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In this letter, a design of broadband microstrip three‐way directional coupler (TWDC) is presented. The broadband performance of the microstrip TWDC is realized by the method of cascading multi‐section. The broadband TWDC is designed to achieve equal power division and −120°, 0°, and +120° phase differences between output signals. To verify the broadband design, a prototype of three‐section microstrip TWDC operating at C‐band is designed, fabricated and measured. The measured results show that the power division error of the designed broadband TWDC is less than ±0.7 dB and phase error is less than ±12° at a relative bandwidth of 16%. To verify its performance in multibeam application, the designed TWDC is used as a beamforming network for multibeam antenna array to generate three orthogonal beams. [ABSTRACT FROM AUTHOR]

A microwave power transmission (MPT) demonstration system was assembled to comprehensively emulate the operating mode of MPT in space solar power station (SSPS). Based on solid power amplifier and phased antenna array, this system comprised three main parts, that is, microwave power transmitting subsystem, microwave power rectenna subsystem, and power beam steering subsystem. It was employed to validate the constraint relationship between beam collection efficiency and the sizes of transmitting antenna and rectenna, transmission distance, operation frequency. High efficiency rectifying and accurate beam steering were also demonstrated. The power transmitting antenna was composed of 64 sub‐arrays of patch antennas, with the dimension of 1.2 × 1.2 m2. In addition, the rectenna array was constructed as a corner truncated square with the side length of 2 m. Its design was based on the concept of perfectly matched layer and integrated rectifying surface. The power beam steering subsystem, implemented with software retrodirective idea, pointed the microwave beam to the rectenna according to the direction of arrival of the pilot signal. The experimental MPT system, operating at 5.8 GHz, transmitted 910 W microwave power across 30 m distance. At the power receiving end, the optimum rectenna conversion efficiency of 49.3% was obtained. With aid of the beam steering subsystem, beam granularity, and beam steering accuracy of 0.23 and 0.18° were achieved, respectively. The compositive experiment verified all function as power transmitting, receiving, rectifying, and steering of MPT system. MPT technology is thus driven toward engineering application, and will ultimately space solar power exploration. [ABSTRACT FROM AUTHOR]

A design of millimeter wave (mm‐wave) dual‐polarized multibeam antenna array (MAA) with a boresight beam is presented. In order to generate a boresight beam, a 5 × 6 Butler matrix based on three‐way directional couplers is designed as the beamforming network, which achieves equal power division and −60°, +120°, 0°, −120°, +60° progressive phase differences among the output ports when the five input ports are excited, respectively. By four‐layer design, the two 5 × 6 BMs for horizontal polarization (HP) and vertical polarization (VP) are constructed. The patch is used as radiator element, and the HP and VP wave are excited by aperture coupling and microstrip feed, respectively. A prototype is fabricated and measured to verify the design. The measured results show that the designed mm‐wave dual‐polarized MAA can generate five radiation beams including a boresight beam and the five beams with HP and VP cover the range of ±50° at 28 GHz. In addition, the designed mm‐wave dual‐polarized MAA can be a potential option for mm‐wave multibeam application. [ABSTRACT FROM AUTHOR]

A design of planar dual‐polarized differentially fed multibeam patch antenna array (DFMPAA) is presented in this article. The dual‐polarized DFMPAA is composed of two circular 4 × 4 butler matrixs (BMs) and a 1 × 4 dual‐polarized patch antenna array. The two BMs are designed in the top and bottom layer as the feeding network of horizontal polarization (HP) and vertical polarization (VP), respectively. The patch is designed as the radiation element of the dual‐polarized DFMPAA, which is fed by the slot and aperture coupling to generate the HP and VP wave, respectively. To achieve high cross‐polarization discrimination (XPD), the antenna element is fed differentially. A prototype working at 5.5 GHz is fabricated and measured in order to validate the performance of the proposed dual‐polarized DFMPAA. The dimension of the dual‐polarized DFMPAA is 3.8 λ0 × 1.7 λ0. Measured results show that when the beam scan to the maximal pointing angle, the XPD of the dual‐polarized DFMPAA in HP and VP are higher than 27 and 29 dB, respectively. Additionally, the beams of the dual‐polarized DFMPAA can cover the range of ±42° in horizontal plane. [ABSTRACT FROM AUTHOR]

In this letter, a design of multibeam antenna (MBA) with two-dimensional (2-D) beam steerable capability is proposed. The proposed MBA is composed of a circular 4 × 4 butler matrix (BM) and a 2 × 4 patch antenna array. And the 2 × 4 patch antenna array consists of four two-element subarrays uniformly arranged along the E-plane. By introducing the switching diodes in the subarray and controlling the switching diodes on and off, elements of the subarray are excited through the paths with different lengths, and the beam of the subarray is steered subsequently in the H-plane. The circular 4 × 4 BM is designed as the beamforming network to excite the four subarrays uniformly arranged along the E-plane and steer the beam in the E-plane. The proposed MBA can generate 12 beams by selecting the excitation port and controlling the on–off state of the switching diodes. To validate the performance of the proposed MBA, a prototype is fabricated and measured. By design, the dimension of the designed MBA has reduced to 2.9 λ0 × 1.3 λ0. The designed MBA operates at 5.7 GHz, and the results show that the beams of the MBA can cover the range of ±36° in the E-plane and ±22° in the H-plane, respectively. [ABSTRACT FROM AUTHOR]

Adaptive beamformers at the element level usually require a great number of training samples and the computational cost for calculating the weight vector for large phased array antennas is very high, which make it difficult for real-time applications. To address this problem, a two-dimensional (2-D) adaptive beamformer applicable to large planar array antennas that have low computational complexity and low training sample requirement is proposed. In the proposed method, the weight matrix is first reconstructed as a matrix that has the same or close columns and rows by utilising the special Kronecker property of the array steering matrix. Then, the weight vector is determined by adopting a bi-quadratic cost function and a bi-iterative algorithm. Experimental results show that the proposed method can achieve fairly good performance even when the training samples are small. [ABSTRACT FROM AUTHOR]

A quantity called available directivity is defined for a radiating structure in terms of its characteristic mode content. It is shown how its maximum value can be evaluated when a certain number of such modes are considered to be excited with appropriate modal excitation coefficients. The achievable directivity is found by constraining the associated quality factor. This provides a more precise way of determining the prospective directivity of a structure than the usual estimates in terms of the spherical wave modes related to the smallest sphere enclosing the structure. [ABSTRACT FROM AUTHOR]

This letter presents a novel transmission metasurface to achieve orbital angular momentum (OAM) waves at the X-band. The unit cell of the proposed metasurface consists of three dielectric layers and four metallic layers, where the metallic layer is composed of an outer metallic ring and a center quasi-snow patch. A good transmission coefficient of the unit cell is obtained at the operating frequency. Meanwhile, a full 360° phase shift can be achieved by changing the length of the quasi-snow patch. The method of generating OAM waves is studied and analyzed. Based on this method, a metasurface producing a +1-mode OAM wave is designed and simulated. To verify this concept, one prototype is fabricated, assembled, and measured. The measured results agree well with the simulated ones, showing that the +1-mode OAM wave can be generated successfully with a high gain of 14.5 dBi. Moreover, a narrow divergence angle of +/−9° is achieved in the produced OAM wave. [ABSTRACT FROM AUTHOR]

A novel polarization-reconfigurable planar antenna is presented. The antenna consists of an electronically reconfigurable polarizer integrated with a printed slot. By changing the states of the p-i-n diodes on the polarizer, the linearly polarized (LP) waves radiated by the slot can be converted into either right-hand circularly polarized (RHCP) or left-hand CP (LHCP) waves. The polarizer contains 16 unit cells arranged as a $4\times 4$ array. The antenna radiates RHCP waves if the p-i-n diodes on the top side of the polarizer are switched ON, while LHCP waves are radiated if the p-i-n diodes of the bottom side of the polarizer are switched ON instead. The physical mechanisms of the antenna are discussed and the parametric study is carried out by full-wave simulations. To verify the concept, one prototype at 2.5 GHz is designed, fabricated, and measured. Good agreement between the measured and simulated results is obtained. The antenna achieves a gain ≥8.5 dBic in both RHCP and LHCP with an aperture efficiency of 70%. Advantages of the proposed design include electronically reconfigurable polarizations for RHCP or LHCP, low profile, low cost, high isolation between the dc bias circuit and RF signals, high power handling capability, and easy extension to large-scale arrays without increasing the complexity of the dc bias circuit. To the best of our knowledge, this is the first report of an electronically polarization-reconfigurable CP antenna with a single-substrate polarizer. [ABSTRACT FROM AUTHOR]

A triband antenna with high gain and low profile is proposed. This antenna is based on the concept of Fabry–Perot cavity antenna (FPCA) and three resonances are obtained by employing two frequency selective surface (FSS) layers. Two FSS layers lead to two resonant frequencies by making each FSS layer satisfy the resonant condition of Fabry–Perot cavity. The third resonant frequency is obtained by exploiting the combined effects of the two FSS layers together. The operating principle of this proposed antenna is explained and the achievable frequency range is investigated. It is shown that the proposed method enables all three resonant frequencies to be independently tuned within certain frequency range. Because of the 0° reflection phase of the combined-FSSs, the present antenna has a low profile. To verify the design concept, one C-/X-/Ku-band FPCA is designed, fabricated and tested. Experimental results agree well with the simulated results. High gain with good impedance matching in three bands is obtained, which reaches a peak gain of 13.4 dBi at 5.2 GHz, 18.9 dBi at 9.7 GHz, and 20 dBi at 14.6 GHz. The overall height of the proposed antenna is approximately 0.36 wavelength at its lowest operating frequency. [ABSTRACT FROM PUBLISHER]

This article presents a novel circularly polarized (CP) wide-band printed monofilar square spiral antenna (MSSA) with a low profile and 50-X input impedance, as well as a technique to improve the overlapped bandwidth and reduce the profile of a conventional MSSA. To extend the application of the present design to an array antenna, a square cavity is introduced. This simple and low-cost approach results in a wide-band printed MSSA with high directivity. To verify this design concept, antenna prototypes operating at Ku frequency band have been designed and fabricated. Simulation and measurement results show that the present designs have more than 16% 10-dB return loss and 3-dB axial ratio (AR) bandwidth within the same frequency range with high radiation efficiency. The beam-scanning performance of the array antenna using the present design was investigated, and the calculated results suggest that good CP performance is obtained during the beam scanning. The advantages of our MSSA design are wide overlapped bandwidth, low profile, flexibility in antenna performance tuning, and easy fabrication. The present antennas have the potential to be used in small satellites such as microsatellites and CubeSats for tracking, command function, and data downlink applications. [ABSTRACT FROM AUTHOR]

ABSTRACT A high gain dual-polarized wideband Fabry-Perot (FP) antenna fed by 1 × 2 antenna array is proposed. A metasurface consisting of patch and mesh array is employed as a partially reflective surface, which produces a reflection phase with a positive slope over a wideband frequency range for increasing antenna's gain bandwidth. To obtain dual polarizations and further improve the gain of antenna, a 1 × 2 patch array coupled by two orthogonal slots is designed as the feed of the FP antenna. A prototype is fabricated and measured. The measured results demonstrate that this proposed antenna has a 3-dB gain bandwidth of 22.2% in both polarizations. The peak gain of 15.7 dBi and 15.2 dBi is obtained at two polarization ports, respectively. Within the 3-dB gain bandwidth, good impedance matching with high isolation over 35 dB between the two ports is achieved as well. © 2016 Wiley Periodicals, Inc. Microwave Opt Technol Lett 58:2316-2321, 2016 [ABSTRACT FROM AUTHOR]

This paper presents a novel sequentially rotated patch array antenna with dual circular polarizations (CP). The present design has the advantages of compact size, simple feed networks, low cross polarization, and high isolation. The radiating elements are dual linearly polarized (LP) equilateral triangular patches with hybrid feeds. The vertical polarization (VP) of the patch antenna is obtained by using an aperture-coupled feed and the horizontal polarization (HP) is obtained by using a proximity feed. These two feeds are orthogonally positioned and are printed on different PCB layers, which leads to the high isolation between these two ports and facilitates the design of the feed networks. The array antenna consists of six such dual-LP triangular patches sequentially rotated by 60 ^\circ and fed by separated feed networks. Since LP antenna elements are used, the design of the feed network is much simplified. Through sequentially varying the feeding phase by \pm 60^\circ, dual circular polarizations are obtained. The operation principle of the array antenna is also analytically explained in this paper. To verify the design concept, one dual LP equilateral triangular patch and one dual CP equilateral triangular patch array resonating at 10.5 GHz are designed, fabricated, and tested. There is a good agreement between the simulation and measurement results, both of which show that the array antenna exhibits high port isolation and good circular polarizations with low cross polarization at different planes. The proposed design technique can be applied to the design of dual CP array antennas operating at other frequency bands. [ABSTRACT FROM PUBLISHER]

A wideband and dual-polarization antenna array with high efficiency and high isolation is proposed. In order to achieve the desired performance, a wideband radiating element and a full-corporate waveguide feed network are employed in the design. In particular, ${{E}}-plane waveguides are utilized for the feed-network configuration so as to suppress wave leakage between adjacent layers when the antenna is fabricated via conventional machining techniques. The operational mechanism is presented and a \text16 \times \text16 antenna array is tested for verification. Experimental results show that the bandwidths of VSWR < \text2.0 for both of the polarizations are about 17.1% (12.45–14.78 GHz) and the isolation between the two polarization ports is better than 39.5 dB. In addition, more than 70% antenna efficiency with higher than 29.4 dBi gain is achieved over the operational bandwidth. [ABSTRACT FROM PUBLISHER]

In this letter, a simple approach to design a reconfigurable feeding network (RFN) for antenna array beam scanning is presented. By combining a 3 dB power divider and a reconfigurable delay line group (RDLG), the two output signals with 2 m+n sets of uniformly distributed phase gradients (PGs) can be obtained. And by adopting multi two-output RFNs and multi-stage design, a RFN for generating 2 m+n continuously distributed beams is constructed. For verifying the design method, a microstrip four-output RFN for generating four scanning beams is implemented, fabricated and measured. The measured results are consistent with the theoretical analysis, which provides the validity of the design. And the design of the RFN can be used as a candidate of the feeding network for antenna array beam scanning. [ABSTRACT FROM AUTHOR]