This paper investigates beampattern synthesis methods based on a novel Receive Delay Array (RDA) to mitigate interferences located in the mainlobe of the beampattern. In our system design, the RDA is developed by transmitting a stepped frequency linear frequency modulation waveform and delaying the received echo with a small time offset between adjacent receive antenna elements. In doing so, a range-angle-dependent beampattern is obtained in the joint transmit-receive spatial domain. A two-stage beamforming scheme, including the equivalent data-independent transmit beamforming and dimension-reduced data-dependent receive beamforming, is then proposed to mitigate mainlobe interferences. Furthermore, according to the adaptive array theory, by designing a transmit weight vector dependent of the interference steering vector, two beampattern synthesis algorithms are developed respectively based on the maximum gain and minimum deviation to adjust multiple responses of the transmit beampattern precisely. The mainlobe of the receive beampattern is also broadened with the use of the derivative constraint. By combining the devised transmit and receive weight vectors, a two-dimensional joint transmit-receive beampattern with a flat-top mainlobe and broadened nulls can be formed, where the interferences are mitigated against the direction-of-arrival (DOA) mismatch. Theoretical and practical analysis as well as parametric studies are provided to demonstrate the effectiveness of the proposed beampattern synthesis methods in mitigating mainlobe interferences.

Frequency diverse arrays (FDA) have a more flexible beamforming ability than phased arrays since they provide degrees-of-freedom (DOFs) in both range and angle domains by applying a tiny frequency offset across adjacent elements. Nevertheless, the beampattern of an FDA is not only range-angle-dependent but also time-variant when only considering the transmit procedure. In this paper, an enhanced transmit-receive beamforming approach is proposed to achieve the time-invariant and symmetrical beampattern with only a single maximum value in range-angle space. Firstly, two FDAs with symmetric logarithmically increasing frequency offsets (SLFOs) are proposed to achieve a maximum value at the desired range-angle region while exhibit sidelobe in the region out-of-interest. Secondly, the receive procedure is devised to compensate the time-variant terms with multiple mixers corresponding to different frequencies. To maintain the shape of the mainbeam and simultaneously reduce the peak sidelobe level (PSLL) of the pattern, the optimization problem is constructed into a semidefinite programming problem. Numerical results show that both of the two proposed FDAs exhibit fine focused, symmetrically distributed transmit-receive beampatterns in range and angle domains.

Incontrast to the steady angle-dependent transmit beampattern of the conventional phased array, the counterpart of a frequency diverse array (FDA) is basically time variant and range–angle coupled, which limits its potential application in many scenarios. In this article, we consider the beamforming in joint transmit and receive domains to handle the time-variant problem and propose a novel range–angle transceiver beamforming approach based on the semicircular-FDA scheme. In particular, the transceiver scheme of semicircular-FDA is first established.In the sequel, the periodicities of its transceiver beampattern in range and angle dimensions are briefly analyzed. Based on this analysis, a semicircular-FDA applied with nonlinearly increasing frequency offset (NIFO), termed as NIFO semicircular-FDA, is proposed to achieve the beampattern with a single mainlobe peak in range–angle space. Then, an optimization problem is constructed based on an advanced bat algorithm to further reduce the sidelobe level (SLL) of the NIFO semicircular-FDA. Numerical results show that focused time-invariant beampattern with low SLL in both range and angle dimensions can be achieved with the proposed approach.

A novel compact magneto-electric (ME) dipole antenna with size of 0.31λ ₀ ×0.31λ ₀ ×0.12λ ₀ (λ ₀ is the wavelength at central frequency herein and after), gain of around 8 dBi, and bandwidth of 39.7% is presented for millimeter-wave beam steering applications with the combination of the fractal technique and reactive impedance surface (RIS) loading. In particular, a fractal ME dipole antenna with four modified second-order Minikowski structures is firstly designed, where an aperture size of 0.38λ ₀ ×0.38λ ₀ is achieved. Herein, the antenna gain is dropped with the size reduction. Then a capacitive RIS structure is designed and loaded to improve the antenna gain and further lower down the antenna operating frequency range. With the RIS structure, the antenna gain is increased by around 4 dB, and the operating center frequency is shifted to left side by 9.0 GHz, thus achieving a further size reduction. Simulation and measurement results are provided to demonstrate the excellent properties of the proposed antenna. Subsequently, the antenna is arranged into a 5 mm-spaced (half wavelength at 30 GHz) 16-element uniform linear array. The beam steering characteristics of the array are investigated with the influence of phase quantization errors into consideration.

The approach, proposed in “Range-Angle-Dependent Beamforming of Pulsed-Frequency Diverse Array,” IEEE Trans. Antennas Propag. vol. 63, no. 7, pp. 3262–3267, Jul., 2015, is intended to achieve a quasi-static transmit beampattern with pulsed-frequency diverse array (FDA). The derived constraint is too rigorous; thus, FDA approaches the conventional phased array to some extent. This paper proposes an effective approach to resolve the time-varying issue of FDA at the receiver based on the model established in the above paper. The proposed approach exhibits a more flexible capability in receive beamforming as the constraint imposed on the pulse duration is released.