets 102 that support the antenna elements and the corporate feeds. As before, the high-permittivity dielectric layers 107 overlie or are aligned with the corporate feeds 106 of their respective antennas. Further, suitable electromechanical movement mechanisms, such as electric motors 109 having threaded shafts for interacting with threaded receiving elements, i.e., jack screws 110, are used to position the high-permittivity dielectric layers 107 with respect to the phase shift transmission lines of the corporate feed 106 that each layer overlies to thereby control the air gap between the high-permittivity dielectric layer and the phase shift transmission lines of the corporate feed.
While, as noted above, the high-permittivity dielectric layers included in the embodiments of a low-cost, steerable, phased array antenna assembly formed in accordance with the invention illustrated in FIGS. 6–8 and 9–11, may be single dielectric sheets or layers formed of a high-permittivity material that is self supporting or mounted on a supporting sheet that is also formed of a dielectric material, alternatively, as illustrated in FIG. 12, the high-permittivity dielectric layers may be formed by a plurality of low cost, high-permittivity dielectric sections or slugs 113a, 113b, 113c, 113d, 115a, 115b, and 117 mounted on one surface of a supporting sheet 111 also formed of a dielectric material. The high-permittivity dielectric slugs are preferably rectangularly shaped. Regardless of shape, the high-permittivity dielectric slugs 113a, 113b, 113c, 113d, 115a, 115b, and 117 are sized and positioned on the supporting sheet 111 so as to be alignable with and overlie the respective phase shift transmission lines of the corporate feed. In this regard, as clearly illustrated in FIG. 12, the high-permittivity dielectric slugs include four relatively short slugs 113a, 113b, 113c, 113d, two intermediate length slugs 115a and 115b, and one long slug 117, each respectively equal in length to the short, intermediate, and long phase shift transmission lines of the corporate feed illustrated in FIG. 5 and described above.
FIGS. 13–15 illustrate a third alternative embodiment of a low-cost, steerable, phased array antenna assembly formed in accordance with the invention that, in some ways, is similar to the embodiment of the invention illustrated in FIGS. 6–8. More specifically, the embodiment of the invention illustrated in FIGS. 13–15 includes an L-shaped housing 121. Located at each leg of the L-shaped housing 121 are two PCB sheets 123, each supporting the elements and corporate feed of a phased array antenna. One of the sheets in each leg of the L-shaped housing is located adjacent the outer surface of the leg and the other sheet in the same leg is located adjacent the inner surface of the leg. Located on the outer surface of each of the PCB sheets 123 are a plurality of phased array antenna elements 125a, 125b, 125c, 125d, 125e, 125f, 125g, 125h. Located on the opposite side of each of the PCB sheets 123 is a corporate feed 126 connected to the antenna elements mounted on the sheet. The corporate feeds 126 are similar to the corporate feed illustrated in FIG. 5 and described above. Overlying each of the corporate feeds 126 is a high-permittivity dielectric cylinder 127, i.e., a cylinder formed of a low-cost, high-permittivity material, such as Rutile, or a Rutile compound containing alkali earth metals, such as Barium or Strontium. Located at one end of each of the high-permittivity dielectric cylinders is a suitable rotation mechanism, such as an electric motor 129. As best illustrated in FIG. 15, the rotational axes of the high-permittivity dielectric cylinders are offset from the rotational axes of their related electric motor 129. As a result, as the motors rotate their respective high-permittivity dielectric cylinders, the air gap between the cylinders and their respective phase shift transmission lines changes to thereby control the time delay or phase shift created by the phase shift transmission lines of the corporate feed in the manner previously described. As with other embodiments of the invention, support mechanisms for supporting the PCB sheets, high-permittivity dielectric cylinders, and electric motors are not illustrated in FIGS. 13–15, in order to avoid unduly complicating these figures.
FIGS. 16–18 illustrate a fourth alternative embodiment of a low-cost, steerable, phased array antenna assembly formed in accordance with the invention. The embodiment of the invention illustrated in FIGS. 16–18, in essence, is a combination of the embodiments of the invention illustrated in FIGS. 9–11 and FIGS. 13–15. More specifically, the embodiment of the invention illustrated in FIGS. 16–18 includes an L-shaped housing 131. Mounted in the center of each of the legs of the L-shaped housing 131 is a PCB sheet 133 that supports the elements and corporate feeds of two phased array antennas. More specifically, located on both of the outer faces of each of the PCB sheets 133 is a linear array of antenna elements 135a, 135b, 135c, 135d, 135e, 135f, 135g, 135h and 137a, 137b, 137c, 137d, 137e, 137f, 137g, 137h. Located on both sides of the PCB sheets 133 are corporate feeds 134, 136 for the antenna elements. Mounted outboard of each of the antenna feeds is a high-permittivity dielectric cylinder 138. The high-permittivity dielectric cylinders each overlies a respective corporate feed. Each of the cylinders 138 is rotated by a related rotation mechanism, such as an electric motor 139. As with the embodiment of the invention illustrated in FIGS. 13–15, and as illustrated in FIG. 18, the axis of rotation of each of the high dielectric cylinders is offset from the axis of rotation of its related motor 139. As a result, as the motors rotate their respective cylinders, the air gap between the cylinders and the phase shift transmission lines of their respective corporate feeds change whereby the time delay or phase shift of the phase shift transmission lines of the corporate feed changes in synchronism.
As will be readily appreciated by those skilled in this art and others, the embodiments of the invention illustrated in FIGS. 6–18 are based on an electromechanical system for controlling the air gap between a high-permittivity dielectric layer or cylinder and the phase shift transmission lines of a corporate feed. Because the air gap changes in synchronization for all of the corporate feed phase shift transmission lines, the same time delay or phase shift change occurs for each incremental section of the phase shift transmission lines. Because, as illustrated in FIG. 5 and discussed above, individual sections have different lengths related by the factor ½ the delays per phase shift transmission line are mathematically related. Because the incremental amount of change remains constant, the mathematical relationship between the various phase shift transmission lines remains constant, even though the total delay of each phase shift transmission line is different as determined by the length of the individual phase shift transmission lines.
As noted above, the embodiments of the invention illustrated in FIGS. 6–18 all depend on electromechanically controlling the air gap between a high-permittivity dielectric layer or cylinder and the phase shift transmission lines of a corporate feed. An alternate to electromechanically varying the air gap is to electrically control the permittivity of a fixed position dielectric layer that overlies the phase shift transmission lines of a corporate feed. It is well known that the permittivity of ferroelectric materials varies under the influence of an electric field. Rutile and compounds of Rutile containing alkali earth metals such as Barium or Strontium exhibit this ferroelectric property. Thin films of such materials have been used to form ferroelectric lenses.
FIGS. 19–22 illustrate alternative embodiments of low-cost, steerable, phased array antenna assemblies formed in accordance with the invention that employ ferroelectric materials whose permittivity is varied under the influence of an electric field to control the delay time (i.e., phase shift) of the phase shift transmission lines of a corporate feed of the type illustrated in FIG. 5 and employed in a phased array antenna. More specifically, as with other embodiments of the invention, the embodiment of the low-cost, steerable, phased array assembly illustrated in FIGS. 19 and 20 includes an L-shaped housing 141. Mounted in each of the legs of the L-shaped housing 141 are two PCB sheets, i.e., two sheets of dielectric material 143. One of the PCB sheets in each of the legs is positioned adjacent to the outer face of the related leg of the L-shaped housing and the other sheet is positioned adjacent the inner face of the leg. The outer facing sides of the PCB sheet each includes a plurality of linearly arrayed antenna elements 145a,145b, 145c, 145d, 145e, 145f, 145g, 145h and 147a, 147b, 147c, 147d, 147e, 147f, 147g, 147h. Thus, as with the FIGS. 6–18 embodiments of the invention, the antenna elements of the FIGS. 19–20 embodiment point outwardly from the four faces of the legs of the L-shaped housing 141. Mounted on the opposite sides of the PCB sheets 143 from the antenna elements 145a, 145b, 145c, 145d, 145e, 145f, 145g, 145h and 147a, 147b, 147c, 147d, 147e, 147f, 147g, 147h, i.e., on the inwardly facing sides of the PCB sheets are corporate feeds 148 of the type illustrated in FIG. 5 and described above. Overlying each of the corporate feeds 148 is a ferroelectric layer 149, i.e., a layer of material whose permittivity varies under the influence of an electric field. The position of the ferroelectric layers 149 is fixed with respect to the related corporate feed 149. As illustrated by the wires 150, electric power is supplied to the ferroelectric layers 149. Controlling the electric power applied to the ferroelectric layers controls the time delay or phase shift of the phase shift transmission lines of the related corporate feed similar to the way controlling the air gap controls the time delay or phase shift of the phase shift transmission lines of the previously described embodiments of the invention.
FIGS. 21 and 22 illustrate a further embodiment of a low-cost, steerable, phased array antenna assembly formed in accordance with the invention that also employs ferroelectric layers to control the phase shift of the phase shift transmission lines of corporate feeds. More specifically, as with the other embodiments of the invention, the low-cost, steerable, phased array antenna assembly illustrated in FIGS. 21 and 22 includes an L-shaped housing 151. As with the embodiments of the invention illustrated in FIGS. 9–11 and 16–18, located in the center of each leg of the L-shaped housing is a PCB sheet 153. Located on both of the outer surfaces of each of the PCB sheets is a linear array of antennae elements 155a, 155b, 155c, 155d, 155e, 155f, 155g, 155h and 157a, 157b, 157c, 157d, 157e, 157f, 157g, 157h. Also located on both sides of the sheet is a corporate feed 158 of the type illustrated in FIG. 5 and described above. The corporate feeds 158 are connected to the antenna elements located on the same sides of the PCB sheets as the corporate feeds. Overlying each of the corporate feeds is a ferroelectric layer 159, i.e., a layer formed of a ferroelectric material whose permittivity varies under the influence of an electric field. As with the embodiment illustrated in FIGS. 19 and 20, varying the electric power applied to the ferroelectric layer controls the time delay or phase shift created by the phase shift transmission lines of the related corporate feed.
FIG. 23 is a block diagram illustrating a control system suitable for controlling the pointing of any of the low-cost, steerable, phased array antennas illustrated in FIGS. 6–22. The control system includes a pointing direction controller shown coupled to four linear phased array antennas 165a, 165b, 165c, 165d of the type illustrated in FIGS. 6–22 and described above. A steering control signal 161 is applied to the pointing direction controller 163. The steering control signal includes data that defines the antenna pointing direction. The pointing direction controller first decides which of the four linear phased array antennas 165a, 165b, 165c, 165d covers the quadrant within which the location to be pointed to lies. The pointing direction controller then determines the transmission line phase shift necessary to precisely point at the location. The transmission line phase shift information is used to control the position of the high-permittivity dielectric layers (FIGS. 6–12), the rotation angle of the high-permittivity dielectric cylinders (FIGS. 13–18), or the power applied to the ferroelectric layers (FIGS. 19–22).
FIGS. 24 and 25 illustrate exemplary uses of a low-cost, steerable, phased array antenna formed in accordance with this invention. Such antennas can be used in various environments. FIGS. 24 and 25 illustrate the invention used in connection with a WiFi system, included in a house or business residence. More specifically, FIG. 24 illustrates a plurality of residences 171a, 171b, 171c, 171d, each containing a low-cost, steerable, phased array antenna 173a, 173b, 173c, 173d formed in accordance with the invention. The antennas 173a, 173b, 173c, 173d are each shown as separately wire connected to an Internet service provider, such as a cable company 175. The service provider, in turn, is shown as connected to the Internet 177.
FIG. 25, like FIG. 24, includes a plurality of residences 181a, 181b, 181c, 181d each containing a low-cost, steerable, phased array antenna 183a, 183b, 183c, 183d formed in accordance with the invention. However, in contrast to FIG. 24, only one of the residences 181b has its antenna 183b wire connected to an Internet service provider such as a cable company 185. The Internet service provider is connected to the Internet 187. All of the other residences 181a, 181c, and 181d have their respective antennas 183a, 183c, and 183d coupled in a wireless manner to the antenna 183b of the house 181b connected to the Internet service provider.
While various embodiments of the invention have been illustrated and described, as will be readily appreciated by those skilled in the art and others, various changes can be made therein without departing from the spirit and scope of the invention. For example, the antenna elements can be arrayed other than linearly. Mechanisms for moving high-permittivity dielectric layers or cylinders other than those specifically disclosed can be employed in other embodiments of the invention. Further, antenna housing other than L-shaped housings can be employed. And the antennas can be deployed separately rather than in an assembly of four antennas. Hence, within the scope of the appended claims it is to be understood that the invention can be practiced otherwise than as specifically described here.
Patent Grant
7034748
