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A gap waveguide (GW)-based 4 × 4 dual-band, dual-circularly polarized antenna array is proposed. The antenna is composed of two stacked layers which are responsible for right-handed circularly polarized (RHCP) radiation in K-band and left-handed circularly polarized (LHCP) radiation in Ka-band. Each stacked layer consists of a GW power distribution network to excite 16 radiating units from a single input. A waffle grid is mounted on top of the array structure to increase effective aperture areas and reduce grating lobes. A prototype was fabricated using stereo lithography appearance (SLA) 3D printing and metallization technology, which significantly decreased the fabrication cost and complexity. Measurement results for the antenna prototype demonstrate the operating bandwidths of 19.91–20.52 GHz in K-band and 28.26–29.19 GHz in Ka-band, over which the reflection coefficients of <−10 dB and axial ratios of <3 dB are achieved. The prototype provides peak gains of 20.1 and 20.3 dB with total efficiencies of >90% in the two respective bands. The combination of dual-band, dual-circularly polarized capability, high gain, high efficiency, lightweight, low cost and compact size renders the proposed design a potential candidate for commercial millimeter wave communication applications. [ABSTRACT FROM AUTHOR]

We present a low-profile, mechanically beam-steerable antenna that implements the Risley prism beam-steering concept using only a single flat prism. The proposed antenna achieves 2-D beam steering and consists of two parts: a holographic leaky-wave antenna and a phase-shifting surface (PSS) that acts as a flat prism. The lower holographic leaky-wave antenna acts as the feed for the prism and provides a phase-shifting gradient over its output aperture. When paired with the flat prism, the system can provide 2-D beam steering by mechanically rotating the two layers against each other. Unlike conventional Risley-prism-based beam-steerable antennas, the proposed approach results in a very low-profile antenna and does not need spatial illumination of a two-prism system with a separate feed antenna. The flat prism is implemented using a PSS consisting of low-pass, hexagonal-shaped, spatial phase shifters. A prototype antenna with an overall thickness of only $1.1\lambda _{0}$ at 10 GHz was designed, fabricated, and experimentally characterized. Measurement results agree well with theoretical predictions and both show wide-angle beam scanning ranging from 0° to 57° in the elevation plane and 0° to 360° in the azimuth plane. The proposed antenna system has an equivalent aperture diameter of $7.1\lambda _{0}$ and a measured peak gain of 22.3 dBc at 10 GHz corresponding to an aperture efficiency of 34.5%. The proposed concept is expected to be useful in designing low-profile, beam-steerable antennas in which the scanning speed can be traded off to reduce system complexity. [ABSTRACT FROM AUTHOR]

We present a wideband reflectarray antenna with electronic beam-steering capability. The beam-steerable reflectarray uses an electronically reconfigurable polarization-rotating unit cell (PRUC) that acts as a wideband 1 bit phase shifter. The unit cell consists of four metallic single-headed arrows placed above a ground plane. The four arrows are connected to the unit cell’s bottom surface, which contains two p-i-n diodes for switching and three lumped inductors for RF–DC isolation. Changing the bias states of the two antiparallel p-i-n diodes reconfigures the unit cell between two operating states that provide a +90° and −90° polarization rotation (PR). Simulation results for the unit cell show a wide frequency range of 8.5–11.5 GHz over which the reconfigurable unit cell provides dominant reflection coefficients of >−2 dB and relative phase shifts of 0° and 180° for the two operating states. The proposed unit cell was used to construct a 256-element, fully electronically reconfigurable reflectarray prototype with aperture dimensions of 192 mm $\times192$ mm to demonstrate the design concept. The digital control circuitry needed to individually control the unit cells was also designed and fabricated. Experimental characterization of the reconfigurable reflectarray demonstrated the 2-D beam scanning capability within the scan range of ±60° over a 30% bandwidth. [ABSTRACT FROM AUTHOR]

This article presents a wideband Rotman lens multibeam array implemented with substrate integrated coaxial lines (SICLs) for millimeter-wave (mmW) applications. Unlike other dispersive transmission lines commonly used with printed circuit boards, SICL is a nondispersive planar coaxial line that supports the propagation of transverse electromagnetic waves, thus enabling broadband designs of mmW Rotman lenses. Two types of wideband, compact transition structures consisting of small strips and blind vias were designed to transfer energy between the input–output SICLs and parallel-plate lens cavity. Wideband tapered slot antennas excited by SICLs, with a compact lateral size and wide beamwidths, were introduced as the radiating elements to realize a wide scanning range over a large bandwidth. For a proof-of-concept demonstration, a multibeam array prototype that includes seven beam ports and ten array ports connected to ten antenna elements was designed and fabricated. Experimental results agree well with simulation results and show that the proposed multibeam array has an overall bandwidth of 57% (25–45 GHz) with nearly frequency-invariant beam steering performance within ±45°. The desirable wideband operation in conjunction with the ease of integration with planar circuits and low-cost fabrication make the proposed multibeam array design a promising solution for various mmW applications. [ABSTRACT FROM AUTHOR]

An analytic technique for synthesizing two-element biomimetic antenna arrays (BMAAs) is presented. This method addresses the shortcomings of previous methods used to design such arrays, which uniformly relied on using a numerical optimization procedure to find acceptably suboptimal solutions for the design of the coupling networks of such arrays. We first present an analytic method for determining all possible S-parameters that satisfy the requirements of the four-port external coupling network (ECN) of a two-element BMAA. Subsequently, all possible lumped element implementations of the ECNs are presented. Finally, we present a method for determining the values of the reactive elements constituting the ECN from its S-matrix. We demonstrate the proposed design procedure for a BMAA consisting of two 10.3 cm-long monopole antennas separated by 5 cm. The design procedure is used to determine the reactive elements constituting the ECNs for two (out of infinity) S-matrices and 13 different ECN architectures. Two representative coupling networks were also fabricated and the responses of the BMAAs using them were experimentally characterized. The measurement results are found to be in good agreement with the simulations, verifying the validity of the proposed synthesis technique. [ABSTRACT FROM AUTHOR]

We present a new technique for designing wideband, single-layer reflectarray antennas. The proposed reflectarray exploits a wideband, polarization rotating unit cell that rotates the polarization of the reflected wave with respect to that of the incident wave by 90°. This unit cell and its mirror image were used as 1 bit spatial phase shifters capable of providing a 0°/180° phase shift over a wide bandwidth of 5.4–12.7 GHz. Using this, a reflectarray antenna with 1 bit phase quantization was designed to operate at ${X}$ -band with aperture dimensions of $28.8\,\,\text {cm}\times 28.8$ cm and a focal length of 30 cm. A prototype of the proposed reflectarray was fabricated and characterized using a spherical near-field measurement system. We determined the antenna’s 3 dB gain bandwidth to be approximately 37.4% with a maximum realized gain of 24.2 dBi. Over its entire band of operation, the polarization purity of the antenna remains better than 13 dB and sidelobe levels of better than 12 dB were achieved. [ABSTRACT FROM AUTHOR]