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.

This paper presents a conformal log-periodic array covering an ultra-wide band of 2-18 GHz. It employs monopoles of different heights for the high band, top-hat monopoles for the middle band, and folded top-hat monopoles for the low band. The top hats help to achieve a low profile of the monopoles while the folding is to maintain a good input resistance at the low band. A meandering microstrip line on the bottom is used to feed the array. The proposed antenna is mounted on a conducting cylindrical surface with all the top hats conformal and aligned to the outline of the cylinder. A prototype is fabricated and tested. Measured results show that an impedance bandwidth from 2 GHz to 18.3 GHz (9.15: 1) for VSWR < 2 is obtained. Over the same band, the measured gain is better than 7.2 dBi. The antenna has a very low profile of 0.053 λL at the lowest operating frequency, which should be useful in many communication systems such as missile and airborne applications.

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..

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.

Focused aperture (FA) antenna with phase center of its feeder moving along the focal plane or focal arc is an effective and low-cost approach for beam scanning. Dual polarization is always desired in the communication system. In this paper, a dual-polarized linear array with overlapping handover of subarray (OHSA) is proposed to produce continuous displacement of virtual point source on the basis of Huygens equivalence principle. As the feeder of an FA antenna, the proposed OHSA not only enables continuous beam scanning electronically, but also reduces the profile of the antenna. To validate the proposed scheme, a dual-polarized electronic beam-scanning transmitarray antenna with the profile of 3.46λ0 is designed and measured. At the designed frequency 5.5 GHz, for both x- and y-polarizations, the measured gains are higher than 20.9 dBi, and the sidelobe levels are lower than −16 dB; within the bandwidth of 5.3 to 5.9 GHz and the scanning range of ±30°, the gains are higher than 16 dBi, and the sidelobe levels are lower than −8 dB. The isolation between dual-polarizations in the broadside radiation is higher than 29 dB. The back lobe is lower than −15 dB. The measured results are in reasonable agreement with the simulated ones.