Ever since the deployment of the first-generation of mobile telecommunications, wireless communication technology has evolved at a dramatically fast pace over the past four decades. The upcoming fifth-generation (5G) holds a great promise in providing an ultra-fast data rate, a very low latency, and a significantly improved spectral efficiency by exploiting the millimeter-wave spectrum for the first time in mobile communication infrastructures. In the years beyond 2030, newly emerged data-hungry applications and the greatly expanded wireless network will call for the sixth-generation (6G) communication that represents a significant upgrade from the 5G network – covering almost the entire surface of the earth and the near outer space. In both the 5G and future 6G networks, millimeter-wave technologies will play an important role in accomplishing the envisioned network performance and communication tasks. In this paper, the relevant millimeter-wave enabling technologies are reviewed: they include the recent developments on the system architectures of active beamforming arrays, beamforming integrated circuits, antennas for base stations and user terminals, system measurement and calibration, and channel characterization. The requirements of each part for future 6G communications are also briefly discussed.

Recently, much attention has been focused on beams carrying orbital angular momentum (OAM) for radio communication. Here we experimentally demonstrate a planar-spiral phase plate (planar-SPP) for generating arbitrary mixed OAM beams. This proposed planar-SPP uses the concept of transmit array antenna having a perforated substrate to control the outputting phase for generating beams carrying OAM with arbitrary modes. As demonstrations, three planar-SPPs with a single OAM mode and two mixed OAM modes around 94[emsp14]GHz have been investigated with design and experiments in this paper, respectively. The typical experimental intensity and phase patterns show that the proposed method of generating OAM beams really works.

It is known that the substrate integrated waveguide (SIW) features high-pass characteristics of the conventional waveguide, and a periodic structure (PS) generally presents bandstop characteristics. Therefore, a super-wide-band bandpass characteristic should be realized by combining some sort of PS into the SIW. In this paper, three types of compact SIW-PS wide-band bandpass filters are proposed and investigated with simulation and experiment. Performances of a super-wide bandpass, for instance, 8.5-16.5 GHz in this case study, with low insertion loss and sharp out-of-band characteristics are observed from both simulated and measured results.

A novel frequency selective surface (FSS) based on substrate integrated waveguide (SIW) technology is investigated with simulation and experiment. The periodic unit is made of a SIW cavity with slots on the top and bottom surfaces, and the whole FSS is fabricated on a microwave substrate with standard PCB process. The high-Q property of SIW cavities greatly improved the frequency selectivity of the FSS, which is significant for the application in antenna cover or object stealth etc. The finite difference frequency domain (FDFD) method is adopted to simulate the transmission and reflection characteristics of the proposed FSS, and the simulated results are in good agreement with the experiment data. Both simulated and experiment results show that the FSS proposed in this paper takes the advantages of low passband insertion loss, good frequency selectivity, and insensitive to the incident angle and polarization etc. Besides, the FSS can be easily fabricated using normal PCB process with low cost.

This paper presents the complete design of a wideband transmit-array antenna with high gain and high efficiency for D-band applications based on the low-temperature co-fired ceramic (LTCC) technology. The proposed unit cell is composed of a pair of wideband magneto-electric dipoles as the receive/transmit elements, together with a substrate integrated waveguide (SIW) aperture-coupling transmission structure for independent phase adjustability. A 360-degree phase coverage is obtained by the proposed phasing element, and its phase response curves are nearly parallel within a broad frequency band, which indicates a wideband performance. To verify the design, the fabricated prototype is measured by using a vector network analyzer (VNA) in a THz compact-range anechoic chamber. The measured peak gain is 33.45 dBi at 150 GHz with the aperture efficiency of 44.03%, and the measured 3-dB gain bandwidth is 124-158 GHz (24.29%). The good radiation performance ensures that the proposed SIW aperture-coupling transmit-array antenna is a promising candidate for D-band applications.

This letter presents the design and experiment of a novel elliptic filter based on the multilayered substrate integrated waveguide (MSIW) technique. A C-band elliptic filter with four folded MSIW cavities is simulated by using high frequency structure simulator software and fabricated with a two-layer printed circuit board process, the measured results show good performance and in agreement with the simulated results.