In this study, a measurement methodology is proposed for characterising wearable antennas on different locations of the human body. With the conventional roll-over-azimuth far-field system, it is impractical to capture the full spherical radiation pattern. A cylindrical near-field (CNF) technique is employed here which facilitates wearable antenna measurements on a solid full-body anthropomorphic phantom and readily produces the antenna radiation efficiency. The installed antenna efficiency is an important parameter for optimising a wearable system design and improving channel performance. The procedure of the CNF measurement is validated using a printed dipole antenna as a reference in horizontal and vertical polarisation parallel to body surface. Two textile wearable antennas with distinct radiation characteristics are designed, fabricated and assessed on the body phantom to operate at 2.4 GHz ISM band. Near-field and transformed far-field measurement results are presented and compared with electromagnetic simulations in order to demonstrate the benefits of the proposed measurement method.

This study presents a new side slotted Vivaldi antenna (SSVA) with size reduction and improve gain with directive featured as compared with traditional Vivaldi antenna. A number of parameters are studied and optimised for breast imaging system over ultra-wideband frequency (3.1–10.6 GHz). The parameter such as substrate type, radiating fins, cavity diameter, stub radius, stub angle is optimised to reduce the size of the antenna with better antenna performance in terms of bandwidth, gain, efficiency, and directivity. The radiating fins are modified by etching a number of side slot to enhance the gain and electrical length. The optimised size of the antenna is 45 (L) × 37 (W) mm², 8.5 mm cavity diameter, 9.5 mm stub radius with the angle of 80° by using Rogers 5870 substrate. Results show that the antenna has a bandwidth from 3.9 to 9.15 GHz for reflection co-efficient <−10 dB with directional radiation pattern. The peak gain of proposed prototype is 6.8 dBi and the radiation efficiency is about 88% on an average over the operating bandwidth. The fidelity factor for face to face is 0.92 and for side by side is 0.62, which prove the directionality and lower distortion of the signal. A number of design iteration is done to achieve the optimum result of the antenna. The prototype of proposed SSVA antenna is successfully fabricated, simulated, and measured. Later, the antenna is used in breast phantom measurement system for microwave imaging application.

A systematic approach to sidelobe reduction of broadside linear antenna arrays by design of corporate feeds implementing non-uniform excitation is proposed. The approach comprises of the two major stages. First, candidate excitation sets (corporate feeds) are searched among excitation sets which might energize a particular array aperture. The range of the corporate networks is restricted – based on the implementation and performance considerations – to the ones constructed using only T-junctions with equal power split. The reference for the candidates in terms of the sidelobe level is the uniformly excited and spaced array aperture with the same number of elements. The search is performed over realizable excitations and constrained elements’ spacings using the array factor and the model of excitation amplitudes due to corporate feeding. At the second stage, an excitation providing reduced sidelobes and simple routing is implemented as a microstrip corporate feed within the antenna array model. The entire antenna-feed circuit is adjusted and validated using numerical optimization and discrete electromagnetic simulations at the high-fidelity level of description. The proposed feeds and the approach to their systematic design offer flexibility in design of linear antenna arrays without extra complications and allow substantial sidelobe reduction. A demonstration example is provided.

In this study, design methodology and equations necessary for low-loss high-order absorptive filters in the reflective-type configuration are introduced, derived and described in detail. Initially, a simple single, absorptive filter is described and its use in radio frequency front-ends is discussed. Based on this, improvements to the single, first-order absorptive filter are discussed and novel circuits that cater for lower loss higher-order absorptive filters are proposed. The necessary conditions for the achievement of the proposed higher-order absorptive filters from the proposed circuits are derived in order to establish the potential of the proposed circuits. As an experimental verification, first-, second- and third-order reflective-type absorptive filters are fabricated and their performances measured. In particular, in the case of a third-order absorptive filter, it is shown that the depth of the introduced attenuation is at least 27.4 dB across the frequency range of 2.17–2.27 GHz. Further, the use of the obtained absorptive filters was put to a test by inserting them in series with a commercially available band-pass filter.

A new substrate integrated waveguide resonator in the form of a square- or cross-shaped pedestal is proposed. The structure is developed from T-shaped ridge waveguides, and utilises the mode separation characteristics of this type of guide to achieve wider spacing between the first two resonances, as well as miniaturisation of the resonator. Two fourth-order X-band filters, one with cross-coupling, are designed using, respectively, square- and cross-shaped pedestal resonators, and validated by simulation and measurement.

A new microstrip patch antenna feeding technique for millimetre-wave imaging applications is proposed. The technique utilises a substrate integrated waveguide line that orthogonally feeds the patch antenna through a coupling aperture. A rectangular microstrip patch antenna was designed to operate at 32 GHz. Measurement and simulation results for rectangular patch antenna are presented showing good agreement with 9% bandwidth (|S ₁₁| < −10 dB). The aperture-coupled rectangular patch antenna provided 5.5 dBi gain and 72% efficiency at the design frequency. Finally, the rectangular patch antenna is used for near-field and wideband synthetic aperture radar imaging to demonstrate the potential of the proposed antenna for imaging applications at millimetre wave frequencies.

A composite right/left-handed (CRLH) structure-based high-impedance surface (HIS) is investigated to improve gain and front-to-back ratio of planar microstrip antennas. An unbalanced CRLH unit cell with a wide band-stop region from 2.0 to 6.44 GHz is modelled and designed for HIS to enhance the antenna performance. A novel via-less structure composed of an interdigital capacitor and four spiral arms is used for the microstrip implementation of the CRLH unit cell. The HIS is formed by the repetition of the unbalanced CRLH unit cells in two-dimensional form. The microstrip patch antennas operating at three different frequencies: 2.34, 3.77 and 5.64 GHz in the band-stop region of the HIS are designed with and without HIS to compare the antenna performances. An increase in gain of 1.91, 2.03 and 0.7 dB and an improvement in the front-to-back ratio of 4.9, 6.0 and 4.2 dB are achieved for the patch antennas operating at 2.34, 3.77 and 5.64 GHz, respectively. To demonstrate the effectiveness of HIS, a patch antenna over HIS is fabricated and measured results show good correlation with the simulated results. An overall antenna size at 2.26 GHz is 0.378λ _o × 0.303λ _o × 0.012λ _o.

Antenna arrays with shaped patterns have drawn significant attention for their wide applications in radar, sonar and communication systems. The combination of genetic algorithm (GA) and fast Fourier transform (FFT) has been used to synthesise shaped pattern of antenna array's factor without considering coupling effects. In this work, the GA-FFT method is generalised by integrating with a new virtual active element pattern (AEP) expansion method which approximates each AEP as the radiation pattern by exciting several equally spaced virtual elements surrounding the real element position. The generalised GA-FFT can be applied for the shaped pattern synthesis of unequally spaced linear arrays including mutual coupling and platform effect. Several synthesis examples with different pattern shapes and different antenna structures are given to demonstrate the effectiveness, accuracy and robustness of the proposed method.

Microwave over-the-horizon (OTH) propagation through troposcatter is a valuable candidate for remote targets detection. Array antenna is promising to handle the contradiction between real-time wide spatial coverage requirement and high antenna gain to capture weak scattering signal. The detection tactics and performance of array receiving systems are significantly affected by the fading correlation between array antennas, but there is no analytical study which considers the fading correlation in troposcatter passive sensing environments for uncooperative targets. In this study, an analytical method based on a scattering transfer function is proposed to derive the channel fading correlation, and the result is a function of transmitter deviation and spatial, temporal, frequency, angular separations of receiving array antennas in uncooperative troposcatter circumstances. In addition, the OTH troposcatter array receiving signal model is derived by exploiting the fading correlation to form the covariance structure of the received array signal, adding up with the signal transmission loss. Existing experimental results validate the derived fading correlations, and the simulation results validate the OTH passive detection performance based on the provided signal model.

A selectable multiband isolation of single pole double throw (SPDT) switch with switchable transmission line stub resonators for applications of WiMAX and LTE in 2.3 and 3.5 GHz bands is presented. Two SPDT switches are presented. (Design 2) either allows selecting only one band while unselecting the other or selecting both of them. However, (Design 1) does not allow so. The transmission line stub resonator used in this design is an open stub resonator with quarter wave of the electrical length. By using a simple mathematical model, the theory of the transmission line stub resonator was discussed where it can be cascaded and resonated at centre frequencies of 2.3 and 3.5 GHz. Moreover, the cascaded transmission line stub resonators can be reconfigured between all-pass and band-stop responses using discrete PIN diodes. The key advantage of the proposed SPDT with switchable transmission line stub resonators is a multiband high isolation with a minimum number of PIN diodes. Therefore, the simulated and measured results showed the followings: <3 dB of insertion loss, >10 dB of return loss and >30 dB of multiband isolation in 2.3 and 3.5 GHz bands.

A full-wave numerical scheme of polarisability (polarisability) tensors evaluation is presented. The method accepts highly conducting bodies of arbitrary shape and explicitly accounts for the radiation as well as ohmic losses. The method is verified on canonical bodies with known polarisability tensors, such as a sphere and a cube, as well as on realistic scatterers. The theoretical developments are followed by a freely available code whose sole user input is the triangular mesh covering the surface of the body under consideration.

Very low frequency/ultra-low frequency coupling communication systems suffer from severe disturbance from non-Gaussian impulsive noises which producing significant long tails. Considering the significant in-band parts of the impulse, traditional noise-suppression methods are not adequate in improving the signal-to-noise ratio (SNR), and the performance of existing dipole–loop double antennas active noise suppression systems are limited to a low level due to the different directionality of the antennas. A new double-loop antennas active noise suppressing system was proposed, in which one multi-turn loop antenna was employed to receive the useful signals, and one single-turn loop was employed as the noise reference antenna. A mathematical morphology processor and a time-switch filter were employed to extract the impulsive noise, and the digital equivalent model of the multi-turn loop antenna was established filtering the extracted impulsive noise to obtain a duplicate transient, which is highly correlated with the transients received from the multi-turn loop antenna. The system SNR was improved by subtracting the transient duplicate from the received signals. Simulations were carried out with Monte Carlo method, showing that the SNR can be improved with the gain of about 18 dB with communication error rate extremely reduced by orders of magnitude. Experiment system was also designed and established to verify the feasibility and efficiency, and a 50 m communication experiment in an industrial environment showed that the error rate can be decreased from 0.2 to 0.06% while employing the proposed noise suppression method.

In this study the authors present a possible solution for a compact printed folded dipole antenna, designed to match an nRF51822 Bluetooth Smart device. The use of a differential design avoids the need for a balun and the matching network between the IC and the antenna, therefore, reducing the power loss in these components. The performance of the proposed printed dipole is compared with the standard application of a quarter-wave monopole antenna as proposed by the manufacturer and a commercial ceramic antenna. It is shown that the proposed design presents better radiation properties than the other two approaches, which resulted in an increased communication range of the system by 50%. Measurements are compared with simulation to attest the validity of the authors’ proposal.

A broadband circularly polarised antenna with a compact structure is proposed based on a microstrip-coplanar waveguide (CPW) fed rectangular slot antenna. The wideband feeding network power divider (PD) consists of a Wilkinson PD and a 90° phase difference comparator. The even modes of four CPW feed lines are generated to provide equal amplitudes but in phase quadrature. Circular polarisations can be excited over a very broad frequency band. A reflector is added to the antenna structure to improve the antenna gains. The inverted configuration, which places the reflector in the slot side, is ultilised to enhance the impedance matching. The measured impedance bandwidth for |S ₁₁| < −10 dB is 74.4%. A broad 3-dB axial ratio bandwidth of 70.8% is also obtained. The measured 3-dB gain bandwidth is 53.65% with the peak gain of 7.4 dBic.

Design approach of a novel, triple-mode wideband slotline antenna is proposed and studied. The proposed antenna is realised and implemented by employing the multiple resonant modes within a narrow slotline radiator, rather than utilising the traveling-wave effect. At first, a triple-digit, fork-like microstrip tuning stub is used to excite the first and the second odd-order mode within a slim, 3/2-wavelength slotline radiator. Then, a pair of slotline stubs is introduced near the E-field nulls of the third odd-order mode. By finely tuning the parameters of the microstrip/slotline stubs, the three radiation modes are perturbed and merged to generate a wideband, radiation characteristic with three resonances. Prototype antennas are then fabricated and measured. Finally, the design approach is experimentally validated. It is shown that the proposed antenna's radiation bandwidth has been effectively increased to 33.2% while keeping a single, basic-form narrow slotline radiator with a simple, non-traveling-wave configuration.

A compact dual-polarised slot antenna with improved gain is presented in this study. A cross-shaped slot antenna fed by two orthogonal microstrip feed lines is proposed to achieve dual polarisations. A symmetrical feeding structure is employed to realise high isolation between the two ports by utilising a one-to-two divider. The working principles of the slot antenna fed by a fork-like microstrip are investigated in detail for the first time. In addition, a parasitic cross-shaped slot is added to improve the impedance matching and directivity of the proposed antenna. The measured results show that the proposed antenna can cover the whole WiMAX band ranging from 3.27 to 3.68 GHz. The cross-polarisation levels are less than −30 dB in the boresight direction and lower than −25 dB within 3-dB beamwidth in both E- and H-planes. The gain of the antenna is 9.15 dBi ± 0.25 dB and the port isolation is greater than 27 dB across the operating band.

The statistical properties of the received signal are significantly dependent on the direction of arrival at the receiving antenna. Therefore, knowledge of the arrival angles is useful in simulation studies of wireless channels. This study presents a method for determining the arrival angles and their intensity in the azimuth and elevation planes. Besides, the impact of the propagation environment and radiation pattern of the transmitting antenna on the scattering intensity of the arrival angles is shown. This significantly distinguishes the proposed technique from the methods for determining signal direction that have been previously described in the literature. The procedure is based on a geometric description of the scattering areas, which are a set of half-ellipsoids. Their number and size result from the parameters of the power delay spectrum or profile for modelled propagation environment. Simulation studies offer the possibility of adapting the statistical properties of the arrival angles to the type of propagation environment examined. The inclusion of the propagation phenomena in the azimuth and elevation planes provides a better representation of the empirical results compared with two-dimensional modelling. This fact is shown by a comparison of statistical properties between the simulated directions and the measurement results for selected types of propagation environments.

To further develop the advantages of loading artificial material units, layout rules of unit cells were investigated and presented for the first time in this study. Based on the analysis of transmission characters of metamaterial unit cells, some tapered slot antennas loaded with different unit layouts were designed. The result comparison showed that after the layout optimisation, the operation frequency band with a gain above 10 dB increased by about 13% and the gain increased by 0.4–2.6 dB in the high frequency band. In addition, the sidelobe level of H-plane also decreased by 0.7–4 dB at different frequency points.

This study aims to present the formulation of the partial element equivalent circuit (PEEC) for dispersive and lossy linear magneto-dielectric materials under the quasi-static hypothesis. The magnetic permeability and dielectric permittivity are usually available as tabulated data at different frequency samples. They are incorporated in the time-domain PEEC formulation by resorting to a rational approximation of their frequency-dependent constitutive relations. Thus, a set of ordinary differential equations is obtained besides those obtained by enforcing Kirchoff voltage and current laws to the PEEC equivalent circuit. The resulting augmented model preserves the circuit structure of the usual PEEC model and, hence, can be run in Spice-like circuit solvers. The robustness and accuracy of the proposed time-domain approach is tested by comparison with its frequency-domain counterpart despite the larger number of unknowns.

A small-size reconfigurable smartphone antenna using a PIN diode for WWAN/LTE and global navigation satellite system (GNSS) smartphone application is presented. When the diode is in ‘OFF’ state, a T-shaped feeding strip and an encircled T-shaped parasitic shorted strip formed a coupled-fed antenna, which achieves a low-wideband covering GSM850/900 bands and a high-wideband covering GSM1800/1900/UMTS2100/LTE2300/2500 bands. When the diode is in ‘ON’ state, a loop antenna working at 1/2 wavelengths is formed to cover the bands of GNSS, which includes four positioning systems (COMPASS, GALILEO, GPS and GLONASS). In addition, the proposed antenna is easily printed on a small ground clearance of 375 mm² without loading any lumped element. Also, the proposed simple and compact antenna is convenient to be optimised for desired bands. Finally, the good agreement of simulated and experimental results proves that the proposed antenna is suitable for practical mobile terminal equipment.

This study presents full-wave analytical explicit expressions for the time-harmonic surface fields of a large horizontal circular loop antenna located on a multilayer Earth. The expressions are derived by applying the following procedure. First, the complete integral representations for the EM field components are decomposed into three parts, that is, the residue contributions from the poles of the integrands and the two branch-cut integrals associated with the wavenumbers in free-space and in the bottom layer of the stratified medium. Next, the square-root term that generates the branch cut is extracted from the integrand of the generic branch-cut integral. Finally, the square-root algorithm-based partial fraction expansion is applied to each extracted square-root term, so as to convert the branch-cut integrals into closed-contour integrals around a set of pole singularities, which can be straightforwardly evaluated. As a result of the developed procedure, the fields are expressed as convergent sums of special functions. Numerical results are presented to validate the proposed formulation. In addition to being accurate, the derived formulas offer advantages in terms of computation time over standard numerical integration techniques.

This paper studies the use of NURBS-UTD method in analyzing radiation of antenna set on perfectly conducting convex surfaces. The electromagnetic ray path is traced by numerical algorithm built from parametric domain in order to take advantage of the mapping definition for parametric surfaces. The presented algorithm can be applied to arbitrary shaped surfaces and provide accurate and stable geometrical parameters to calculation of electromagnetic fields afterwards. The algorithm is verified by cylinder on which analytical solution of ray path is available and good agreement is achieved by comparison. Radiation patterns of antennas mounted on arbitrary shaped surfaces are calculated and compared to commercial software to testify the accuracy and ability of the presented method. Evaluated by RMS error, the deviation between the presented method and commercial software is about 1 dB.

This study presents a Ka-band radio frequency (RF) micro electro mechanical systems (MEMS) capacitive switch with low loss, high isolation, long-term reliability and high power handling based on GaAs microwave monolithic integrated circuit (MMIC) technology. In this design, a T-matching structure is employed to realise impendence matching at ‘up-state’ by modifying the dimensions of centre signal line. Thus, the reflection loss and insertion loss are improved effectively. Measurement results show that in ‘up-state’ position, the input reflection coefficient (S ₁₁) is less than −20.4 dB with the forward transmission coefficient (S ₂₁) of better than −0.27 dB at Ka-band (27–40 GHz). At ‘down-state’, the switch is designed in a state of self-resonance to obtain high isolation. The measured isolation is better than 20 dB over Ka-band and can reach 35 dB at its self-resonant frequency of 35 GHz. The measured actuation voltage is about 36 V. The measured lifetime is at least 5.76 × 10⁷ cycles. The measured power handling capability can reach up to 39 dBm. The proposed compact RF MEMS capacitive switch possesses excellent performances in terms of low insertion loss, high isolation, long lifetime and high power handling capability.