WIDE-SCAN-CAPABLE POLARIZATION-DIVERSE POLARIZER WITH ENHANCED SWITCHABLE DUAL-POLARIZATION PROPERTIES

Abstract

A dual-mode polarizer for selectively switching between linear polarization and circular polarization includes a first meander-line polarizer, and a second meander-line polarizer spaced apart from the first meander-line polarizer to define a first gap therebetween. A first angular orientation between the first and second meander-line polarizers produces variably-oriented linear polarization of a signal passing through the first and second meander-line polarizers, and a second angular orientation between the first and second meander-line polarizers produces variably-oriented circular polarization of a signal passing through the first and second meander-line polarizers.

Claims

1. A dual-mode polarizer for selectively switching between linear polarization and circular polarization, comprising: a first meander-line polarizer; and a second meander-line polarizer spaced apart from the first meander-line to define a first gap therebetween, wherein a first angular orientation between the first and second meander-line polarizers produces variably-oriented linear polarization of a signal passing through the first and second meander-line polarizers, and a second angular orientation between the first and second meander-line polarizers produces variably-oriented circular polarization of a signal passing through the first and second meander-line polarizers.

2. The dual-mode polarizer according to claim 1, wherein the first and second meander-line polarizers are rotatable about an axis, further comprising: a first actuator coupled to the first meander-line polarizer and operative to rotate the first meander-line polarizer about the axis; and a second actuator coupled to the second meander-line polarizer and operative to rotate the second meander-line polarizer about the axis.

3. The dual-mode polarizer according to claim 1, wherein the first meander-line polarizer and the second meander-line polarizer are concentric with one another.

4. The dual-mode polarizer according to claim 1, further comprising a first foam spacer arranged in the first gap.

5. The dual-mode polarizer according to claim 1, wherein the first and second meander-line polarizers each comprise at least two layers.

6. The dual mode polarizer according to claim 1, wherein the first and second meander-line polarizers are mounted on a spindle and rotate about an axis of the spindle.

7. An antenna system, comprising; an antenna comprising a linearly-polarized aperture for transmitting and receiving a signal; and the dual-mode polarizer according to claim 1 spaced apart from the linearly polarized aperture to define a second gap therebetween, wherein the first meander-line polarizer is arranged between the aperture and the second meander-line polarizer.

8. The antenna system according to claim 7, wherein the antenna comprises a variable inclination continuous transverse stub (VICTS) antenna.

9. The antenna system according to claim 1, further comprising a second foam spacer arranged in the second gap between the linearly-polarized aperture and the dual-mode polarizer.

10. A method of providing dual-mode polarization for a linearly-polarized aperture, wherein a first meander-line polarizer is spaced apart from the linearly-polarized aperture to define a first gap therebetween, and a second meander-line polarizer is spaced apart from the first meander-line polarizer to define a second gap therebetween, the first meander-line polarizer arranged between the linearly-polarized aperture and the second meander-line polarizer, the method comprising: selectively orienting the first meander-line polarizer at a first angular orientation relative to an E-field of the linearly-polarized aperture; and selectively orienting the second meander-line polarizer at a second angular orientation relative to the E-field of the linearly-polarized aperture, the second angular orientation different from the first angular orientation.

11. The method according to claim 10, further comprising configuring the polarizer for circular polarization by: orienting the first meander-line polarizer relative to an E-field of the linearly-polarized aperture to maintain substantial linear polarization of a signal passing through the first meander-line polarizer; and orienting the second meander-line polarizer relative to the E-field of the linearly-polarized aperture to change polarization of a signal passing through the second meander-line polarizer from substantial linear polarization to circular polarization.

12. The method according to claim 10, further comprising: receiving, by the first meander-line polarizer, a substantially linearly-polarized signal from the linearly-polarized aperture, wherein the angular orientation of the first meander-line polarizer relative to the E-field substantially maintains linear-polarization of the received linearly-polarized signal as the received substantially linearly-polarized signal passes through the first meander-line polarizer; and receiving, by the second meander-line polarizer, the substantially linearly-polarized signal from the first meander-line polarizer, wherein the angular orientation of the second meander-line polarizer relative to the E-field circularly-polarizes the received linearly-polarized signal as the received substantially linearly-polarized signal passes through the second meander-line polarizer.

13. The method according to claim 10, wherein selectively orienting the first meander-line polarizer comprises orienting the first meander-line polarizer at an angle of approximately 0 degrees or approximately 90 degrees relative to the E-field of the linearly-polarized aperture, and wherein selectively orienting the second meander-line polarizer comprises orienting the second meander-line polarizer at an angle of approximately −45 degrees or approximately 45 degrees relative to the E-field of the linearly-polarized aperture.

14. The method according to claim 10, further comprising configuring the polarizer for linear polarization by: orienting the first meander-line polarizer relative to an E-field of the linearly-polarized aperture to change polarization of a signal passing through the first meander-line polarizer from substantially linear polarization to circular polarization; and orienting the second meander-line polarizer relative to the E-field of the linearly-polarized aperture to change polarization of a signal passing through the second meander-line polarizer from circular polarization to a variable orientation of substantial linear polarization.

15. The method according to claim 10, further comprising: receiving, by the first meander-line polarizer, a substantially linearly-polarized signal from the linearly-polarized aperture, wherein the angular orientation of the first meander-line polarizer relative to the E-field circularly-polarizes the received substantially linearly-polarized signal as the received substantially linearly-polarized signal passes through the first meander-line polarizer; and receiving, by the second meander-line polarizer, the circularly-polarized signal from the first meander-line polarizer, wherein the angular orientation of the second meander-line polarizer relative to the E-field substantially linearly polarizes the received circularly-polarized signal as the received circularly-polarized signal passes through the second meander-line polarizer.

16. The method according to claim 10, wherein selectively orienting the first meander-line polarizer comprises orienting the first meander-line polarizer at an angle of approximately −45 degrees or approximately 45 degrees relative to the E-field of the linearly-polarized aperture, and wherein selectively orienting the second meander-line polarizer comprises orienting the second meander-line polarizer at an angle anywhere between approximately −90 degrees and approximately 90 degrees relative to the E-field of the linearly-polarized aperture.

17. The method according to claim 10, further comprising biasing the angular orientation of the first meander-line polarizer relative to the E field of the linearly-polarized aperture to compensate and/or cancel non-ideal properties of the second meander-line polarizer.

Description

BRIEF DESCRIPTION OF DRAWINGS

[0025] In the annexed drawings, like references indicate like parts or features.

[0026] FIGS. 1A and 1B illustrate the relative arrangement and orientation of both an inner polarizer and an outer polarizer, mounted proximal to a (generic) linearly-polarized planar antenna aperture, when operating in circular and linear polarization modes, respectively, in accordance with an embodiment of the invention.

[0027] FIG. 2 shows a typical construction and cross-section of a representative meander-line polarizer.

[0028] FIG. 3A illustrates a typical orientation and sense of polarization incident upon and exiting from the polarizing layer when linear polarization passes unchanged through the “inner” polarizer (“De-activated” Condition). The “outer” polarizer of the invention has been removed for clarity.

[0029] FIG. 3B illustrates a typical orientation and sense of polarization incident upon and exiting from the polarizing layer when converting incident linear polarization to circular polarization through the “inner” polarizer (“Activated” Condition). The “outer” polarizer of the invention has been removed for clarity.

[0030] FIG. 4 is a schematic diagram illustrating a means for providing relative rotation between the meander-line polarizers.

[0031] FIG. 5 illustrates the relevant “cascade” block diagram for simulation and modeling of the stack-up of two meander-line polarizers and the antenna.

DETAILED DESCRIPTION OF INVENTION

[0032] Embodiments of the present invention will now be described with reference to the drawings, wherein like reference numerals are used to refer to like elements throughout. It will be understood that the figures are not necessarily to scale.

[0033] As used herein, “substantially linearly polarized” and “substantial linear polarization” are defined as polarization that is highly elliptical, i.e., having an Axial Ratio of 15 dB or higher.

[0034] A device and method in accordance with the invention utilize a pair of meander-line polarizers to provide a novel, simple, low-cost add-on dual-mode polarization capability to any planar single-polarized aperture. The resulting polarizer provides higher performance (better polarization purity and control over operating frequency and scan range) as compared to current approaches for realizing similar dual-mode capability. More particularly, a pair of meander-line polarizers, which are independently and mechanically rotatable about a common axis, are utilized to implement dual-mode polarization. In this regard, each polarizer includes similar meander-line traces and is mountable proximal to a generic planar single orientation linearly-polarized antenna aperture surface. An “inner” polarizer (proximal to and separated by a fixed distance from a surface of the aperture) “selects” a desired composite polarization “mode” (either “circular” or “linear”). Such selection is accomplished through appropriate rotation and orientation of the inner polarizer's meander-line axes relative to the orientation of the linear-polarization of the planar antenna aperture.

[0035] When the inner polarizer is set for the linear polarization mode, the outer polarizer is used to provide continuously variable linear polarization orientation, e.g., the resulting linear polarization rotates with rotation of the outer meander-line polarizer. When the inner polarizer is set to the circular polarization mode, the outer polarizer is used to select the sense of polarization, i.e., left-hand circular polarization (LHCP) or right-hand circular polarization (RHCP). The “sense” of the resultant circular polarization (LHCP or RHCP) is determined by the + or −polarization orientation of the incident linear field coming from the inner polarizer. In a strictly reciprocal manner, the meander-line polarizer converts incident circular polarization to linear polarization, with that linear polarization oriented in a direction approximately +45 or −45 degrees relative to the meander-line traces 15a, depending on the right-hand or left-hand nature of the incident CP field.

[0036] The device and method in accordance with the present invention enable support of the desirable dual-mode capability, but without the added complexity and cost of employing individual dual-polarized radiators. In other words, dual-mode capability is provided when paired with much simpler and less expensive single-polarized antennas. In a generic sense, the device and method in accordance with the invention can be considered as a stand-alone add-on to existing single-polarized planar apertures, both scanning and non-scanning, thereby enabling full dual-mode dual-polarization capabilities with only a minor impact on overall antenna complexity.

[0037] Referring initially to FIGS. 1A and 1B, illustrated is a top exploded view of an exemplary antenna system 10 that includes a dual-mode polarizer 11 for selectively switching between linear polarization and circular polarization in accordance with the present invention. FIG. 1A illustrates the dual-mode polarizer 11 configured for circular polarization (LHCP or RHCP) while FIG. 1B illustrates the dual-mode polarizer configured for linear polarization.

[0038] The exemplary dual-mode polarizer 11 of FIGS. 1A and 1B includes a first (inner) meander-line polarizer 12, and a second (outer) meander-line polarizer 14 spaced apart from the inner meander-line 12 to define a first gap 16 between the inner and outer polarizers 12, 14. In one embodiment, air resides in the first gap 16, while in another embodiment a first foam spacer 18a is arranged in the first gap 16. A purpose of the foam spacer 18a, which may be formed from low-density foam, is to maintain a constant spacing between the inner and outer meander-line polarizers 12, 14. Although not shown in FIGS. 1A and 1B, the inner meander-line polarizer 12 and the outer meander-line polarizer 14 are concentric with one another.

[0039] Referring briefly to FIG. 2, illustrated is a perspective view along with section views of an exemplary meander-line polarizer 12, 14 that may be used with the device and method according to the present invention. The exemplary meander-line polarizer 12, 14 has a circular form factor to facilitate rotation of multiple meander-line polarizers about a common axis. A benefit of using a circular form factor is that it ensures the surface area of each meander-line polarizer, when the polarizers are arranged on a common axis through the center of each polarizer, completely overlap regardless of the angular orientation of the respective polarizers. The exemplary meander-line polarizer of FIG. 2 is formed from three individual layers, 13a, 13b, 13c, each layer arranged parallel to the other and spaced apart by a preset distance. Each layer includes a plurality of meander-line traces 15a formed on a substrate 15b, with a spacer 15c arranged between adjacent substrates. While the exemplary meander-line polarizer 12, 14 of FIG. 2 includes three layers, it is possible to utilize a meander-line polarizer 12, 14 with less layers (e.g., two layers) or more than three layers (e.g., four, five, six or more layers).

[0040] The meander-line polarizers are generically designed to provide the typical “quadrature” (90 degree) differential transmission phase difference between parallel and perpendicular incident linearly-polarized wave components, relative to a common axes of the meander-line traces 15a. In this manner, incident linear polarization is converted to circular polarization when the incident linear polarization is oriented at approximately +45 or −45 degrees relative to these axes (thereby presenting approximately equal magnitudes of parallel and perpendicular field components). As used herein, reference to an “approximate” angular orientation includes the specified angular orientation plus or minus 15%. Thus, “approximately +45 degrees or −45 degrees” includes +60 to +30 degrees or −30 degrees to −60 degrees.

[0041] Referring back to FIGS. 1A and 1B, the antenna system 10 includes an antenna with a linearly-polarized aperture 20 for transmitting and receiving a signal. In the illustrated embodiment the linearly-polarized aperture 20 is a variable inclination continuous transverse stub (VICTS) antenna. However, the dual-mode polarizer 11 in accordance with the invention can be used with other types of linearly-polarized apertures.

[0042] The dual-mode polarizer 11 in accordance with the invention is spaced apart from the linearly polarized aperture 20 to define a second gap 22 formed between the first meander-line polarizer 12 of the dual-mode polarizer 11 and the aperture 20, the first meander-line polarizer 12 being arranged between the aperture 20 and the second meander-line polarizer 14 (FIG. 4, discussed below, illustrates the spacing). In one embodiment, air resides in the second gap 22, while in another embodiment a second foam spacer 18b is arranged in the second gap 22 to maintain spacing therebetween.

[0043] For a desired (resultant) CIRCULAR polarization 23 from the composite polarizer structure 11 as shown in FIG. 1A, the inner (first) polarizer 12 is rotated/oriented such that a longitudinal axis of the meander-lines of the inner polarizer 12 are approximately 0 or 90 degrees relative to the “natural” linear polarization 24 (also referred to as the E-field) of the antenna aperture 20 as shown in FIG. 3A. This essentially “deactivates” the inner polarizer 12 such that it has no primary polarization impact. As a result, linear-polarization is passed through and unchanged from the linear polarized aperture 20 to the “outer” polarizer layer 14, with this binary choice (selection of 0 or 90 degrees) based on second-order considerations in overall performance (polarization purity and transmission efficiency) over operating frequency range and scan angle. The outer (second) polarizer 14 subsequently converts the linear polarization 27 exiting the inner polarizer 12 to the desired sense of circular polarization 23 via rotation of the outer polarizer 14 by approximately +45 degrees or −45 degrees depending upon which sense of circular polarization has been selected, as shown in FIG. 1A.

[0044] For a desired composite (resultant) LINEAR polarization 26 as shown in FIG. 1B, the inner polarizer 12 is rotated/oriented such that the longitudinal axis of the meander-lines of the inner polarizer 12 are approximately +45 or −45 degrees relative to the “natural” polarization 24 of the antenna aperture 20 as shown in FIG. 3B (essentially “activating” the inner polarizer 12 such that it converts the intrinsic linear polarization of the aperture 20 to circular polarization), with this binary choice (selection of +45 or −45 degrees) based on second-order considerations in overall performance (polarization purity and transmission efficiency) over operating frequency and scan angle. The outer (second) polarizer 14 subsequently converts the circular polarization 28 exiting the inner polarizer 12 to any desired orientation of linear polarization 26 via rotation of the outer polarizer within the range of approximately +90 degrees or −90 degrees relative to the inner polarizer 12, as shown in FIG. 1B.

[0045] The outer polarizer 14 is used in conjunction with the (properly-oriented) inner polarizer 12 to (1) select between Right-Hand and Left-Hand circular polarization when the inner polarizer is set to the “circular polarization” mode 27 as shown in FIG. 3A and (2) provide for continuously variable linear polarization orientation when the inner polarizer is set to the “linear polarization” mode 28 as shown in FIG. 3B. In the case of the “circular polarization” mode, the “sense” is set by orientation of the longitudinal axis of the meander-lines of the outer polarizer 14 to either approximately +45 or −45 degrees relative to the longitudinal axis of the meander-lines of the inner polarizer 12. In the case of “linear polarization” mode, the orientation of the linear polarization “turns” (approximately degree-for-degree) as the outer polarizer 14 is rotated relative to the inner polarizer 12, with the resultant linear polarization oriented at approximately +45 or −45 degrees (depending on the selected CP sense for the inner polarizer) relative to the meander-line axes on the outer polarizer 14.

[0046] The dual-mode polarizer 11 and method in accordance with the invention affords additional degrees-of-freedom for optimization of the polarization and transmission qualities of the composite polarizer over frequency and scan ranges. More specifically, the fixed spacing (“second (lower) polarizer gap” 22) between the inner meander-line polarizer 12 and the generic planar antenna aperture 20 and the fixed spacing (“first (upper) polarizer gap” 16) between the inner meander-line polarizer 12 and the outer meander-line polarizer 14 are optimized in order to minimize the reflection coefficient of the composite “universal” polarizer structure (optimize transmission efficiency) and/or to improve/optimize overall polarization purity (expressed as X-Pol Discrimination (XPD) when operating in linear polarization mode and referred to as Axial Ratio (AR) when operating in circular polarization mode). The optimization may be via a cascade-mode analysis or other similar method.

[0047] In addition, the exact orientation, referred to as the rotational angle, of the inner meander-line polarizer 12 relative to the planar antenna aperture 20 can be perturbed/varied from the approximate +45 or −45 degree orientations (for linear mode) or the approximate 0 or 90 degree orientations (for circular mode) in order to create a complementary polarization ellipticity that “fine-tunes” the overall performance characteristics (e.g., primarily polarization purity, XPD or AR) to compensate for non-ideal properties in the outer polarizer 14. Such perturbation may be ±5 degrees, which may be in addition to the +/−15 for “approximate” orientation as referenced herein. This is particularly useful when implemented in scanning applications, where imperfect linear-to-circular polarization characteristics of the outer meander-line polarizer 14, such as undesired deviations from perfect circular polarization, referred to as polarization “ellipticity” as commonly encountered at increasing large scan angles, can be counter-acted (cancelled). Such cancelation may be by purposeful introduction of complementary-oriented “ellipticity” in the inner meander-line polarizer 12 (by purposeful departure from the its “perfect” +45/−45 or 0/90 degree orientation). This optimization can be accomplished, for example, via a theoretical cascade (or similar) model and/or through empirical optimization techniques. Similarly, the outer meander-line polarizer 14 can be perturbed/varied from nominal −45° or +45° orientation to balance polarization ellipticity of the inner polarizer 12.

[0048] Further, these purposeful perturbations of the inner and outer meander-line polarizer orientation angles as functions of operating frequency and scan angle can be pre-determined and recorded in tabular form. In this regard, the controlled rotational orientations of the two polarizers 12, 14 relative to each other and the generic antenna aperture 20 to which they are mounted, is varied (e.g., via rotational actuators) as functions of frequency, scan angle, selected polarization mode (Linear or CP), and desired polarization sense (RHCP or LHCP in the case of circular polarization and polarization orientation in the case of linear polarization.)

[0049] Additionally, independent motion control of each meander-line polarizer 12, 14 ensures that the desired polarization diversity can be achieved. Such motion can be accomplished by direct drive, gear drive, belt drive, or other common rotation methods. For example, and briefly referring to FIG. 4, the polarizers 12, 14 may be mounted on a spindle 30 and rotatable about the spindle, and a first actuator 32 may be drivingly coupled to the inner meander-line polarizer 12 and a second actuator 34 may be drivingly coupled to the outer meander-line polarizer 14. The actuators 32, 34 may be electric motors, for example, or like device, and may be coupled to the polarizers via a drive coupler 36, such as a belt drive, a gear drive, a screw drive, spindle drive or the like. A controller 38 communicates with the actuators 32, 34 to rotate the respective polarizers 12, 14 to produce desired orientations. Feedback devices (not shown) operatively coupled to the polarizers 12, 14 and communicatively coupled to the controller 38 enable closed loop position control.

[0050] Referring now to FIG. 5, as previously described specific air-gap heights between the two meander-line polarizers 12, 14 and the aperture 20 are used to mechanically facilitate independent rotation of the polarizers with respect to one another as well as setting the controlled CP and LP polarizations. The air-gap 16 between the polarizers 12, 14 and the air gap 22 between the polarizer 12 and the antenna aperture 20 are represented by the two interconnecting lines (paths) modeling the two dominant electromagnetic modes (TE and TM) which propagate back and forth and account for the interaction between each of the two polarizers 12, 14 and the planar antenna aperture 20 to which they are both attached. The two ports 14a, 14b above the outer meander-line polarizer 14 represent the final TE and TM modes emanating into free space. The electromagnetic superposition, which is the complex sum of the magnitude and the phase of these two radiated field components/modes, then form the desired total radiated field, polarized in the desired mode sense (“circular” or “linear”) and with the desired polarization orientation (“RHCP” or “LHCP” in circular mode or “Linear field orientation” in linear mode.)

[0051] The mechanism of the operation is as follows. First, the generic linear-polarized planar antenna aperture 20 radiates a linearly-polarized wave that includes (depending on rotational orientation) both TE and TM mode components in the region of the air-gap 22, then impinging on the inner meander-line polarizer 12. Depending on linear field orientation, these modes are approximately 0 or 180 degrees out of phase with respect to one another. Upon hitting the inner meander-line polarizer 12, the majority of the energy in these two modes passes through it toward the outer meander-line polarizer 14, encountering a differential phase-shift between the two components. The differential phase shift is based on the rotational orientation of the inner meander-line polarizer 12 relative to the polarization of the aperture 20, with small amounts reflected back toward the aperture 20 and then subsequently re-reflected back toward the inner meander-line polarizer 12 (i.e., complex multi-order reflections that are fully-modeled via the employed “cascade” method.)

[0052] A similar process of reflection and transmission is repeated between the inner meander-line polarizer 12 and the outer meander-line polarizer 14 in the region of the air-gap 16. With each passing of the waves through the polarizers 12, 14, the TE and TM waves' amplitudes and phases are modified based on the relative rotational orientation of the two polarizers 12, 14 (meander-line axes) relative to each other and relative to the intrinsic linear-polarization of the planar aperture 20. In this manner, multi-order “cascaded” reflections between the aperture-and-inner polarizer and the inner-polarizer and the outer-polarizer continue until steady-state field values are ultimately transmitted through the outer meander-line polarizer 14 and then ultimately radiate to free space. The relative magnitudes and phases of the emanated TE and TM waves then describe and establish the “polarization” of this radiated energy. Although this description is based on “transmission” from the planar antenna 20 to free space, the reciprocal “receive” path from free space to the planar antenna 20 is identical (via the well-established “Reciprocity Theorem.”)

[0053] As for operation in scanning applications where the fields emanating from the generic planar antenna aperture 20 are radiated at an angle/direction away from the mechanical normal of the aperture itself (e.g., phased-arrays, electronically-scanned antennas, VICTS antennas, etc.), the TE and TM mode characteristics (and descriptions) provide a convenient generalized analysis method and solution to such cases.

[0054] The present invention finds particular utility in commercial and non-commercial satellite communication terminals for which highly flexible polarization capabilities provide for a single common antenna/terminal (enabled with polarization diverse capabilities) to support a broad(er) range of satellite types, including both Geosynchronous Orbit (GSO) and non-Geosynchronous Orbit (NGSO) varieties (which typically require different types of antenna polarizations and orientations.) Similarly, Terrestrial communication radios/terminals and High-Performance Radar Systems (employing diverse polarizations for enhance properties) would also benefit.

[0055] Although the invention has been shown and described with respect to a certain embodiment or embodiments, equivalent alterations and modifications may occur to others skilled in the art upon the reading and understanding of this specification and the annexed drawings. In particular regard to the various functions performed by the above described elements (components, assemblies, devices, compositions, etc.), the terms (including a reference to a “means”) used to describe such elements are intended to correspond, unless otherwise indicated, to any element which performs the specified function of the described element (i.e., that is functionally equivalent), even though not structurally equivalent to the disclosed structure which performs the function in the herein exemplary embodiment or embodiments of the invention. In addition, while a particular feature of the invention may have been described above with respect to only one or more of several embodiments, such feature may be combined with one or more other features of the other embodiments, as may be desired and advantageous for any given or particular application.