Pattern reconfigurable antennas with multiple switchable beams, especially with both boresight and endfire directions, are highly desired for wireless communications. In this letter, a novel pattern reconfigurable antenna is proposed that provides an efficient solution. By reconfiguring parasitic strip lines placed around a radiating dipole and reflecting metal pieces under the dipole using PIN diodes, the antenna main beam can be switched to five directions in elevation plane, approximately from -90° (left endfire), -45°, 0° (boresight), +45°, to +90° (right endfire). The proposed antenna operates at 2.45 GHz with dimensions of about 0.57${\lambda}{\times}$0.45${\lambda}{\times}$0.28${\lambda}$. An antenna prototype is fabricated and measured. For all five directional beams, the measured ${\vert}$S11${\vert}$values are below -13 dB, and the measured realized gains range from 5.2-6.5 dBi. They agree reasonably well with the simulated ones.

A novel fixed frequency beam scanning leaky-wave antenna based on a period-reconfigurable structure is presented. Operating at 5GHz, the antenna consists of a slotted substrate integrated waveguide and 54 electrically small patches. Each patch element is etched with two dumbbell-shaped slots, and its operating state can be flexibly controlled by the biasing of PIN diode on a parasitic strip. An ideal array model employing isotropic point sources is used for the analysis on the scanning mechanism, based on which a new method for suppressing the higher-order space harmonics is developed. Using this method, the mono-harmonic radiation range can be dramatically extended, and a wide-angle beam scanning can be achieved by manipulating the period length of the leaky-wave antenna. An FPGA controlling platform is designed for the electronic control of the antenna. The measured results validate that the proposed antenna achieves good performance of wide-angle scanning (125°) with a peak gain of 11.8 dBi at a fixed frequency.

For many leaky-wave antennas (LWAs), it is challenging to realise beam scanning through the broadside. A problem is the presence of an open stopband (OSB), which restricts radiation in the broadside direction. In this paper, a novel substrate integrated waveguide (SIW)-based LWA is described to overcome the OSB problem and provide beam scanning continuously from the backward to the forward direction from a conventional periodic LWA. It is demonstrated that the n = -1 spatial harmonic can be excited efficiently from a SIW LWA and enables broadside radiation. However, it was found in our initial design that when the beam scans through the broadside the cross-polarization level increases significantly compared to the beam close to the backfire direction. A technique is developed to reduce the cross-polarization level. As a result a new antenna configuration is created. The antenna design has been realized and measured to validate the concept. The measured beam scanning range of the prototype is from -74° to + 45° (119° of beam scanning) when the frequency sweeps from 7.625 to 11 GHz, and the measured cross-polarization level is 20.8 dB low at the main beam direction for the broadside beam.

A reconfigurable, wideband, and low profile circular polarization (CP) antenna is presented. Its wideband CP reconfigurability is realized by incorporating RF switches in a cross-bowtie radiator. A compact, wide bandwidth, and polarization independent artificial magnetic conductor (AMC) ground plane is developed to minimize the overall profile of the antenna while maintaining its wide bandwidth. The simplicity of this single element design facilitates the realization of a reconfigurable, wide bandwidth CP array that achieves higher directivity without changing its overall profile. Prototypes of the single element and of a 1×4 array of these elements were fabricated and tested. The measured results for both prototypes are in good agreement with their simulated values, validating their design principles. They are low profile with a height ~ 0.05 λ0. The array exhibits a wide fractional operational bandwidth: 1.65 GHz (21.7%), and a high realized gain: 13 dBic. Since they would enhance their channel capacity and avoid polarization mismatch issues, these reconfigurable CP antenna systems are very suitable for modern wireless systems.

Phased array antennas (PAAs) with flexible and agile wide-angle beam scanning (WABS) abilities have drawn rapidly increasing attentions in recent years. They have found significant applications in beyond fifth-generation (B5G) and sixth-generation (6G) wireless communications, satellite communications, sensing, etc., for their outstanding capability to achieve wide spatial coverage, enable critical frequency reuse, and improve the system capacity. In this review, we aim to investigate and discuss several challenges that hinder WABS for conventional PAAs, including the strong mutual coupling, narrow beamwidth of the element antenna, etc. We then review and summarize a variety of innovative techniques to overcome these challenges. Subsequently, we discuss and analyze potential research gaps of WABS PAAs for future emerging applications. This timely review fulfills the demand of a thorough and detailed investigation on WABS technologies for PAAs and provides detailed introduction and guidance for interested researchers and engineers.

Circularly-polarized (CP) antennas are highly desired for future wireless communications. To advance the development of CP substrate-integrated-waveguide (SIW) leaky-wave antennas (LWAs) with the intent to meet this demand, a novel benzene-ring-shaped slot-loaded LWA with partially reflecting wall (PRW) vias is investigated and verified to realize wide-angle continuous beam scanning with consistent gain. The dispersion features of slot-loaded SIW LWAs with PRW vias are theoretically explored using an equivalent circuit model. The CP radiation feature is investigated numerically utilizing the E-and H-field distributions of an initial design and its equivalent magnetic currents. The results of these studies are used to demonstrate that improved CP performance over a wide-angle scan range can be attained with a change from a standard slot shape to a benzene-ring-shaped slot. The resulting benzene-ring-shaped slot-loaded CP SIW LWA was optimized, fabricated, and measured. The measured results verify that a CP beam was continuously scanned through a wide angle from backward to forward directions with a consistent gain. The prototype exhibits a continuous 97.1° CP beam scan with a gain variation between 8 and 11.3 dBic when the source frequency is swept from 9.35-11.75 GHz.