A wideband low-profile slot-loop antenna is proposed based on an artificial magnetic conductor (AMC) reflector which is applied to a slot-loop antenna to obtain directional radiation patterns. Compared with an antenna using a metal reflector, the AMC reflector can reduce the profile of the antenna and enhance operating bandwidth. The AMC consists of 4 × 6 patches with ring slots and slits. A coplanar waveguide is introduced to the proposed slot-loop antenna so that the antenna can directly attach to the AMC surface. Thus, a low profile of 0.05λ_L is realised (λ _L is the wavelength at the lowest operating frequency). Simulation and experimental results indicate that the proposed antenna obtained a 37.9% impedance bandwidth, a 36.7% 3-dB gain bandwidth, and a 6.85 dBi peak gain.

A microstrip patch antenna with circular polarisation is presented by using an intrinsically asymmetric 3D-printed substrate. Unlike conventional circularly polarised (CP) antenna, the perturbation for generating CP waves is caused by the asymmetry of substrate, where a pair of triangular air insertions is symmetrically etched in one of diagonals of the square substrate. Besides, a slot is etched on the centre of patch and parallel to its side for good impedance matching. Actually, in consideration of the fact that in 3D printing, the dimensional tolerance for dielectric is less than the one for metal, the presented approach has more superiority than the conventional methods. A prototype is fabricated and measured. Measured results are found in reasonably good agreement with the simulated ones. Stereo lithography apparatus technology is here employed in the 3D printing process.

A novel miniature wideband microstrip antenna is presented. The proposed miniature design is achieved by exploiting the idea of a quasi-radiator. Here, a part of the radiator is connected to the ground plane through a shorting pin or via. The proposed antenna achieves a starting frequency of 1.8 GHz with a small antenna area of 20 mm². An electrical size of 0.05λ is realised leading to a miniaturised design. The proposed antenna is broadband, compact, and produces stable radiation patterns.

A purely radio-frequency wireless sensor capable of measuring physical parameters with a very low energy consumption is presented. By integrating a capacitive temperature sensor (a change in temperature is traduced by a change in a capacity value) to a very narrowband antenna, the antenna operating frequency band becomes controlled by the surrounding temperature that translates it, depending on its value. By making sure that there is a bijection between the surrounding temperature and the antenna operating band in the considered two ranges, there is no need to use any digital data to wirelessly transmit the information about the temperature. In this case, an important energy consumption reduction could be achieved since the whole wireless sensor would be composed of only a wideband pulse generator and the sensor antenna that selects the band to transmit based on the temperature. To demonstrate the concept, a prototype has been built by modelling the capacitive sensor with a varying capacitance. Both simulated and measured results show a reasonably good agreement which validates the concept.

To date, the authors are not aware of an in-depth investigation about embedded applications of the convolutional neural network (CNN) algorithm on small, lightweight, and low-cost hardware (e.g. microcontroller, FPGA, DSP, and Raspberry Pi) applied to detect faults in structural health monitoring (SHM) systems. In this Letter, the authors implement and evaluate both feasibility and performance of an embedded application of the CNN algorithm on the Raspberry Pi 3. The CNN-embedded algorithm quantifies and classifies dissimilarities between the frames representing healthy and damaged structural conditions. In a case study, the CNN-embedded application was experimentally evaluated using three piezoelectric patches glued onto an aluminium plate. The results reveal an impressively effective 100% hit rate. This performance may significantly impact the design and analysis of CNN-based SHM systems where embedded applications are required for identifying structural damage such as those encountered by aerospace structures, rotating machineries, and wind turbines.

MRI for patients with implanted medical devices is usually restricted due to the heating hazard arising from the interaction between the device and the electromagnetic field generated by the RF coil. RF coils used clinically have diverse dimensions and their heating effect remains unexamined. By numerical simulation, the similarity of the phantom magnetic field distribution of various coils was characterised by regression, and the heating around a standard implant was examined by correlation analysis. It was shown that the magnetic field distributions in the phantom were similar (>0.95) in the central area. This similarity was more significantly affected by the coil length rather than the diameter. As for the RF heating, the temperature distributions at the implant tips were much more similar (>0.9999) across all the coils. Although there were some differences in the temperature rise per unit RF magnetic field, these differences were within 20%, especially in the central region. These data reveal the influence of coil dimensions on the RF heating.

An efficient dual-mode input and output transceiver scheme is proposed. The transceiver can achieve the data speed from 0.5 up to 4.4 Gbit/s with 0.6 V supply voltage and can support the near-ground mode for low-power memory interface application. The transceiver can transmit both PAM4/NRZ signals flexibly depending on the channel loss conditions. The prototype bi-directional two-channel transceiver is implemented in 45 nm CMOS process and occupies 0.0516 mm² chip area. The IP shows power consumption of 2.24/2.78 mW during 4.4 Gbit/s PAM4/NRZ mode operation, each, respectively.

A real-time temperature detection circuit with 0.1°C accuracy is presented. The temperature sensor is composed by a current controlled oscillator (ICO). Its oscillating frequency is proportional to the temperature but independent with the power supply. The frequency change will be digitised by a counter and thus realise the temperature detection. The detection accuracy is limited by the linearity of ICO. In order to improve temperature detection accuracy, a temperature segmentation algorithm is proposed. The temperature sensor is implemented with 0.18 μm CMOS technology and the core area is 0.023 mm². The power consumption of the proposed sensor is 0.3 mW with 1.8 V supply. Experimental results show that this sensor can detect the temperature from −40 to 125°C with 0.1°C accuracy and the detection error is within ±0.8°C.

A new scheme for CMOS-based fluorescence lifetime imaging with hardware-level exponential-to-linear conversion is proposed. The exponential relationship between drain current and drain-to-source voltage in a subthreshold MOSFET is explored for linearisation of the photocurrent generated during a fluorescence decay. Simple measurement of the resulting slope, either through voltage or time measurement, provides lifetime information in a single excitation cycle. The scheme is less sensitive to time and voltage errors compared with charge modulation techniques and are suitable for applications, where high-frame rate and rapid extraction are desired.

This Letter presents an inverter-type time amplifier (TA)-based phase noise filter (TAPNF) with 8 dB phase noise suppression and −133 dBc/Hz phase noise sensitivity at 1 MHz offset. The phase noise improvement strategy, low noise TA design and power consumption reduction techniques are presented. The TAPNF is fabricated in a 65 nm CMOS process with 1.4 mm × 1.6 mm chip area and consumes 50 mW power. To authors’ best knowledge, the TAPNF achieves the best phase noise and figure-of-merit compared with state-of-the-arts with similar technologies and carrier frequencies.

The authors present the realisation and characterisation of an additively manufactured (AM) microwave resonator cavity for double-resonance (DR) vapour-cell atomic clocks. The design of the compact microwave cavity is based on the loop-gap resonator approach, previously demonstrated for conventionally-machined aluminium components. In the present study, the resonator is fabricated by AM using a metal-coated polymer. A resonance frequency at the desired 6.835 GHz rubidium atomic frequency is obtained. When employed in an atomic clock setup, the AM cavity enables a DR signal of <500 Hz linewidth and of nearly 20% contrast, thus fulfilling the stringent requirements for DR atomic clocks. A clock short-term stability of 1 × 10⁻¹² τ ^−1/2 is demonstrated, comparable to state-of-the-art clock performances.

A low insertion loss (IL) analogue predistorter using non-linear composite right–left-handed transmission line (CRLHTL) is presented. The proposed predistorter consists of two symmetrical CRLHTL unit cells. In the experiment, this predistorter can achieve about 2.2 dB gain expansion and 17° phase shift during 4.4–4.5 GHz with only 4.3 dB IL. A C-band 40 W solid-state power amplifier observes 8.1 dB enhancement in the intermodulation at −6 dB output power backoff when linearised by the proposed predistorter.

The introduction of a compact switching architecture in the design of a monolithic microwave integrated voltage-controlled oscillator (VCO) is described, that is able to provide enhanced characteristics in term of both linearity and tunability. The proposed solution is applied to the design of a C-band GaAs MMIC (monolithic microwave integrated circuit) VCO. The chip has been realised with the heterojunction bipolar transistor (HBT) HB20M technology process provided by UMS Foundry. Measurements show a relative tuning range of about 30%, an average sensitivity of about 83 MHz/V, a minimum output power of 11.4 dBm and a phase noise at 100 kHz of frequency offset from the carrier lower of −107 dBc/Hz.

A low-temperature co-fired ceramic (LTCC) filtering power divider with harmonic suppression is presented. It is composed of three resonators and one resistor. By using 3D technology, the two output resonators are symmetrically coupled to the input resonator to obtain the power splitting response. Each splitting path is composed of two resonators to achieve the filtering response. The resistor for isolation is located on the top layer and connected to the two output ports by vertical strips on the side walls. The broadside couplings between resonators produce required passband and stopband. A compact filtering power divider with the core size of 0.122λ _g × 0.1λ _g × 0.059λ _g is implemented. Good filtering, power splitting and isolation performance are achieved. What is more, the second harmonic is successfully rejected below 20 dB without any extra circuit.

The authors compare transmission reach of 100 Gb/s four-level pulse amplitude modulated signals over single-span systems constructed with three optical fibre types. They demonstrate reach up to 160 km with fibres having ultra-low attenuation, one with a large effective area.

The continual increase in demand for extremely high data-rate systems spans the full range of network systems from local area networks to long-haul systems. While coherent optical systems dominate the long-haul market, there is significant interest in using simpler direct detection systems for application areas, where simplicity and lower-cost is a key driver. Pulse-amplitude modulation (PAM) is appropriate to consider as it enables the reduction of the channel symbol rate for a given data rate, without unduly increasing the complexity of the system. A route to the design of optimum post-detection filter for PAM systems is presented that offers significantly improved robustness to timing jitter, which is an impairment of increasing import as symbol rates are increased.

A novel optimisation method for designing new and highly complex mode converters is presented. Owing to the complex relationship between the structural parameters and the output performance merit factor, it is very difficult to obtain a general algorithm. As a case study, a mode converter with eight structural parameters is designed with the proposed method. Owing to a large number of structural parameters and complexity of the designing process, the problem is formulated and optimised by using a recent optimisation algorithm called Grey Wolf Optimiser. Six optimal mode converter designs are obtained for LP₀₁–LP_0m (m = 2, 3,…, 7). These optimal designs outperform existing state-of-the-art designs. Furthermore, achieving these results is done without any human involvement.

A hollow-waveguide-output uni-travelling-carrier photodiode (UTC-PD) module operating at frequencies from 400 to 900 GHz has been developed. The module consists of a UTC-PD, a photodiode-to-waveguide coupler, and a metallic package with a waveguide rectangular (WR)-1.5 rectangular waveguide. The coupler is monolithically integrated with the UTC-PD chip. The fabricated module exhibits the output power as high as −19 dBm at 500 GHz and the 3 dB bandwidth of 340 GHz, which is the widest among ever-reported photodiode modules.

A single-sideband opto-RF oscillator based on a monolithic InGaAsP chip containing two distributed feedback (DFB) lasers is demonstrated. The heterodyne signal is stabilised by a hybrid method, combining optical and electronic feedback. It leads to a locking of the beating frequency onto a filtered version of itself. The table-top setup provides a phase noise level down to −75 dBc/Hz at 1 kHz offset from a 10 GHz carrier. Potential phase noise improvement and integration scheme in a single component are discussed.

The authors propose and demonstrate a photonics-based wideband Doppler frequency shift (DFS) measurement scheme through in-phase and quadrature detection. The system has a compact structure applying cascaded phase modulation and polarisation modulation. It is easy to implement since both the value and sign of the DFS can be estimated by simple signal processing. More importantly, the proposed scheme is suitable for both DFS measurement and direction discrimination over a very wide frequency range. In the experiment, accurate DFS measurement with a large carrier frequency range from 5 to 40 GHz is demonstrated with the measurement error kept within ±12 Hz.

A new step-up DC–DC converter is presented, based on quasi-Z-source network intended for photovoltaic applications. The proposed converter combines voltage multiplier cells to the secondary winding of the coupled inductor which is included in the second inductor of the quasi-Z-source network. In the output of the quasi-Z-source network, a switched capacitor is connected. This converter shows attractive characteristics such as high voltage gain, low voltage stresses on their components, continuous input current. A detailed description of the operating principles of the proposed converter is presented and experimental results on a 250 W prototype show that a high efficiency above 91.4% can be achieved.

This Letter addresses the coherent integration problem for air and space moving target detection in a staggered pulse repetition interval (PRI) radar system. In this algorithm, a range-compressed signal is firstly transformed into the one in the range frequency domain, and then the authors resample the non-uniformly sampled signal into a uniform grid along azimuth direction. Subsequently, the well-known Keystone transform is applied to compensate the range cell migration caused by target motion. Finally, a moving target can be well focused in the range-Doppler domain after motion compensation. Simulated results are provided to validate the effectiveness of the proposed algorithm.

The radar cross-section (RCS) measurements for cylinders with different surface roughness have performed in the terahertz bands. The terahertz radar system has 220 and 440 GHz carrier frequencies. It is a solid-state system whose base band signal is generated by a phasor network analyser. The original recorded data are calibrated by the results of the smooth surface cylinder. These calibrated RCS results are compared with calculated results. The experiments suggested that targets with the rough surface will provide complicated scattering in terahertz. The results of this experiment can prove that the surface roughness of the target has a certain impact on RCS measurement results in the terahertz band.

A novel programmable negative differential resistance (NDR) device based on the field-effect diode is proposed. The field-effect diode (FED) is a gated diode and compatible with semiconductor on insulator (SOI) CMOS technology. Semiconductor device simulator tools are used to simulate the structure of the FED. Then, it is employed to design the programmable NDR device. The operating principles of this new device are similar to the comparable MOSFET device. The proposed design is a unique device that consists of only three transistors and can be programmed by an isolated gate.

In this Letter, the authors propose an approach to evaluate the average signal-to-clutter ratio loss (ASCRL) of an adaptive radar filter with a parametrically constrained clutter covariance matrix (CCM). The approach is a two-step strategy, the constrained Cramér–Rao bound of the CCM estimate is first derived, and then it is used to derive the ASCRL. More specifically, the ASCRL of an adaptive filter with a trace constrained CCM is derived. Simulation results show that our approach performs well in evaluating the trace constrained ASCRL for both complex Gaussian clutter and compound-Gaussian clutter.

A novel key-dependent audio fingerprinting technique is proposed by introducing the quantisation minimum distance (QMD) as a hash extractor in the discrete wavelet transform (DWT) domain. The quantiser dithers of the QMD are generated using a chaotic map whose initial value is used as a secret key for fingerprint extraction. Experimental results show that the proposed audio fingerprinting technique achieves with a small fingerprint size an excellent discrimination between audio signals of different contents and outperforms the existing Philips robust hash based techniques in terms of the robustness.

In a given speech signal, transition at the vowel offset points (VEPs) is quite different when compared to the vowel onset points (VOPs). Consequently, most of the features reported for the detection of VOPs fail to detect VEPs. To address this issue, a front-end speech parametrisation approach is proposed for simultaneously detecting VOPs and VEPs. In the proposed approach, first energy due to the high-frequency unvoiced sound units is suppressed by using discrete wavelet transform (DWT). Then, weight values (WVs) are assigned to each of the sample points by computing similarity between the analysis frames within a search neighbourhood using non-local means (NLM) estimation. The WVs computed from the NLM are significantly less when the frames under consideration are similar in comparison to the dissimilar ones. Since vowels are longer regions and exhibit periodicity, there will be more similarity in the case of frames belonging to these regions. In this work, this aspect of the WVs is used as a feature for detecting VOPs and VEPs. The proposed feature is observed to outperform the earlier reported features for the task of detecting VOPs as well as VEPs. The improvement observed in the detection accuracy of VEPs is significant.

Outage events caused by dynamic blockage of a radio signal propagation path are one of the key challenges in 5G millimetre-wave (mmWave) cellular networks. To mitigate them, Third Generation Partnership Project standardisation has recently ratified multi-connectivity techniques aiming to enable user connectivity to several base stations simultaneously, while switching between them whenever the currently active connection becomes blocked. A closed-form upper bound on the probability density function of the respective system capacity in a random field of moving blockers is obtained.

Relay communication has been receiving considerable attention for its advantage of extension in communication coverage and enhancement of communication performance. In this Letter, the author studied the performance of dual-hop communication systems with a decode-and-forward protocol. The author first analyses the performance of dual-hop communication systems with various modulation schemes. Then, the author found the optimum energy allocation depending on the relay location for each modulation scheme. Finally, the performance of dual-hop communication systems with equal energy allocation and optimum energy allocation was compared.