The simulated characterisation and tuning of prototype antennas prior to manufacture is described in this study. The antennas incorporate Schottky diodes so as to frequency triple incident sub-THz power. Such a dual frequency, non-linear, device has been called a multenna. A metrology is outlined for ease of multiple measurements to permit exploring scenarios of multenna element design. Four options are optimally oriented and assembled onto an appropriately dimensioned tile substrate to minimise mutual coupling during characterisation of each element individually. Transmission measurements of the multennas are performed at 100 and 300 GHz: an example of resonant behaviour is presented.

Radiation from antennas integrated with indium phosphide (InP)-based resonant tunnelling diode (RTD) oscillators is mainly through the substrate because of the effects of the large dielectric constant. Therefore, hemispherical lenses are used to extract the signal from the backside of the substrate. In this study the authors present a broadband bow-tie slot antenna with a tuning stub which is diced and mounted on a ground plane to alleviate the substrate effects. Here, the large dielectric constant substrate around the antenna conductor is removed. In addition, the ground plane underneath the diced substrate acts as a reflector and, ultimately, the antenna radiates to the air-side direction. Antenna integration with RTD oscillators is described in this study as well. Two-port bow-tie slot antennas were designed and characterised and showed the suitability of integration with power combining RTD oscillator circuits which are based on mutual coupling. The antennas were fabricated using electron beam lithography on a semi-insulating InP substrate. Simulated and measured bandwidth almost extends the entire frequency range 230–325 GHz. Simulations shows air-side radiation pattern and antenna gain of around 11 dB at 280 GHz. Simulations also show that the antenna may be fed with a 50-Ω or 30-Ω feed line, i.e. suitable feed lines, without compromising its performance which may prove beneficial for optimum loading of RTD oscillators.

A novel spinning disk approach is reported, to achieve video-rate compressive imaging at infrared (IR) and terahertz (THz) frequencies. It uses a 200-mm-diameter circular stainless steel disk with a number of chemically etched 2-mm-diameter holes as a spatial light modulator (SLM). The authors demonstrate that this mechanical SLM is well suited for imaging at both optical and THz frequencies since the stainless steel is opaque to all optical and electromagnetic radiations while the holes are totally transparent. Using a single pair of IR emitter and receiver, the authors demonstrate that the system is capable of capturing a 96 × 96 video sequence at 10 frames/s. The achieved spatial resolution is better than 2 mm using the spinning disk where the diameter of the holes is 2 mm. The authors also present a key-frame extraction method based on this SLM disk, which allows us to capture the shape of a sample even when its size is larger than the effective imaging area of the system.

Vector network analysers (VNAs) are used extensively for measurements that are made at frequencies ranging from a few kilohertz to at least one terahertz. At radio and microwave frequencies, there are well-established methods for assessing the quality and confidence of these measurements, when they are made in coaxial lines. These methods are usually based on determining the size of residual errors that remain in the VNA after calibration. To date, the performance of these methods has not been investigated in rectangular waveguide, and, at millimetre- and submillimetre-wave frequencies. This study investigates the application of one of these techniques for waveguide measurements at microwave, millimetre- and submillimetre-wave frequencies. Typical values of residual errors obtained over these frequency ranges are given, and range from 0.001 to 0.024 linear units up to 220 GHz. Above this frequency, the technique is shown to underestimate some residual errors. The values reported up to 220 GHz are considered representative and so can be used by other users of waveguide VNAs to compare with values obtained on their own systems; therefore, helping to verify the performance of their systems.

The increasing ageing population is leading to a wide-scale demand for health-state monitoring by a wireless body area network (BAN). Wireless BAN needs each vital sensor to act as a wearable device for collecting blood pressure, electrocardiogram (ECG), electroencephalogram and so on in daily life. On the other hand, wireless power transfer is also getting into our daily life because of its convenience, which suggests a potential electromagnetic interference (EMI) problem on the wearable devices in healthcare and medical BAN. In this study, the authors quantitatively evaluated the EMI on wearable ECG for 6.8 MHz wireless power transfer system. They employed electromagnetic field analysis technique to derive the common-mode voltage between the human body with a wearable ECG and the ground plane, and circuit simulation or measurement to derive the interference voltage at the wearable ECG output. The result first time gave a quantitative evaluation for EMI of wireless power transfer on wearable ECG. The approach is also available to be applied to EMI evaluation of other wearable devices in healthcare or medical applications.

This study proposes a range- and angle-dependent directional modulation (DM) scheme using frequency diverse array (FDA) for secure wireless communications. It uses uniform element spacing and symmetrically and non-linearly increasing frequency increments to decouple range- and angle-dependent transmit beampattern for the uniform FDA and DM techniques for secure signal transmission. The transmitted signal symbols are purposely distorted to be unrecoverable at unintended positions, but they could be recovered successfully at the intended position. The proposed method is evaluated by examining the signal-to-noise ratio, detection probability, and bit error rate. Numerical results show that the symmetrical FDA-based method outperforms both the phased-array-based method and the standard FDA-based method in security performance for wireless communications.

Using the concept of a metallic cylinder and a linearly tapered metallic baffle loaded in a circular waveguide to convert TM₀₂ circular waveguide mode into TE₁₁ circular waveguide mode, a novel and compact circular waveguide TM₀₂-TE₁₁ mode converter is designed, fabricated, and measured. The detailed design methods, experimental setups and results are presented in this study. Simulation results show that the purity of output fundamental TE₁₁ mode of the converter exceeds 99.6% for an operating frequency of 9.4 GHz and the power capability is as high as 1.66 GW, the mode conversion efficiency is more than 90% from 9.23 to 9.83 GHz band and the relative bandwidth is about 6.38%. A good agreement between measurements and simulations is observed. The circular waveguide TM₀₂-TE₁₁ mode converter has many advantages, such as the simple structure, coaxial input and output, high conversion efficiency, proper bandwidth and high power-handling capability. When used in the field of high power microwave transmission and radiation, the proposed converter could significantly enhance the compactness of all the radiation systems.

Novel capacitively loaded half-mode substrate integrated waveguide (CHMSIW) filters with transmission zeros (TZs) are presented in this study. The CHMSIW is proposed by embedding a metallic stripline and inductive post in the HMSIW, which introduces a series inductor-capacitor (LC) branch circuit in waveguide thereby generating TZ above the passband. Furthermore, as the embedded stripline introduces additional capacitance, a significant size reduction can be achieved for the CHMSIW in comparison with conventional HMSIW. Two types of CHMSIW resonator topologies are developed by varying the number of LC branches, with multiple TZs achieved by inserting multiple LC branches in waveguide. On the basis of the CHMSIW resonators, compact bandpass filters are designed and fabricated, where TZs are obtained in the upper stopband and a sharp transition is achieved from the passband to the stopband. To further improve the selectivity, mixed coupling is introduced in CHMSIW filters to generate additional TZs in the lower stopband. A prototype of the mixed-coupled CHMSIW filter is designed and tested, and high selectivity as well as compact size and good out-of-band rejection have been achieved for the proposed mixed-coupled CHMSIW filter.

A novel short- and open-stub loaded spiral resonator (SOSL-SR) is presented and analysed by the odd- and even-mode method to obtain three controllable resonant modes. Therefore, a triple-mode bandpass filter (BPF) has been designed with good frequency selectivity based on the proposed SOSL-SR. Then, by dividing these three resonant modes into two passbands or stopbands, a dual-band BPF and a dual-band bandstop filter using the proposed SOSL-SR have been demonstrated. Because of the spiral structure, the sizes of these three designed microstrip filters are reduced significantly. Good agreement between simulated and measured results validates the design concept.

A coplanar waveguide (CPW)-fed octagonal super-wideband fractal antenna is presented. It comprises four iterations of an octagonal slot-loaded octagonal radiating patch, CPW feedline, and modified ground plane loaded with a pair of rectangular notches. An impedance bandwidth of 3.8–68 GHz (179%) – i.e. a17.89:1 ratio bandwidth – is achieved. Desirable radiation performance characteristics, including relatively stable and omnidirectional radiation patterns, are obtained over this range. The experimental and simulation results are found to be in good agreement. The designed antenna has the advantages of wider bandwidth and miniaturised size over the previously reported structures.

A new class of Wilkinson-type power dividers with reconfigurable quasi-elliptic-type filtering characteristics is reported. Their design exploits the connection of resonators to the branches of a Wilkinson-type power divider through impedance inverters that in turn produce power transmission zeros (TZs) at their natural frequencies. In this manner and by making frequency-controllable these resonators, the created TZs can be tuned to attain an adaptive bandpass-filtering/power-division double functionality in terms of centre frequency, passband-width, and stopband bandwidth/attenuation characteristics. Furthermore, bandstop-filtering actions can be generated through this technique in wide-band power divider realisations for the suppression of in-band interfering signals. Key advantages of the proposed filtering power divider include: unequal transmission-band spectral widths and out-of-band power-rejection profiles for the transfer functions of the two power-divider branches, as well as the intrinsic switching-off of one or both of them. The theoretical foundations of the engineered fully-tunable filtering power divider and its corresponding RF design guidelines are expounded in this work. In addition, a UHF-band microstrip prototype is manufactured and characterised for practical-demonstration purposes.

This work investigates the available ambient radio frequency (RF) power density in dynamic, outdoor environments with a specific focus in the uplink. A spectrum survey was carried out around Bristol, UK between 500 MHz and 3 GHz using a handheld spectrum analyser and an omnidirectional broadband discone antenna. Measurements were performed while walking, travelling in a car and on a train. The results are compared with baseline indoors measurements, and as expected, ambient RF power densities in the outdoor environments were significantly higher. Interestingly, in some cases the power contained in the uplink of cellular communication networks is shown to be a better energy source than the downlink. It was found that in a train during rush hour, there is 17 times the mean power density and 45 times the peak power density in the uplink compared with the downlink. This shows that there is scope for ambient energy harvesting in environments with a large density of user equipment. Finally, by accounting for the rectifier efficiency it is estimated that during the train commute between Bristol and Bath in the UK a total of 27.2 mJ of energy could be collected.

The authors showed in a previous work that it is possible to transmit N signals without crosstalk or return loss through a lossless multiconductor transmission line (MTL) of N + 1 conductors. Such algorithm can increase the data rate twice (in the absence of noise), relative to the usual transmission of differential signals. In this work, they analyse lossy MTLs and test the above algorithm on the lossy lines.

A metallic, dual-band, dual polarised slot-based transmitarray antenna is presented. The antenna consists of three thin metallic layers do not use any dielectric substrates, with air gaps in between the layers. The unit cell uses interleaved orthogonal slots, as well as crossed-dipole slot and uniplanar compact photonic bandgap slot elements to provide the lower and upper frequency band resonators, respectively. The frequency separation between the two resonances can be adjusted from closely spaced to far from each other. The antenna provides dual linear polarisation and circular polarisation with the use of the appropriate feed. The fabricated transmitarray antenna provides two independent frequency bands with a band ratio of 1.13 and low mutual coupling. The measurement of a 14 × 14 element transmitarray antenna at 11 GHz shows a maximum gain of 23.74 dB with −1 dB gain bandwidth of 6.8% and aperture efficiency of 38%; at 12.5 GHz, a maximum gain of 24.45 dB is obtained with −1 dB gain bandwidth of 5.4% and aperture efficiency of 34.6%. The antenna is simulated by using the CST software; the ADS package is used for equivalent circuit simulation.

This study presents integration of transistor based inductive source degeneration and specially shielded transformer into a millimetre-wave power amplifier (mm-wave PA) operating at wideband. A new configuration of high Q distributed inductor is devised and embedded in CMOS transistor source to enhance stability, maximum stable gain and bandwidth of mm-wave CMOS PAs. The source inductance selection is conveniently investigated by the proposed admittance matrix condensation. In power splitting and combining part, a novel X-shape pattern-ground shielding is inserted in high turn ratio transformer to ameliorate wideband matching. Based on these techniques, a fully differential mm-wave PA was implemented in 65 nm low-power CMOS with 0.25 mm² core area. The measurement results show that its differential drive gain and common mode rejection ratio are above 10 and 26 dB, respectively, in a wide frequency range of 41 to 61 GHz, while the power added efficiency (PAE) is still above 10.8% at 46–62 GHz. This CMOS PA also achieves 11.9 dBm output referred 1-dB compression point (P _1 dB) and 15.2 dBm saturated power (P _sat) with 12.4% peak PAE.

This study presents a hybrid electromagnetic isolation mechanism in a transceiver array antenna operating at 5.8 GHz. Maximum isolation between transmitting and receiving array antennas, at a very close spacing (3 mm = 0.058λ ₀), and minimum mutual coupling between each array elements is achieved without antenna radiation pattern degradation. The achieved separation is equivalent to 44% size reduction compared with conventional half wavelength spacing criterion. Each of the transmitting and receiving array antennas is a four-element linear microstrip patch array antenna. The employed hybrid isolation technique is composed of defected ground structure, to minimise coupling between array elements, and uniplanar electromagnetic bandgap, to minimise the coupling between the transmitting and receiving antennas. The resulting transceiver array antenna system fulfils −35 dB mutual coupling between array elements, and 60 dB isolation between opponent transmitting and receiving array antennas. The proposed design procedures are discussed and analysed using electromagnetic full wave simulations. Results were verified through experimental measurements for reflection coefficient, mutual coupling and radiation characteristics in which a good agreement with simulated results is granted.

Coupled oscillator arrays (COAs) can be used to control the phase distribution across the aperture of an array antenna in such a manner as to affect steering of the beam without the use of phase shifters. Given the various possible planar configurations of COAs, a systematic design approach is necessary. In this study, the authors present a comprehensive comparison of various configurations of planar COAs based on their sensitivity to random errors in their free running frequencies. The parameters considered are (a) the beam pointing error of the array, (b) the locking probability, (c) the side lobe level, and (d) the beam width of the radiation pattern. These results can serve as a design strategy for choosing optimal configurations of planar COAs based on the needs of each particular application.

Radio-frequency identification (RFID) systems with ‘peel-and-stick’ labels are currently limited to tracking items with nearly electromagnetically transparent material properties. This limitation stems from the antenna choice for these labels – a dipole variant. A ground plane edge treatment along with a feed slot with unique tuning capabilities is investigated as an alternative RFID antenna option. Ease of fabrication was maintained as a priority in all design decisions. The measured antenna displays true placement insensitivity with a constant impedance when attached to metal, lossy dielectric, or electromagnetically-transparent objects.

This comment demonstrates that in a recent study by Bhattacharyya et al., a linear reflective polarisation converter is erroneously interpreted as broadband absorber. It is clearly shown that the incident electromagnetic wave is reflected with its orthogonal polarisation state due to which co-polarised reflection is reduced. Total absorption, when both the co- and cross-polarised reflected components are considered, is less than 20% in the operating band claimed by the authors.