With the blooming of wireless technologies for communications, the fifth-generation (5G) mobile communications have become one of the hottest topics in recent years. For any wireless devices and systems, antennas, filters, amplifiers, mixers, and so on are crucial components for the RF front-end. Thus the demand for different kinds of advanced and high-performance antennas and circuits is increasing exponentially. However, most conventional designs have difficulty to satisfy those stringent requirements of the 5G mobile communications on bandwidth, radiation pattern, size, and cost. High-performance antennas and circuits for 5G mobile applications are therefore very attractive for researchers from both academic and industrial areas. This special issue solicits high-quality contributions regarding the design of microwave and millimeter-wave antennas and circuits for the upcoming communication systems.
In this special issue, we have 5 papers investigating antennas for 5G mobile communications. Specifically, in “Reconfigurable Magneto-Electric Dipole Antennas for Base Stations in Modern Wireless Communication Systems”, the authors reviewed several reconfigurable directional antennas for base station applications. The results showed that magneto-electric dipole antennas provide wide bands, high gains, and well-controlled radiation patterns and are suitable to be employed in reconfigurable base station antennas.
In “Magnetoelectric Dipole Antenna with Dual Polarization and High Isolation”, the authors aimed at modeling and analyzing a novel dual-polarized antenna element which was suitable to be applied in the further 5G mobile base stations.
The work in the paper titled “Single-Layer, Dual-Port, Dual-Band, and Orthogonal-Circularly Polarized Microstrip Antenna Array with Low Frequency Ratio” proposed a method to realize an orthogonal-circularly polarized antenna array with dual bands.
The paper with the title of “A Low VSWR and High Efficiency Waveguide Feed Antenna Array” introduced a high-efficiency slot antenna array by using waveguide feed. The radiation efficiency could achieve as high as larger than 80%.
The paper “Low Profile Flexible UHF RFID Tag Design for Wristbands Applications” presented a low profile RFID tag antenna for healthcare applications. The proposed slotted design can easily allow the tag’s input impedance to be tuned to the complex impedance of typical UHF RFID chips.
In this special issue, we have 4 papers investigating passive and active radio-frequency (RF) circuits for 5G communications. Specifically, in “A Reactance Compensated Three-Device Doherty Power Amplifier for Bandwidth and Back-Off Range Extension”, the authors proposed a new broadband Doherty power amplifier topology with extended back-off range. Underlying bandwidth extension mechanism of the proposed configuration was comprehensively analyzed.
In the paper titled “A Doherty Power Amplifier with Large Back-Off Power Range Using Integrated Enhancing Reactance”, a symmetric Doherty power amplifier based on integrated enhancing reactance (IER) was proposed for large back-off applications.
The work in “A Compact Differential-Mode Wide Stopband Bandpass Filter with Good and Wideband Common-Mode Suppression” aimed at presenting a new coupling topology to realize a differential-mode bandpass filter by integrating a pair of half-wavelength microstrip transmission lines and two multimode resonators.
In the paper with the title of “A Wide Stopband Balun Bandpass Filter with Its Application to Balanced Quasi-Yagi Antenna”, the authors utilize the out-of-phase open-ended microstrip line and the resonant characteristics of the triple-mode resonators to realize a new microstrip balun bandpass filter with a wide stopband.
In this special issue, 2 papers aim at RF systems for 5G mobile communications. In “Uplink Multiuser MIMO-OFDM System in the Presence of Phase Noises, Power Imbalance, and Correlation”, the effects of phase noises (PNs), power imbalances, and correlations on multiuser orthogonal frequency division multiplexing (OFDM) multiple-input multiple-output (MIMO) systems were studied. And the analytical results were verified by simulations.
The paper “CORDIC-Based Multi-Gb/s Digital Outphasing Modulator for Highly Efficient Millimeter-Wave Transmitters” described a high-speed CORDIC-based digital outphasing modulator. The complete outphasing modulator was fully custom designed in 40 nm CMOS, which could be integrated in a millimeter-wave outphasing transmitter to enhance the system average efficiency. Tested with 10.56 Gb/s 64-QAM, the presented work achieved an EVM of 3.2% and fulfilled the IEEE 802.11ad spectral mask requirements.
Two other papers of this special issue investigate over-the-air (OTA) test of MIMO technology and frequency selective surfaces for 5G applications, respectively. Specifically, the paper “Impact of Probe Configurations on Maximum of Test Volume Size in 3D MIMO OTA Testing” presented a method to determine the maximum of test volume size (MTVS) and investigated the impact of probe configurations on MTVS in order to obtain larger MTVS in the OTA testing.
In the paper “Design of a Novel Miniaturized Frequency Selective Surface Based on 2.5-Dimensional Jerusalem Cross for 5G Applications”, a compact frequency selective surface (FSS) for the application to 5G antenna radomes was proposed based on 2.5-dimensional Jerusalem cross.
Lei Ge
Jianpeng Wang
Mingjian Li
Ting-Yen Shih
Shichang Chen