Patent ID: 12261365

DETAILED DESCRIPTION

The present disclosure describes a novel electronical-scanning (e-scanning) dual-polarized array constructed with slotted-waveguide antenna (SWGA) technology that is designed for 200 MHz bandwidth, has a one-dimensional (1D) e-scanning range of 84°(±42°), or more and has cross-polarization isolation of about −60 dB or less. The disclosed ultra-compact X-band dual-polarization SWGA array unit cell having high polarized performance over 200 MHz bandwidth and wide scan in the azimuth plane is ideal for use in high-power dual-polarized radar systems such as those used for observing and tracking weather. The array uses an ultra-compact array unit cell where the overall dimensions are reduced to about 50% in comparison with that of a dual-polarization SWGA array that uses conventional rectangular waveguides. The new design overcomes a fundamental limitation of zero e-scanning caused by large element spacing (1.2λo) in antennas which use conventional waveguides. Reducing the element spacing to at least 0.6λo(in the azimuth plane), based on partial H-plane waveguides, enables a 1D e-scanning range up to at least 84° (±42°) in the azimuth plane perpendicular to the waveguide axis. In one non-limiting embodiment, the design uses an active sub-array panel of 8×8 elements, excited with 8 high-power transmit and receive modules. This active sub-array can be scaled to obtain a large array without constraints in size and power. The disclosed system uses the broad wall shunt slots for VP antenna and non-inclined edge wall slots for HP antenna. The disclosed system offers stable impedance, gain, cross-polarization isolation, and excellent co-polar mismatch over the whole frequency band of interest. Having a cross-polarization isolation below −60 dB and co-polar mismatch below ±0.12 dB across the scanning range, make this array unit cell (e.g., with 8×8 elements) ideal for high power e-scanned dual-polarization phased array radar, for example for weather observations. In the present disclosure, the term “ultra-compact” refers to a SWGA array unit cell having element spacing reduced to 0.6λo(in the azimuth plane) or less (i.e., a reduction of 50% or more vs. a conventional spacing of 1.2λo). In certain embodiments, the element spacing can be as low as 0.5λo(in the azimuth plane) providing a reduction of about 58%, enabling a 1D e-scanning range up to about 180° (±90°) in the azimuth plane perpendicular to the waveguide axis.

Before describing various embodiments of the present disclosure in more detail by way of exemplary description, examples, and results, it is to be understood that the present disclosure is not limited in application to the details of methods and compositions as set forth in the following description. The present disclosure is capable of other embodiments or of being practiced or carried out in various ways. As such, the language used herein is intended to be given the broadest possible scope and meaning; and the embodiments are meant to be exemplary, not exhaustive. Also, it is to be understood that the phraseology and terminology employed herein is for the purpose of description and should not be regarded as limiting unless otherwise indicated as so. Moreover, in the following detailed description, numerous specific details are set forth in order to provide a more thorough understanding of the disclosure. However, it will be apparent to a person having ordinary skill in the art that the embodiments of the present disclosure may be practiced without these specific details. In other instances, features which are well known to persons of ordinary skill in the art have not been described in detail to avoid unnecessary complication of the description.

Unless otherwise defined herein, scientific and technical terms used in connection with the present disclosure shall have the meanings that are commonly understood by those having ordinary skill in the art. Further, unless otherwise required by context, singular terms shall include pluralities and plural terms shall include the singular.

All patents, published patent applications, and non-patent publications mentioned in the specification are indicative of the level of skill of those skilled in the art to which the present disclosure pertains. All patents, published patent applications, and non-patent publications referenced in any portion of this application are herein expressly incorporated by reference in their entirety to the same extent as if each individual patent or publication was specifically and individually indicated to be incorporated by reference.

As utilized in accordance with the methods and compositions of the present disclosure, the following terms, unless otherwise indicated, shall be understood to have the following meanings:

The use of the word “a” or “an” when used in conjunction with the term “comprising” in the claims and/or the specification may mean “one,” but it is also consistent with the meaning of “one or more,” “at least one,” and “one or more than one.” The use of the term “or” in the claims is used to mean “and/or” unless explicitly indicated to refer to alternatives only or when the alternatives are mutually exclusive, although the disclosure supports a definition that refers to only alternatives and “and/or.” The use of the term “at least one” will be understood to include one as well as any quantity more than one, including but not limited to, 2, 3, 4, 5, 6, 7, 8, 9, 10, 15, 20, 30, 40, 50, 100, or any integer inclusive therein. The term “at least one” may extend up to 100 or 1000 or more, depending on the term to which it is attached; in addition, the quantities of 100/1000 are not to be considered limiting, as higher limits may also produce satisfactory results. In addition, the use of the term “at least one of X, Y and Z” will be understood to include X alone, Y alone, and Z alone, as well as any combination of X, Y and Z.

As used herein, all numerical values or ranges include fractions of the values and integers within such ranges and fractions of the integers within such ranges unless the context clearly indicates otherwise. Thus, to illustrate, reference to a numerical range, such as 1-10 includes 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, as well as 1.1, 1.2, 1.3, 1.4, 1.5, etc., and so forth. Reference to a range of 1-50 therefore includes 1, 2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 15, 16, 17, 18, 19, 20, etc., up to and including 50, as well as 1.1, 1.2, 1.3, 1.4, 1.5, etc., 2.1, 2.2, 2.3, 2.4, 2.5, etc., and so forth. Reference to a series of ranges includes ranges which combine the values of the boundaries of different ranges within the series. Thus, to illustrate reference to a series of ranges, for example, of 1-10, 10-20, 20-30, 30-40, 40-50, 50-60, 60-70, 60-75, 75-100, 100-150, 150-200, 200-250, 250-300, 300-400, 400-500, 500-750, 750-1,000, includes ranges of 1-20, 10-50, 50-100, 100-500, and 500-1,000, for example. A reference to degrees such as 1 to 90 is intended to explicitly include all degrees in the range. A reference to the number of unit cells in a sub-array panel, such as 4-256, 4-400, or 4-676, is intended to include all whole numbers (positive integers) within each range.

In certain embodiments, the element spacing of the disclosed SWGA array units can be in a range of about 0.6 λoto about 0.5 λo(in the azimuth plane), providing a reduction of from about 50% to about 58% vs. a conventional spacing of 1.2 λo, thereby enabling a 1D e-scanning range in a range of from about 84° (±42°) up to at about 180° (±90°) in the azimuth plane perpendicular to the waveguide axis. For example, the element spacing may be from 0.6λo, to about 0.59λo, to about 0.58λo, to about 0.57λo, to about 0.56λo, to about 0.55λo, to about 0.54λo, to about 0.53λo, to about 0.52λo, to about 0.51λo, to about 0.50λo, or fractional portions thereof, thereby enabling a 1D e-scanning range of from about 84° (±42°), to about 86° (±43°), to about 88° (±44°), to about 90° (±45°), to about 92° (±46°), to about 94° (±47°), to about 96° (±48°), to about 98° (±49°), to about 100° (±50°), to about 102° (51°) to about 104° (±52°), to about 106° (±53°), to about 108° (±54°), to about 110° (±55°), to about 112° (56°), to about 114° (±57°), to about 116° (±58°), to about 118° (±59°), to about 120° (±60°), to about 122° (61°), to about 124° (±62°), to about 126° (±63°), to about 128° (±64°), to about 130° (±65°), to about 132° (66°), to about 134° (±67°), to about 136° (±=68°), to about 138° (±69°), to about 140° (±70°), to about 142° (71°), to about 144° (±72°), to about 146° (±73°), to about 148° (±74°), to about 150° (±75°), to about 152° (76°), to about 154° (±77°), to about 156° (±78°), to about 158° (±79°), to about 160° (±80°), to about 162° (81°), to about 164° (±82°), to about 166° (±83°), to about 168° (±84°), to about 170° (±85°), to about 172° (86°), to about 174° (±87°), to about 176° (±88°), to about 178° (±89°), to at about 180° (±90°). Cross-polarization isolation may be within a range of about −55 dB to about −70 dB, but will generally be within a range of about −60 dB to about −70 dB.

As used herein, the words “comprising” (and any form of comprising, such as “comprise” and “comprises”), “having” (and any form of having, such as “have” and “has”), “including” (and any form of including, such as “includes” and “include”) or “containing” (and any form of containing, such as “contains” and “contain”) are inclusive or open-ended and do not exclude additional, unrecited elements or method steps.

The term “or combinations thereof” as used herein refers to all permutations and combinations of the listed items preceding the term. For example, “A, B, C, or combinations thereof” is intended to include at least one of: A, B, C, AB, AC, BC, or ABC, and if order is important in a particular context, also BA, CA, CB, CBA, BCA, ACB, BAC, or CAB. Continuing with this example, expressly included are combinations that contain repeats of one or more item or term, such as BB, AAA, AAB, BBC, AAABCCCC, CBBAAA, CABABB, and so forth. The skilled artisan will understand that typically there is no limit on the number of items or terms in any combination, unless otherwise apparent from the context.

Throughout this application, the terms “about” and “approximately” are used to indicate that a value includes the inherent variation of error. Further, in this detailed description, each numerical value (e.g., degrees or frequency) should be read once as modified by the term “about” (unless already expressly so modified), and then read again as not so modified unless otherwise indicated in context. As noted, any range listed or described herein is intended to include, implicitly or explicitly, any number within the range, particularly all integers, including the end points, and is to be considered as having been so stated. For example, “a range from 1 to 10” is to be read as indicating each possible number, particularly integers, along the continuum between about 1 and about 10. Thus, even if specific data points within the range, or even no data points within the range, are explicitly identified or specifically referred to, it is to be understood that any data points within the range are to be considered to have been specified, and that the inventors possessed knowledge of the entire range and the points within the range. The use of the term “about” may mean a range including ±10% of the subsequent number unless otherwise stated.

As used herein, the term “substantially” means that the subsequently described parameter, event, or circumstance completely occurs or that the subsequently described parameter, event, or circumstance occurs to a great extent or degree. For example, the term “substantially” means that the subsequently described parameter, event, or circumstance occurs at least 90% of the time, or at least 91%, or at least 92%, or at least 93%, or at least 94%, or at least 95%, or at least 96%, or at least 97%, or at least 98%, or at least 99%, of the time, or means that the dimension or measurement is within at least 90%, or at least 91%, or at least 92%, or at least 93%, or at least 94%, or at least 95%, or at least 96%, or at least 97%, or at least 98%, or at least 99%, of the referenced dimension or measurement (e.g., degrees, frequency, width, length, etc.).

As used herein any reference to “one embodiment” or “an embodiment” means that a particular element, feature, structure, or characteristic described in connection with the embodiment is included in at least one embodiment. The appearances of the phrase “in one embodiment” in various places in the specification are not necessarily all referring to the same embodiment.

The processes described in the present disclosure can be performed with the aid of a computer system running software adapted to perform the functions, and the resulting images and data may be stored on one or more non-transitory computer readable mediums. Examples of a non-transitory computer readable medium include an optical storage device, a magnetic storage device, an electronic storage device or the like. The term “Computer System” as used herein means a system or systems that are able to embody and/or execute the logic of the processes described herein. The logic embodied in the form of software instructions or firmware may be executed on any appropriate hardware which may be a dedicated system or systems, or a specially programmed computer system, or distributed processing computer system. When the computer system is used to execute the logic of the processes described herein, such computer(s) and/or execution can be conducted at a same geographic location or multiple different geographic locations. Furthermore, the execution of the logic can be conducted continuously or at multiple discrete times. Further, such logic can be performed about simultaneously with the capture of the optical images, thermal images, RF information, or thereafter or combinations thereof.

More particularly, in a non-limiting first embodiment, the present disclosure is directed to an X-band dual-polarized slotted waveguide antenna (SWGA) array unit cell which comprises a partial H-plane waveguide with a metal vane; and a conventional waveguide in a side-by-side arrangement with the partial H-plane waveguide, wherein a spacing between elements of the X-band dual-polarized SWGA array unit cell in an azimuth plane is in a range of about 0.6λoto about 0.5λo, wherein the X-band dual-polarized SWGA array unit cell has a one-dimensional (1D) electronic-scanning range of at least 84° (±42°) in the azimuth plane perpendicular to a waveguide axis, and wherein the X-band dual-polarized SWGA array unit cell has a cross-polarization isolation of about −60 decibels (dB) or less. In implementations of this embodiment, the 1D electronic-scanning range is within a range of 84° (±42°) to 180° (±90°). The cross-polarization isolation is in a range of about −60 dB to about −70 dB. The conventional waveguide comprises standardized dimensions. λois a free-space wavelength.

In a non-limiting second embodiment, the present disclosure is directed to a sub-array panel comprises a plurality of the X-band dual-polarized SWGA array unit cell of the first embodiment or its implementations. In implementations of this embodiment, the plurality of the X-band dual-polarized SWGA array unit cell may be in a range of from 4 to 676, such as from 4 to 400, or from 4 to 256, or from 64 to 144, for example. The plurality of the X-band dual-polarized SWGA array unit cell comprises n2of the X-band dual-polarized SWGA array unit cell arranged in an n×n configuration, wherein n is in a range of from 2 to 26. The plurality of the X-band dual-polarized SWGA array unit cell comprises n2of the X-band dual-polarized SWGA array unit cell arranged in an n×n configuration, wherein n may be in a range of from 4 to 16, such as from 8 to 12.

In a third non-limiting embodiment, the present disclosure is directed to a radar array comprising a plurality of the sub-array panel of the second embodiment or its implementations.

In a fourth non-limiting embodiment, the present disclosure is directed to a method of radar tracking comprising using the radar array of the third embodiment to monitor weather or track moving objects.

Any of the above embodiments may be combined with any of the other above embodiments to create a new embodiment. These and other features will be more clearly understood from the following detailed description taken in conjunction with the accompanying drawings and claims.

The present disclosure will now be discussed in terms of several specific, non-limiting, examples. The examples described below, which include particular embodiments, will serve to illustrate the practice of the present disclosure, it being understood that the particulars shown are by way of example and for purposes of illustrative discussion of particular embodiments of the present disclosure only and are presented in the cause of providing what is believed to be a useful and readily understood description of construction procedures as well as of the principles and conceptual aspects of the inventive concepts.

Solution to the Problem of Using Conventional Waveguides in SWGA Array Unit Cells

As noted above, the performance of prior dual polarized SWGA arrays using conventional rectangular waveguides is limited because the scan in the plane perpendicular to the waveguide axis is restricted.FIGS.1A-1Fshow results of a grating lobe diagram analysis to illustrate the impact of dual polarization unit cell spacing in the visible region at 9.4 GHz.FIGS.1A-1Cpresent the case for a conventional waveguide structure in which the azimuth is separated by 1.2λo. In this case, grating lobes in the azimuth plane fully overlap the visible region at any scanning angle. Therefore, it is impossible to scan the antenna beam without grating lobes appearing in the visible space.FIG.1Cshows that using this spacing for a linear array with 32 elements will produce grating lobes in the visible region even though the beam is not scanned. In this case, conventional WR-90 waveguide structures are used for HP and VP.

In the present disclosure, in one embodiment, a compact waveguide structure was used where the unit cell spacing in azimuth plane can be between 0.6λoand 0.7λo.FIGS.1D-1Fillustrate the grating lobe analysis for both cases. For 0.7λo, the WR-90 waveguide is used for HP and WR-51 waveguide is used for VP. Because of 0.7λospacing, a scanning range up to 50° (±25°) in the azimuth plane can be obtained. Spacing of 0.6λocan be obtained with a customized waveguide structure. This element spacing increases the scanning range up to 84° (±42°).FIGS.1D-1Eillustrate both cases, andFIG.1Fshows the ideal e-scanned patterns of a linear array with 32 elements. Grating lobes appear only when the array is scanned after ±42°. The scanning performance of a dual-polarization SWGA using spacings of 1.2λo, 0.7λoand 0.6λois summarized in Table 1.

TABLE 1Scanning performance of a dual-polarization linear SWGAusing a spacing of 1.2λo, 0.7λo and 0.6λo at 9.4 GHz.A Novel Dual Polarization Antenna ArrayConventional [23]ProposedWR-90WR-90WR-90WR-51CustomizedH-polV-polH-polV-polH-polV-polElement1.2λo1.2λo0.7λo0.7λo0.6λo0.6λospacingMax.0°50°84°scanning(−25° to +25°)(−42° to +42°)

In the present disclosure, in one embodiment, a dual-polarized slot array comprises a VP linear array and an HP linear array. A small array, as an array unit cell, was used to verify the proposed concept. Both VP and HP linear arrays used to build dual polarization compact planar antenna arrays are explained below.

The VP Linear Array

The partial H-plane waveguide is a rectangular waveguide with a quarter reduction in the cross-sectional area which is implemented by a concept of folded waveguide. Recently, structures such as filters were designed based on partial H-plane waveguides. It has been widely utilized to design compact waveguide filter named as partial H-plane filter. Nowadays, these structures are being used to design linear slotted waveguide antenna arrays with single polarization.

The partial H-plane waveguide is a transversely folded rectangular waveguide that has a partially inserted metal vane in the H-plane. The dominant and second modes of the rectangular waveguide are TE10 and TE20, respectively. Since these modes do not depend on the waveguide height, it is possible to reduce the height for these modes. Thus, the flat waveguide can be transversely folded once, which results in a quarter reduction in the cross-sectional area of the waveguide forming a compact structure. As shown inFIG.2, the first two modes of a partial H-plane waveguide can have the same dispersion characteristics as those of a conventional rectangular waveguide, while its cross section is one quarter. Therefore, both conventional and compact waveguides can achieve the same usable bandwidth. These two modes can be separately controlled if required for different applications. This new type of compact waveguide brings up numerous possibilities to use this waveguide for microwave applications that have space and weight limitations.

The dispersion characteristics of the partial H-plane waveguides have been theoretically investigated by applying Galerkin's method in Fourier domain to obtain the propagation constant and, consequently, the fields in the structure. The E-field distributions of dominant mode of a conventional waveguide are the same as of the partial H-plane waveguide if it is unfolded with respect to the metal vane. Thus, a partial H-plane antenna can be constructed by using the same structure, broad wall longitudinal shunt slot, of a conventional slot antenna.

For a longitudinal shunt slot on a conventional waveguide, a model of the antenna may be constructed by considering the slots as shunt admittances linked by sections of ideal transmission lines, as shown inFIG.3. The active admittance of each slot in the slot array, Ya, in the equivalent model usually includes both the self-impedance, Yn, and the effect of the mutual coupling with the remaining slots. The procedure for the design of a linear array of longitudinal slots fed by rectangular waveguide has been shown previously in one version to rest on two design equations. The first, Equation (3) where Equations (4) and (5) define variables of Equation (3), and the second, Equation (6), where Ysis the admittance of the slot, G0is the characteristic conductance of the waveguide, x0is the slot offset, Vsis the slot voltage, Vnis the modal voltage at Ys, and 2L is the slot length.

YsG0=-K1⁢f⁡(x0,L)⁢(VsVn)(3)K1=-2⁢YiG0⁢j⁢π⁢2β10⁢k0⁢a⁢ab(4)f⁡(x0,L)=-π2⁢kL⁢cos⁢(β10⁢L)(π2⁢kL)2-(β10k)2⁢cos⁢(π⁢x0a)(5)YaG0=22YsG0+1Γ⁢VscouplVs(6)

The design equations are solved iteratively. Further details regarding the iterative design algorithm for standing wave arrays are shown in Robert S. Elliott, “An Improved Design Procedure for Small Arrays of Shunt Slots,” IEEE Transactions on Antennas and Propagation, Vol. AP-31, No. 1, pp. 48-53, 1983, which is incorporated by reference. The aim of the design procedure is to determine the length and offset of each slot in such a way as to achieve the desired voltage distribution on the different slots.

A formula, shown as Equation (7), was derived by A. F. Stevenson, “Theory of Slots in Rectangular Waveguides,” Journal of Applied Physics, Vol. 19, No. 1, pp. 24-38, 1948, which is incorporated by reference, for the normalized resonant conductance of a single longitudinal slot as a function of its offset x0from the centerline. In Equation (7), Gsis the conductance of the slot. Equation (7) indicates that the normalized conductance of the longitudinal slot in the broad wall of a rectangular waveguide is offset dependent, as shown inFIG.4using a WR-90 standard at 9.4 GHz. It is shown that by adjusting the slot offset from the center line of the waveguide, the slot conductance can be controlled and then the slot excitation.

GsG0=2.09a/bβ/k⁢cos2⁢(β⁢πk)⁢sin2(π⁢x0a)(7)

The design of the partial H-plane slot array antenna is described below. The structure of a 1-D resonant slot array antenna using partial H-plane waveguide, as constructed in accordance with the present disclosure, is shown inFIG.6. The slot length is nearly 0.5λo, and its width is assumed to be very small. To be excited in phase for all slots, the array with slots spaced 0.5λgapart and with alternating slots on the opposite side of the center line is employed. The designed array follows the uniform array with a side lobe level (SLL) of 13.26 dB, and the operation frequency is 9.4 GHz. The slot offsets of xn′s, which control the conductance and excitation level of each slot, are determined from Equation (7). The designed parameters are listed in Table 2. The thickness and width of each slot resonant array antenna is 1.27 mm and 1.533 mm, respectively. The thickness (d4) and length (d7) of the metal vane are set to be 0.5 mm and 9.5 mm, respectively. The longitudinal slot is cut in the narrow wall of the partial H-pane waveguide parallel to the waveguide with an offset xn=2 mm from the center line. The polarization is perpendicular to the waveguide axis. The excitation is controlled mainly by the offset. It is the maximum at the edges and zero at the center. In order to radiate in the boresight, the longitudinal slot antennas are arrayed by a spacing of a half-guided wavelength, and the offset direction is opposite among the adjacent slots.

Partial H-plane waveguide to coaxial adapter is used where a probe was inserted into a rectangular cut-out in the H-plane vane at the center of waveguide structure. The adapter was optimized using a commercial full wave simulator, specifically a high-frequency structure simulator (HFSS), where the cut-out width and depth were optimized to maximize the return losses.

TABLE 2Summary of the dimensions of VP and HP linearslotted waveguide antenna arrays.The HP Linear ArrayCross sectionFrequencySlotIris dimensions(mm × mm)(GHz)(mm)(mm)a × bfolowbtbhsxnlgdxdydzH-pol22.68 × 10.169.4—1.5331.273.75—22.27042.52.56.5V-pol11.43 × 69.415.41.5331.27—222.2704———

The second commonly used slot array antenna is the edge slot waveguide antenna array which has slots modified in a sidewall of the waveguide to a beam pattern in H-plane. For an edge slot antenna, to obtain the desired shunt conductance value which is determined by a tilted angle of sidewall slot, the slot is cut into the sidewall and wrapped around the broad wall of the waveguide because the height of a sidewall of the conventional waveguide is usually smaller than the resonant length of the slot. Each slot is approximately one half-wavelength long and is spaced by a half guide wavelength from its adjacent slots at the design frequency if a standing wave feed is used to obtain a radiating element of in-phase. In order to excite each slot with in-phase spaced by half a wavelength, the adjacent edge slots in the sidewall are oppositely inclined with respect to the vertical centerline.

Stevenson, 1948 (op. cit.) derived the values of the resonant conductance, normalized to the waveguide impedance, for a slot in the narrow wall of the rectangular waveguide using transmission-line theory and the waveguide modal Green's functions. The conductance of narrow-wall (edge) shunt slot is given by Equation (8), where θinis the inclined angle of the slot relative to the vertical direction ‘b’.

GsG0=3073⁢π⁢λgλo⁢λo4a3⁢b⁢(sin⁢θin⁢cos⁢(π⁢λo2⁢λg⁢sin⁢θin)1-(λoλg)2⁢sin2⁢θin)2(8)

As shown inFIG.5, with increasing the inclination angle, the slot conductance in the narrow wall of the WR-90 waveguide increases. The reason for the inclination is that the non-inclined slot disrupts a negligible current in the narrow wall of the waveguide when TE10 dominant mode propagates inside the waveguide. Consequently, the slot will not radiate because a very weak electric field is excited in the slot. However, the inclined slot does interrupt the wall current by an amount controlled by the slot tilt. Unfortunately, the excitation technique applied to the edge wall slots using the inclination has some drawbacks. In addition to the desired longitudinally polarized electric field, the inclination produces a vertically polarized electric field, which is often undesirable. The presence of the unwanted polarization increases the cross-polarization levels.

Non-inclined narrow-wall slots in waveguide generate the horizontal polarization with suppressed cross-polarization. The slots have to extend into the neighboring broad walls of the waveguide to be resonant. The edge slots in the narrow wall need to be excited with a pair of wires inside the waveguide and not by slot tilt in order for minimum cross polarization generation. The excitation of the edge slots is controlled by the iris dimensions and location. As noted above, the structure of the 1-D resonant slot array antenna using non-inclined narrow-wall slots is shown inFIGS.6A-6B.

The design of a linear slotted waveguide array antenna begins by determining the aperture distribution, and hence the slot excitation, required to achieve the beamwidth, gain, and side lobe level needed at the center frequency. The square of the voltage excitation of a slot is proportional to its radiated power and its resonant conductance. The resonant normalized conductance gnof the nth slot, for a given aperture voltage distribution, is given by Equation (9) where, N is the number of slots in a linear array, and anis the voltage excitation for the nth slot. For the uniform illumination, gn=1/N.

gn=an2∑i=1Nai2(9)

Once the slot conductance is obtained based on its voltage excitation, the slot placement and orientation can be calculated using Equations (3)-(8). The dimensions of the exemplary customized dual-polarized array unit cell shown inFIG.6are shown in Table 2 and Table 4, but are not to be limited to those. For example, the value of any given variable shown in Tables 2 and 4 can be increased by 50% or more, or can be reduced by 50% or more, as long as the resulting configuration functions, and is structured in accordance with the limitations and the characteristics of the apparatus disclosed herein.

Performance of the antenna unit cell (8-slot linear array) was analyzed using High-Frequency Structure Simulator (HFSS). The S-parameters and gain of the basic unit of both VP and HP are depicted inFIGS.7A-7B. The reflection coefficients of the VP and HP units are lower than −10 dB over the frequency range from 9.3 GHz to 9.5 GHz. The bandwidth for |Svv| (or |Shh|) <−10 dB is about 2.3% (9.3-9.5 GHz). The isolation (|Shv|) between the V and H ports of the antenna is higher than 60 dB. The realized gain versus the frequency is exhibited inFIG.7B. It is shown that the variation of gain for both polarizations over the frequency bandwidth is about 0.5 dB.

FIGS.7C-7Dshow the co-polarized and cross-polarized radiation patterns of several frequencies in the band (9.3 GHz, 9.4 GHz and 9.5 GHz) in elevation plane (along the waveguide axis) of a conventional antenna and a compact antenna, respectively. It is observed that the radiation patterns of both antennas are stable over the frequency band. The maximum SLL is −13 dB with cross-polarization level of −60 dB below the main lobe for HP and VP array. Performance comparison of the linear array antenna for both polarizations (H and V) is summarized in Table 3.

TABLE 3Radiation parameters of the dual-polarization slottedwaveguide antenna array with eight slots. Planar Dual-Polarized Antenna ArrayTypeBandwidth (%)Gain (dBi)SLL (dB)Cross-polarization level (dB)Conventional antenna (H-pol)2.2316.7212.96−60Compact antenna (V-pol)2.2917.2314.65−60

A non-limiting example of a structure of a dual-polarization planar SWGA array constructed with the novel unit cells of the present disclosure is shown inFIG.8A. With the VP and HP linear arrays successfully designed using HFSS, the dual-polarization planar antenna is composed of an 8×8 VP sub-array and an 8×HP sub-array. When the vertical polarization linear array is designed, the effect of the horizontal polarization array is considered, and vice versa. Both waveguides used for the VP and HP linear arrays have the same guide wavelength, thus both antennas have the same length. In the back, at the centers of the linear array, 50Ω probe adapters for both polarizations are arranged. It is arranged with HP and VP waveguide array side by side, eight linear array for each (FIG.8A), in which the HP waveguide linear arrays are higher than the VP waveguide linear arrays. The width of two linear arrays together is up to 0.58λoin order to obtain a ±42° beam scanning.

Simulated radiation pattern scanning performances of the disclosed planar array for both polarizations in the azimuth plane perpendicular to the waveguide axis at 9.4 GHz with uniform illumination are shown inFIG.8Bfor the VP, and inFIG.8Cfor the HP. The main beam direction can scan from −45° to +45° with a step of 15°. At the maximum scanning angle of ±45° in the E-plane of the VP antenna, the gain decreases by 3.2 dB, meanwhile the side lobe degradation is 1 dB. However, in the H-plane of the HP antenna, the gain decreases 2.6 dB and the side lobe degradation is 1.0 dB when the scanning angle reaches ±45°. Another advantage of this design configuration is a high polarization purity in all scanning angles with the cross-polarization level below −60 dB in the main beam directions. We can also observe that the side lobe levels in all scanning angles are lower than 13 dB. The array also enables individual excitation for each 1×8 element sub-array. Amplitude tapering can be applied using a 6-bit attenuator. Side lobe reduction using a Taylor 25 dB (n−=3) amplitude distribution, and the radiation pattern scanning performances of the disclosed planar array for VP and HP in the azimuth plane perpendicular to the waveguide axis at 9.4 GHz are depicted inFIGS.8D-8E. For both VP and HP, the main beam is scanned from −45° to +45° with a step of 15°. At the maximum scanning angle of ±45° in the E-plane of the VP antenna, the gain decreases by 3.2 dB, meanwhile the sidelobe degradation is 1 dB. However, in the H-plane of the HP antenna, the gain decreases by 2.6 dB and the side lobe degradation is 1.0 dB when the scanning angle reaches ±45°. It can be seen that the maximum SLL is −24.5 dB with cross-polarization level of −60 dB below the main lobe for HP array. The maximum SLL is −25 dB with cross-polarization level of −60 dB below the main lobe for VP array. In order to design a dual polarization slotted waveguide array antenna with low SLL, a tapering amplitude distribution is required. The desired amplitude distribution is a two parameter Taylor distribution with 8 elements, ñ=3 and side lobe level of −25 dB. The definition of the parameter ñ and the details of the Taylor distribution can be found in Constantine A. Balanis, “Antenna Theory: Analysis and Design, Fourth Edition, 2016,” which is incorporated by reference.

FIG.9illustrates the overlapped normalized e-scanned gain of the 8×8 array antenna at 9.4 GHz. Mismatched co-polar beam patterns and cross-polarization isolation are key metric parameters for dual-polarized radars used in weather applications. Typically, cross-polarization isolation below −40 dB, and less than ±0.2 dB is the maximum tolerable mismatch between HP and VP. Using the novel design disclosed herein the cross-polarization below −60 dB across and a co-polar mismatch below ±0.12 dB was obtained over a scanning range of 84° (±42°).

The array unit cell of 8×8 elements can be easily integrated with active modules for 1D e-scanning capability. This active array can be used to create a large aperture array for 2°×2° antenna beamwidth. Conventional or customized electronics using GaAs or GaN can be used for the front-end controller (FEC), where power levels from 1 to 20 Watts per 8-element sub-array can be easily obtained. Radio-frequency complementary metal-oxide-semiconductor (RF-CMOS) technology is commercially available for control modules (CMs). CMOS technology enables high integration of 7-bit digital phase shifter, 7-bit digital attenuators, high isolation T/R and polarization switches and gain blocks. The SWGA arrays and radar systems disclosed herein are very attractive for airborne and weather radar applications that require 1D e-scanning beam patterns, high power, high polarization purity, and lower costs.

Feeding Technique and Structure

Standard rectangular waveguides are generally used as transmission lines for high power applications. Like other transmission lines, these waveguides have a characteristic impedance which requires matching for maximum power transfer. Therefore, there is a need for an adapter between 50Ω coaxial cables and the rectangular waveguides, a so-called coax-to-waveguide adapter. This adapter will introduce the coaxial cable mode to the rectangular waveguide mode. Coupling loops and probes are common ways to inject or remove a microwave signal to the waveguide. The probes couple to an electric field of a certain mode inside the waveguide and the loops couple to a magnetic field of the same mode, but both an electric and a magnetic field will be set up in each case because the two are inseparable. The majority of commercially available coax-to-waveguide adapters are monopole probes. Resonantly-fed SWGA arrays have a long history of use. The end feed and center feed are the most common ways to feed the one-dimensional slotted waveguide antenna arrays with standing-wave excitation. In the end feed configuration, the waveguide antenna array is fed from one end of the waveguide and terminated by a short circuit at the other end. The feed needs to be positioned at odd multiples of λg/4 or λg/8 at the center frequency from the waveguide feeding end and the short circuit is λg/4 away from the end slot. The normalized conductance of the end-fed slotted waveguide antenna arrays for the matching conditions at the feed is given by Equation (10), where N is the number of slots in the waveguide, and gnis the normalized conductance of the slot n.

∑Nn=1gn=1(10)

The center feed is another popular way to feed the one-dimensional slotted waveguide antenna arrays where the antenna waveguide is fed from the center and is terminated by short circuits λg/4 away from both end slots. A center feed configuration is introduced to enhance the bandwidth as well as to suppress the frequency dependent beam squinting. In addition, a more compact antenna system with symmetrical radiation patterns is obtained. Similarly, the matching condition at the feed is given by Equation (11).

∑Nn=1gn=2(11)

In the present disclosure, in at least one non-limiting embodiment, the center feed configuration has been selected to feed both conventional and partial H-plane waveguides. For the VP waveguide antenna, the slotted partial H-plane waveguide is used. A coaxial to partial H-plane waveguide adapter with a conducting disc attached to the end of the probe is used where a probe was inserted into a rectangular cut-out in the H-plane vane at the center of the waveguide. And a hole is drilled in the bottom wall of the waveguide to insert the probe into the waveguide. The diameter dpand length lpof the probe, the diameter d5and thickness d6of the disc, and the rectangular cut dimensions wc, hcwill influence the impedance matching between the coaxial transmission line and the partial H-plane waveguide. The transition structure was designed using a commercial HFSS simulator to realize the input impedance requirements. The obtained values of all parameters are presented in Table 4.

TABLE 4Summary of the dimensions of HP and VP feeding structuresL-shape probe (mm)H-pold3d1d3d21.2711.431.275.08Disc-shape probe (mm)V-poldplpd5d6wchc1.2715.53.2584.25

For the HP waveguide antenna, L-loop side launcher coaxial-to-waveguide transition is used to inject energy into a waveguide by setting up an H-field in the waveguide. By L-shape loop coupling in a rectangular waveguide first an H-field is produced which causes an E-field. A hole is drilled in the narrow wall of the waveguide to insert the probe into the waveguide and the L-loop is formed by soldering the coaxial probe onto the broad wall of the waveguide and is used to generate a current loop, then the current loop becomes a proper excitation for the magnetic field of the dominant TE10 mode. A simple L-shape transition structure was designed using a commercial HFSS simulator to realize the input impedance requirements. The obtained values of all parameters are presented in Table 4.

As depicted in Table 5, the presently disclosed ultra-compact high-performance waveguide antenna array is compared with previous customized waveguide structures shown in Jeffrey B. Knorr, “Analysis of Performance Characteristics of the Naval Postgraduate School MWR-05XP Mobile Weather Radar,” December 2005 (“Knorr”/“Ref [7]”), and Ming Chen, et al., “Dual-Band Dual-Polarized Waveguide Slot Antenna Array for SAR Applications,” IEEE Antennas and Wireless Propagation Letters, Vol. 19, No. 10, Aug. 7, 2020 (“Chen”/“Ref [10]”), which are incorporated by reference. The waveguide of the present disclosure has improved cross-polarization isolation and large scanning range. This is due to less element spacing of the disclosed structure. In addition, the disclosed design discussed about the co-polarization mismatch (<−0.12 dB), which is the critical parameter for dual polarized applications. The only trade-off of the disclosed structure is the narrow bandwidth as compared to that of Knorr.

TABLE 5Comparison of previous and presently disclosed systems*.ParametersRef [7]Ref [10]This workFrequency bandX-bandL-, C-bandX-bandBandwidth (MHz)300200200Waveguide typesPartiallyFollyStandard (0.7λ∘)customizedcustomizedCustomized (0.6λ∘)Element spacing0.7λ∘0.7λ∘0.7λ∘0.6λ∘Max. scanning range40º (±20°)40º (±20°)84° (±42°)Cross-pol isolation<−40 dB<−30 dB<−60 dBMax. co-pol mismatchNANA<0.12 dB

The presently disclosed X-band dual polarized planar SWGA array design, in certain embodiments, provides high polarized isolation (within the range of about −60 dB to about −70 dB) over 200 MHz bandwidth and wide scanning performance 84°(±42°) in the azimuth plane, which are ideal for high-power dual-polarized radar systems for atmospheric applications. The system uses a compact array unit cell where the overall dimensions are reduced by 50% in comparison with that of a dual-polarization SWGA array which uses conventional rectangular waveguides. This presently disclosed design overcomes a fundamental limitation of electronically scanning with conventional waveguides, which have large element spacing (1.2λo). Reducing the element spacing to 0.6λo(in the azimuth plane), the present design uses the broad wall shunt slots for the VP antenna and non-inclined edge wall slots for the HP antenna. Results demonstrate 200 MHz bandwidth centered at 9.4 GHz (2.2% fractional bandwidth), in terms of radiation pattern and input impedance match. Side lobe level can be synthesized to obtained uniform and taper using the attenuators for each subarray (1×8 elements) in the azimuth plane. The polarization purity is excellent with a cross-polarization level below −60 dB at the boresight and scanned patterns up to at least ±45° or more. Reducing the element spacing to 0.6λo(in the azimuth plane), based on a partial H-plane waveguides, enables a 1D e-scanning range of, for example, 84°(±42°) in the azimuth plane. An active sub-array panel of 8×8 elements (unit cells), excited with 8 high-power transmit and receive modules are described. This active sub-array can be scaled to obtain a large array without any constraint in size and power.

In summary, in at least certain non-limiting embodiments, the present disclosure is directed to an X-band dual-polarized slotted waveguide antenna (SWGA) array unit cell which comprises a partial H-plane waveguide with a metal vane, and a conventional waveguide in a side-by-side arrangement, wherein the spacing between elements in the azimuth plane is in a range of about 0.6λoto about 0.5λo, and having a one-dimensional (1D) electronic-scanning range of at least 84° (±42°) in the azimuth plane perpendicular to the waveguide axis, and having cross-polarization isolation of about −60 dB or less. The 1D electronic-scanning range may be within a range of 84° (±42°) to 180° (±90°), for example. The cross-polarization isolation may be in a range of about −60 dB to about −70 dB. In at least certain embodiments, the present disclosure is directed to a sub-array panel comprising a plurality of said X-band dual-polarized SWGA array unit cells. In certain embodiments, the plurality of unit cells in the sub-array panel is in a range of from 4 to 676, or a range of from 4 to 400, or in a range of from 4 to 256, or in a range of from 64 to 144. In certain embodiments, the sub-array panel may comprise n2unit cells arranged in an n×n configuration, where n is in a range of from 2 to 26, or in a range of from 4 to 16, or in a range of from 8 to 12. In at least certain embodiments, the present disclosure is directed to a radar array comprising a plurality of any one of the above-described sub-array panels claims, and to a method of using such a radar array for various well-known and conventional radar uses such as in monitoring weather or tracking moving objects.