Total radiated power (TRP) is a key performance metric in over-the-air (OTA) testing of wireless devices. The TRP is evaluated by integration of the power density over a surface enclosing the device under test (DUT). In principle, this total power flow shall be independent from the surface. However, the power received at the instrumentation in a given polarisation typically relates to the intensity of the corresponding component of the impinging E-field. In the far-field, the E-field magnitude and power density are straightforwardly related, but not in the near-field. Therefore, the measured TRP generally depends on the scanned surface and test distance. This study introduces a closed-form expression for the measured power integrated over a surface surrounding the DUT, including the influence of the probe. The formulas are first applied to simulated spherical testing systems, where three different measurement probes coupled to a DUT model radiating at 28 GHz. Results are then validated experimentally in two spherical scanners, using physical samples of one of the modelled probes and the DUT. Both numerical and experimental results confirm the Fraunhofer distance as a lower bound range length for OTA TRP evaluation with negligible influence from the measurement probe.

The next generation of wireless device utilises higher frequencies and a large array of form factors. With miniaturisation of devices and the growth of internet-of-things applications having no connectors for testing, the use of conducted tests is no longer an option and verification of this equipment requires over-the-air measurements. Additionally, some important metrics such as receiver sensitivity requires an actual communication link. Reverberation chambers loaded with lossy absorbers provide an efficient environment to measure such averaged quantities with flexibility in a test volume as well as device size, shape, and placement. Here, the authors present an overview of OTA measurements in reverberation chambers compared to anechoic measurements. The authors show the consistency and flexibility of reverberation chambers through measurements of a wireless device in three different reverberation chamber setups and compare to an anechoic chamber measurement. By using a proper chamber setup, and by showing a coherence bandwidth (CBW) as a universal metric for comparing chamber loading between setups, excellent chamber-to-chamber consistency is shown, without precise placement of the device in each chamber. The authors show empirical evidence for the choice of threshold in determining the CBW.

The emerging machine-to-machine (M2M) communications and Internet-of-things techniques bring new challenges in over-the-air (OTA) tests. The inexpensive M2M device usually aims at low-cost and low-power consumption rather than high data rate and, therefore, is usually equipped with a single antenna. Testing such M2M device in massive production requires efficient and cost-effective OTA techniques. The reverberation chamber (RC) is a suitable solution for such tests of M2M (especially large-form-factor) devices. Since RC measurements are in essence stochastic measurements (with repeatable results), uncertainty analyses are of primary importance. This study gives an overview of the start-of-the-art research on measurement uncertainty for both conventional and M2M OTA applications. In addition, new results about mode stirrers and diffusers (for uncertainty reduction) are provided.

Due to the increasing and urgent demands of automotive over-the-air (OTA) and electromagnetic compatibility (EMC) tests, it is necessary to evaluate the performance of a reverberation chamber (RC) loaded by a vehicle under test. Previous works mainly focus on qualitative analyses on the RC performance for a static vehicle. This article realises the idea of using rotated vehicles to improve field uniformity. Two methods are adopted to estimate the number of independent samples and to predict the uncertainty. In addition, the uncertainty is also estimated from many independent simulations. The estimated uncertainties show good agreements. It is shown that the uncertainty can be significantly improved by rotating the vehicle under test using a large turn-table platform. Authors’ results show that the bigger the volume of the vehicle is, the better the improvement is. Besides, the authors find that the restriction of the volume of the vehicle under test can be relaxed in automotive tests by utilising the vehicle as a rotating mode stirrer. In addition, it is found that the Weibull distribution provides the best fit to the field of RC working near the lowest usable frequency (LUF) for all the cases.

The polarimetric massive multiple-input multiple-output (MIMO) radio channel of an indoor line-of-sight scenario is investigated at 1.35 GHz using a real-time radio channel sounder. The 8 × 12 massive MIMO transmitter is constructed using a hybrid architecture including a vertical uniform linear array translated at different horizontal positions forming a virtual, yet realistic, uniform rectangular array. The performance of the system is evaluated with six users distributed in the room for different polarisation schemes and receiver orientations using propagation channel-based metrics (such as receiver spatial correlation and Rician factor) and system-oriented metrics such as sum-rate capacity and signal to interference and noise ratio. The results show a clear dependence of the performance to the polarisation schemes and receiver orientation and showing that when facing the array, cross-polarisation can be very beneficial. Furthermore, it is concluded that the additional degree of freedom brought by the polarisation diversity can contribute to improve spectral efficiency (∼20% depending on the configuration), paving the way for further capacity enhancements in massive MIMO systems. It was also found that the receiver spatial correlation can be modelled using a Burr distribution.

In this study, based on channel measurements for a fifth generation (5G) hotspot of a large waiting hall of a high-speed railway station at 28 GHz, the channel modelling, simulation, and validation are performed. To investigate clustering sparse features at a millimetre-wave band, an adaptive kernel-power-density algorithm is used to identify clusters. Moreover, by using a quasi-deterministic radio channel generator (QuaDRiGa) simulation platform, the large-scale channel parameters such as delay spread, azimuth spread of arrival, and time-evolution characteristics are simulated and validated. The QuaDRiGa simulation results agree well with measurement data, which verifies the applicability of QuaDRiGa in a millimetre-wave band. The results could be very useful in millimetre-wave over-the-air testing and system performance evaluation in the 5G hotspot scenario.

Multiple-input multiple-output (MIMO) over-the-air (OTA) testing is often executed in multi-probe anechoic chamber (MPAC), the size of which is generally large enough so that the waves radiated from the probes can be considered plane waves in test area. The physical dimension of test setups is a key cost factor. In order to save laboratory space and reduce the cost, a compensation technique for spherical waves synthesising plane waves is proposed, which can be applied in small anechoic chamber. The object is to investigate the performances of the proposed plane wave compensation technique on MIMO terminal OTA testing in small MPAC. In the simulation, this technique presents good performances on various metrics, e.g. field distribution, spatial correlation, power angular spectrum estimation. As demonstrated in simulation, the ring radius of anechoic chamber can be reduced and the conventional far field criteria can be relieved.

High speed data streams are everywhere in the fifth generation (5G) system measurement. To develop a high efficient and low cost 5G testbed in a reverberation chamber, the authors propose a high efficient measurement method in the time, frequency and space coherence measurement. In this study, the one-bit technique is introduced to measure the time domain, frequency domain and space domain correlations in a reverberation chamber. The coherence time, coherence bandwidth and correlated angle can all be measured using the one-bit correlation; float number calculations are simplified to logical operations which accelerate the data processing greatly. Measurements are performed to verify the results.

The backscatter modulation has been used as an emerging technology in the Internet of Things (IoT), due to the hardware simplicity and low power consumption. Moreover, this technology is being combined with wireless power transfer scenarios in order to overcome a large number of batteries used. With recent development of backscatter systems for high bit-rate communications, the design of a calibrated measurement system to characterise and calculate the optimum performance for M-ary quadrature amplitude modulations, emerge as a requirement in IoT measurements. The main objective of this work is to characterise a backscatter modulation system, considering two characterisation approaches, a cable test measurement, and an Over-The-Air measurement. Thus, the characterisation of high-order backscatter modulators can be executed to anticipate its performance in real scenarios. In this work, a dual-band high-order backscatter modulator will be presented and characterised for different modulations in free-space, and the Error Vector Magnitude results will be computed.

This study reports a multi-layered dual-mode substrate integrated waveguide (SIW) bandpass filter (BPF), in which the input and output ports are located on the same substrate layer (i.e. the upper one). The dual-mode SIW cavity in the lower substrate layer is coupled to the upper dual-mode SIW cavity by two crossed slots, which can independently control the inter-couplings. The proposed filter can be modelled by a dual-extended doublet coupling scheme with considering bypass couplings between source and load. Based on the proposed structure, single- and dual-band filtering responses with four controllable finite-transmission zeros (FTZs) are realised and analysed. For the demonstration, a single-band filter and a dual-band filter were fabricated and measured. The measured results agree well with simulated ones.

In this study, a novel design of tunable metasurface (MS) is proposed and demonstrated. The MS can realise multiple functions, such as radiation and scattering manipulation. To design MS unit, four varactor diodes are used so that resonant and in-phase reflection band can be tuned through adjusting diode bias voltage. For the whole MS array, feeding structures are added to realise radiation performance. Meanwhile, adjusting reflection phase of different units can achieve low scattering performance. Measured results agree well with simulations, verifying the validity of the proposed design. This work offers us an effective strategy to design multi-functional tunable MS and other related practical applications.

A metamaterial slab covered antipodal Vivaldi antenna (MSAVA) is proposed to improve the radiation properties of the antipodal Vivaldi antenna (AVA). The metamaterial covers (MCs) consist of two types of metal rectangular ring arrays that have a higher effective permittivity than the substrate. The MCs can achieve a guiding effect and direct electromagnetic waves radiated from the side of AVA to the end-fire direction. The original AVA and the proposed MSAVA are simulated, fabricated and measured. The results show that of the two antennas is less than −10 dB in the frequency band of 0.95–11 GHz. Due to the introduction of MCs, MSAVA obtains a much narrower H-plane's half-power beamwidth, and the E-plane's is narrowed as well. The radiation gain is also improved in the frequency band. Moreover, the maximum gain of the proposed MSAVA is 17.67 dBi. Compared with the original AVA, the maximum gain is enhanced by 6.86 dB for the proposed MSAVA. The presented MSAVA featuring broad bandwidth, high gain and narrow beam has a high potential in ground penetrating radar, microwave imaging application and other broadband wireless systems.

This study presents a 5G antenna array for millimetre-wave communications. Overall size of the proposed antenna array is 40 × 15 mm², and operates in a measured 23.76–42.15 GHz frequency range. A planar four-way feed network has been designed, optimised and used to excite the antenna array elements. The single element of the array is spiral monopole surrounded by a boundary of vias with extended ground plane in an inverted U-shaped manner. Hexagonal parasitic patches have been introduced at the backside to enhance impedance performance of the antenna element. Peak gain of the proposed antenna array is 11.5 dBi with radiation efficiency more than 83% in its entire operating band. The antenna gives a narrow beam-width of as low as 10.1°. Single element and its 1 × 4 array have been fabricated using standard printed circuit board (PCB) process. Measured results show excellent compliance with the simulated design objectives. The antenna is low cost, low profile with simple design and is capable of being deployed in future 5G communication mobile networks.

With the development of large-aperture and high-frequency radio telescopes, a surface adjustment procedure for the compensation of surface deformations has become of great importance. In this study, an innovative surface adjustment strategy is proposed to achieve an automated adjustment for the large radio telescope with adjustable dual reflectors. In the proposed strategy, a high-precision and long-distance measurement instrument is adopted and installed on the back of the sub-reflector to measure the distances and elevation angles of the target points on the main reflector. Here, two surface adjustment purposes are discussed. The first purpose is to ensure that the main reflector and sub-reflector are always positioned at their ideal locations during operation. The second purpose is to adjust the main reflector to the location of the best fitting reflector, and the sub-reflector to the focus of the best fitting reflector. Next, the calculation procedures for the adjustments of the main reflector and the sub-reflector are discussed in detail, and corresponding simulations are carried out to verify the proposed method. The results show that the proposed strategy is effective. This study can provide helpful guidance for the design of automated surface adjustments for large telescopes.

This study presents a systematic experimental analysis of the noise figure and the gain of an optical sensing low-noise amplifier (LNA) in the X-band region (8.5–10.5 GHz). The study has been carried out with the purpose of analysing the effects of a 635 nm optical radiation on the gain and noise figure of the LNA, by modifying the bias operating points. Upon varying the bias conditions from those suggested into the component datasheet towards the device pinch-off, the role of the light exposure changes from causing degradation of the gain and noise figure into a clear performance enhancement. In the middle, a bias condition is found where the above LNA parameters become unresponsive to light exposure. Whilst the detrimental role played by the strong gate current increase under light exposure on the noise figure degradation is already clear, the experimental results show that close to pinch-off this effect is completely overcome by the drain current and transconductance increases.

A miniaturised wideband four-way out-of-phase power divider is presented in this study. The presented divider is developed based on a microstrip-line Marchand balun, which achieves the power-dividing function through the coupling between parallel microstrip lines (MLs). The coupling performance is improved by etching the rectangular-ring slots under the coupled MLs, which improved the operating bandwidth. The air-bridge resistance isolation circuit is used to improve the output impedance matching and isolation. Moreover, the even- and odd-mode equivalent-circuit method is applied to the presented power divider. The design has been verified by measurements, which show good agreements with simulations. The measured results show that the centre frequency is 3.4 GHz, the 15 dB input return loss bandwidth is >59.6%, and the output isolation is >15 dB.

The disturbing effects of scattering objects such as wind turbines (WTs) and other buildings on the flight navigation aid Doppler very high frequency omnidirectional radio range (DVOR) have been addressed in previous publications. Nevertheless, a practically feasible possibility to precisely and consistently predict the DVOR bearing deviation before the buildings’ construction is still missing. In this contribution, a method based on numerical simulations is presented which allows calculating the DVOR receiver's antenna voltage in the time domain for dynamically disturbed environments. Separating its frequency modulated and amplitude modulated content, the indicated DVOR bearing is calculated subsequently by determining the corresponding phase difference. Finally, the calculation results are validated by in situ measurements of DVOR signal disturbances in the environment of eight WTs.

This study presents system-based models of stepped impedance resonators (SIRs) based on the singularity expansion method. Analytical expressions of the transfer function and the impulse response for two types of dual-band step resonators are derived (open-circuited λ/2 and short-circuited λ/4) for general impedance ratio (K). The accurate physical poles of the structures are acquired using a pole-energy-based refined matrix pencil scheme. Then, the frequency domain expression is used to develop a precise equivalent lumped element circuit model for the dual-band SIRs. Based on that, a direct pole-zero placement synthesis method is applied to design a three-stage dual band-pass filter. Very good matching between the transfer function of the system model and the frequency response data of the synthesised SIR filter is observed. The explored system-based modelling and synthesis procedures can be generalised systematically to design more complex filter structures.

Three-dimensional (3D)-MIMO beamforming realised by adaptive quantum particle swarm optimisation (AQPSO) algorithm for the 36-element cylindrical conformal phased array is proposed in this study. The cylindrical conformal phased array consists of 36 circularly polarised microstrip antenna elements with ultra-wideband and high gain characteristics. The conformal array is divided into 12 subarrays using reconfigurable technology, and each subarray produces six beams to cover the corresponding spatial area. The 3D-MIMO beam is formed by AQPSO, and the active element pattern data of array elements is introduced to AQPSO to improve the accuracy of the algorithm. The simulated and measured results show that the cylindrical conformal phased array can achieve 3D-MIMO beam coverage from 0° to 360° in the azimuth plane and from 67.5° to 112.5° in the elevation plane. It can be applied for satellite communication and fifth-generation base station communication.