Millimeter wave (mmWave) systems with effective beamforming capability play a key role in fulfilling the high data-rate demands of current and future wireless technologies. Hybrid analog-to-digital beamformers have been identified as a cost-effective and energy-efficient solution towards deploying such systems. Most of the existing hybrid beamforming architectures rely on a subconnected phase shifter network with a large number of antennas. Such approaches, however, cannot fully exploit the advantages of large arrays. On the other hand, the current fully-connected beamformers accommodate only a small number of antennas, which substantially limits their beamforming capabilities. In this paper, we present a mmWave hybrid beamformer testbed with a fully-connected network of phase shifters and adjustable attenuators and a large number of antenna elements. To our knowledge, this is the first platform that connects two RF inputs from the baseband to a 16× 8 antenna array, and it operates at 26 GHz with a 2 GHz bandwidth. It provides a wide scanning range of 60°, and the flexibility to control both the phase and the amplitude of the signals between each of the RF chains and antennas. This beamforming platform can be used in both short and long-range communications with linear equivalent isotropically radiated power (EIRP) variation between 10 dBm and 60 dBm. In this paper, we present the design, calibration procedures and evaluations of such a complex system as well as discussions on the critical factors to consider for their practical implementation.

Base stations (BSs) rely on the massive multiple-input multiple-output (mMIMO) technology in the fifth generation of mobile networks (5G). A technology having a major impact on the nature of the electromagnetic field (EMF) exposure in such systems. This work has used a fully reconfigurable mMIMO testbed (operating at 2.63 GHz), capable of mimicking realistic 5G new radio (NR) BS beamforming performance, to first gather experimental-based evidence of 5G BS EMF exposure within a real-world outdoor environment, to then analyze its stochastic behaviour, and to finally understand its impact on the definition of exclusion boundaries for 5G BSs. The exposure data of our testbed have been complemented by exposure data collected from a typical commercial 5G BS (operating at 3.65 GHz) to confirm the result trends and findings of our analysis. A robust metrology has been followed to obtain all the EMF exposure data. Our data and analysis indicate that significant exposure variations can be noticed according to the beam directions, i.e. the relative position of the exposure measurement location to the beam directions as well as the environment, confirming the stochastic nature of 5G BS exposure. The variance of the exposure tends to decrease as the number of users increase for a constant traffic load. Whereas the exposure grows sub-linearly with the traffic load, regardless of the number of users. As far as the exclusion boundary of 5G BS is concerned, its revised definition based on 95-th percentile seems still not flexible enough to accommodate the deployment of 5G BS in countries/places with stringent EMF exposure limits, as for instance in Belgium.

The coexistence of TV broadcasting and mobile services causes interference that leads to poor quality-of-service for TV consumers. Solutions usually found in the market involve external band-stop filters along with TV reception log-periodic and Yagi-Uda antennas. This paper presents a log-periodic antenna design without additional filtering that serves as a lower cost alternative to avoid interference from mobile services into the UHF TV. The proposed antenna operates in the UHF TV band (470–790 MHz-passband) and rejects the 800 MHz and 900 MHz bands (stopband) of 4G/LTE-800 and GSM900 services, respectively. Matching to 50 Ohms is very satisfactory in the passband with values of S11 below −12 dB. Furthermore, the antenna is highly directive with a realized gain of approximately 8 dBi and a front-to-back ratio greater than 20 dB.

This paper presents a study into radiation pattern measurements of an electrically small dielectric resonator antenna (DRA) operating between 2.4 and 2.5 GHz in the industrial, scientific and medical (ISM) radio band for body-centric wireless communication applications. To eliminate the distortion of the radiation pattern associated with the unwanted radiation from a metallic coaxial cable feeding the antenna we have replaced it with a fibre optic feed and an electro-optical (EO) transducer. The optical signal is then converted back to RF using an Opto-Electric Field Sensor (OEFS) system. To ensure traceable measurements of the radiation pattern performance of the wearable antenna a generic head and torso solid anthropomorphic phantom model has been employed. Furthermore, to illustrate the benefits of the method, numerical simulations of the co-polar and cross-polar H-plane radiation patterns at 2.4, 2.45, and 2.5 GHz are compared with the measured results obtained using: (i) an optical fibre; and (ii) a metallic coaxial cable.