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Estimating the quality ( $Q$ ) factor of an unloaded reverberation chamber (RC) is a challenging problem in practice. To answer this question conservatively and confidently, this paper reviews the measured unloaded $Q$ factors of 38 RCs worldwide. The effective wall conductivities are summarized from the reported measurement results. Broadband $Q$ factors of RCs from the same supplier but with different dimensions are highlighted to compare. The measurement results show that the effective wall conductivity is frequency dependent and the dependency behaves in a similar way. The empirical values of the effective wall conductivity are extracted to estimate the unloaded $Q$ factors conservatively.

This letter presents a millimeter-wave circular polarized dielectric loaded antenna (DLA) using an inset waveguide-to-dielectric transition. Driven from demands over the perspective of low cost and high integration, the proposed design provides a cost-effective small volume and light-weight solution for millimeter-wave (mm-wave) communications. A low-profile low-loss high-integration transition $({0.17\boldsymbol{\lambda }})$ is realized between air-filled waveguide and dielectric-filled waveguide. The proposed DLA could be excited with high-order modes to achieve narrower beamwidth and lower cross polarization. The seamless integration of DLA with the transition has been implemented by the use of 3-D printing fabrication technique. It has a light weight of 4.17 g, which is less than the weight of a standard A4 size paper. The simulated results show that the designed DLA can achieve a 28.6% impedance- and axial-ratio bandwidth and a peak gain of 12.0 dBic. The factors with strong influences on the measured results are analyzed. Comparing with the air-filled metallic waveguide antenna with similar performance, the proposed 3-D-printed DLA shows a 43% reduction in volume and a 90% reduction in weight, which is suitable for 5G/6G enabling antenna systems.

This letter presents a microstrip patch antenna array fed with a low-loss and highly efficient feeding structure called empty substrate-integrated waveguide (ESIW). The proposed antenna array targets 5G wireless communication systems operating at 28 GHz. The antenna array consists of 4 × 4 radiating patches, where every four radiating elements are grouped together forming a 2 × 2 subarray and each of the subarrays is fed by ESIW feeding network by aperture coupling. The experimental results demonstrate good agreement with the simulated results, offering a wide | S 11| < −10 dB bandwidth of 12.4%, i.e., 26.5–30 GHz. A peak gain of 18.2 dBi and a high efficiency of about 91% are achieved using the proposed structure. Furthermore, the low-profile substrate of the ESIW feeding structure makes seamless integration of the proposed antenna array with the millimeter-wave front end. The advantages, such as low fabrication cost and high efficiency, make the proposed antenna array a suitable solution for millimeter-wave 5G wireless communication systems.

IEEE In a reverberation chamber (RC), the angular correlation coefficient of a stirrer is an important parameter. It has been used to evaluate the performance of a stirrer or to estimate the number of independent samples in a measurement. In the previous work, the angular correlation coefficient (ACC) was evaluated numerically and no analytical equation was proposed. In this study, we propose an approximate analytical equation to fit the measured angular correlation that shows good agreements with measurement results. General properties of ACC are explored with physical insights; the equivalency of the mean value of the angular correlation and the $K$-factor is revealed. This study provides further understandings on the control of the stirrer angular correlation and the $K$-factor in an RC.

This letter proposes a closed-form expression of the radiation and the total efficiency for the entire lossy multiport antenna system with simultaneous excitations. The equivalent circuit model and the detailed analysis process of the two-element lossy multiport antennas as well as a generalized expression for N -element lossy multiport antennas were considered. The required inputs to the closed-form expression are S -parameters, embedded radiation efficiency of each antenna element, and radiation efficiency of the entire antenna pair with identical simultaneous excitations. This method can be used for the analysis of multiple-input–multiple-output (MIMO) and antenna arrays, when the multiple elements are simultaneously excited with arbitrary amplitude and phase. To validate the proposed method, two different lossy MIMO antennas, namely, a pair of parallel end-fed dipoles and 4 × 1 layout printed bowtie antennas, were studied with various amplitude- and phase-feeding schemes. Full-wave numerical simulations were performed to provide inputs to the closed-form expression. Excellent agreement was observed between the radiation efficiencies of these antennas obtained through the closed-form expression and the full-wave numerical simulations, which demonstrates accuracy of the proposed closed-form expression. Furthermore, the proposed method can significantly reduce the total number of measurements for charactering the efficiency of the entire simultaneously excited lossy multiport antennas.

This paper presents a discussion on theoretical solution for realizing accurate spatial channel model extension (SCME) in reverberation chamber (RC) and highlights the practical challenges on its implementations. For SCME to be correctly implemented in RC, the theoretical solution considers a reverse engineering approach, which requires an additional channel to be convoluted with the known RC channel. This additional channel could be divided into two parts, namely, the reference part and the delay-and-inverse part. This paper also presents the potential solutions in the realization.

This paper presents an ultra-wideband one-dimensional plane wave generator antenna array. Tightly coupled Vivaldi antennas is used with active VSWR nearly lower than 2 across the frequency band from 1 to 7 GHz. A new plane wave excitation optimization algorithm using full wave simulation transfer matrix is proposed and compared with the traditional ideal point source plane wave optimization algorithm. One-dimensional quasi-plane waves with amplitude vibrations within ±0.75dB and phase vibrations within ±7.5° ranged from 1GHz to 6GHz is realized by carefully optimizing the feed amplitude and phase of the tightly coupled array element.

This paper initially presents an overview of different miniaturization techniques used for size reduction of printed log-periodic dipole array (PLPDA) antennas, and then continues by presenting a design of a conventional PLPDA design that operates from 0.7–8 GHz and achieves a realized gain of around 5.5 dBi in most of its bandwidth. This antenna design is then used as a baseline model to implement a novel technique to extend the low-frequency response. This is completed by replacing the longest straight dipole with a triangular-shaped dipole and by optimizing the four longest dipoles of the antenna using the Trust Region Framework algorithm in CST. The improved antenna with extended low-frequency response operates from 0.4 GHz to 8 GHz with a slightly reduced gain at the lower frequencies.

This paper investigates the effects of antenna vibration occurring due to suspension variation during the movement for vehicle-to-infrastructure (V2I) communication by developing a two dimensional (2D) model. With highly directional antennas fitted on a car's rear bumper and at a base station (BS), different beamwidths from 10° to 50° are investigated for a moving vehicle at 70mph. The gain sensitivity of the radiation pattern and the micro-Doppler shift are modelled for suspension variations between 5cm and 20cm. The analysis has been performed based on the observed angle of arrivals (AoA) at the receiver antenna in the elevation plane. The gain sensitivity represents the BSs’ main lobes' misalignments and receiver antennas’ radiation patterns at 26GHz. The results reveal a significant impact on gain sensitivity during the first 200m of movement away from the BS. Furthermore, the total Doppler shift increases due to the micro-Doppler with vertical displacements from the suspension variation. However, this can be mitigated if the beamwidth increases relative to the link budget or the BS height increases. The 2D model is validated by utilising accelerometer data recorded whilst the vehicle is moving at 70mph on a motorway, by extracting the displacements and computing the gain sensitivity.

This letter presents a compact dual-polarized over-the-air testing antenna with low radar cross section (RCS) for the fifth-generation and emerging wireless communication systems. The proposed antenna design is achieved by slotting two orthogonal Vivaldi antennas in a cross-shaped form into a two-part three-dimensional printed radome and loading microwave-absorbing materials (MAMs) at the antenna's outer edges. The proposed antenna has a rocket-nest shape with a diameter of 63.4 and 113.68 mm length. The −10 dB impedance bandwidth ( S 11) is obtained from a range of 2.1 up to 6 GHz. The two-part radome is formed by polylactic acid and acrylonitrile butadiene styrene dielectric materials, respectively. Their respective dielectric constants are approximately 2.6 and 4.5 within the −10 dB impedance bandwidth. The MAMs geometry and distribution location are optimized to suppress induced current over the antenna. An antenna prototype has been fabricated and measured. The measured results agree reasonably well with the simulated results. The results show that the use of the two-part radome enables the achievement of low RCS with compact form factor. Furthermore, a low bistatic RCS of between 2 and 6 GHz is observed in simulation for angular ranges of ${{\boldsymbol \theta }} \in [ { - {\text{30}^\circ }, + {\text{30}^\circ }} ]$ and $\boldsymbol{\Phi } \in [ { - {\text{90}^\circ }, + {\text{90}^\circ }} ]$ .

Current trends in developing cost-effective and energy-efficient wireless systems operating at millimeter-wave (mm-wave) frequencies and with large-scale phased array antennas for fulfilling the high data-rate demands of 5G and beyond has driven the needs to explore the use of hybrid beamforming technologies. This paper presents an experimental study of a wide-bandwidth millimeter-wave fully-connected hybrid beamformer system that operates at 26 GHz with 128 antenna elements arranged in a 16 × 8 planar array, 6-bit phase shifter, 6-bit attenuators and two separate radio frequency (RF) channels each capable of fully independent beamforming. The linearity, phase, and attenuation performance of the beamformer system between 25.5 GHz and 26.5 GHz are evaluated as well as the beamforming performance of a 128-element planar phased array at 26 GHz where the measured radiation patterns with and without amplitude tapering are compared.

The ever increasing demand for higher data rates and seamless wireless connectivity have forced both academic and industrial strategists of wireless communications to consider exploring higher frequency bands other than the heavily utilised sub-6 GHz radio spectrum. The millimetre, infrared, and visible light spectra of electromagnetic waves are three of the most favourable choices. In this paper, we examine two wireless communication testbed systems operating in the millimetre-wave (mmWave) and visible spectra. Both systems are based on commercially available off-the-shelf components. Different aspects, e.g., modulation, link distance and partial link blockage, are studied. We experimentally show that both systems are capable of providing giga-bit-per-second data rates, and infer that a hybrid system can be the solution that mitigates drawbacks of each individual technology.

A broadband reference antenna is proposed for antenna efficiency measurements in a reverberation chamber. The proposed antenna consists of two elliptical shaped dipole arms with elliptical slots etched on opposite sides of a thin FR4 substrate and fed by an exponential tapered microstrip balun. Measurements have been conducted to verify the antenna performance. The results show that this design shows acceptable radiation efficiency from 200 MHz to 6 GHz.

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&ndash, 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 &minus, 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.

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 article, 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 article, 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.

The digital economy is essential for wealth creation. Over the past few decades, the market for modern wireless communication systems has grown rapidly in response to consumer demand. As 'connectivity' becomes more and more ubiquitous and reliable and offers higher capacity, it will become the new 'lifeblood' of the digital economy and connected society with over 8.9 billion mobile subscriptions by 2022. Focusing on user experience, the fifth generation (5G) network is envisaged to offer a dramatic improvement over fourth generation (4G)'s network capabilities. 5G network promises more reliable, faster, and near -instant connections. With strong global momentum, multiple worldwide 5G research projects are defining, developing and standardizing the technology for 5G and beyond. To develop the necessary infrastructure to meet the aforementioned promises, significant efforts have been devoted in international liaison on seeking for a global consensus over visions, applications, standards and the identification of suitable spectrums. Following the approval of 3GPP (Third -Generation Partnership Project) Release 15 5G new radio (NR) standard in June 2018, 5G commercial networks were quickly launched in the United States (Verizon and AT&T) and South Korea (KT, LG UPlus and SK Telecom) by the end of the year. While the standardization process for 5G NR is ongoing, industry had already begun efforts to implement infrastructure compliant with the draft 5G NR standard.

The recent studies on hybrid beamformers with a combination of switches and phase shifters indicate that such methods can reduce the cost and power consumption of massive multiple-input multiple-output (MIMO) systems. However, most of the works have focused on the scenarios with frequency-flat channel models. This letter proposes an effective approach for such systems in frequency-selective channels and presents the closed-form expressions of the beamformer and the corresponding sum-rates. Compared to the traditional subconnected structures, our approach with a significantly smaller number of phase shifters results in a promising performance.

Current radiofrequency electromagnetic field (RF-EMF) exposure limits have become a critical concern for fifth-generation (5G) mobile network deployment. Regulation is not harmonized and in certain countries and regions it goes beyond the guidelines set out by the International Commission on Non-Ionizing Radiation Protection (ICNIRP). Using a massive multiple-input-multiple-output (mMIMO) testbed with beamforming capabilities that is capable of mimicking realistic 5G base station (BS) performance, this paper presents an experimental and statistical assessment of its associated RF-EMF exposure within a real-world indoor environment. The mMIMO testbed has up to 128 channels with user-programmable software defined radio (SDR) capability. It could perform zero-forcing precoding after channel state information (CSI) acquisition for different beamforming scenarios with respect to the associated user terminal antenna setups and positions. With 64 active mMIMO transmit antennas, 8 beamforming scenarios have been considered for single-user (SU) and multi-user (MU) downlink communications at different locations. Using a calibrated triaxial isotropic field-probe, the received channel power heat map for each beamforming scenario was acquired and then converted into an RF-EMF heat map. The relevant RF-EMF statistics was evaluated based on the variations of beam profiles and number of users., Comment: The 14th European Conference on Antennas and Propagation (EuCAP 2020)

This article presents a millimeter-wave antenna to cover 28- and 38-GHz bands recommended by Federal Communications Commission for the 5G cellular networks. The conventional narrowband Franklin antenna is modified geometrically to transform into a multiband antenna provided with a linear array arrangement to fit multiple patches in a compact assembly to achieve smaller form factor and improved gain profile. The suggested structural modifications are deployed to diversify the fundamental theory of Franklin antennas to generate wideband and multiple resonances. The measured results show an impedance bandwidth of 28-39 GHz covered by the three resonances. The realized gain is above 7 dBi in the complete range of operation, while the peak gain is 10.23 dBi at 36 GHz. The proposed antenna signifies its high potential to fulfill demands of 5G wireless systems.

In this study, the evaluation of chamber effects on antenna efficiency measurements using non-reference antenna (NRA) methods is presented. Two reverberation chambers have been employed and they differ in dimensions and paddle stirrer configurations, therefore the corresponding electrical characteristics such as quality factors, decay constants, and enhanced backscatter coefficients are envisaged to be different. However, it is found that these differences have little influence on the efficiency measurement of antennas-under-test (AUTs). The AUTs used for this study were a directional antenna and an omnidirectional antenna. The discrepancy in the efficiency of the two antennas measured between the two chambers is