Apparatus for coupling electromagnetic signals

[0002] The following applications contain subject matter similar to the subject matter of this application.

[0003] U.S. patent application Ser. No. 12/199,724, filed Jul. 19, 2002, entitled “A TUNABLE ELECTROMAGNETIC TRANSMISSION STRUCTURE FOR EFFECTING COUPLING OF ELECTROMAGNETIC SIGNALS”;

[0004] U.S. patent application Ser. No. 10/199,732, filed Jul. 19, 2002, entitled “WAVEGUIDE APPARATUS”; and

[0005] U.S. patent application Ser. No. 10/199,680, filed Jul. 19, 2002, entitled “ANTENNA APPARATUS”.

[0006] The present invention is directed to electromagnetic antennas, and especially to electromagnetic antennas employing a plurality of antenna elements known as patch antenna elements. Such patch antenna construction is advantageous in constructing antennas that are known as steerable beam antennas. Steerable beam antennas employ fixed antenna elements, such as patch antenna elements, to “steer” loci of sensitivity (i.e., transmitting beams or bearings of reception) by establishing predetermined interference patterns among the various patch antenna elements. The desired predetermined interference patterns are commonly effected by imposing phase differences among the various patch antenna elements.

[0007] It is desirable that patch antenna elements in steerable beam antennas be closely or densely situated in order that maximum interaction among the various patch antenna elements may be realized. Prior art coupling structures employed for coupling the respective patch antenna elements with a signal coupling locus (e.g., a transmission line leading to a host device such as a transceiver for radio or radar operations) have heretofore occupied an undesirable lateral expanse about the respective antenna patch elements. As a result, antenna patch elements have not been as densely situated as desired. One solution has been to provide larger antenna patch elements. Installing an antenna patch element that occupies a larger area provides a larger expanse in the vicinity of that patch element for effecting the requisite electromagnetic coupling. However, the larger the respective patch elements, the less resolution that can be established in steering beam operations. That is, larger patch elements yield coarser beam patterns that result in coarser control of beam steering operations.

[0008] There is a need for an apparatus for coupling electromagnetic signals that permits closely arranged arrays of small antenna patch elements.

[0009] While such an apparatus is particularly useful for steerable beam antennas using closely arranged antenna patch elements, the apparatus has utility in other antenna coupling structures and arrangements. The invention disclosed, described and claimed herein is not limited to steerable beam antenna devices.

[0010] An apparatus for coupling electromagnetic signals from a signal transfer locus for electromagnetic transfer with a proximal medium includes: (a) An antenna element presenting elements in a spaced parallel relation with an antenna plane on a first dielectric substrate. (b) A transmission structure including a second dielectric substrate parallel with a transmission plane perpendicular with the antenna plane and including a slot line structure and a ground plane. The slot line structure has a first end proximal with the signal transfer locus and a second end within electromagnetic coupling range of the antenna element. The ground plane cooperates with the slot line structure and the second dielectric substrate to effect transmission of electromagnetic signals between the first end and the second end. (c) A coupling aperture traverses a respective antenna element adjacent each respective second end in register with the respective second end.

[0011] It is, therefore, an object of the present invention to provide an apparatus for coupling electromagnetic signals that permits closely arranged arrays of small antenna patch elements.

[0012] Further objects and features of the present invention will be apparent from the following specification and claims when considered in connection with the accompanying drawings, in which like elements are labeled using like reference numerals in the various figures, illustrating the preferred embodiments of the invention.

[0013] FIG. 1 is a schematic perspective view of a prior art electromagnetic signal coupling arrangement with an antenna element.

[0014] FIG. 2 is a schematic section view of the antenna apparatus of the present invention.

[0015] FIG. 3 is a schematic perspective view of an electromagnetic signal coupling arrangement with an antenna element employed with the preferred embodiment of the present invention.

[0016] FIG. 4 is a schematic section view of the coupling arrangement illustrated in FIG. 3, taken along Section 4—4 in FIG. 3.

[0017] FIG. 5 is a schematic perspective view of a signal coupling element employed in the preferred embodiment of the present invention.

[0018] FIG. 6 is a schematic perspective view of an electromagnetic signal coupling arrangement with a radial waveguide element employed in the present invention.

[0019] FIG. 7 is a top plan schematic view illustrating details relating to construction of the preferred embodiment of selected portions of the antenna apparatus of the present invention.

[0020] FIG. 1 is a schematic perspective view of a prior art electromagnetic signal coupling arrangement with an antenna element. In FIG. 1, an antenna element 10 and a slot line electromagnetic coupling structure 12 are illustrated in an installed orientation. Antenna element 10 is illustrated in a partially exploded view in order to simplify FIG. 1. Antenna element 10 includes a first dielectric substrate 20 with a first conductive element 22 on first substrate 20. Antenna element 10 further includes a second dielectric substrate 24 with a second conductive element 24 on second substrate 24. First conductive element 22 is separated from second conductive element 26 by second substrate 24. First substrate 20, first conductive element 22, second substrate 24 and second conductive element 26 are all substantially planar. In an assembled orientation, first substrate 20, first conductive element 22, second substrate 24 and second conductive element 26 are in a substantially parallel abutting relationship and substantially in register, as indicated by dotted lines 28, 29.

[0021] An aperture 30 traverses first conductive element 22. Antenna element 10 is designed for efficient performance at an operating frequency f₀. Dimensions of aperture 30 are determined for efficient operation as a function of operating frequency f₀. Aperture 30 is preferably substantially rectangular oriented about a major axis 32.

[0022] Slot line coupling structure 12 includes a first dielectric slot line substrate 40 with a first transmission conductive layer 42 on a side of first slot line substrate 40 that is distal from antenna element 10, and a second transmission conductive layer 44 on a side of first slot line substrate 40 that is proximal to antenna element 10. Second transmission conductive layer 44 has a slot 50 traversing second transmission conductive layer 44. Slot 50 extends from a first edge 46 toward a second edge 48 opposing first edge 46 to a slot termination locus 51. Slot 50 is oriented about an axis 52. Axes 32, 52 are substantially perpendicular.

[0023] Thus, electromagnetic signals are transmitted, for example, from a signal coupling locus (not shown in FIG. 1) along slot 50 toward slot termination locus 51. As the transmitted signals pass aperture 30, electromagnetic coupling occurs through aperture 30 to establish a transmission path with respect to antenna element 10. That is, the coupled signals are transmitted by cooperation of first conductive element 22 and second conducive element 24. In such manner, signals from a host device (not shown in FIG. 1) are transmitted to antenna element 10 for transmission via slot 50 and via signal coupling via aperture 30.

[0024] One skilled in the art of antenna design will recognize that receive operations by antenna element 10 will be carried out in substantially the same manner to couple signals received by antenna element 10, via aperture 30 to slot 50 and thence via slot 50 to a host device (not shown in FIG. 1). Transmitting operations of antenna elements, including the antenna apparatus of the present invention, are used frequently throughout this specification as illustrative of the operation of antenna apparatuses in either transmission or reception operations.

[0025] A significant shortcoming of the prior art coupling arrangement illustrated in FIG. 1 is the parallel relationship of antenna element 10 and slot line coupling structure 12. One must provide sufficient expanse for antenna element 10, or provide sufficient space between adjacent antenna elements 10 (i.e., in an array of a plurality of antenna elements 10), to accommodate the lateral room required by slot line coupling structure 12 to reach its host device (not shown in FIG. 1). This requirement for lateral room by slot line coupling structure 12 is a drawback in antenna devices using a plurality of antenna elements 10, such as by way of example and not by way of limitation an array of antenna patch elements configured for operation as a steerable beam antenna device. The lateral room requirement for slot line coupling structure 12 limits how close adjacent antenna patch elements (e.g., antenna element 10; FIG. 1) can be placed, and may also limit how small each respective antenna element 10 may be.

[0026] FIG. 2 is a schematic section view of the antenna apparatus of the present invention. In FIG. 2, an antenna apparatus includes a radial waveguide 102 coupled with a signal transfer structure 104 at a signal transfer locus 106. Signal transfer structure 104 is representatively illustrated in FIG. 2 as a coaxial cable 108 borne in a grounded sheath 110. Other signal transfer structures, such as a waveguide, a two-line transmission line, a slot line or another signal transmission structure may be employed within the intended scope of the invention.

[0027] Coaxial cable 108 is coupled with a transition element 112. Transition element 112 facilitates substantially even distribution of energy coupled from coaxial cable 108 to radial waveguide 102. Radial waveguide 102 includes a first conductive member 120 and a second conductive member 122. Conductive members 120, 122 are preferably metal, preferably substantially circular and centered on a common axis 116, preferably planar and preferably parallel. FIG. 2 illustrates radial waveguide 102 in a section view taken substantially along a diameter of conductive members 120, 122. Signal transfer locus 106 is substantially at axis 116. A dielectric material may be introduced between conductive members 120, 122 if desired (not shown in FIG. 2). Grounded sheath 110 is connected with conductive member 120. A wall 118 of signal absorbing material preferably establishes an outer boundary for radial waveguide 102.

[0028] Second conductive member 122 is provided with a plurality of signal coupling loci embodied in a plurality of signal coupling apertures, or slots 130, 132, 134, 136. Signal coupling slots 130, 132, 134, 136 traverse second conductive member 122.

[0029] A plurality of signal coupling elements 140, 142, 144, 146 are provided. Each respective signal coupling element 140, 142, 144, 146 is substantially in register with a respective signal coupling slot 130, 132, 134, 136. Each respective signal coupling element 140, 142, 144, 146 is embodied in a slot line signal transmission structure having one side of a substrate clad or covered in a conductive, preferably metal, layer, and an opposing side of the substrate bearing two conductive, preferably metal, lands with a narrow substantially linear slot separating the two lands. Antenna apparatus 100 is designed for efficient performance at an operating frequency f₀. The width of the slot that separates the two conductive lands on one side of each respective signal coupling element 140, 142, 144, 146 is a function of operating frequency f₀.

[0030] Thus, signal coupling element 140 has two metal lands 150, 152 separated by a slot 154. A substrate 156 is visible in FIG. 2 between lands 150, 152. Another conductive land on the opposing side of substrate 156 is not visible in FIG. 2. Signal coupling element 142 has two metal lands 160, 162 separated by a slot 164. A substrate 166 is visible in FIG. 2 between lands 160, 162. Another conductive land on the opposing side of substrate 166 is not visible in FIG. 2. Signal coupling element 144 has two metal lands 170, 172 separated by a slot 174. A substrate 176 is visible in FIG. 2 between lands 170, 172. Another conductive land on the opposing side of substrate 176 is not visible in FIG. 2. Signal coupling element 146 has two metal lands 180, 182 separated by a slot 184. A substrate 186 is visible in FIG. 2 between lands 180, 182. Another conductive land on the opposing side of substrate 186 is not visible in FIG. 2.

[0031] A plurality of antenna elements 190, 192, 194, 196 are couplingly provided electromagnetic signals by signal coupling elements 140, 142, 144, 146. Each respective antenna element 190, 192, 194, 196 is substantially in register with a respective signal coupling element 140, 142, 144, 146. Each respective antenna element 190, 192, 194, 196 is embodied in a substrate clad or covered in a conductive, preferably metal, layer on each of two opposing faces, or sides. Thus, antenna element 190 is embodied in a substrate 200 with conductive, preferably metal, layers 202, 204 on opposing faces of substrate 200. Antenna element 192 is embodied in a substrate 210 with conductive, preferably metal, layers 212, 214 on opposing faces of substrate 210. Antenna element 194 is embodied in a substrate 220 with conductive, preferably metal, layers 222, 224 on opposing faces of substrate 220. Antenna element 196 is embodied in a substrate 230 with conductive, preferably metal, layers 232, 234 on opposing faces of substrate 230.

[0032] Coupling apertures are provided in each respective antenna element metal layer adjacent with a respective coupling element for effecting coupling between a respective signal coupling element—antenna element pair. Thus, metal layer 204 of antenna element 190 is provided with an aperture 203 substantially in register with slot 154 of signal coupling element 140. Metal layer 214 of antenna element 192 is provided with an aperture 213 substantially in register with slot 164 of signal coupling element 142. Metal layer 224 of antenna element 194 is provided with an aperture 223 substantially in register with slot 174 of signal coupling element 144. Metal layer 234 of antenna element 196 is provided with an aperture 233 substantially in register with slot 184 of signal coupling element 146.

[0033] Energy is couplingly provided from coaxial cable 108 at signal transfer locus 106. Transition element 112 assists in substantially evenly distributing electromagnetic energy in the form of electromagnetic waves 126. Energy embodied in electromagnetic waves 126 is couplingly transferred with signal coupling elements 140, 142, 144, 146 via signal coupling slots 130, 132, 134, 136. Signal coupling elements 140, 142, 144, 146 couplingly transfer electromagnetic energy via slots 154, 164, 174, 184 and apertures 203, 213, 223, 233 with antenna elements 190, 192, 194, 196. Orientation of each respective signal coupling slot 130, 132, 134, 136 determines the portion of the respective electromagnetic wave 126 traversing a respective signal coupling slot 130, 132, 134, 136. It is by selectively orienting respective signal coupling slots 130, 132, 134, 136 that one may assure that respective electromagnetic signals 126 arriving at respective signal coupling elements 140, 142, 144, 146 are substantially of equal signal strength. This aspect of the antenna apparatus of the present invention is discussed in greater detail in connection with FIG. 7.

[0034] FIG. 3 is a schematic perspective view of an electromagnetic signal coupling arrangement with an antenna element employed with the preferred embodiment of the present invention. Elements illustrated in FIG. 2 are indicated with like reference numerals in FIG. 3. In FIG. 3, signal coupling element 140 has two conductive, preferably metal lands 150, 152 on one face, or side of a substrate 156. A slot 154 extends to substrate 156 and separates metal lands 150, 152. Another metal land 151 is borne upon an opposing face of substrate 156. Antenna element 190 is embodied in a substrate 200 with conductive, preferably metal layers 202, 204 on opposing faces of substrate 200. Antenna element 190 is in substantially abutting relationship with signal coupling element 140. Antenna element 190 includes a coupling aperture 203 traversing metal layer 204. Signal coupling element 140 is illustrated in phantom to clearly indicate its relationship with coupling aperture 203. Coupling aperture 203 is substantially in register with slot 154. Electromagnetic signals are conveyed or transmitted by slot 154 to be coupled via coupling aperture 203 with antenna element. Signal coupling element 140 is substantially planar. Antenna element 190 is substantially planar. Signal coupling element 140 is substantially perpendicular with antenna element 190. In the substantially perpendicular arrangement between signal coupling element 140 and antenna element 190 there is little lateral space required by signal coupling element 140 for delivering electromagnetic signals to antenna element 190. The advantageous structure illustrated in FIG. 3 permits using smaller antenna elements 190 in denser, more closely juxtaposed arrays of antenna elements than is feasible using the prior art coupling arrangement illustrated in FIG. 1.

[0035] FIG. 4 is a schematic section view of the coupling arrangement illustrated in FIG. 3, taken along Section 4—4 in FIG. 3. Elements illustrated in FIG. 3 are indicated with like reference numerals in FIG. 4. In FIG. 4, signal coupling element 140 has two conductive, preferably metal lands 150, 152 on one face, or side of a substrate 156. A slot 154 extends to substrate 156 and separates metal lands 150, 152. Another metal land (metal land 151; FIG. 3) that is borne upon an opposing face of substrate 156 is not visible in FIG. 4. Antenna element 190 is embodied in a substrate 200 with conductive, preferably metal layers 202, 204 on opposing faces of substrate 200. Antenna element 190 is in substantially abutting relationship with signal coupling element 140. Antenna element 190 includes a coupling aperture 203 traversing metal layer 204. Coupling aperture 203 is substantially in register with slot 154. Electromagnetic signals are conveyed or transmitted by slot 154 to be coupled via coupling aperture 203 with antenna element. Signal coupling element 140 is substantially planar. Antenna element 190 is substantially planar. Signal coupling element 140 is substantially perpendicular with antenna element 190. An additional feature that may be employed in connection with antenna element 190 is illustrated in FIG. 4 in dotted line format to indicate the alternate nature of the additional structure. That is, in an alternate embodiment of the antenna apparatus of the present invention, an additional substrate 215 may be borne upon metal layer 202, and an additional conductive, preferably metal layer 217 may be borne upon substrate 215 on a face distal from conductive layer 202. Providing an additional metal layer 217 within electromagnetic coupling range of metal layer 202 permits operation of antenna element 190 as a broadband antenna.

[0036] FIG. 5 is a schematic perspective view of a signal coupling element employed in the preferred embodiment of the present invention. In FIG. 5, a signal coupling element 240 is configured substantially as described earlier in connection with FIGS. 2-4, with the additional feature that signal coupling element 240 is configured for phase shifting operation. Thus, signal coupling element 240 has two conductive, preferably metal lands 250, 252 on one face, or side of a substrate 256. Another metal land 251 is borne upon an opposing face of substrate 256. A slot 254 extends to substrate 256 and separates metal lands 250, 252.

[0037] Slot 254 is filled with a dielectric phase shifting material 258. Phase shifting material 258 may somewhat overfill slot 254, so long as an electrical potential may be applied across phase shifting material 258, as by applying a voltage across metal lands 250, 252 from terminals 260, 262 via electrical leads 264, 266. Phase shifting material 258 can be tuned at room temperature to alter the phase of electromagnetic signals traversing phase shifting material 258 in slot 254 by controlling an electric field across phase shifting material 258. Such tuning may be effected, for example, by altering electrical potential across metal lands 250, 252 via terminals 260, 262 and electrical leads 264, 266. Phase shifting material 258 is preferably substantially the same material as is described in U.S. patent application Ser. No. 09/838,483, filed Apr. 19, 2001, by Louise C. Sengupta and Andrey Kozyrev, for “WAVEGUIDE-FINLINE TUNABLE PHASE SHIFTER”, assigned to the assignee of the present invention. That is, the preferred embodiment of phase shifting material 258 is comprised of Barium-Strontium Titanate, Ba_xSr_1−xTiO₃(BSTO), where x can range from zero to one, or BSTO-composite ceramics. Examples of such BSTO composites include, but are not limited to: BSTO-MgO, BSTO-MgAl₂O₄, BSTO-CaTiO₃, BSTO-MgTiO₃, BSTO-MgSrZrTiO₆and combinations thereof. Other materials suitable for employment as phase shifting material 258 may be used partially or entirely in place of barium strontium titanate. An example is Ba_xCa_1−xTiO3, where x ranges from 0.2 to 0.8, and preferably from 0.4 to 0.6. Additional alternate materials suitable for use as phase shifting material 258 include ferroelectrics such as Pb_xZr_1−xTiO3 (PZT) where x ranges from 0.05 to 0.4, lead lanthanum zirconium titanate (PLZT), lead titanate (PbTiO₃), barium calcium zirconium titanate (BaCaZrTiO₃), sodium nitrate (NaNO₃), KNbO₃, LiNbO₃, LiTaO₃, PbNb₂O₆, PbTa₂O₆, KSr(NbO₃) and NaBa₂(NbO₃)₅and KH₂PO₄. In addition, phase shifting material 258 may include electronically tunable materials having at least one metal silicate phase. The metal silicates may include metals from Group 2A of the Periodic Table, i.e., Be, Mg, Ca, Sr, Ba, and Ra, preferably Mg, Ca, Sr and Ba. Preferred metal silicates include Mg₂SiO₄, CaSiO₃, BaSiO₃and SrSiO₃. In addition to Group 2A metals, metal silicates in phase shifting material 258 may include metals from Group 1A, i.e., Li, Na, K, Rb, Cs and Fr, preferably Li, Na and K. For example, such metal silicates may include sodium silicates such as Na₂SiO₃and NaSiO₃-5H₂O, and lithium-containing silicates such as LiAlSiO₄, Li₂SiO₃and Li₄SiO₄. Metals from Groups 3A, 4A and some transition metals of the Periodic Table may also be suitable constituents of the metal silicate phase of phase shifting material 258. Additional metal silicates may include Al₂Si₂O₇, ZrSiO₄, KAlSi₃O₈, NaAlSi₃O₈, CaAl₂Si₂O₈, CaMgSi₂O₆, BaTiSi₃O₉and Zn₂SiO₄.

[0038] FIG. 6 is a schematic perspective view of an electromagnetic signal coupling arrangement with a radial waveguide element employed in the present invention. Elements illustrated in FIGS. 2-4 are indicated with like reference numerals in FIG. 6. In FIG. 6, conductive member 122 is provided with a signal coupling aperture, or slot 130. Signal coupling slot 130 traverses second conductive member 122. Signal coupling element 140 is substantially in register with signal coupling slot 130. Signal coupling element 140 is embodied in a slot line signal transmission structure having one side of a substrate clad or covered in a conductive, preferably metal, layer, and an opposing side of the substrate bearing two conductive, preferably metal, lands with a narrow substantially linear slot separating the two lands. Antenna apparatus 100 (FIG. 2) is designed for efficient performance at an operating frequency f₀. The width of the slot that separates the two conductive lands on one side of signal coupling element 140 is a function of operating frequency f₀. Thus, signal coupling element 140 has two metal lands 150, 152 on one side or face of a substrate 156 separated by a slot 154. Another conductive land 151 is on the opposing face of substrate 156.

[0039] FIG. 7 is a top plan schematic view illustrating details relating to construction of the preferred embodiment of selected portions of the antenna apparatus of the present invention. In FIG. 7, a circular conductive member 322 of an antenna apparatus has two signal coupling elements 340, 342. Conductive member 322 is similar to second conductive member 122 (FIG. 2); signal coupling elements 340, 342 are similar to signal coupling elements 140, 142 (FIG. 2). Signal coupling apertures, or slots 330, 332 traverse conductive member 322. Signal coupling slots 330, 332 are similar to signal coupling slots 130, 132 (FIG. 2).

[0040] Signal coupling element 340 has two metal lands 350, 352 on one side or face of a substrate 356 separated by a slot 354. Another conductive land 351 is on the opposing face of substrate 356. Signal coupling element 342 has two metal lands 360, 362 on one side or face of a substrate 366 separated by a slot 364. Another conductive land 361 is on the opposing face of substrate 366. Signal coupling elements 340, 342 are oriented on conductive member 322 with their respective substrates 356, 366 parallel with a radius 301 from center 300 of conductive member 322. A second radius 302 is substantially perpendicular with radius 301 so that substrate 356 is substantially perpendicular with radius 302. A coupling element angle φ defines the angle established between the planar face of a respective signal coupling element and a radius substantially bisecting a coupling slot in the respective signal coupling element. Thus, angle φ₁is established for signal coupling element 340 with respect to radius 302 at substantially 90 degrees. Angle φ₂is established for signal coupling element 342 with respect to radius 301 at substantially 0 degrees. The antenna apparatus of the present invention typically employs a greater number of signal coupling elements (and associated antenna elements) in a more closely packed, denser distribution on conductive member 322 than are shown in FIG. 7. Only signal coupling elements 340, 342 are shown in FIG. 7 in order to simplify the drawing to facilitate understanding the invention. It is preferred, but not required that the various signal coupling elements 340, 342 be oriented parallel with a common radius, as illustrated in FIG. 7. However, also in the interest of simplifying FIG. 7 to facilitate understanding the invention, signal coupling elements 340, 342 are both parallel with radius 301.

[0041] Signal coupling slot 330 is substantially rectangular having a major axis 333 and a minor axis 331 substantially perpendicular with major axis 333. Energy is transferred across signal coupling slot 330 substantially parallel with minor axis 331 for effecting electromagnetic signal coupling with signal coupling element 340. Major axis 333 establishes a coupling slot angle θ₁with radius 302. Energy transferred across signal coupling slot 330 parallel with minor axis 331 is a vector component of signals propagated from center 300 (described in connection with FIG. 2). If minor axis 331 is perpendicular with radius 302, then no component of energy will be available for transfer across signal coupling slot 330 parallel with minor axis 331. Signal coupling slot 332 is substantially rectangular having a major axis 335 and a minor axis 337 substantially perpendicular with major axis 335. Energy is transferred across signal coupling slot 332 substantially parallel with minor axis 337 for effecting electromagnetic signal coupling with signal coupling element 342. Major axis 335 establishes a coupling slot angle θ₂with radius 301. Energy transferred across signal coupling slot 332 parallel with minor axis 337 is a vector component of signals propagated from center 300 (as described in connection with FIG. 2). If minor axis 337 is perpendicular with radius 301, then no component of energy will be available for transfer across signal coupling slot 332 parallel with minor axis 337.

[0042] The inventor has discovered that it is preferable for coupling element angle φ and coupling slot angle θ to be related according to the following expression in order to assure effective coupling across respective coupling slots to respective coupling elements:

[0043] φ=180−2θ  [1]

[0044] Given such a relation between coupling element angle φ and coupling slot angle θ it may be observed that the respective angles may range among the following values:

[0045] φ→0 degrees to 90 degrees  [2]

[0046] θ→90 degrees to 45 degrees  [3]

[0047] By arranging the dimensions of signal coupling slots, such as signal coupling slots 330, 332, to accommodate a desired operating frequency f₀and by adjusting the attitude (manifested in respective coupling slot angles θ and coupling element angles φ) of respective signal coupling slots, such as signal coupling slots 330, 332, one can control the amount of energy couplingly transferred between a respective signal coupling slot and its associated signal coupling element for further transfer with a respective antenna element (not shown in FIG. 7; see FIG. 2). This capability to control the mount of energy couplingly transferred permits a designer to assure that varying distance from a signal transfer locus (e.g., signal transfer locus 106; FIG. 2) at center 300 of conductive member 322 may be accommodated to ensure that signals couplingly provided to respective signal coupling elements via respective signal coupling slots will be of substantially equal signal strength. Thus, coupling slot angles θ₁, θ₂may be individually selected for signal coupling slots 330, 332 to assure that signals couplingly transferred with signal coupling elements 340, 342 have substantially equal signal strength despite signal coupling slots 330, 332 being at different distances from center 300, and despite coupling element angles φ₁, φ₁being different for respective signal coupling elements 340, 342.

[0048] The antenna apparatus of the present invention permits denser juxtaposition of smaller individual antenna patch elements than is permitted using prior art coupling technology (FIG. 1). Moreover, the antenna apparatus of the present invention is particularly well suited for steerable beam antenna arrays because it provides a compact phase adjusting structure and a design facility for equalizing signal strengths of various signals couplingly provided to respective antenna patch elements.

[0049] It is to be understood that, while the detailed drawings and specific examples given describe preferred embodiments of the invention, they are for the purpose of illustration only, that the apparatus of the invention is not limited to the precise details and conditions disclosed and that various changes may be made therein without departing from the spirit of the invention which is defined by the following claims: