Xiaowen Zhao

In this paper, an adaptive iterative Fourier technique (AIFT) algorithm is developed for the synthesis of multiple circular/elliptical beams with low sidelobe levels (SLLs) through phase-only optimization. The key innovation of the AIFT algorithm is the introduction of an elliptical beam model, which facilitates the adaptive determination of main beam regions and offers additional flexibility in controlling pencil beam shapes. Unlike conventional IFT-based algorithms, the AIFT algorithm eliminates the need for prior knowledge of main beam regions and avoids repetitive adjustments of sidelobe correction thresholds. This not only simplifies the configuration process but also prevents the generation of defective radiation patterns. Extensive synthesis experiments with different beam numbers, distributions, and ellipticities demonstrate that the elliptical beam model consistently outperforms its circular counterpart in multibeam scenarios, achieving lower SLL and higher directivity. These advantages are particularly pronounced in asymmetrical beam distributions, highlighting the elliptical beam’s superior potential for reducing SLLs of multi-spot-beam patterns and offering new insights for advancing the performance of point-to-multi-point communication systems.

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.

This paper presents a novel Ku wideband circularly polarized (CP) antenna array composed of crossed-dipole element (CDE) and fed through sequential rotation (SR) feeding technique. Unlike the traditional CP-CDE fed by coaxial cable that usually works at low frequencies, the proposed CDE consists of two orthogonal heart-shaped patch dipoles that can work at frequencies as high as Ku-band, at the same time achieving a larger bandwidth. A feeding structure is proposed without welding, so potential errors in the antenna assembly process can be mitigated. A 2 × 2 CP antenna array with wideband SR feeding network is designed based on the CDE to further expand the axial ratio (AR) bandwidth. The designed antenna array is fabricated using the multilayer printed circuit board (PCB) technology and measured in anechoic chamber using the planar near-field measurement facility. The measured results show that −10 dB impedance bandwidth of 44% (11.6–18.15 GHz) along with 3 dB AR bandwidth of 38.7% (12–17.65 GHz) and 3 dB gain bandwidth of 34.6% (12.2–17.3 GHz) as well as 11.02 dBic peak gain have been achieved while maintaining a lower profile.

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.

A type of dominant composite right/left-handed (CRLH) rectangular waveguide leaky-wave antennas (LWAs) is designed in this paper. A detailed parametric study is carried out to give a guidance of optimizing this CRLH unit cell. Similar to the traditional rectangular waveguide, slot with offset from the broadwall centerline will cut the induced surface current, thus radiation occurs. Two CRLH waveguide are designed and fabricated. One is with straight long slot cut on the waveguide broadwall, and the other is with meandering long slot cut. Intensive analysis of the measured results is given to evaluate the performance of this type of antenna, which shows the advantages of consistent high gain and high radiation efficiency, and is very suitable for actual radar systems.

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.

In this study, a novel strategy is proposed for synthesis of sparse concentric ring arrays composed of uniformly excited elements. The synthesis problem herein is aimed at determining the sparse ring radii and the corresponding number of elements equally spaced on each ring simultaneously in order to produce circularly symmetric patterns. By using the proposed method, the above synthesis problem can be simply transformed to a single‐type‐variable optimisation problem since the relationship between the sparse ring radius and the element number is derived according to the properties of Bessel function. The proposed method is very efficient and flexible for synthesising direct radiating arrays and/or the scanned ones. Numerical experiments are conducted to validate the effectiveness of the proposed method. Compared with other methods, the proposed method can obtain circularly symmetric patterns using fewer elements. On this basis, the comparison of sparse array and thinning array is given through numerical experiment. Meanwhile, a scanned sparse array of 908 elements is synthesised in a circular aperture of 25 λ diameter with invariant peak sidelobe level of −28.9 dB, which can steer the beam from 0° to 30° in elevation and from 0° to 360° in azimuth.

Compressed sensing (CS) has been successfully applied to the synthesis of maximally sparse non‐uniform linear array with the synthesised pattern matching the reference pattern very well by using as few elements as possible. According to the CS theory, a sparse or compressible high‐dimensional signal can be first projected onto a low‐dimensional space through a measurement matrix, and then recovered accurately by using a variety of practical algorithms based on the low‐dimensional information. The proposed approach can synthesise the sparse linear arrays fitting the desired patterns with a minimum number of elements. Numerical simulations validate the effectiveness and advantages of the proposed synthesis method. Moreover, compared with the existing sparse‐array synthesis methods, the author's method is more robust and accurate, while maintaining the advantage of easy implementation.