WAVEGUIDE ADAPTER FOR SLOT ANTENNAS

Abstract

Embodiments if the present disclosure relate to a radio frequency (RF) adapter configured to mimic the load that an antenna element would see if it was otherwise radiating into free space. The adapter is configured to come in direct contact with an antenna ground plane so that modes of propagation may be established, and energy coupled from a radiating antenna element into the adapter. The adapter may be of any form that will support direct coupling and include a waveguide (WG) that is coupled to a planar slot radiating element of an antenna array. The WG can have a length, width, height, and a central longitudinal axis and an internal surface. A resistive load can be disposed along the central longitudinal axis of the WG and a reactive load can be disposed in the internal surface of the WG.

Claims

1. A radio frequency (RF) adapter comprising: a waveguide having a length, width, height, and a central longitudinal axis and internal electrically conducting surfaces; an impedance material disposed within an interior of the waveguide; and a reactive obstacle disposed in the interior of the waveguide contacting one or more of the conducting surfaces; and a resistive obstacle disposed in the interior of the waveguide and along the central longitudinal axis; and a resistive obstacle disposed in the interior of the waveguide free from contact with any of the conducting surfaces and along the central longitudinal axis.

2. The RF adapter of claim 1, wherein: the waveguide is adapted to directly couple with an antenna ground plane to receive energy from a radiating element and into the waveguide; and the waveguide, the impedance material, and the reactive and resistive obstacles are arranged to provide a loading impedance substantially similar to that of free space.

3. The RF adapter of claim 1, wherein the waveguide comprises an outer conductor.

4. The RF adapter of claim 1, wherein the impedance material comprises dielectric insulator.

5. The RF adapter of claim 1, wherein the impedance material electrically attenuates an RF signal.

6. The RF adapter of claim 1, wherein the impedance material magnetically attenuates an RF signal.

7. The RF adapter of claim 6, wherein the resistive obstacle comprises a resistive card (R-card) configured to attenuate a primary electric field along the length of the waveguide.

8. The RF adapter of claim 7, wherein the resistive R-card is tapered along the length of the waveguide.

9. The RF adapter of claim 4, wherein the dielectric insulator comprises a loss dielectric configured to attenuate a primary electric field along the length of the waveguide.

10. The RF adapter of claim 7, wherein the impedance material comprises a magnetic media configured to attenuate a primary magnetic field along the length of the waveguide.

11. The RF adapter of claim 7, wherein the impedance material comprises a ferromagnetic media configured to attenuate a primary surface currents along the length of the waveguide.

12. The RF adapter of claim 1, wherein the reactive obstacle presents an inductance to counter a capacitive waveguide effect.

13. The RF adapter of claim 1, wherein the reactive obstacle comprises metallic fins disposed along one or more walls of the waveguide.

14. The RF adapter of claim 13, wherein the reactive obstacle comprises metallic posts disposed along one or more walls of the waveguide.

15. A radio frequency (RF) sensor testing fixture comprising: a housing; a plurality of waveguides disposed within the housing and having a length, width, height, and a central longitudinal axis and an internal surface; and a connector coupled to a first end of each distinct one of the plurality of waveguides such that each connector is operable to output an RF signal from each waveguide to an RF testing device.

16. The RF sensor testing fixture of claim 15 further comprising: a dielectric material disposed throughout the interior of each waveguide; a resistive impedance disposed along the central longitudinal axis of each waveguide; and a reactive impedance disposed on the internal surface of each waveguide.

17. The RF sensor testing fixture of claim 16 further comprising an antenna interface configured to directly couple each of the waveguides to a distinct one of a plurality of radiating elements of an antenna array.

18. The RF sensor testing fixture of claim 17, wherein each of the waveguides and their respective impedances are arranged to provide an antenna loading impedance substantially similar to that of free space.

19. The RF sensor testing fixture of claim 17, wherein each of the waveguides comprises an outer conductor and an internal volume of each waveguide comprises impedance transforming materials.

20. The RF sensor testing fixture of claim 18, wherein the impedance transforming material comprises a Teflon dielectric insulator.

21. The RF sensor testing fixture of claim 18, wherein the resistive impedance comprises a tapered resistive card (R-card) configured to attenuate a primary electric field along the length of each of the waveguides.

22. The RF sensor texting fixture of claim 18, wherein each reactive impedance presents an inductance to counter a capacitive waveguide effect.

23. The RF sensor testing fixture of claim 16, wherein each reactive impedance comprises metallic fins disposed along one or more walls of the waveguide.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The foregoing and other objects, features and advantages will be apparent from the following more particular description of the embodiments, as illustrated in the accompanying drawings in which like reference characters refer to the same parts throughout the different views. The drawings are not necessarily to scale, emphasis instead being placed upon illustrating the principles of the embodiments.

[0018] FIGS. 1-1C are block diagrams of a radio frequency (RF) waveguide adapter according to example embodiments described herein.

[0019] FIG. 2 is a graph illustrating a slot feed impedance provided by the RF waveguide load of FIG. 1 as compared to a slot feed impedance provided by a free space load on a slot antenna according to example embodiments described herein.

[0020] FIGS. 3-3A are block diagrams of an RF waveguide adapter according to example embodiments described herein.

[0021] FIGS. 4-4A are block diagrams of the RF waveguide adapter being directly coupled to a slot antenna according to example embodiments described herein.

DETAILED DESCRIPTION

[0022] Referring to FIGS. 1-1C, in which like elements are provided having like reference designations, a waveguide adapter 100 is coupled to a planar antenna array 125 that comprises an antenna ground plane 127 and internal stripline circuits as is generally known (for clarity, only a portion of waveguide adapter 100 and one antenna element of the antenna radiating element 125 are shown in FIG. 1). A skilled artisan understands that the adapter 100 is tailored to a slot style radiating element and can be directly coupled to any antenna system such as a phased array antenna system comprising any type of slot or printed circuit antenna element (e.g. a dipole element, a patch element, or any other type of element. Also, it is understood that the antenna radiating elements need not lay on a planar surface but can be conformal. Furthermore, one skilled in the art recognizes that other non-rectangular wave guiding structures can be employed for a multitude of radiating elements. Any wave guiding structure employed should contact an antenna ground surface, couple to the radiating element, and present an equivalent free space radiation load to the antenna element.

[0023] The waveguide adapter 100 comprises a waveguide (WG) 107 that is directly coupled to a slot antenna element 120 (here illustrated as a so-called dog-bone slot element) disposed on or otherwise provided in a ground plane 127 of the planar antenna array 125. Although the WG 107 is depicted as a rectangular waveguide, a skilled artisan understands that any wave guiding structure can be employed, e.g., a circular or square waveguide, that is configured to mimic a free space load. For example, by making direct contact with the antenna element 120 and the antenna ground plane 127, the WG 107 enables modes of propagation to be establish and enables energy to be coupled from the radiating element 120 into the waveguide 107.

[0024] The WG 107 comprises loads 105, 110, 115 configured to mimic a load that an antenna element 120 would see if it was otherwise radiating into free space. For example, the WG 107 can comprise an impedance material (e.g., a filled dielectric) 105, and a resistive load (also referred to as a resistive obstacle) 110 and a reactive load (also referred to as a reactive obstacle) 115 that are configured to provide the antenna element 120, when driven, with a similar reaction as free space which is demonstrated by the reflection plot 210 of FIG. 2 described in greater detail herein.

[0025] In embodiments, the WG 107 comprises a conductor 106 having an internal surface. The internal surface is configured to receive the loading dielectric 105, and resistive load 110. The resistive load 110 is secured or otherwise held along a central longitudinal axis of the WG so that a primary electric field is gradually attenuated along a length of the WG 107. In embodiments, the loading dielectric 105 can hold the resistive load 110 such that it may be separate or in contact with 106 internal surface. The resistive load 110 can either be held in place (e.g., sandwiched) or directly attached (e.g., sputtered) to the loading dielectric 105 along the central longitudinal axis. Contemporaneously, the reactive load 115 is secured or otherwise held in the WG 107 so as to present an inductive load to counter a capacitive waveguide effect.

[0026] In embodiments, the conductor 106 comprises a conductive material (e.g. brass, copper, silver, aluminum, or any metal that has low bulk resistivity or even metals having poor conductivity characteristics (including, but not limited to dielectric materials) and having interior walls which are plated or otherwise covered with a material having good conductivity characteristics). The waveguide loading material 105 can be any suitable non-conducting dielectric, such as Teflon, that allows the waveguide size to be constrained through dielectric loading of the waveguide. The resistive load 110 can comprise a tapered resistive material. For example, the tapered resistive material can be a tapered resistive card (R-card). The resistive material serves to alter the wave impedance seen at the antenna load side of the adapter and gradually attenuate the field so to mimic directional propagation. An attenuating material can be dispersed throughout the dielectric and or deposited along the waveguide walls to create this effect. In some examples, the reactive load 115 can comprise metallic fins. Persons skilled in the art understand other structures such as imbedded rings, inductive posts, etc. may be used to affect a reactance which counters the coupled waveguide reactive element.

[0027] In embodiments, the resistive load 110 can be disposed along a central longitudinal axis of the waveguide 107. In some examples, the reactive load 115 forms an inductive iris that is disposed along the waveguide at a distance from the antenna element 120 so as to cancel a waveguide coupling reactance as seen by the antenna element 120.

[0028] As stated herein, the rectangular waveguide adapter 100 comprising the WG and the loading elements 105, 110, 115 transforms a standard waveguide impedance to an impedance that mimics or corresponds to that of a free space load for the antenna element 120. As such, the adapter 100 can be used with a measurement fixture (e.g., fixture 400 of FIG. 4) so that a single or multitude of antenna elements can be tested in a working production environment through standard scattering parameter (S-parameter) measurement techniques. By measuring and analyzing S-parameters, the adapter 100 provides a means to identify antenna component irregularities at a sub-system level (e.g. by comparing measured S-parameters to expected S-parameter values such as threshold values or expected ranges of values).

[0029] For example, by mimicking free space load (e.g. by modelling a free space impedance to be present to an antenna element), the adapter 100 enables a testing device (not shown) that can be mechanically and electrically coupled to the adapter 100. For example, the adapter 100 can enable the RF testing device to obtain transmission phase and amplitude measurements of one or more radiating slot antenna elements 120 of the antenna array 125. In this way, the adapter 100 enables the capture of registration errors and performance deviations of antenna elements.

[0030] Although FIGS. 1-1C illustrate one technique for loading a rectangular waveguide adapter, a skilled artisan understands that other loading methods and/or waveguide shapes may be used to achieve a similar loading effect for antenna element 120. It should be further noted that the structure and materials shown in FIGS. 1-1C are one method of creating a direct contact adapter. Persons skilled in the art could use other waveguide shapes, loading materials, reactive and attenuating loads to achieve a similar result. For example, structures and materials can be employed that act on a magnetic field component and/or act on both the electric and the magnetic field components together. For instance, the resistive load 110 can comprise a MAG-RAM material (magnetic field absorber material) to attenuate the energy and shift the waveguide impedance.

[0031] Referring to FIG. 2, a Smith chart 200 includes curve 205 which corresponds to free space impedance reflection coefficient (i.e. S11) at a first frequency. Curve 210 corresponds to a free space mimicked impedance reflection coefficient at the first frequency (e.g. as may be measured at the feed port (not shown) for the radiating element 120 with the concepts, structures and techniques described herein such as the waveguide adapter described above in conjunction with FIGS. 1 and 1A). By comparing curves 205, 210 it can be seen that good correspondence is achieved (i.e. the reflection coefficient of the radiating element with the waveguide adapter coupled has good correspondence with the reflection coefficient radiating element radiating into free space).

[0032] Thus, the impedance loaded adapter 100 of FIG. 1 provides the slot antenna element 120 of FIG. 1, when driven, an impedance corresponding to a free space mimicked impedance as illustrated by curve 210 which is similar to that of free space impedance, as illustrated by free space impedance curve 205.

[0033] Referring to FIGS. 3-3A in which like elements are provided having like reference designations, an antenna array adapter 300 comprises a grouping of waveguide adapters 100. In this embodiment a housing 340 having a top portion 309, center portion 303 and a bottom portion 307. The top portion 309 comprises connectors (or RF ports) 315. The center section 303 comprises a reactive element and the bottom portion 307 contacts the antenna array. In embodiments, the connectors 315 form a 12-port adapter (or testing interface) that enable a testing device (not shown) to perform measurements on an antenna and/or antenna feed (so as to characterize the antenna elements transfer function). Those of ordinary skill in the art will appreciate, of course, that adapter 300 may include any number of pins necessary to suit the needs of a particular application. Also, not shown for clarity is the waveguide loading dielectric 105 and resistive material 110.

[0034] In embodiments, the waveguide adapter 300 can comprise a plurality of WGs 305. The number of WGs 305 can correspond to a number of antenna elements (e.g., slot antenna elements) included in an antenna array onto which the adapter 300 is to be directly coupled. The WGs 305 can be spaced apart so as to directly couple to each antenna element and enable energy to be coupled from each antenna element into each respective WG 305.

[0035] In further embodiments, the bottom portion 307 can comprise an antenna array interface 310 configured to couple the adapter 300 onto an antenna array (e.g., antenna array 420 of FIG. 4). The array interface 310 can be any known or yet to be known mechanical interface means that enable the adapter 300 to be coupled to the antenna array.

[0036] Referring to FIGS. 4-4A, an antenna array 420 comprising a plurality of antenna elements 421a-N includes an adapter interface 410. For example, the adapter interface 410 can be formed as receiving slots that receive antenna tabs (not numbered) that define the antenna array interface 310. The slots 410 can secure the antenna tabs based on a friction fit means, press fit means, interference fit means, and/or any other mechanical means. Accordingly, the adapter interface 410 enables the adapter 300 to electrically couple to the antenna array 420 such that energy is coupled from each of the antenna elements 421a-N into one of each of the WGs 305 of the adapter 300. Accordingly, a testing device can be used such that RF testing can occur during a subassembly workflow process. As such, antenna verification can occur by a supplier.

[0037] Comprise, include, and/or plural forms of each are open ended and include the listed parts and can include additional parts that are not listed. And/or is open ended and includes one or more of the listed parts and combinations of the listed parts.

[0038] One skilled in the art will realize the concepts described herein may be embodied in other specific forms without departing from the spirit or essential characteristics thereof. The foregoing embodiments are therefore to be considered in all respects illustrative rather than limiting of the concepts and embodiments described herein. The scope of the concepts sought to be protected herein is thus indicated by the appended claims, rather than by the foregoing description, and all changes that come within the meaning and range of equivalency of the claims are therefore intended to be embraced therein.