New broadband antennas loaded with split ring resonators (SRR) are proposed and investigated. The results illustrate that by loading the conventional monopole antennas with an asymmetrical meander lines SRR, a lower resonance frequency mode can be excited. The dimensions of the SRR have been selected to provide a resonance close the resonance of the monopole antennas. The results illustrate that when both resonance coincide the antennas bandwidths and radiation properties can be enhanced. The length and width of the antennas are 25 × 10 ^{− 2} λ ₀ × 11 × 10 ^{− 2} λ ₀ and 25 × 10 ^{− 2} λ ₀ × 21 × 10 ^{− 2} λ ₀ at 4 GHz for monopole antennas, and 29 × 10 ^{− 2} λ ₀ × 21 × 10 ^{− 2} λ ₀ at 2.9 GHz for both monopole antennas loaded with SRR. For antennas without SRR loading, maximum of measured gains and efficiencies are 3.6 dBi and 78.5% for F-antenna, and 3.9 dBi and 80.2% for T-antenna, hence they appear at 5 GHz. For antennas with SRR loading, these parameters are 4 dBi and 81.2% for F-antenna, and 4.4 dBi and ∼83% for T-antenna, which appeared at 6 GHz. By implementing the meander lines SRR as a matching load on the monopole antennas, the resulted antennas cover the measured frequency bandwidths of 2.9–6.41 GHz and 2.6–6.6 GHz (75.4 and ∼87% fractional bandwidths), which are ∼2.4 and 2.11 times more than monopole antennas with an approximately same in size.

A novel class of supershaped dielectric lens antennas, whose geometry is described by the three-dimensional (3D) Gielis’ formula, is introduced and analysed. To this end, a hybrid modelling approach based on geometrical and physical optics is adopted in order to efficiently analyse the multiple wave reflections occurring within the lens and to evaluate the relevant impact on the radiation properties of the antenna under analysis. The developed modelling procedure has been validated by comparison with numerical results already reported in the literature and, afterwards, applied to the electromagnetic characterisation of Gielis’ dielectric lens antennas with shaped radiation pattern. Furthermore, a dedicated optimisation algorithm based on quantum particle swarm optimisation has been developed for the synthesis of 3D supershaped lens antennas with single feed, as well as with beamforming capabilities.

Tri-polarised antennas are exploited to synthesise the optimal polarised beampattern in this study. First, the characteristics of a single tri-polarised antenna are studied with an infinite current sheet model. Using the cross-product algorithm, the authors find that three co-located orthogonal current sheets are equivalent to a pair of orthogonal current sheets in a particular orientation. It implies that the tri-polarised antenna is just virtually equivalent to a rotatable dual-polarised antenna. Then by formulating the problem in a convex form, they adopt the convex optimisation algorithm to synthesise optimal polarised beampattern of the tri-polarised array. The simulation results show that due to the increased orientation degree of freedom, the sidelobe and cross-polarisation level of tri-polarised array are significantly lower than the dual-polarised array.

The surface integral equation is adopted to analyse the characteristics of the arbitrarily arranged spherical conformal microstrip antenna array based on the moment method. The Rao–Wilton–Glisson basis function and triangle function are used to simulate equivalent current on the patch and probe, respectively. A novel basis function at the junction of wire and surface is proposed to ensure continuity of the current from probe to patch. Then, the magnetic frill loop is used as excitation source in this study, and the field on the antenna surface generated by magnetic frill loop is deduced with the help of magnetic dyadic Green's functions on the surface of sphere. For the antenna array analysis, the characteristic basis function method combined with equivalent dipole method is employed to save the consumed memory and computation time. The characteristics of several pairs of conformal spherical microstrip antennas are presented and shown to be in good agreement with data from literatures and FEKO software. At last, a result comparison between the method in this study and FEKO software is drawn to show the efficiency of this method.

In this study, a novel one-step leapfrog weakly conditionally stable finite-difference time-domain (WCS-FDTD) method for body of revolution (BOR) is presented. The singularity of some field components on and adjacent to the axis are solved specially, in accordance with the one-step leapfrog WCS-FDTD scheme. The electric and magnetic fields of the proposed method are interlaced half a time step apart and no sub-time steps are used. The novel method obtains a higher computational efficiency while preserving the properties of the conventional WCS-BOR-FDTD method. Its stability condition and dispersion error are presented analytically. Moreover, two numerical examples are given to demonstrate the proposed method.

This contribution presents a comprehensive methodology for the global prediction of monthly total tropospheric attenuation statistics. This goal is achieved by combining the outputs of physically-based models for the estimation of the attenuation induced by each relevant atmospheric constituent (gases, clouds and rain). To evaluate the model's accuracy, worst month total attenuation statistics are first derived from the monthly attenuation predictions, and tests are performed against the measurements included in the global DBSG3 database of International Telecommunication Union-Radiocommunication Sector. Results show a good prediction accuracy, which corroborates the use of the proposed physical model to aid engineers in planning future high-frequency satellite communication systems on the basis of the worst month concept.

In this study, a new compact coplanar waveguide-fed wideband circularly polarised slot antenna is designed and fabricated. To achieve circular polarisation, the slot in the ground plane is truncated at one corner and excited by a modified L-shaped radiating element. To achieve wide axial ratio bandwidth (ARBW), one end of the L-shaped patch is connected with the ground via a slit. The ARBW is further improved by properly placing two additional narrow slots in the ground plane. The measured impedance bandwidth and ARBW at boresight are achieved 87.2% (from 2.2 to 5.6 GHz) and 81.05% (from 2.2 to 5.2 GHz), respectively. For the better understanding, the surface current distribution and parametric studies are presented. To characterise the antenna in the time domain, group delay and system fidelity factor (SFF) are measured. The measured group delay has less variation (of 0.5 ns) in the operating band and the measured SFF is found to be 0.89. The measured and simulated results are in good agreement.

The aim of this study is to design a new microstrip-fed patch antenna for cell phone applications. The antenna design is composed of slots and Flame Retardant 4 dielectric substrate fed by a partial ground plane and a microstrip line. The user's effects on antenna performances are also analysed using standard specific anthropomorphic mannequin head phantom. The specific absorption rate (SAR) values of the proposed antenna are evaluated for different frequency bands considering cheek position of talk mode. The proposed antenna has an impedance bandwidth of 230.4 MHz (0.725–0.95 GHz, lower band), and 522.24 MHz (1.74–2.25 GHz, upper band), which can cover global system for mobile (GSM) 900 MHz, digital communication system 1800 MHz, personal communications service 1900 MHz, GSM 1900 MHz, and universal mobile telecommunications service 2100 MHz bands. Moreover, the proposed antenna produces lower SAR values in the human head than that of a dipole antenna, helical antenna, and planar inverted-F antenna.

Compact switchable diplexer and quadplexer are proposed using the capacitively loaded multicoupled line and the common resonator technique. The proposed single-pole double-throw (SPDT) switchable diplexer integrates the functions of SPDT radio frequency switch and bandpass filter, and each signal path can be independently synthesised using the insertion loss method. In addition, by a simple modification to the common resonator, a single-pole quadruple-throw switchable quadplexer can be achieved by the connection of two proposed SPDT switchable diplexers. Low-loss, compact size, good selectivity, and high-linearity are achieved.

To accurately design wideband filters composed of three-coupled-lines, an improved equivalent circuit is derived by taking the cross-coupling between non-adjacent lines into consideration. Since the cross-coupling between non-adjacent lines is also dependent on the coupling between adjacent lines, conventional synthesis techniques cannot be used directly. Instead, an improved synthesis scheme based on successive iterations is proposed to synthesise the filters. As examples, two 2-stage microstrip three-coupled-line filters [bandwidth: 2.67–5.33 GHz (fractional bandwidth: 67%)] with a reversed connection sequence are synthesised, simulated, and experimentally realised to validate the proposed theory. The frequency responses of the designed filters using the authors’ new model and synthesis theory compare well with those by simulation and experiment, whereas an error of about 17% is found in bandwidth if the authors use the conventional model that neglecting the cross-coupling between non-adjacent lines. In addition, the asymmetric property of the three-line unit is revealed.

Array scanning method (ASM) is employed to study the input impedance and radiation pattern of a two-dimensional periodic leaky-wave antenna (LWA). The antenna consists of a narrow horizontal strip dipole of arbitrary length underneath a two-dimensional (2D) periodic screen of metallic patches, which acts as a partially reflective surface (PRS), and backed by a ground plane. First, the Green's function in the presence of the 2D array of metallic patches is calculated by means of the ASM and then the current distribution and input impedance of the source dipole are calculated through the electric field integral equation and method of moments. The far-field pattern is computed using the reciprocity theorem. Compared to the Hertzian dipole, which is the only type of source that has been considered in the literature, the resonant dipole substantially improves the performance of periodic LWA in terms of radiated power, efficiency and bandwidth. Numerical results are given for a resonant dipole over the frequency range of 60–70 GHz and compared with those obtained from commercial softwares, FEKO^® and Ansys HFSS^®, showing an excellent agreement with considerable improvement in terms of memory usage and computational speed.

In this study, the authors developed an ultra-wideband (UWB) planar loop antenna for implant communication, and confirmed its usefulness by comparing its designed and measured reflection and transmission characteristics. With the planar loop antenna as the implant transmitting antenna, then they calculated the implant path loss and specific absorption rate (SAR) using the finite difference time domain method together with an anatomical human body numerical model. Moreover, through a link budget analysis based on the calculated path loss with selection diversity, they derived the transmitting power required to achieve a specific bit error rate performance, and clarified the corresponding local SAR with respect to the international safety limits. As a result, the UWB implant communication is found to be feasible at a data rate as high as 40 Mbps under the SAR safety limits.

A novel microstrip patch antenna is proposed for automotive application. The antenna design has been investigated through both the parametric study and the demonstration of surface currents on the antenna structure. The surface currents related to the co-polarisation increased, and those related to the cross-polarisation is reduced by attaching shorted parasitic element. The four types of single antenna are designed to compare of gain and cross-polarisation level. The cross-polarisation level of proposed antenna has been reduced by 5.9 dB compared with the rhombic antenna. The rhombic array antenna and proposed array antenna were fabricated and tested for input reflection coefficient and radiation performance. The measured and simulated results have been presented and discussed.

A planar microstrip circuit is proposed to design a kind of coupled-line balun with good ports matching and high output-ports isolation for complex source to complex load impedance transformation. This balun prototype essentially consists of three coupled-line sections, a tapped open transmission-line stub (TOTS) on the left-hand side, and a tapped complex equivalent-impedance part (TCEP) on the right-hand side. The TCEP is the key to realise high output isolation and all ports matching. Based on the traditional even-odd mode technique and the transmission-line theory, closed-form mathematical equations for circuit electrical parameters are obtained. To demonstrate this proposed design theory, a practical microstrip coupled-line balun is designed, simulated and measured to operate at approximately 2 GHz, indicating high isolation and balanced output. Good agreements between the simulated and measured results verify this design.

A compact two-port diversity antenna is proposed and experimentally investigated. One of the ports is connected to a microstrip feed, whereas the other port to a coplanar waveguide feed. The radiating elements are semi-circular disc-shaped monopoles rotated around their centres. By shaping the common ground plane, ultra-wide impedance bandwidth is achieved. The measured bandwidths are 2–12 GHz at port 1 and 2.3–10.2 GHz at port 2. To obtain good isolation between the ports, a slant inverted tree-shaped structure is attached at the corner of the ground plane. The measured isolation is about 20 dB throughout the band. The antenna has omni-directional radiation patterns with a moderate peak gain of 2–7 dBi. To evaluate the diversity performance, the envelope correlation coefficient, diversity gain and capacity loss are calculated. A modified design with impedance bandwidth at port 2 extending beyond 11 GHz is also presented. The proposed diversity antenna is an attractive candidate to provide polarisation diversity and enhance channel capacity in a rich scattering environment.

This study studies optimal design of focused antenna arrays for microwave-induced hyperthermia. The phases and amplitudes of the driving signals of array elements are determined by optimising the power transmission efficiency of the system consisting of the transmitting antenna array, a receiving antenna located in the target area, and an equivalent phantom representative of human tissues. On the basis of the proposed technique, a 4 × 2 focused patch array is designed to operate on a fat-mimicking phantom with working frequency at 433 MHz. The measured patterns for specific absorption rate indicate that the energy is focused in the desired spot and are in close agreement with simulations, which validate the optimisation method in a medium with low permittivity and low loss. A 4 × 3 focused patch array operating on a human body phantom with same working frequency is then designed, in which an air space and two additional dielectric layers have been introduced between the planar array and the body-mimicking phantom for impedance matching. A good focal performance at desired spot is also achieved, and the simulated and measured specific absorption rate patterns agree very well. This demonstrates the validity of the proposed design method in a medium with high permittivity and high loss.

In this study, the effect of loading microstrip antenna using epsilon near zero (ENZ) metamaterial is investigated. It is known that ENZ material may help to improve the transmission through a boundary condition and that the scattering parameters may be completely independent of such boundary properties. This idea is demonstrated to significantly increase the bandwidth of a simple rectangular microstrip patch antenna. To realise the ENZ material, a periodic wire medium is designed, simulated, fabricated, and tested. Simulation results based on CST Microwave studio have good agreement with measurements.

A tuneable ferrite resonator antenna (FRA) based on nanostructured nickel ferrite (NiFe₂O₄) material is proposed. Magnetic and dielectric characteristics are determined for the NiFe₂O₄ material such as electrical permittivity, and hysteresis loops. This ferrite material is used as a microwave resonator in the designing and fabrication of a cylindrical FRA. Ansoft high-frequency structure simulator software is used to provide simulated results for the antenna parameters such as resonant frequency, return loss, input impedance, and radiation pattern. A resonant frequency tuning capability with the application of a varied external magnetic bias field is shown. Measurement of the antenna prototype is also carried out and the obtained results are in good agreement with the simulated ones.

This study presents a K-band differential voltage-controlled oscillator (VCO) with robust start-up. A hybrid technique that combines open-loop digitally controlled tail current with switchable auxiliary cross-coupled pairs (ACCPs) is proposed to ensure robust start-up for wideband operation. Compared with prior closed-loop current controlling method, the proposed technique does not suffer from phase-noise degradation. Furthermore, by evenly distributing the ACCPs, transistors with smaller size are allowed to achieve the same start-up condition, which leads to frequency boost and phase-noise improvement. Implemented in 0.18 μm complementary metal–oxide–semiconductor technology, the VCO achieves a wide-frequency tuning range of 21.4–26.29 GHz (20.5%) and a low phase noise of −108.8 dBc/Hz at 1 MHz offset from 25.8 GHz carrier frequency. At 1.1 V power supply, the power consumption of the core circuit is 7.9–11.4 mW across the entire output frequency range.

Automatic dependent surveillance-broadcast (ADS-B) system requires higher performance, highly reliable, and smaller size, lighter weight and lower cost transceiver. To reduce the size and cost and to increase the manufacturability it is desirable to integrate the whole ADS-B system into a single-chip complementary metal–oxide–semiconductor (CMOS) technology platform. Watt level power is required from the ADS-B transmitter for transmitting the information about aircraft's precise location at larger distances. This study presents CMOS voltage-controlled oscillator (VCO) circuit, as a part of ADS-B transmitter, operating at the centre frequency of 978 MHz, delivers the highest output power with the highest efficiency ever reported to the best of authors’ knowledge. The 0.738 mm × 0.606 mm VCO chip fabricated using 0.18 μm CMOS technology, exhibits the single-ended peak output power of −0.46 dBm and the differential peak output power of 2.54 dBm at the frequency of 1 GHz, with the frequency tuning range from 954.3 to 1009.4 MHz and phase noise of −109 dBc/Hz at 1 MHz offset centred at the frequency of 978 MHz, consuming 19 mW power from 1.8 V supply, thus, showing state-of-the-art-performances. This promising result shows a path towards realising high-power single-chip CMOS ADS-B transmitter.

This study provides a simple broadband method for determining the dielectric properties of laminate substrate materials used in integration and packaging solutions for commercial millimetre-wave applications. Relative permittivity and loss tangent are extracted from coplanar lines using closed-form equations that account for as-fabricated transmission line dimensions. The method is applied to a low loss substrate alumina and further tested on glass impregnated epoxy resin materials with metals that have an appreciable metal surface roughness. The work expands existing material characterisation methods that are typically based on thin films. The dielectric substrates are thin, similar to integrated circuits, but the metal thicknesses remain on the order of packaging substrates. This study considers the critical parameters and manufacturing features for designs and millimetre-wave material measurements on these types of materials. The method has an accuracy of within 10% of known values, utilises off-the-shelf software solutions when available, and requires no fixturing beyond the sample material. Error analysis is provided with material information on Isola FR408 up to 110 GHz.

A suitable method for improving the isolation of slot-coupled directional couplers with elliptical-shaped slot and patches is introduced. It is shown that the even- and odd-mode phase velocities depend on the width of the patches and slot of the slot-coupled directional couplers. For couplers with tight couplings, the even- and odd-mode phase velocities can be effectively equalised by cutting some parallel slots into the patches, while for couplers with weak couplings, the even- and odd-mode phase velocities can be equalised by cutting some teeth into exterior part of the slot in the common ground plane. For various slot lengths and tooth depths, various design graphs are derived by sweeping some dimensions of the coupler. On the basis of the design graphs, three couplers with tight, moderate and weak couplings are designed and simulated. The designed coupler with tight coupling is also constructed and tested. The results show that by employing the proposed method, the isolation of the slot-coupled directional couplers has improved significantly.