A broadband linearly polarized single-layer reflectarray antenna constructed by element cells of triple gapped rings with phase-delay lines (TGR-PDL) attached to the outer one is presented in this paper. The novel TGR-PDL element is composed of three circular rings, each with a pair of gaps which are orthogonally positioned, and two identical phase-delay lines are attached to each half of the outer ring. The characteristics of the proposed element are first analyzed and then a linear and smooth phase response covering about 600° is obtained by adjusting the length of the phase-delay line. Based on the element cell, an offset-fed reflectarray antenna of an octagon-shaped aperture with 266 mm in diameter, is designed, fabricated, and measured to verify the broadband property of the proposed element. The measurement results show that about 31.5% of 1-dB gain bandwidth is realized, and the maximum gain at the center frequency of 10 GHz is about 25.78 dBi, which is equivalent to about 50% aperture efficiency.

A novel X-band single-layer unit-cell structure with enhanced bandwidth for linearly polarized microstrip reflectarray antenna is proposed. The unit-cell structure is composed of two circular rings, each with a pair of gaps that are orthogonally placed, and two identical phase-delay lines attached to the outer circular ring. With this novel structure, a linear phase response ranging about 550° is achieved by varying the length of the phase-delay line. An offset-fed reflectarray antenna composed of 277 elements forming an octagon-shape aperture is designed, fabricated, and measured to verify the broadband characteristic of the proposed unit cell. Measurement results show that 20% 1-dB gain bandwidth is realized. Moreover, the maximum gain at 10 GHz is about 26.38 dBi, which means about 51.3% efficiency is achieved. At the same time, the sidelobe level and cross polarization for E-plane are also measured which are below -17.5 and -26 dB, respectively.

An innovative method based on Compressed Sensing (CS) is presented for synthesizing subarrayed linear arrays (SLAs) using as few subarrays as possible with unequal sizes and weights. According to the CS theory, the related synthesis can be transformed into a sparse signal recovery problem since the element weight vector is compressible and can be sparsely represented due to only subarray-level excitation is conducted. Specifically, the synthesis herein is formulated as a convex problem with minimization of the l1-norm, and the corresponding parameters including the number of subarrays, the subarray weights and sizes can be determined simultaneously via convex optimization to satisfy the prescribed focused and/or shaped beam patterns. The proposed method is very easy to implement and has good computational efficiency. Numerical experiments are carried out to validate the effectiveness and advantages of the proposed method.

This letter proposes an algorithm for airborne synthetic aperture radar (SAR) ground moving target imaging (GMTIm) and motion parameters estimation (MPE), which is applicable in situations whether the Doppler ambiguity occurs or not. To derive the algorithm, the general expression for the received signal after range compression is deduced first, in which the useless exponential term induced by the possible Doppler ambiguity is omitted. Then, the second-order keystone transform (SOKT) is used to correct the range curvature. After the SOKT, the Radon transform is employed to estimate the slope of the target trajectory, and the range walk correction follows. In the following, the scaled Fourier transform and the dechirp technique are utilized to estimate the azimuthal parameters. Finally, the target's motion parameters are obtained by solving equations according to the trajectory slope and the estimated azimuthal parameters, with which the target is focused through azimuth matched filtering. Both simulated and real airborne SAR data are processed to validate the effectiveness of the proposed algorithm.

A novel wideband circularly polarized (CP) microstrip antenna array loaded with dual-layer Metasurface (MTS) is proposed. The dual-layer rhombic MTS with asymmetrical perturbations is designed to excite two CP modes at different frequencies. Moreover, a hybrid phase shifting strategy is proposed and taken to incorporate unequal cross-couple slots into the radiating patches to achieve the phase shifting condition for wideband CP antenna element. Simulated results for the proposed element show that an axial ratio (AR) bandwidth of 40.0% (12.14 - 18.21 GHz) is achieved with good impedance matching. A 4 × 4 CP antenna array composed of four 2 × 2 subarrays fed through a sequential rotation network is designed and fabricated. The measured results show that a -10 dB impedance bandwidth of 67.2% (10.21 - 20.56 GHz) along with an AR bandwidth of 65.5% (10.81 - 21.25 GHz) and 3-dB gain bandwidth of 53.1% (11.46 - 19.74 GHz) as well as a peak gain of 17.19 dBic have been achieved. Parasitic corner-cut square rings are incorporated to reduce the sidelobe levels at high frequencies and make them below -10 dB, as usually achieved by relatively narrow-band arrays, and finally -11.3 dB is achieved.

Composite right/left-handed (CRLH) waveguide leaky-wave antenna (LWA) with low sidelobe level (SLL) and high radiation efficiency is investigated and designed in this paper. Due to the characteristic of negative and positive dominant mode propagation constant of the CRLH transmission line, a backward to forward beam-steering LWA can be realized through frequency scanning. The leaky-wave radiation is analyzed first based on a Ka-band CRLH waveguide with straight slots differently offset on the broadwall. The propagation constant maintains almost invariable as the slot offset varies, meanwhile the attenuation constant has a considerable dynamic range. Thus meandering long slot, whose offset varies along the CRLH waveguide, can be cut on the broadwall to generate a tapered excitation distribution. A prototype of the proposed CRLH waveguide LWA with meandering long slot is designed and fabricated to validate the design. Measurement results show that continuous beam-steering capability from −29° to +31° is achieved, meanwhile the optimized SLLs for the designed antenna patterns are kept below −18.5 dB in the major operating band with the minimum SLL of −22.4 dB at 33 GHz, and the average radiation efficiency is 65.4%. The realized SLLs and radiation efficiency performances of our CRLH LWA surpass others reported in open literatures.