The electromagnetic waves propagation in dispersive media is modelled using symplectic finite-difference time-domain (SFDTD) method based on decomposition technique of the exponential operator. The numerical stability and the dispersion relationships are presented. The numerical dispersion and dissipation errors originated from SFDTD method for non-magnetised collisional plasma medium are computed by comparing the real part and imaginary of numerical wave number with this analytic wave number. The high accuracy and efficiency is also confirmed by computing the reflection and transmission coefficients for a non-magnetised collision plasma slab. The numerical results show that the SFDTD method not only improves computational efficiency but also needs less computer memory as compared with the existing FDTD method. It can also be seen clearly that the eigenfrequency of the cavity resonator is filled with plasma media offsets. This conclusion has potential applications in the design of new types of microwave devices.

A highly reliable small-signal parameter extraction method for parasitic elements of the 0.1-µm GaAs metamorphic high electron mobility transistors is presented. De-embedding scheme for the coplanar waveguide (CPW) feeding structure is utilised in this method in a frequency range of 0.5–110 GHz with an enhancement approach to the correction of source inductance parameter sensitivity derived from oscillating measurements. The parasitic extrinsic capacitances are determined by modelling an ∏ equivalent circuit including the interaction between the sub-model and the CPW feedings. From this method, the authors achieved the most accurate parameter prediction with an effective fitting error of 10.83% among the small-signal models reported to date.

This study presents an experimental verification of the excess path loss for a satellite-to-Earth radio link shadowed by a single tree for elevation angles in the range from 20° to 40°. A measurement campaign was carried out in scale inside an anechoic chamber with five different species of trees at the X (8–12 GHz) and Ku (12–18 GHz) frequency bands to obtain the signal level variation as a function of the distance. It was discriminated the effect of the ground receiver terminal location with respect to the tree that affects the elevation angle value perceived by the receiver and the shadowing introduced by the tree. Results were discussed comparing with excess loss predicted by different vegetation scattering models aiming to characterise the goodness of their performance in terms of the excess signal loss predicted for short thickness of vegetation. In general, the models show a good agreement with measurements far away from the tree, however failing to describe the signal level variation if the terminal is near the tree. Nevertheless, it was determined that the models can be used to establish and upper and a lower limit to the excess signal loss.

This study presents a rigorous theoretical and experimental comparison of two kinds of rectangular waveguide polarisers for use in Ka-band gyro-travelling wave amplifier. It is shown how overall field distribution inside of polariser structures having different kinds of corrugation affects the resulting performances. To the best of the authors’ knowledge, this is the first theoretical estimation of the breakdown power (in watts) of sine-corrugated polariser in competition with conventional polariser having rectangular shaped corrugation. This study also discusses the general practice of smooth structuring in microwave and millimetre-wave component design.

A low profile (height = 3 mm) and wideband dual coplanar feed planar inverted-F antenna (PIFA) is proposed for diversity applications over the frequency range of 2.35–3.25 GHz with a fractional bandwidth of 32%. It covers LTE bands 7, 38, 40, 41 and WiFi frequency bands. The design is based on a comparative study on the mutual coupling between different feed arrangements such as the parallel feed, coplanar feed and orthogonal feed. The results show that the coplanar feed arrangement exhibits a lower mutual coupling level. As a result, the coplanar feed is employed in the proposed antenna and the polarisation diversity is achieved by exciting two orthogonal radiation modes; the antenna fed by Feed 1 uses open ground plane slot in the horizontal plane, while the antenna fed by Feed 2 is linked to PIFA. The modified top plate provides a self-matching circuit for Feed 2. The isolation between the feeds is achieved by an L-shaped ground plane slot. Both simulated and measured results are obtained, and the results demonstrate that the proposed antenna is a very good candidate for mobile diversity and multiple-input and multiple-output applications.

A high-temperature tolerant pattern diversity antenna is presented for body wearable applications in hostile conditions. The proposed system consists of a dielectric resonator antenna (DRA) placed at the centre of a slot loop antenna. The combination yields pattern diversity with broadside and endfire radiation patterns from slot loop and DRAs, respectively. The antenna system offers common bandwidth of 4.95% with port isolation of better than 13 dB at 2.4 GHz. The thermal characteristics of antenna have been studied for high-temperature operation and no discernible change in the radiation behaviour is noted. The antenna undergoes 2% resonant frequency shift when operated at elevated temperature. The antenna diversity has been measured for three on-body communication channels. The antenna offers 9.5 dB diversity gain in a pure non-line-of-sight channel surrounded by a rich fading environment subjected to the selection combining scheme. The antenna has dimensions of 0.4λ_o × 0.4λ_o × 0.1λ_o .

The authors utilise a one-dimensional (1D) stack of three identical unprinted dielectric slabs as a superstructure to design a novel yet simple tri-band electromagnetic bandgap resonator antenna (ERA). The design, inspired from classical single-band 1D ERAs, is conceived by creating two resonant defects in the superstructure configuration to make it suitable for tri-band and high gain operation. A prototype, fabricated using FR4 material, is tested with a waveguide-fed slot antenna at 10.3, 11.9 and 13.7 GHz with a frequency ratio of 1.33:1.16:1. The slot feeds the cavity simultaneously in the three frequency bands and provides good impedance matching in each frequency band. Peak measured gains of 14.3, 13.4 and 16.1 dBi and radiation efficiencies of 83, 85 and 85% are achieved in the lower, middle and higher frequency bands, respectively.

In this study, the design, hardware implementation and characterisation of a self-tuning 406 MHz antenna of a Cospas-Sarsat personal locator beacon are presented. The realised prototype is able to perform automatic tuning of the antenna under time-varying environmental conditions due to human body movements and sea water proximity. The impedance tuning is performed by tracking the instantaneous value of the reflection coefficient and by modifying an appropriate impedance matching network according to a real-time adaptive algorithm. A resilient default/backup software architecture has been designed to ensure that tuning guarantees a return loss higher than 10 dB for the personal locator beacon in most of impedance mismatching conditions.

The binary particle swarm optimisation (BPSO) in conjunction with the time-domain discrete Green's function (DGF) method is proposed for designing of printed ultra wideband (UWB) antennas. In the DGF method, on one hand, a three-dimensional problem is reduced to a two-dimensional one, and on the other hand, the broadband frequency characteristics of the antenna are achieved with a single simulation run. Furthermore, the spatial discrete representation of the current on the antenna, in the DGF method, facilitates implementation of its combination with the BPSO algorithm. Two different UWB antennas are designed using the proposed approach. First, an antenna is designed to minimise voltage standing wave ratio (VSWR). The experimental result shows that the antenna has a VSWR about <1.5 over the UWB range. Second, an antenna is designed to have not only low VSWR, but also stable radiation pattern over the UWB range. The experimental results show a good impedance matching and stable omnidirectional pattern over the UWB range.

Dielectric resonator antennas are widely used in wireless communication systems. A theory of characteristic modes (CMs) for modal analysis of dielectric resonators is highly demanded. Although a few earlier studies had proposed CM theory for modelling scattering from dielectric bodies, the physical characteristics of these CMs and their eigenvalues are not as clear as that of those for conducting bodies. This study revisits the CM theory for dielectric resonators. Following the Poynting's theorem and the PMCHWT (Poggio, Miller, Chang, Harrington, Wu, and Tsai) equation, two generalised eigenvalue equations are formulated. The resultant eigenvalues possess clear physical meanings that are the same as those of perfectly electrically conducting problems. In addition, other possible CM formulations based on the PMCHWT equation are also discussed. Mathematical proofs are given in the Appendix to show how to formulate CM theory to physically describe the fundamental resonant modes of dielectric resonators. Numerical results are given to show the proposed CM formulations are effective in solving resonant frequencies and modal fields for dielectric resonators.

Recent research on harmonic generations in one-dimensional (1D) left-handed non-linear transmission line (LH NLTL) metamaterials has shown that the fundamental wave and its higher harmonics can realise quasi-phase matching, which in turn ensures the high conversion efficiency of the harmonics. In this study, the authors first present the electromagnetic (EM) theory to describe the generation and propagation of both second-harmonic (SH) and third-harmonic (TH) waves in a 2D non-linear transmission line metamaterial. Then, with the aid of the microwave circuit simulations, they fabricate a 2D LH NLTL metamaterial and demonstrate that an EM wave propagation in such medium has three states: left-handed (LH), right-handed (RH), and non-propagation. Furthermore, the response of the medium to applied field intensity shows that it can realise self-tuning between LH and RH states for the TH waves.

A method for robust amplitude beamforming in linear antenna arrays is presented. The admissible tolerances on the array excitations, described as real-valued intervals, are maximised regardless their nominal values, while guaranteeing that the bounds of the radiated power patterns fit a-priori defined mask constraints. A set of representative numerical results, concerned with different mask constraints as well as comparisons with state-of-the-art approaches, is reported and discussed to assess the effectiveness of the proposed approach.

In this study, a new antenna is proposed to achieve uniform perpendicular magnetic field distribution for near-field ultra-high frequency radio-frequency identification. The antenna is based on ‘interdigital-oppositely directed currents (ODCs)’ that is formed by introducing another current between the two oppositely directed currents of ODCs. By adjusting the feeding phase of the newly introduced current, the uniformity of perpendicular magnetic field distribution can be improved. The design procedure of the antenna is presented and the uniform perpendicular magnetic field distribution of the antenna is achieved and verified by experiments. When the transmitting power of the proposed antenna is 1 W, the interrogation area for 100% tag detection is 49 × 16 cm² with an observing height of 5 cm for Impinj J41 near-field tags.

A novel probe-feed single-layer circular patch antenna with dual-band dual-mode dual polarisation is proposed in this study. By using modified mushroom structure, dual-band dual-mode characteristic is realised as former designs. Due to the loading structure including four curved patches added around the circular radiating patch, bandwidth is broadened for the patch mode (n = 1 mode) with unidirectional linearly polarised characteristics at the upper frequency band. By loading with four curved branches in the ground plane, circularly polarised property for the dipole mode (n = 0 mode) with omnidirectional radiation patterns is achieved at the lower frequency band. Parameter analysis is made to study this antenna and one prototype is fabricated to confirm the property. Moreover, the measured results are obtained with −10 dB impedance bandwidths of 227.5 MHz (5.1% at the centre frequency of 4.42 GHz) and 857.5 MHz (14.9% at the centre frequency of 5.74 GHz), and maximum gain of 1.1 and 7.1 dB for the dipole mode and patch mode, respectively. With the advantages of simple structure, wide bandwidth, radiation pattern selectivity and polarisation diversity, this antenna concept is valuable in wireless communications.

The design of multi-band bandpass filters (BPFs) employing stub loaded stepped-impedance resonator with defected microstrip structure (SL-SIR-DMS) is presented in this study for the first time. The proposed SL-SIR-DMS is created by embedding DMS on the low-impedance line of the SL-SIR. It is found that different defected structures can lead to different frequency responses. In addition, by using DMS, tri-band and even quad-band responses can be easily achieved without increasing the resonator size. As verification, one tri-band SL-SIR-DMS and one quad-band SL-SIR-DMS are designed and analysed using even/odd-mode method. Subsequently, one tri-band BPF and one quad-band BPF have been developed with pseudo-interdigital coupling to realise good out-of-band performance. The predicted results are compared with measured ones and good agreement is achieved. Compared with BPFs using only SL-SIR, the proposed filters with DMS are more compact due to the slow-wave characteristic. Compared with the BPFs using defected ground structure to improve the stopband performance, the proposed ones can realise comparable wide stopbands but maintaining the signal integrity on the ground plane for packaging purpose.

The authors propose a new method to optimise the geometry of partially reflective superstrates (PRSs) of resonant-type antennas, which is suggested to enhance both antenna gain and bandwidth at the same time. Specifically, their approach is about finding optimum arrangement of unit cells printed on PRSs. To construct an optimised PRS, they introduce some defected cells that are not covered with ordinary metallic patterns. By determining optimised arrangement of the defected and ordinary cells, they show that they can further improve impedance matching and radiation bandwidths, total efficiency, and antenna gain all at once. They use a real-value hybrid genetic algorithm for the optimisation. All experimental data show excellent agreement with predicted ones, which proves the validity of their approach.