An Overview of Terahertz Antennas

The terahertz(THz)antennas,which have features of small size,wide frequency bandwidth and high data rate,are important devices for transmitting and receiving THz electromagnetic waves in the emerging THz systems.However,most of THz antennas suffer from relatively high loss and low fabrication precision due to their small sizes in high frequency bands of THz waves.Therefore,this paper presents a detailed overview of the most recent research on the performance improvement of THz antennas.Firstly,the development of THz antennas is briefly reviewed and the basic design ideas of THz antennas are introduced.Then,THz antennas are categorized as metallic antennas,dielectric antennas and new material antennas.After that,the latest research progress in THz photoconductive antennas,THz horn antennas,THz lens antennas,THz microstrip antennas and THz on-chip antennas are discussed.In particular,the practical difficulties for the development of THz antennas are discussed with promising approaches.In addition,this paper also presents a short review of the process technology of THz antennas.Finally,the vital challenges and the future research directions for THz antennas are presented.

Robust asymmetric Cherenkov radiation in tilted anisotropic medium

Cherenkov radiation(CR)is available for a wide variety of terahertz(THz)radiation sources,but its efficiency is deeply affected by intrinsic losses.We find that if the tilted angle(α)of anisotropic material and radiation angle(θ)meet the condition ofθ+α=π/2,the intensity of radiation fields for the charged particle bunch(CPB)moving from left to right cannot be influenced by intrinsic losses,which means long-distance radiation can be achieved.Furthermore,we observe an asymmetric CR when the CPB moves from the opposite direction.In addition,we select natural van der Waals(vd W)materialα-MoO3as an example,further confirming that the radiation field can reach the far field and the asymmetric CR radiation can also be observed.These wonderful properties with long-distance radiation will extend the application of CR to a certain extent for future design and fabrication.

Improving Radiation Pattern Roundness of Henge-Like Metaring-Loaded Monopoles Above a Finite Ground for MIMO Systems

A henge-like metaring(HMR)is proposed for improving the radiation pattern roundness of monopole antennas offcenter mounted on a finite ground by localizing the radiation from the monopole and suppressing the scattering by the ground.The improved patterns enhance uniform coverage of multiple-input and multiple-output(MIMO)systems.The study reveals that the radiation pattern of an off-center monopole is distorted by the asymmetric ground currents excited by both the feed and the radiation of the monopole.The distorted radiation patterns severely degrade wireless communication link quality.The HMR,composed of an annular array of mushroom unit cells,simultaneously functions as an electromagnetic bandgap(EBG)and a radiator,and encircles the monopole to form a henge monopole antenna(HMA).The HMR as an EBG is used to suppress the ground currents outside the HMR analyzed by an equivalent circuit model.The HMR as a radiator is designed to decouple the monopole from the ground with its elevated radiation pattern using characteristic mode analysis.As examples,two prototypes of single and four off-center MIMO HMAs are designed and investigated in the 2.45-GHz band.Simulated and measured results show that the single HMA and each of the four HMAs achieve the un-roundness of the radiation pattern atθ=65°plane lower than 2 dB and 3 dB in the 2.45-GHz band.As a result,near the radiation nulls,the SNR is improved by 6 dB.The compact construction and efficient current suppression facilitate the application of HMAs in multi-antenna systems above a finite ground with uniform coverage and reliable connections.

Dispersion-engineered wideband low-profile metasurface antennas

A metasurface(MTS)can be characterized in terms of dispersion properties of guided waves and surface waves.By engineering the rich dispersion relations,setting particular boundary conditions,and selecting proper excitation schemes,multiple adjacent resonance modes can be excited to realize the wideband operation of low-profile MTS antennas.We introduce the operating principles of typical dispersion-engineered MTS antennas,and review the recent progress in dispersion-engineered MTS antenna technology.The miniaturization,circular polarization,beam-scanning,and other functionalities of MTS antennas are discussed.The recent development of MTS antennas has not only provided promising solutions to the wideband and low-profile antenna design but also proven great potential of MTS in developing innovative antenna technologies.