This article reviews the current state-of-the-art of millimeter-wave (mm-wave) antennas for communication and sensing applications in the D-band between 110 and 170 GHz. The most popular design techniques, including Antenna-on-Board (AoB), slotted waveguides, Antenna-in-Package (AiP) and Antenna-on-Chip (AoC), are described using relevant examples from scientific literature. Potential benefits and limitations of integration technologies, such as specialized packaging, chip post-processing steps and interconnects, are listed as well. The reported performances of all listed designs are compared against each other, taking the antenna size relative to operating frequency into account. This novel comparison indicates that small-scale integrated AiP and AoC designs can achieve competitive performance levels with short and low-loss interconnects.

Fifth-generation mobile networks (5G) are the solution for the demanding mobile traffic requirements, providing technologies that fulfill the requisites of different type of services. The utilization of the millimeter-wave (mm-wave) band is the straightforward technique to achieve high bit rates. Moreover, analog radio-over-fiber (ARoF) brings outstanding benefits such as low cost, low power consumption, and high spectral efficiency, among others. Thereby, mm-wave ARoF is a strong candidate to pave the way for common public radio interface (CPRI) in the fronthaul for the future 5G architecture. As orthogonal frequency-division multiplexing (OFDM) is the adopted waveform in the 5G standard, it should be also utilized in mm-wave ARoF systems for 5G. However, phase noise is one of the most degrading factors in mm-wave OFDM ARoF systems. Therefore, in this work, an analysis of the phase noise is carried out through an experimental setup up. The configuration of this setup enables to gradually modify the final phase noise level of the system. Furthermore, an original and novel algorithm to compensate the phase noise in OFDM receivers is proposed. The performance of this algorithm is experimentally evaluated through the setup for different phase noise levels and different subcarrier spacings. The obtained results show the effectiveness of the proposed algorithm under those conditions, highlighting the viability of mm-wave OFDM ARoF for 5G and beyond.

Due to errors in the phase and amplitude of element excitations in an antenna array, the array radiation pattern gets distorted. In order to derive statistical results on this distortion, specifically on determining the probability of exceeding a certain sidelobe level (SLL), it is often assumed that the magnitude of the array amplitude pattern follows a Rician distribution. It is shown that the Rician distribution implies two assumptions, and therefore, a more general Beckmann distribution is proposed to describe the distribution of the magnitude of the array amplitude pattern. Using Monte Carlo simulations, it is shown that the use of a Beckmann distribution outperforms the Rician distribution. Also, the seemingly counterintuitive result that the maximum probability of exceeding a certain SLL, in general, does not have to be at the angle where the highest sidelobe in the error-free case is located, is obtained. Due to this result, the importance of using an angular probability plot is emphasized. Furthermore, a physical explanation for the observed seemingly counterintuitive behavior is given.

A wide-scan and broadband focal-plane array (FPA) concept is introduced in this article, which provides high antenna gain and effective isotropic radiated power (EIRP) with electronic beamsteering within a relatively large field of view (FoV), up to +/-20°. The antenna uses a bifocal double-reflector concept that optimizes the illumination of the focal-plane region. In this way, we have reduced the required size of the feed array and have maximized the number of simultaneously active array elements. By using a photonics beamformer, a broadband system for the 20-40-GHz band can be created with a fiber-based interface to a central processing unit. This hybrid antenna system is a very interesting concept for future 5G and beyond [5G millimeter-wave (mm-wave) base stations, two-way satellite communication systems, and point-to-point wireless backhaul systems]. A silicon BiCMOS low-noise amplifier (LNA) and a photonic integrated circuit (PIC) for the optical beamformer have been developed and integrated into the overall system. A system-level demonstrator was developed and experimentally validated in receive mode. Our concept provides an antenna gain of more than 40 dBi over an FoV of +/-15° at 28.5 GHz.

Gluing an Antenna-on-Chip (AoC) directly on a ground plane or heat sink in the lead-frame is a standard process for commercial applications. To reduce the effect of losses in the silicon substrate and improve the antenna’s radiation efficiency, the wafer thickness is often drastically reduced. However, the close proximity of the antenna and ground plane can cause an impedance mismatch. Metal tiles, which are embedded in silicon dioxide layers, are designed as an Artificial Magnetic Conductor (AMC) to increase the radiation efficiency and tune the antenna impedance. A double-layer AMC is applied instead of a single-layer AMC to reduce the silicon dielectric loss. Additionally, the double-layer AMC has more capacitance to tune the impedance when integrating with a monopole on-chip antenna. The resulting -10 dB impedance bandwidth is increased to 5.8 GHz around the 60 GHz band, the simulated realized gain increases by 3.3 dB, and the simulated antenna radiation efficiency is increased from 11% to 21%. The measured input impedance of the AoC shows good agreement with the simulation results after probe calibration.

A novel base station antenna (BSA) configuration is presented to mitigate degrading physical antenna effects in massive multiple-input multiple-output (MIMO) systems, while minimizing implementation complexities. Instead of using a commonly considered single antenna panel comprising of many elements covering a wide field-of-view (FOV) of 120 degrees, L tilted panels are used employing L times fewer elements and L times smaller FOV per panel. The spatial resolution of each panel is enhanced by employing sparse arrays with suppressed (grating-lobe) radiation outside its corresponding FOV. Therefore, more directive antenna elements can be deployed in each panel to compensate for the effective isotropic radiated power (EIRP) reduction. While sectorisation reduces the antenna gain variation in 120 degrees FOV, cooperation among multiple panels in downlink beamforming is seen to be capable of inter-panel interference suppression for sum-rate enhancement. A network model is used as a multi-user (MU) MIMO simulator incorporating both antenna and channel effects. It is shown that when the number of base station antennas is ten times the number of users, the average downlink sum rate in pure line-of-sight (LOS), rich and poor multipath environments is increased up to 60.2%, 23% and 11.1%, respectively, by multi panel sparse arrays applying zero-forcing (ZF) precoding.