This article presents an enhanced single-sideband time-modulated phased array (ESTMPA) using modulating pulses with stepped waveforms. Based on the in-phase/quadrature (I/Q) complex modulation technique, this phase-only weighting array generates a scanning beam at the 1st sideband. The proposed modulating pulses realized through a reconfigurable power divider in I/Q time modulator can avoid the power loss from the switches during switch-OFF state and eliminate the maximum undesired sideband-the 5th harmonic in STMPA. As a result, it brings a power spectrum with less undesired sidebands, lower sideband level (-16.9 dB), higher harmonic efficiency (94.96%), and wider allowable signal bandwidth (eight times as wide as that of the conventional time modulated array). To experimentally verify the feasibility of the proposed design, a wideband enhanced I/Q time modulator and its corresponding eight-element ESTMPA are designed and manufactured. A detailed study on the effect of the magnitude and phase deviations in the circuit and the transition period of modulating pulse are presented. The measured results of power spectrum and radiation pattern have a good agreement with the simulated ones.

The irregularly located element array within the antenna aperture can be applied to obtain narrow main lobe width and low sidelobe levels with fewer elements as compared with the traditional (periodic) array configurations. In this article, a reconfigurable reflectarray antenna (RRA) combined with hyperuniform disordered distribution is presented. Based on the theoretical radiation pattern of reflectarray, it has been found that the proposed array with reduced elements holds a similar radiation pattern as that of a corresponding periodic array. Meanwhile, the reflectarray avoids the design of complicated feeding network for the disordered phased array antenna. In addition, for a reconfigurable reflectarray to achieve beam scanning, active devices are necessary. In such case, the design of RRA with fewer elements is of particular importance. A 1 bit RRA of 64 elements prototype has been designed, fabricated, and measured. The side length of each element is $0.625\lambda $ . Experimental results agree well with the full-wave simulations, and scan beams within ± 50° range have been obtained with a peak gain of 17.4 dBi at 12.5 GHz.

Single-sideband time-modulated phased arrays (STMPAs) can suppress undesired sidebands and achieve convenient beam scanning without repeated time-consuming optimization, as compared to conventional time modulated arrays (TMAs). However, most of STMPAs are limited to phase-only weighting arrays because the conventional method for achieving amplitude weighting significantly reduces the suppression of undesired sidebands. In order to simultaneously achieve convenient beam scanning, low sideband level (SBL) and low sidelobe level (SLL), a general amplitude weighting method based on stepped time-modulated waveforms with different amplitudes in STMPA is proposed in this paper. By selecting an appropriate number of steps, time-modulated waveforms can achieve various amplitude weighting values with a large dynamic range. This enables continuous and precise control of the amplitude weighting for each element. By utilizing this method, it is convenient to design time-modulated waveforms for each antenna element independently to suppress undesired sidebands, which avoids repeated time-consuming optimization during beam scanning. To verify the proposed method, an eight-element low sidelobe STMPA was fabricated and tested, with a measured SLL of -23.53 dB and a measured SBL of -33.34 dB. Additionally, a calibration method for STMPAs is also presented to ensure accurate amplitude and phase weighting in practice..

Time-modulated array (TMA) antennas, introduce the dimension of time into antenna design to control the radiation patterns and frequency spectral characteristics, thus improve the reconfigurability of array antennas and provide multiple functionalities. They have great application potential in military and civilian fields, such as precision guidance and mobile communication, and are currently a hot spot of academic research. This article provides a review on the fundamentals and applications of TMAs. First, the basic theory and mathematical formulations of TMAs are introduced. Second, the most important applications of TMAs, namely time-modulated phased arrays (TMPA), are discussed from the perspectives of harmonic suppression and harmonic utilization, which are used for single-beam and multibeam radiation. Then, we survey the combination of TMA with various types of novel antenna arrays, such as single-channel digital beamforming (DBF) arrays, frequency diverse arrays (FDAs), and retrodirective arrays, to create new hardware implementation methods and enhance their performance. Next, recent advances in dedicated integrated chips for TMA, which have played a significant role in driving the progress of TMAs from academic research to practical applications, are presented. Finally, the challenges and prospects for TMAs are discussed, including new research directions and emerging application scenarios.

Single-sideband time-modulated phased arrays (STMPAs) are able to generate a scanned beam at the first sideband while suppressing undesired sidebands. In this article, an STMPA with very low sideband level (SBL) suitable for wide-bandwidth signals is proposed. The design utilizes time-modulated pulses with stepped waveforms, which are realized by digital attenuators. This provides more degrees of freedom to improve the performance of STMPAs compared with previous techniques. Optimization of waveforms to achieve low SBLs as a function of the number of steps is discussed. This optimization is subject to some practical restrictions stemming from the characteristics and limitations of digital attenuators. Compared with previous STMPAs designed to eliminate undesired sidebands, the proposed design results in very low SBLs while reducing the impact of aliasing for wideband signals. Quantitative analysis of hardware complexity and aliasing effects is presented to demonstrate it. To validate the analysis presented, STMPAs with four-step and eight-step waveforms were designed and fabricated. Their measured SBLs are −28.72 and −33.57 dB, respectively. Measured frequency spectrum, waveform of modulating pulse, and radiation pattern of scanned beams are all presented.

The gain enhancement using superstrate has been widely investigated. Different from the existing researches, this letter focuses on the study of dielectric slab superstrate (DSS) antenna element with electrically small size. For the electrically small DSS antenna, the gain enhancement mechanism based on the multi-reflections between interfaces with infinite sizes is no longer available. By using a plug-in optimizer based on Python programming and HFSS simulation software, the optimized designs of electrically small 2-layer and 3-layer DSS patch antennas operating at 6 GHz are introduced. To validate the predicted results, the two optimized antennas are fabricated and measured. For the 2-layer DSS patch antenna, the measured peak gain, 3-dB gain bandwidth, impedance bandwidth, and the aperture efficiency are 10.47 dBi, 22%, 20.7%, and 379%, respectively. For the 3-layer DSS patch antenna, the measured peak gain, 3-dB gain bandwidth, impedance bandwidth, and the aperture efficiency are 10.55 dBi, 42%, 28.7%, and 386%, respectively.