This study presents a polarisation-independent metasurface harvester composed of an ensemble of novel electric-field-coupled inductive-capacitive (ELC) resonators. The ELC resonator has full symmetry in a way that its behaviour is highly insensitive to the polarisation of the incident wave. Loading the resonators with resistors (which model the input impedance of a power combining circuit in a harvesting system), it is shown that the metasurface absorbs the incident electromagnetic wave energy, with nearly unity harvesting efficiency, irrespective of its polarisation while simultaneously delivering the absorbed power to the loads. As a proof of concept, a metasurface harvester composed of a 9 × 9 resonator array working at 2.45 GHz was fabricated. Near-unity harvesting efficiency of the metasurface was demonstrated using full-wave numerical simulation for a wide range of polarisation angles. Laboratory tests showed strong agreement between the simulation results and the measurements.

A novel magneto-electric dipole antenna with wide H-plane beamwidth, triple-linear polarisation and frequency reconfiguration is proposed for 5G communications. In this study, the radiated dipoles are designed with the arc-shaped planes to exhibit wide H-plane performance. A bent cross-dipole feed with PIN diodes and varactor diodes inserted into its four arms at different altitudes is utilised to excite and control the antenna. Consequently, a measured wide beamwidth ranging from −67° to 67° can be achieved in H-plane. In addition, the height of the proposed antenna decreased about 30% due to the bent designs. Finally, by controlling the PIN diodes and varactor diodes, the three kinds of linear polarisations and frequency reconfiguration functionalities for 2G/3G/LTE/5G applications can also be easily obtained. With the above-mentioned features, the proposed antenna well suits for intelligent base-station communications.

The deformation of reflector surface can be obtained by Misell algorithm using two far-field amplitude patterns: one with the antenna in focus and the other with the antenna defocused. For reflector antennas with active surface, the defocused pattern can be measured by adjusting the panels to get a more effective phase factor instead of offsetting the sub-reflector. The shape and size of phase factor have a great influence on the accuracy of convergent solution. To improve the performance of Misell algorithm, this study proposed an optimisation method for phase factors under different surface deformations. This method utilises Levenberg–Marquardt algorithm to get an estimation of the aperture distribution and then applies the particle swarm optimisation to optimise the phase factor parameterised by Zernike polynomials. Numerical simulations show that the proposed method is an efficient tool to achieve applicable phase factors under different surface deformations. Using the optimised phase factor, Misell algorithm can get a better convergent performance than traditional Misell algorithm.

This study presents the study of beamforming capabilities of arrays installed on a non-conductive unmanned aerial vehicle (UAV). The main purposes of this study are the application of a beamforming algorithm by including the airframe in the optimisations and the study of simplifications of the aircraft model, so as to allow performing full-wave simulations, even though the UAV is much larger than the operating wavelength. To validate the simplified electromagnetic model, antenna arrays have been designed and installed onto the UAV. Radiation pattern measurements demonstrate that the proposed simplifications yielded very good radiation pattern predictions and can be used as guidelines for simulation of other kinds of non-conductive aircrafts.

A gaseous plasma antenna array (PAA) is an aggregate of plasma discharges and possibly conventional metallic radiating elements, and it constitutes a promising alternative to metallic antennas for applications in which fast reconfiguration of radiation pattern, and gain is desired; such properties can be achieved by exploiting the electronic switch on/off condition of plasma discharges, and tuning of the plasma parameters. Here, the authors present a reconfigurable PAA that features a central metallic half-wavelength dipole working around 1.45 GHz, surrounded by a planar circular lattice of cylindrical plasma discharges. Customised plasma discharges have been realised, and filled with argon gas at 2 mbar so as to have a complete control on the plasma discharge properties (e.g. plasma frequency, collisional frequency). The magnitude of the reflection coefficient, and the gain pattern on the H-plane have been investigated numerically and experimentally; numerical and experimental results exhibit a good agreement and show that the central intrinsically omnidirectional antenna can provide simple beamforming capabilities upon turning on a subset of plasma discharges; as these plasma discharges are turned on, the authors have observed a maximum gain of ∼5 dBi, a half-power beam width of , and an angular steering resolution of ∼.

A standing-wave slot array covered with a two-layer dielectric slab based on substrate integrated waveguide (SIW) technology, which is circumferentially conformed to a cylinder, is designed, fabricated and measured at Ka-band. The radiating part consists of seven slotted cylindrical SIWs, each of which has four-element longitudinal slots. Several such slot arrays fed by Rotman lenses are grouped on a cylinder along the circumferential direction to cover a 2D field of view. The microstrip Rotman lens is employed as the beamforming network with seven input ports, which can generate a corresponding number of beams to cover −35° to 35° along 1D (E-plane). Another dimension (H-plane) is covered from −52° to 52° with four beams generated by the slot arrays group. A prototype antenna is fabricated, the measured results demonstrate its ability of scanning over a 2D field of view with multiple beams. This type of multibeam conformal antenna is a good candidate for high-speed vehicles or communication base stations requiring electronic beam-scanning capabilities and considering conformal reasons.

A beam- and polarisation-reconfigurable substrate integrated waveguide (SIW) ring-slot antenna array is proposed in this study. The ring-slot antenna array can generate beams in four different directions in two orthogonal linear polarisations (LPs). This is achieved by a feeding network consisting of four SIW 3 dB couplers arranged in a multilayer structure for a compact antenna size of 131.6 mm × 65.8 mm × 4.9 mm. The antenna elements’ LP plane is controlled by PIN diodes, switched by a DC bias network integrated on the antenna substrate. The proposed antenna array is designed for the 5.8 GHz industrial, scientific and medical (ISM) frequency band and verified by measurements. Experimental results validate good impedance matching over the entire frequency band as well as the beam and polarisation reconfigurability.

This study proposes two modifications to the classical simplified real frequency technique (SRFT). A hybrid algorithm called invasive weed optimisation Levenberg–Marquardt (IWO–LM) algorithm, which combines the IWO and the LM algorithm, is used to optimise the transducer power gain. So the stochasticity of the IWO is introduced to the classical SRFT, the matching result will not be limited by the initial values. Moreover, an additional programme is added to the classical SRFT, which can transform the lumped matching network to the corresponding microstrip circuit. This improved SRFT is used to design a broadband matching network for a printed dipole base station antenna and compared with the classical SRFT, and the corresponding results show that the improved SRFT is less affected by initial values under the similar matching effect. The microstrip matching network and the antenna are integrated together, and then they are fabricated depending on the simulation. The test result of a vector network analyser shows that the bandwidth after matching is 0.728–1.01 GHz and the relative bandwidth is 32.45%， which is improved by 69.98% compared with the unmatched one.

Herein, a dual-band circularly polarised (CP) antenna for adjustable frequency ratio is proposed. The proposed antenna consists of two square-ring patches with a gap on the stacked substrates. A capacitor is inserted within the gap of each square-ring patch. The two square-ring patches have two resonant frequencies, because the additional resonant frequency is generated by the gap. The two first resonant frequencies of each square-ring patch combine to form the low band and two second resonant frequencies combine to make the high band. In the low band, as the gaps of the two square-ring patches are located on different diagonals, the two first resonant frequencies are orthogonal to each other. In the high band, as the second resonant frequency is perpendicular to the first resonant frequency, the two second resonant frequencies are also orthogonal to each other. In the measurement results, the low and high bands achieve −10 dB bandwidths (BWs) of 3.75 and 2.49%, 3 dB axial ratio BWs of 0.99 and 0.53%, and gains of 1.89 dBi and 0.64 dBi, respectively. By appropriately changing the values of two capacitors, frequency ratio has an available range from 1.065 to 1.336.

Novel design methods for implementing continuous centre-frequency and bandwidth tunability are reported. Coupling bandwidths are tuned through the mechanical rotation of a metallic plate suspended between resonators. Centre-frequency tuning is achieved via the vertical actuation of a moving part mounted within each resonator. In addition, each resonator and transformer is designed so that motors can be housed within them – adding tunability without compromising the overall filter volume. A second-order filter, based on combline cavity structures, capable of bandwidth tunability of 49–67 MHz for all centre frequencies in the range of 1.751–1.998 GHz is presented. Passband insertion loss is kept below 1.2 dB for all tuning states with return loss above 10 dB. A five-pole filter is also fabricated with centre-frequency tunability of 14% from 1.764 to 2.015 GHz and 15 dB bandwidth tunability of 107% from 41 to 85 MHz. Midband insertion loss is kept below 1.4 dB in all tuning states. The five-pole filter is compared to other tunable filters in the UHF range and is shown to reduce midband insertion loss by 36% from the next best filter (2.2–1.4 dB).

A design for beam-switching antennas is proposed in this study. A cylindrical cavity with a reconfigurable conformal slot array distributed evenly along the middle of its side wall is presented. The reconfigurable feature of the slots is achieved by placing a diode switch across each slot. An integrated bias scheme is introduced for the diode switches to activate and disable the slots. By properly selecting the dimensions for the cavity and the number of activated slots, the optimum values for the gain and front-to-back ratio (FBR) of the antenna can be obtained. The gain value is further increased by adding a skirt-like structure to both the top and bottom of the cavity. A design example is presented with the operating frequency set at 5.8 GHz. The conformal array comprises 24 slots to provide a 15° resolution for main beam switching. The simulation results indicate that the design can offer an antenna gain up to 8.62 dBi and a FBR above 10 dB. These results and the corresponding radiation patterns have gone through experimental verification, from which good agreement is observed.

This work presents a new design technique for dual-mode dielectric-loaded resonator filter operating at 2.18 GHz by using T-shape coupling probe. A cylindrical dielectric puck is suspended in the middle of metallic cavity and short-circuited on the side walls. Four vertically etched-slots through the dielectric puck from the top to the base of the ceramic puck offer a high unloaded quality factor of 4300 at the fundamental mode and allows the T-shape coupling to be located close to the centre of the dielectric puck. The size reduction ratio in this resonator was 11% compared with air-filled coaxial resonator. Fourth-poles Chebyshev bandpass filter with planar configuration was designed and implemented by employing two dielectric-loaded cavities. The experimental results show that the spurious-free window of ∼820 MHz from the fundamental frequency of 2.18 GHz and the operational bandwidth of 77 MHz were achieved.

A tri-band planar monopole antenna with one linearly polarised band, two circularly polarised bands, and bidirectional radiation patterns is presented in this study. The antenna consists of a monopole with seven arms etched on the top side of a FR4 substrate, and a slitted ground plane on the bottom side. Measured results show that the antenna has a S ₁₁<−10 dB impedance bandwidth of 9.7% (2.05–2.26 GHz) for the lower band, 11.3% (3.41–3.82 GHz) for the middle band, and 60.2% (4.89–9.11 GHz) for the upper band. The circular polarisation (CP) is radiated within the middle (left hand CP) and the upper (right hand CP) bands, and the measured broadside 3 dB axial ratio bandwidths are 4.9% (3.53–3.71 GHz) and 58.6% GHz (4.69–8.58 GHz), respectively. The proposed antenna has a total size of 25 × 35 × 1.6 mm³ and can be employed for the 2.1 GHz UMTS, whereas the CP bands can be used for the 3.5/5.5 GHz WiMAX, 5.5 GHz Wi-Fi, and 5.2/5.8 GHz WLAN applications.

In this study, a planar arbitrary phase-difference coupled-line coupler having wide bandwidth, tight coupling coefficient, and small phase variation are proposed. The proposed coupler consists of two quarter-wavelength coupled-line sections connected with two different transmission lines. Moreover, the interconnection transmission line can be designed as a small phase variation phase shifter with the introduction of a shorted stub. The detailed theoretical analysis is provided to illustrate the design concept. The circuit parameters of this novel arbitrary phase-difference coupler can be easily determined by the derived closed-form equations. For verification, two 3 dB couplers with 45°/135° and 60°/120° phase differences are fabricated and measured. The 45°/135° coupler achieves 34.2% fractional bandwidth for 45° phase difference with 2° phase variation and 36.3% fractional bandwidth for 135° phase difference with 3.4° phase variation. Moreover, the 60°/120° coupler achieves 30% fractional bandwidth for 60° phase difference with 0.9° phase variation and 32.9% fractional bandwidth for 120° phase difference with 1.5° phase variation.

In this article, a circular microstrip tunable wideband frequency and polarisation reconfigurable antenna are investigated. The wideband tunability is achieved by placing the four varactor diodes between circular microstrip patch and circular ring. The impedance bandwidth of 2.09–2.96 GHz (34.52%) is realised by tuning the capacitance value from 4.15 pF (0 V) to 0.94 pF (6 V). Both frequency tunability and polarisation reconfigurability are controlled in the antenna using the proposed cascaded branch line coupler feed network. The four single pole double throw and two dual in-line package switches are used in the feed network to control the tunable impedance bandwidth of the antenna over a wideband from 1.25 to 2.95 GHz. The vertical linear polarisation and horizontal linear polarisation (H-LP) are achieved by any one of the feed port excited in the antenna. Similarly, the right-hand circular polarisation and left-hand circular polarisation are realised by exciting both the feed ports in the antenna with±90° phase difference. The impedance bandwidth of proposed feed network is well matching with the tunable bandwidth of the patch antenna. Simulated and experimental verification results show good agreement.

A new low profile, multiband, multipolarised single feed antenna is designed. A corner truncated patch loaded with slots and a complementary split ring resonator is used to achieve three frequency bands with different polarisations. The antenna exhibits right-hand circular, linear, and left-hand circular polarisation at three different bands, respectively. To obtain circular polarisation, orthogonal modes are excited by truncating corners of the patch and etching slits. Single feed, single layer geometry with Y-shaped feed structure is employed. The antenna is fabricated on a low-cost FR4 substrate with an overall size of , and the proposed design has been verified experimentally. The selected frequency bands are centred at 2.313, 2.396, and 2.478 GHz, and they have −10 dB impedance bandwidths of 2.14, 2.50, and 2.42%, respectively. The first frequency band exhibits right-hand circular polarisation with a 3 dB axial ratio bandwidth of 0.85%. The second frequency band exhibits linear polarisation, whereas the third frequency band exhibits left-hand circular polarisation with a 3 dB axial ratio bandwidth of 0.81%.

In the study, an improved method for measuring the axial ratio of circularly polarised antennas based on the polarisation rotation is proposed. In the measurements, an auxiliary antenna can work in different rotation senses of polarisation (left-hand or right-hand) according to the status of the antenna polariser. By measuring received signals of the circularly polarised antenna under test when the auxiliary antenna work in the left-hand or right-hand modes at two different axial angles, the axial ratio of the antenna under test can be determined from the polarisation efficiency equations. The measurement of a typical circularly polarised antenna is performed in the anechoic chamber by using this method. Through the comparison between the measured results and the simulation results, the validity of this method is demonstrated. This method improves the measuring efficiency and has important engineering application.

This study proposes the design of the periodic lossy magnetic (PLM) surface with a low profile for enhanced array characteristics. The proposed PLM surface consists of multiple rectangular grooves with equal spacing, and the grooves are filled with lossy magnetic materials to increase the surface impedance between array elements to mitigate the mutual coupling. To verify its feasibility, the authors fabricate a two-element circularly-polarised patch antenna array with the PLM surface inserted into the ground plane and measure antenna characteristics in a fully anechoic chamber. The results demonstrate that the PLM surface is capable of reducing the mutual coupling so that the active array patterns can be improved with higher front-to-back ratios and lower active reflection coefficients for large steering angles.

In wireless system deployment, the system planner must deploy base station antennas at the most appropriate locations to maximise system performance. In this study, the effect of transmitting antenna deployments on coverage in a single room office environment at millimetre wave frequencies is investigated using a three-dimensional implementation of Geometrical Optics. Multiple antenna deployments and artificial environmental modifications (convex reflectors) are also investigated in order to quantify how they might improve coverage compared to a single antenna deployment. A quantitative estimate of shadowing inside the office volume indicated that there are significant non-illuminated regions which cannot be eliminated by simply increasing the transmitted power. It is shown that such regions can significantly be reduced in size if an appropriate deployment of multiple antennas or passive reflectors is adopted.

This study investigates the channel performance of a 28 GHz multiple-input–multiple-output (MIMO) system in a subway tunnel, using ray-tracing-based simulations and experimental measurements in a realistic tunnel environment. The transmitter (Tx) array was deployed at three positions, i.e. in the centre of the tunnel, close to the sidewalls and under the ceiling. The performance was significantly better in the centre and sidewall positions. Good agreement is obtained between simulation and measurement results. Furthermore, it is inferred that the MIMO channel capacity for the Tx–receiver distance of 60 m is higher than that of 15 m. The angular spread calculated for the 60 m case is also larger than that of the 15 m case.