This study brings out the design, fabrication and performance evaluation of a compact, dual band antenna on paper substrate. The two bands of operations are 2.18 to 2.50 and 5.22 to 5.72 GHz. These bands are used by the wireless sensor networks (WSNs) and radio frequency identification systems (RFID). The antenna becomes useful for the WSN nodes and RFID systems at these frequencies. The overall size of the antenna is 40 mm × 20 mm × 0.6 mm, which makes it a compact one. Antenna was tested for the effect of bending by placing it over curvilinear surfaces. The bending was done in horizontal (X) and vertical (Y) axes. These examinations will help to understand the effect of wind loading and other packaging related bending on antenna performance. The main features of this antenna are stability in performance under bent conditions, simple configuration and low cost of fabrication. A thin polyethylene layer has been used to laminate the antenna for permanence. The effect of lamination has also been explained in the course of the study.

Here, the authors formulate second-order cone programs (SOCPs) for synthesising complex weights for far-field directional (single-point mainbeam) patterns for narrowband arrays. These formulations, while constructed here with the uniform circular array (UCA) in mind, are actually quite general in that they control the arbitrary-pol sidelobe level (SLL) and co-pol signal-to-noise ratio loss relative to ideal by minimising either while upper bounding the other. The SLL can be addressed in either an L-infinity sense or an L1 sense, and elements are assumed characterised by individual embedded complex patterns, modelled or measured, and so need not be identical. Conformal arrays are the obvious application, but we leave that for others and here instead apply the SOCPs to UCAs of directional elements. Design examples assume an antipodal Vivaldi element design with an embedded element pattern obtained through simulation using appropriate unit-cell boundary conditions. Rotation and translation of that simulated pattern provides embedded element patterns for all elements of the circular array.

A two-stage common-source (CS) low-noise amplifier (LNA) that uses a forward-body-bias technique in N-type metal–oxide semiconductor devices and intended to achieve a high gain and low power consumption is proposed in this study for ultra-wideband (UWB) applications. Its first stage yields an exceptionally high gain because of high transconductance (g _m1 = 16 mS) of the input device. It also shows simultaneous wideband input matching and low-noise figure (NF) characteristics with the aid of source degenerated inductors. A simple source degenerated CS topology with the shunt-peaking inductor L _d2 is designed as the second stage to enhance the gain response at high frequencies. Using a standard 90 nm complementary metal–oxide semiconductor process, the proposed UWB LNA achieves a gain S ₂₁ ≥ 20 dB in the frequency range of 3.1–10.6 GHz, while consuming only 12.6 mW power from a 0.6 V supply voltage. The simulation results show a minimum NF (NF_min) below 1.7 dB in the frequency range of 3.1–10.6 GHz and input return loss S ₁₁ < −10 dB in the frequency range of 3.5–10 GHz. When a two tone test is performed with a frequency spacing of 2 MHz, a high value of third-order input intercept point of −8 dBm is also achieved.

Water antennas are a special type of antennas and have attracted limited attention so far. In this study, a monopole water antenna with a dielectric layer is chosen as an example to study some less obvious characteristics of the water antenna. The resonant frequency, radiation efficiency and fractional bandwidth are of particular interest. Firstly, the effects of the dielectric layer between the water and the ground plane are studied. The results show that this layer has a crucial effect on the antenna resonant frequency and radiation efficiency. Secondly, the water with different conductivity is investigated. With different conductivity, the antenna may be regarded as a dielectric resonant antenna, a conducting antenna or their combination. Thirdly, a water antenna with a supporting structure is fabricated for validation. Measurements are conducted in an anechoic chamber and a reverberation chamber to evaluate its performance as a function of various parameters. Finally, the water temperature electromagnetic characteristics are investigated. Good agreements are achieved between the simulation and measurement results. It is shown that this type of antenna shows better performance than the conventional antenna in aspects such as broadband, cost, reconfigurability, transparency and it can be a promising candidate for a range of applications.

Three active cold load circuits operating at millimetre-wave frequencies are presented. The circuits have been manufactured using 100 nm metamorphic high electron mobility transistor technology. On-wafer measurements of noise temperature and match are presented. Measured noise temperatures are 75 K, 141 K, and 170 K at 31.4 GHz, 52 GHz, and 89 GHz, respectively. Measured reflection coefficients are better than −19 dB for all designs.

This study presents a novel approach to the design and implementation of transmission-type negative group delay (NGD) networks based on a coupled line doublet structure. To improve the reflection coefficients, a quarter-wavelength transmission line is connected between the input and through ports of a coupled line section. For the doublet structure, two coupled line sections are arranged in a symmetrical manner by connecting them back-to-back with the help of the quarter- wavelength through line. For the experimental demonstration, two planar NGD networks (unmatched and matched doublet NGD networks) are designed, simulated and measured at a centre frequency of 2.14 GHz. From the measurement, a group delay (GD) of −5.66 ns and signal attenuation (SA) of 18.78 dB were obtained in the case of an unmatched NGD network. Similarly, for the matched NGD case, a GD of −6.33 ns, SA of 20.69 dB and input/output return losses >29 dB were obtained at the centre frequency.

A wideband circularly polarised array antenna consisting of 10-element bowtie dipole antenna and feed network is presented. A narrow patch connecting the pair of bowtie dipoles as an entity is employed to achieve high gain. To obtain wideband and flat-top beam of radiation patterns, amplitude and phase distribution along the feed are optimised by application of the Self-adaptive Differential Evolution algorithm. Particularly, the feed network with broadband phase shift performance is designed to satisfy bandwidth requirement ranging from 1.1 to 1.6 GHz. The proposed antenna can achieve an excellent impedance matching and Axial Ratio characteristics over the entire operating band. Moreover, the ripple of co-polarisation radiation pattern covering ±12° in the elevation plane is better than 0.92 dB; whereas the gain is also better than 11.8 dB and the side lobes are below −13 dB. Measured results validate the design concept and indicate that the proposed array exhibits good radiation characteristics.

To implement full-wave simulation of electromagnetic wave impinging invisible cloaks, an efficient multidomain pseudospectral time-domain algorithm is developed in this study. The proposed method solves the same forms of Maxwell's equations in both the regular and cloaking areas, and then applies different methods to update the electric and magnetic field components, respectively. The new method requires less grid points per wavelength, meanwhile, the multidomain strategy relieves the complicated treatment of electric and magnetic field components based on Yee grids within finite-difference time-domain methods, and shows advantage of dealing with internal inhomogeneities within the cloaking materials. The results validated feasibility and efficiency of the proposed method in left-hand materials.

Two novel bandpass filters with multiple transmission zeros using open/shorted stubs are presented in this study. By utilising shorted coupled lines and the open/shorted stubs, five and eight out-of-band transmission zeros can be realised for the two bandpass filters from 0 to 2f ₀ (f ₀ is the centre frequency of the passband). Five and eight transmission zeros can be adjusted freely by only changing the electrical length of the open/shorted stubs. Two planar bandpass filters (3-dB fractional bandwidths 7.44%, 3.88–4.18 GHz and 7.5%, 3.85–4.15 GHz) are designed and fabricated. The theoretical and measured results all show good in-band filtering performances and high selectivity.

An efficient method for wide-band electromagnetic (EM) scattering properties analysis of three-dimensional arbitrarily shaped perfectly electric conductor (PEC) objects is proposed in this study. The electric field integral equation (EFIE) is solved by the method of moments (MoM) base on the loop-tree basis functions. The EM properties not only can be achieved accurately in high frequency band, but also in low frequency band within the desired bandwidth using loop-tree basis functions. To improve the computation efficiency, the Maehly approximation method is utilised. Compared with the direct solution method and asymptotic waveform evaluation technique, the proposed technique is found to be efficient in a broadband and wide angular domain with the lower central processing unit time required and without loss of accuracy.

This study presents a hybrid technique for the analysis of circular waveguide junctions loaded with axially symmetrical ferrite posts of irregular shape. The method is based on a combination of the finite-difference frequency-domain technique with a mode-matching technique. The proposed approach is validated by comparing the presented results with numerical ones obtained from commercial software. The application of a cylindrical junction loaded with ferrite posts with reciprocal and non-reciprocal devices is presented and discussed.

The transmission-line matrix method enhanced with the compact wire model in a cylindrical grid is used for modelling of a coaxially loaded cylindrical cavity resonator with probes inserted into the cavity. Benefits of using a cylindrical grid instead of rectangular, related to precise modelling of cavity boundaries, a coaxially shaped dielectric sample and radially placed wire elements, are explored. The accuracy of the simulated results is verified by measurements of an experimental model of the cavity-wire structure.

To investigate the effects of both the drain and gate bias voltages on the performance of GaN high electron-mobility transistors (HEMT) oscillator, a 0.25 µm GaN-on-SiC HEMT oscillator is presented in this study. Utilising the designed oscillator, the trade-off between phase noise and output power is effectively investigated at the circuit level. As a result, the designed oscillator can provide low phase noise and medium output power simultaneously. The phase noise at V _GS = −2.3 V and V _DS = 3.3 V is measured to be −112 dBc/Hz and −143 dBc/Hz at 100 kHz offset and 1 MHz offset, respectively, from a 4.954 GHz carrier, with an output power of more than 14 dBm. Moreover, the output power can be boosted to 26 dBm, if a drain bias 16 V is used, while good phase noise of −132 dBc/Hz @ 1 MHz is still achievable. The achieved phase noise is low among all reported GaN HEMT oscillators. This work has successfully demonstrated that the monolithic oscillator fabricated in GaN-on-SiC HEMT technology features low phase noise as well as medium output power simultaneously.

A novel millimetre wave waveguide diplexer topology that can be fabricated using relaxed fabrication tolerances is presented. This is achieved by using a highpass filter/hybrid coupler topology in addition to a low order capacitive iris bandpass filter. By targeting the most sensitive centre resonators in the bandpass filter and increasing their length to full wavelength, the sensitivity to fabrication errors associated with changes to the resonator length can be reduced without the introduction of spurious responses close to the passband. The main benefit of this topology is that only one bandpass filter is required to realise the final diplexing response. This is advantageous when tolerance is considered as it is found that resonating structures associated with bandpass filters contribute to tolerance effects. In addition to this, the authors find that the choice of iris discontinuity used to realise the impedance inverters in the bandpass filter can help to relax fabrication tolerances. By subjecting the proposed circuit to a tolerance analysis, simulated results suggest that the circuit can be fabricated with relaxed fabrication tolerances. These discussions are verified with the fabrication of a Ka-band waveguide diplexer, where the measured and simulated scattering parameters are in very good agreement.

Annular through-silicon via (TSV) is one of the promising solutions for vertical interconnects in three-dimensional integration, which diminishes mismatch effects of the coefficients of thermal expansion between two different materials and saves cost, as compared with other TSV structures. In this study, an analytical impedance model is proposed. Closed-form formulas for calculations of the per-unit-height resistances and inductances are derived by calculating the electromagnetic field quantities in the cylindrically multilayered media, via solving the longitudinal current densities in the conducting layers. Combining with the conventional admittance model, a compact transmission line model is obtained, which can be used to model the electrical properties of annular TSVs. These formulas appropriately capture the real current distribution because of skin effects in metal conductors as well as the eddy current loss in semiconductor regions. The results from these analytical formulas have comparable accuracy as those obtained by the full-wave solver in a wideband frequency range, yet much higher computational efficiency than existing modelling methods.

This study presents the design of water-loaded metal diagonal horn antenna at 2450 MHz along with simulation and experimental studies of specific absorption rate (SAR) and temperature distributions in a bio-medium (muscle) in direct contact with the water-loaded antenna for hyperthermia application. The metal diagonal horn is a multimode horn antenna, with identical aperture field distribution in the E- and H-planes. The SAR distribution in a phantom muscle in direct contact with water-loaded horn antenna measured at 2450 MHz is nearly in agreement with the corresponding simulated distribution. The simulation results for SAR distribution owing to diagonal horn are also compared with those owing to square aperture horn/box horn, of same aperture cross-section/broader dimension as the diagonal horn at 2450 MHz. The results indicate that the diagonal horn provides higher penetration depth/better transverse resolution over square aperture horn/box horn. In addition, the proposed diagonal horn provides circularly symmetric effective field size. Finally, thermal simulation results are also provided for the proposed applicator, which is in direct contact with a realistic model of muscle medium without and with small spherical as well as oval-shaped tumours of different dielectric properties embedded within the muscle medium.

A compact multiple-input multiple-output (MIMO) antenna with a small size of 26 × 55 mm² and low correlation has been proposed for the ultra-wide-band (UWB) applications operating over a frequency range of 3.1–12.3 GHz at −10 dB. The MIMO antenna consists of two identical elements each of which has a planar radiator with microstrip-fed over half-sized ground plane. The antenna elements are placed orthogonally to achieve a good isolation between the two input ports. The antenna's characteristics such as the bandwidth, isolation, radiation pattern, peak gain and surface current distributions have been investigated. Moreover, diversity performance in terms of envelope correlation coefficient and mean effective gain has been analysed. Furthermore, a parametric study has been carried out to provide more design information. An arrangement with quad-elements has been designed for MIMO operations, as well. The simulation and measurement results show that the proposed antenna has an impedance bandwidth larger than the frequency range of UWB with low correlation and high diversity performance. The proposed MIMO antenna has been compared in detail with the previous works reported elsewhere in terms of antenna size, geometric complexity, bandwidth, mutual coupling and use of additional structure to obtain more isolation. From this point of views, the antenna is more preferable than other suggestions.

The semi-active laser /millimetre wave (MMW) beam combiner design methods including the MMW transmission structure design method and laser diffuse surface design method were proposed. The transmission line theory was adopted to design the MMW transmission structure. The Lambert's law assumption was adopted when the diffuse reflection surface of the beam combiner was designed. In the aim of illustrating the design methods, a thin plate beam combiner design case was given to meet the performance requirements which were proposed according to the test requirements of the unit under test. In order to validate the MMW transmission structure design method, a prototype made of polytetrafluoroethylene was fabricated and it was tested in a Ka band compact range anechoic chamber. In order to evaluate the laser reflection performance, the laser reflection performance at a wavelength of 1.064 μm was also tested and analysed by an empirical bidirectional reflectance distribution function model.

A channel sounder based on the cross-correlation properties of pseudo-noise random sequences, known as swept time delayed cross-correlation channel sounder, is presented. This sounder enables the characterisation of doubly selective channels, providing both amplitude and Doppler spectra information. It performs real-time measurements of specific radio channels with a high resolution of 2 ns for adjacent multipath component, and a current maximum Doppler spread of ±100 Hz, but that can go beyond ±1 kHz, if some components are upgraded. The amplitude measurements given by the sounder, presented as power delay profiles, have a dynamic range of about 35–40 dB. This study provides detailed information on the most relevant components used to develop the sounder, and presents some of the calibration measurements performed on the bench, as well as specific radio frequency measurements at 18.7 and 60 GHz in a controlled environment. Finally, improvements that are feasible to be implemented in the near future are proposed.

This study presents the application of a differential six-port reflectometer to the design of a portable system for measurement of the dry rubber content (DRC) of latex. The proposed DRC measurement system consists of a 1 GHz reflectometer used with an open-ended coaxial-probe sensor, a temperature sensor, a display and a microcontroller. The complex permittivity and temperature of the rubber latex are measured, and a temperature-dependent model for DRC determination based on a dielectric mixture theory is used. The reflectometer performance is verified by comparing the measured complex permittivity with the results obtained from a commercial dielectric measurement system. Finally, the accuracy of the DRC measurement system is assessed by comparing the measured DRCs from different latex samples over the range of 10–40°C with the standard oven-drying method.