In this Letter, a symmetric feeding network is proposed for constructing circular polarisation (CP) reconfigurable antennas. The proposed feeding network is based on the sequentially rotated serial feed with three outputs, which has been employed for circularly polarised antennas, extensively. The reconfigurability is obtained by using an additional line and bias circuits. A circular patch antenna is stacked on the proposed feeding network, designed for the frequency band 2–2.3 GHz, to obtain a wideband CP reconfigurable antenna. The performance of the proposed reconfigurable antenna is validated using simulation and measurement results.

In this Letter, a dual-polarised aperture-coupled microstrip patch antenna with low cross-polarisation and high isolation is presented. A microstrip patch antenna is designed and fabricated to meet the multifunction phased array radar requirements. The proposed single element is fabricated and the measurement results along with simulation results have been presented, showing the performance of the designed single element. An input isolation of better than 50 dB and a cross-polarisation level of <−30 dB are achieved in the measurements.

An attempt has been made in this Letter to analyse term (week of gestation (WOG) >37) and preterm (WOG ≤ 37) conditions using uterine electromyography (uEMG) signals and generalised Hurst exponent (GHE) features. For this analysis, public database signals recorded from the surface of abdomen are considered. Multifractal detrended fluctuation analysis is performed on the signals and the GHE is calculated. From the exponent, seven features are extracted and data-balancing based on synthetic minority over-sampling technique is used to retain a balanced feature contribution by the term and preterm records. Two classification algorithms namely, Naive Bayes and logistic regression (LR) are employed to classify the signals. Ten-fold cross validation approach is executed and the performance is validated using accuracy, precision and recall. The results show the uEMG signals exhibit multifractal characteristics and five GHE features are significant in distinguishing the term and preterm uEMG signals. The LR classifier gives the highest accuracy of 97.8%. Therefore, it appears that the multifractal Hurst exponent features in combination with LR classifier can be used as biomarkers for predicting the preterm or term delivery during the early stage of gestation.

A scheme is proposed for reducing phase noise in a spatially extended oscillator using tunnel-diode (TD) transmission line. It is observed that a voltage edge oscillates on a TD line when supplied by an appropriate DC voltage at the end. When the TD line is bypassed by a linear transmission line, part of the oscillating edge is inputted to and moves on the linear line to interact with the oscillating edge at the another crosspoint. The proper length of the linear line makes the bypassed voltage arrive at the crosspoint at the same time as the oscillating edge. It results in significant phase-noise reduction of the oscillating edge through self-injection locking. Herein, the principle of operation is described with its experimental validation.

The novel relaxation digital-to-analogue conversion technique, which takes advantage of the exponential impulse response of a first-order RC network to generate binary-weighted voltages, is proposed to design standard-cell based, mismatch-insensitive, ultra-low power, tiny digital-to-analogue converters targeting the requirements of Internet of Things applications. The effectiveness of the approach is validated by simulations and measurements performed on a proof-of-concept 10 bit, 300 S/s field programmable gate array prototype.

Thermal problems in conventional mobile devices are primarily managed by using software-based techniques due to compact sizes and limited power budgets. Since these software-based techniques incur inevitable performance degradation to reduce temperature, efficient thermal management techniques are essential for modern mobile devices. In this letter, the authors propose a novel control algorithm, which adaptively controls the threshold based on the power efficiency of mobile CPUs in real-time. The authors validate the thermal mitigation capability and system performance of their proposed scheme using a commercial smartphone. The evaluation results indicate that the proposed scheme reduces the CPU and PCB temperature by 1.20 and 1.38%, respectively, and simultaneously improves overall system performance by 5.44%.

Path planning is a classic decision problem in computer games and robotics. It is common to discretise the continuous planning space into grids with blocked cells to represent obstacles. Any-angle path planning methods, such as Theta* and Lazy Theta*, use line-of-sight check (LoS-Check) to find the nearly shortest path because the path will not be constrained to grid edges. The authors propose a new method called Late LoS-Check A* (LLA*), which contains two parts: employing the delayed LoS-Check to reduce the collision detection amount (late LoS-Check) and partially updating the path cost of the successor vertexes based on A* (partially updating). The experiment results show that LLA* costs less execution time than Lazy Theta* and retains even shorter path length. Through reducing the LoS-Check amount, the planning will be faster, but the path length will hardly be shorter. Therefore, it is the discriminatory updating strategy that makes both the path length and execution time of LLA* shorter than those of Lazy Theta*.

Clothing parsing is a special type of semantic segmentation in which each pixel is assigned with clothing labels. Unlike general scene semantic segmentation, stylish match (e.g. skirts + blouse, jeans + T-shirt) is an important cue for recognising fine-grained categories in clothing parsing. In this Letter, the authors propose a context-aware outfit encoder (COE), as a side branch, that drives the convolutional neural network to take the stylish match into account for clothing parsing. The proposed COE provides information on matching clothes that can be utilised to improve the prediction accuracy of the base network significantly. Experimental results show that fully convolutional network and MobileNet with the COE improve the mean intersection of the union of those without the COE by 2.5 and 2.8%, respectively, on CFPD dataset.

In this Letter, a general space–time line code (STLC)-based two-way relay (TWR) method is proposed to enable a power control for individual data streams transmitted to source nodes. Optimal power control factors are derived to ensure fairness between two source nodes under per-antenna power constraints. When the two-way channels are unbalanced, numerical results verify that the proposed method outperforms the existing TWR methods, an STLC TWR method without power control, and a space division multiple-access-based TWR method.

A compact single-layer balanced bandpass filter using just one half-mode substrate-integrated waveguide (HMSIW) multimode resonator with slots is proposed. The pair of microstrip direct-feed lines with space about 0.5λ _g (λ _g is the guide wavelength of HMSIW at the centre frequency f ₀) makes TEHM 103, TEHM 104 and TEHM 105 modes of the HMSIW multimode resonator operate in differential mode and TEHM 102 and TEHM 106 modes operate in common mode (CM). As a result, the features of wide bandwidth and low insertion loss (IL) can be achieved when compared with the state-of-art substrate-integrated waveguide balanced filters. Furthermore, the etched slots can be slightly tuned to make up for the performance deviations caused by the manufacturing error. A prototype is designed with a total size of 1.2λ ₀ × 0.14λ ₀ (λ ₀ is the wavelength in free space at f ₀), the 3 dB fractional bandwidth (FBW) of 28% at the centre frequency of 6 GHz, the minimum IL of 0.86 dB, and the bandwidth of 20 dB CM suppression of 0.25f ₀.

A substrate integrated waveguide cavity filter is designed by loading with two split rings capacitive posts. Using these split rings posts results in high quality factor, low insertion loss (2.1 dB), very narrow bandwidth (2%) at 4.6 GHz centre frequency and compact (0.97×0.5 λ_g ²) bandpass filter structure. The filter measured results are in good agreement with the simulation ones which prove the idea.

This Letter presents a multi-order bandpass filter (BPF) based on unit cells, which are constructed by coupled lines and microstrip stubs. This BPF unit cell features ultra-wide upper stopband and excellent stopband rejection performance. The external quality factors and coupling coefficients of unit cells are analysed in detail for multi-order BPF design, where transmission lines are adopted as a coupling structure for easy post-fabrication tuning. Following filter coupling matrix theory, two- and three-pole Chebyshev-response BPFs are designed and measured, centred at 1.0 GHz with 3-dB fractional bandwidth of 10%. Experimental results demonstrate excellent out-of-band rejection performances. In two-pole BPF, the upper stopband can reach 4.8 GHz (4.8 f ₀) with the rejection level of 37 dB. In three-pole BPF, within the stopband frequency of 3.4 GHz (3.4 f ₀), the rejection level is better than 55 dB, while the upper stopband can be extended to 6.5 GHz (6.5 f ₀) with the suppression level of above 26.8 dB.

A method to reduce the spectral linewidth of a laser source by direct phase noise compensation is proposed and demonstrated experimentally. To extract the phase noise information, the laser output is phase modulated and the in- and quadrature-phases are detected by homodyne mixing. Phase noise compensation is achieved by simply applying an error signal to an external phase modulator, where the error signal is generated to keep the same power level for the detected in- and quadrature-signals. The spectral linewidth of the laser is reduced significantly from 450 to 60 kHz.

The authors present a new compact optically pumped vertical external-cavity surface-emitting laser (OP-VECSEL), which consists of an optically pumped semiconductor chip surrounded by vertical-cavity surface-emitting laser (VCSEL) chips mounted together on one heat sink. This configuration allows to reach 10 W optical output power in single-mode operation with a very compact design. Furthermore, the authors reveal further improvements, which lead to a compact laser module with high power, highest beam quality and potentially low manufacturing costs.

An active clamping circuit for voltage sharing among series-connected insulated gate bipolar translators (IGBTs) during turning-on process is proposed at first, which detects the C–E voltage of the leading IGBT and generates gate pumping current to slow down the turning-on speed, and thus reduces the voltage difference between the IGBTs. Then, a turn-on edge regulation algorithm for the driving signal is proposed, which further reduces the voltage spike and turn-on power loss, and optimises the regulation speed. A time detection circuit is introduced to detect the pulse signal indicating the working time of the active clamping circuit for driving signal regulation. The turn-on edge regulation for each IGBT is determined by the feature that the rising edge of the detected pulse signal coincides with the corresponding IGBT turn-on edge delay. The experimental results prove the feasibility and effectiveness of the proposed method.

A method is presented to improve the determination of the rotational velocity of an on-axis spinning object. It uses the Orbital Angular Momentum (OAM) of an electromagnetic wave at 2.47 GHz, and measures the rotational Doppler frequency shift of a reflected wave. From this shift, the rotational velocity and the direction of rotation can be directly estimated with very good accuracy.

The authors present an experimental study of recovery time of a bulk gallium arsenide (GaAs) avalanche semiconductor switch that operates in low-energy-triggered mode. The voltage-biased bulk GaAs avalanche semiconductor switch is first triggered to be in a conducting state by a laser pulse, and then the other biased voltage is applied without laser triggering after a delay time. The self-breakdown will be observed experimentally in the bulk GaAs avalanche semiconductor switch by reduction of the delay time, and the recovery time can be achieved accordingly. When the biased voltage of the 0.625 mm thickn switch decreases from 5.0 to 2.0 kV the recovery time reduces from ∼4.4 to ∼1.3 µs.

The Gini index is a statistical dispersion metric widely used in economic and social sciences to measure inequalities. In this Letter, it is used to build the novel Gini index detector (GID) for cooperative spectrum sensing. The GID is blind, is robust under unequal and dynamical noise and signal powers, suits to line-of-sight channels with mild dominant component (the need for dominance is relaxed if the number of primary transmitters increases), has the constant false alarm rate property, outperforms state-of-the-art robust detectors, and is one of the simplest detectors devised so far.

In this Letter, the authors propose a handover optimisation scheme (HOS) for multipath transmission control protocol-based concurrent multipath transfer in heterogeneous networks. HOS includes two sections, proactive packet scheduling and access network selection. The former one proactively stops scheduling packets to the subflow about to be switched in order to reduce out-of-order packets during handover, while the latter one aims to select the optimal network for handover from multiple candidate networks by jointly considering multiple influential factors, i.e. path quality and dwelling time. Simulation results verify the effectiveness of the proposed scheme, which can achieve relatively higher throughput with fewer handovers.