This Letter explains the design and development of a wideband circularly polarised (CP) antenna based on composite metamaterial (MTM) structures which are applicable for use in small satellite applications. The presented antenna is based on a modified co-planar waveguide feeding technique. The proposed antenna unit cell offers compact size due to its MTM property with dimensions of 0.088λ₀ × 0.19λ₀ at 2.4 GHz. The CP radiation is obtained by placing two composite right/left-handed transmission line unit cells orthogonally and exciting two orthogonally-polarised modes simultaneously. A new 4 × 4 unit cell artificial magnetic conductor metasurface is designed with a compact size at the same operating frequency of MTM-based CP antenna as a ground plane for the proposed antenna, which is found to be increased bandwidth, improved gain, and wider axial ratio bandwidth without altering the antenna compactness. The final antenna obtains an overall dimension of 0.37λ₀ × 0.37λ₀ × 0.18λ₀ at 2.5 GHz. The measured result shows a wider impedance bandwidth of 860 MHz (33.07%), improved axial ratio bandwidth of 410 MHz (15.92%), and a good gain of 5.76 dBic is obtained which are adequate for the use in modern small satellite applications.

An oblique fed ring antenna designed and fabricated for its use in automotive applications is presented. The ring antenna is mounted on a car headlight at a certain height around the bulb with the help of a nylon supporting post. The reflector of the car headlight polished with conducting paint is made to act as the reflector for the ring antenna. Return loss performances are measured and compared for different heights of the ring antenna as well as for different parts associated with the headlight. Free space radiation pattern measurement of the ring antenna is carried out to have an insight of the effect of the light reflector for both the vertical and horizontal polarisations.

A square patch radiator supports both TM₀₁ and TM₁₀ modes with equal resonant frequencies. Feeding the patch in its diagonal can excite both modes with equal amplitudes and phases. By utilising this property, an effective technique is proposed to realise dual-band dual-polarised patch antenna. While the lower resonant frequency can be calculated using an existing analytical formula, an expression of the higher resonant frequency is still missing in the literature. To this end, an approximate expression of the higher resonant frequency is devised using the equivalent transmission line model in this work. It is a function of the distance between the shorting post and the feeding location. In order to validate the accuracy of the expression, three different antenna configurations are designed and manufactured. Good agreements between theoretical, simulated, and measured results are observed.

This Letter presents a novel, wrist-worn heart rate sensor, which is comprised of only a passive resonator and a voltage controlled oscillator (VCO). It is clearly demonstrated that valid heart rate data can be extracted off the DC bias circuit of the VCO, making this sensor one of the simplest of its kind ever reported. Experimental results are shown for successful measurements of the user's heart rate when the VCO was tuned to 2.42 GHz, with a DC bias voltage fluctuation of up to 10 mV representing the heart rate. These results are in agreement with those taken using a commercial optical sensor based heart monitor.

A front-end adaptive folder with a filter is presented to instantaneously push jammers to higher frequencies while preserving the integrity of small signals of interest. A programmable filter is utilised to further suppress folded jammers for achieving a widely scalable dynamic range over a large frequency range. To achieve maximum programmability with a minimal increase of power and area, combinatorial intrinsic device characteristics are exploited to tune folding points for rapid adaptation to a changing electromagnetic environment.

Digital signal processing (DSP) cores (kernels) are key components of modern consumer electronics devices. However, protection of DSP kernels is very crucial considering its vulnerability to hardware threats such as reverse engineering (RE). Functional obfuscation is one of the security mechanisms which provide protection against RE. However, functional obfuscation logic is in itself vulnerable to removal attack. This Letter presents a novel anti-removal logic (ARL) unit which ensures protection against the removal attack on functional obfuscation logic. Further, the ARL unit is itself safeguarded against removal attack by incorporating design architecture customisation and camouflaging. Designer can customise and camouflage the internal gate structure network of the ARL blocks post-synthesis (post-mapping and fitting). The proposed ARL unit integrated with functionally obfuscated DSP design, yielded lightweight and highly secured solution against removal attack when compared to an existing approach. The proposed approach reported on an average 42.57% reduction in gate count and on an average 66.67% enhancement in security compared to a recent existing approach.

A novel offset-cancelling current-mode sense amplifier (OC-CSA) to improve the sensing speed of embedded flash (eFlash) memory is proposed. To reduce the precharge time related to random address transitions, this OC-CSA adopts a new precharge acceleration scheme. Moreover, by employing offset cancellation, double sensing margin and strong positive feedback techniques, the new OC-CSA can achieve a sensing speed 1.6 × faster than other OC-CSAs. A 130 nm 1 Mb eFlash macro to confirm the high-speed capability of the proposed OC-CSA is fabricated. The experiment results show the new OC-CSA can achieve a read access time of 11 ns at VDD = 1.3 V.

The objective of this Letter is to report the development of the simplest hyperchaotic system in comparison with all existing simplest hyperchaotic systems. The proposed system does not contain any non-linear (product, quadratic or cubic) term and has a total of eight terms including the only one piecewise linear term. The circuit of the proposed simplest hyperchaotic system is implemented in hardware with fewer components and without using a multiplier. To the best of the authors’ knowledge, such simplest hyperchaotic system is not reported in the literature.

The dense matching of pairs is the basis of advanced image processing applications, such as 3D reconstruction and simultaneous localisation and mapping (SLAM). However, it is difficult to obtain efficient dense matching results in wide baseline image pairs due to various conditions. For this reason, the authors propose a dense matching method for wide baseline images based on an equal proportion of triangulation. Firstly, this Letter proves the mathematical property of equal proportion of triangulation affine transformation, and then builds a triangulation based on the set of sparse matching points. By using this property, the positions of equal proportion points in the corresponding triangulation of the two images to be matched are calculated, respectively. Secondly, to eliminate the points and obtain the inner point set, these proportional points are used to check the similarity of the matching triangle regions. Finally, the inner point set is used to calculate the positions of the dense matching points as the final dense matching result. The experimental results verified the validity and accuracy of the proposed method and this method is suitable for tilt photography, multispectral and multidate remote sensing image dense registration, and more.

The efficiency of any texture classification model confides on descriptor used for similarity matching. The formation of image descriptor is a challenging and important task in computer vision. This Letter introduces a local ZigZag Max histograms of pooling pattern (LZMHPP) for classification of texture images. To compute the descriptor, first the dissimilarity between centre pixel and its neighbours is computed for each image patch over the whole image, then the dissimilarity map is encoded with different type of ZigZag ordering mechanism, and finally the Max histograms pooling is used to form LZMHPP descriptor from two complementary ZigZag weighted structures and achieves sufficient robustness under geometric variations. The experimental study on KTH-TIPS and CUReT texture databases indicates the efficiency and supremacy of LZMHPP descriptor for texture classification.

In this Letter, the authors propose a novel revised regularisation to improve the performance of compressive sensing (CS) reconstruction. They suppose that a specific regularisation term is insufficient to accommodate the prior information of CS while it can be improved by further imposing a linear approximation term. They also prove that the revised regularisation is substantially equivalent to the CS preprocessing methods. They conduct extensive experiments on various CS algorithms, which show the effectiveness of their revised regularisation.

In this Letter, multichannel weighted region-scalable fitting segmentation model (M-WRSF) is proposed for medical image segmentation. The authors have utilised a new edge detection function to improve the performance of image segmentation approaches that already exists on weak edges and the grey-scale inhomogeneity of some medical images. The M-WRSF model introduces a novel punishment item to improve numerical stability and augments time interval to boost iterative efficiency. The Gaussian kernel function is added on the basis of original model to enhance robustness. On the other side, the original medical images need to make de-noising operation before the multichannel active contour model segment them, and also level-set initial curve has no effect on the segmentation results. The benefits of the new M-WRSF model, specifically, the increased efficiency and usability, are verified in the simulation experiment.

A new design of wideband four-way filtering power divider (FPD) based on substrate-integrated waveguide (SIW) loaded square patch resonator is presented. The wideband operation is realised by utilising the TM₂₀ mode of the patch and the TE₁₁₀ mode of the SIW cavity resonator. Afterwards, the selectivity is obtained by adding four open-ended coupling lines to each side of the square patch. Besides, an extra isolation network is introduced between each output port. To verify the design concept, a prototype of the proposed FPD operating at 3.55 GHz with a fractional bandwidth of 21.3% is fabricated and measured. Results indicate that the input return loss is >10 dB and the insertion loss is <2 dB. The amplitude and phase imbalances are >0.3 dB and 3°, respectively. Both simulated and measured results are in good agreement.

This Letter presents a novel deep learning approach for optimising the receiver performance with respect to the error vector magnitude (EVM) metric, which was verified and evaluated by applying it to a self-developed proprietary vector signal analyser (VSA). A four-layer neural network was built and trained to estimate and correct the systematic error of the VSA receiver by using a calibrated commercially available vector signal generator as the training source. Experimental results show that the EVM performance of the self-developed VSA is improved and approaches that of a state-of-the-art VSA.

A GaN monolithic microwave-integrated circuit (MMIC) driver and high power amplifier (HPA) chipset solution are presented for two commonly utilised satellite communications frequency bands. The MMICs represent first pass designs utilising Qorvo's recently released 0.15 µm GaN on SiC process featuring slot via devices.

A wideband filtering power divider (FPD) with wide rejection bandwidth and good isolation is presented, based on conventional Wilkinson structure. Parallel coupled lines and two pairs of open-circuit stubs are used for achieving bandpass filtering response and enhancing the performance of the rejection bandwidth. Furthermore, by properly choosing two resistors between two pairs of open-circuit stubs allows good isolation performance. Measured results indicate that the FPD operates at 2.35 GHz (f ₀) with a − 20 dB bandwidth of 55.3%. In the upper stopband range from 3.7 to 8.8 GHz (3.74f ₀), the minimum rejection is 20 dB. Within working band, the isolation between the output ports is higher than 24 dB. In addition, ultra-wide isolation better than 20 dB from DC to 10 GHz is obtained.

Transmission characteristics of an optical signal, which is converted from a high-speed terahertz-wave signal with high spectral efficiency, are investigated and reported. A Nyquist time division multiplexing 40 Gbit/s on–off keying signal in the terahertz band is generated with high-speed photo-mixing. The generated terahertz-wave signal is again converted into an optical signal with heterodyne detection, optical intensity modulation, and optical filtering. Then the chromatic dispersion tolerance of the converted optical signal is investigated in order to obtain knowledge for realising the connection between the fibre-optic and the wireless links. After briefly explaining the conversion method, some related experimental results are reported. The results include evaluation of chromatic dispersion tolerance with regard to the optical signal at the final stage. As a sequel to bit error rate measurement, the optical signal can be transmitted to a 9 km-long single-mode fibre without chromatic dispersion compensation.

The authors present an expanded porous polytetrafluoroethylene terahertz fibre transmission link using resonant tunnelling diodes integrated with photonic-crystal waveguides as a transmitter and a receiver. The measured coupling efficiency between the terahertz fibre and the photonic-crystal waveguide integrated with a silicon tapered coupler is ∼30% with a 3 dB bandwidth of 50 GHz at the 0.3 THz band. Error-free 10 Gbit/s transmission and uncompressed 4 K high-definition video transmission have been successfully demonstrated using 1 m-long terahertz fibre.

A new hysteresis-current-controlled buck converter with alternating current (AC) sensing techniques is presented in this Letter. The proposed AC sensing technique senses the inductor current ripple by sensing the voltage at two terminals of the inductor. Accompanying with hysteresis-current-controlled technique and a type-III compensator, the transient response can be accelerated. The simulation result shows the response time is 0.7 µs when the load current switch from 150 to 600 mA and the maximum efficiency is 94.6%.

When the energy storage battery (ESB) is introduced into the DC microgrid, the DC microgrid can perform demand side management well. To achieve flexible charge and discharge controls of the ESB, the grid-connected device of the ESB needs to have a bidirectional power transmission control function with constant power. Based on this, this Letter first designs circuit topology of bidirectional boost converter for high-power transmission between the ESB and the DC microgrid. Secondly, the control system based on the staggered timing trigger mechanism is developed, and the working process of the converter in the forward and reverse transmission of power is analysed. Finally, the bidirectional boost converter and its control system are verified by real-time digital simulator platform. Simulation results show that the proposed converter and its control system can realise stable high-power bidirectional transmission between the ESB and the DC microgrid, and achieve accurate tracking of the power reference value.

The authors are reporting for the first time the fabrication of GaN-based fully-vertical high-power metal-oxide-semiconductor field effect transistors on Si. The electrical measurements of the fabricated device exhibited both vertical and lateral modes of operation. The transfer characteristics of the device in vertical mode showed a peak trans-conductance () of 23.6 mS/mm with a threshold voltage () of V. The maximum current drain density () of 249.3 mA/mm was observed with ON-resistance () of 44.2 -mm. The electrical results obtained in the vertical mode were also compared with the laterally oriented devices. The comparison of the electrical results indicates a relatively higher ON-resistance of the device in the vertical configuration, due to the contribution of the series resistance of the buffer layers in the epi-structure.

To better explore the underlying intrinsic structure of tensorial data, in this Letter, the authors propose a low-rank approximation-based tensor decomposition (LRATD) algorithm for subspace clustering. LRATD aims to seek a low-dimensional intrinsic core tensor representation by projecting the original tensor into a subspace spanned by projection matrices. Different from traditional approaches that impose additional constraints on basis matrices to further eliminate the influence of data noise or corruption, they directly add a low-rank regulariser on the core tensor to encourage more robust feature representation. Noticeably, they develop an accelerated proximal gradient algorithm to solve the problem of LRATD. Experimental results demonstrate the excellent performance compared with state-of-the-art methods.

This Letter presented a new-order optimal method for lowering the computational complexity of the traditional minimax design of digital finite impulse response (FIR) filter utilising linear programming (LP) in bandwidth interleaving digital-to-analogue converter (BI-DAC). In this order optimal method, a one-by-one increasing method was presented to optimise all of digital FIR subfilters' orders in BI-DAC so that these digital FIR subfilters' orders could be optimised to simultaneously satisfy all of given upper bounds of the distortion and aliasing errors. A design example was used to verify the effectiveness and low computational complexity of the presented low-complexity minimax design utilising LP, and the simulation results were well-pleasing.

The sensor selection is a technique to reduce the cost, energy consumption, and complexity of a system by discarding redundant or less useful sensors. In this technique, one attempts to select a subset of sensors within a larger set so as to optimise a performance criterion. In this work, the authors consider the detection of sources in the 3D space when the source space could be sparsely represented. The application of compressive sensing (CS) methods in this setting has been extensively studied. Their aim in this work is to carry out the task of sensor selection in a planar array without sacrificing the detection performance. Their approach is to adopt the equivalent CS model and reduce the mutual coherence of the associated sensing matrix. This minimisation task is non-convex, for which they propose a convex relaxation. Numerical simulations demonstrate that the gap between their relaxed solution and its optimal counterpart is negligible. The proposed sensor selection method is also shown to outperform the uniform approach in terms of source detection.

The accurate prediction for the tropical cyclone (TC) intensity is a recognised challenge. Researchers usually develop dynamical models to address this task. However, since the TC intensity is highly influenced by various factors such as ocean and atmosphere conditions, it is difficult to build the very model which can explicitly describe the mechanism of TC. A new idea is developed, utilising the massive historical observation data by a deep learning approach, to conduct a completely data-driven TC intensity prediction model. All the TC intensity and track data which have been observed in Western North Pacific since 1949 are collected, and recurrent neural network for TC intensity prediction is constructed. In general, their motivation as well as novelty is to develop a data-driven approach instead of empirical models. There are very few researches similar to their exploratory work. The proposed method has presented 5.1 ms error in 24 h prediction, which is better than some widely used dynamical models and is close to subjective prediction.

Robust principal component analysis (RPCA), a novel method for speech enhancement (SE), is expected to decompose the spectrogram of a noisy speech into a low-rank matrix and a sparse matrix, which contain noise components and speech components, respectively. However, some speech components, which are not so variable in different time frames, are possible to be decomposed into a low-rank matrix as noise mistakenly. To address this problem, a novel SE method based on spectrogram-rearranged RPCA (SRPCA) is proposed for a sparse matrix with better decomposition for all speech components in white noise environments. For further improvement under coloured noises corruption, the multi-band method is introduced for SRPCA to be applied in all bands individually. Accordingly, a time-domain enhanced speech is reconstructed from the processed sparse matrix. Numerical experiments show the effectiveness of the proposed method.

In this Letter, a wireless transmitter using the new architecture of programmable metasurface is presented. The proposed transmitter does not require any filter, nor wideband mixer or wideband power amplifier, thereby making it a promising hardware architecture for cost-effective wireless communications systems in the future. Using experimental results, the authors demonstrate that a programmable metasurface-based 8-phase shift-keying (8PSK) transmitter with 8 × 32 phase adjustable unit cells can achieve 6.144 Mbps data rate over the air at 4.25 GHz with a comparable bit error rate performance as the conventional approach without channel coding, but with less hardware complexity.

Non-orthogonal multiple access (NOMA) has been considered as one of the key enabling techniques for next-generation wireless networks and the overall performance of these systems largely depends on the power allocation (PA). In this Letter, the authors address the PA problem in a downlink cellular NOMA network. They propose an auction-based mechanism in which the users compete for the transmit power being sold by the base station. Each user places his bid iteratively in order to maximise his own utility. Further, the authors prove the existence of an unique Nash equilibrium theoretically. Simulation results demonstrate the effectiveness of the proposed scheme in terms of the average sum rate of users as compared to an existing algorithm.

In this Letter, for the first time, the in-to-out-body path loss between an antenna placed inside the cows’ rumen and a distant gateway was characterised at 433 MHz. Measurements were conducted on seven different fistulated cows using a signal generator and a spectrum analyser. Subsequent measurement of the antenna in free space was used to quantify the path loss increase due to the cow body. Results have shown an increase of the path loss by 45.5 dB on average (all cows), with a variation between 39.7 and 51.1 dB. Also, the measured path loss values as a function of the transmitter–receiver distance in a dairy barn were well fitted by a log-normal path loss model. The obtained models were used to calculate the range of a LoRa (Long range) based network. Ranges up to 100 m were obtained depending on the used transmit power and bit rate.

Hybrid precoding has become a well-accepted approach to enhance the achievable rate in the adverse millimetre-wave (mm-Wave) MIMO channels. Transceiver impairments are inherent to any practical communication system, yet they are generally omitted when investigating the performance of wireless systems. More particularly, for the case of mm-Wave underground channels, no study has been reported yet. To overcome this limitation, in this Letter, a new architecture encompassing hybrid precoded mm-Wave MIMO structure, in which the hardware impairments have been incorporated in the transceiver processing, is presented. Furthermore, the geometrical one ring model is applied on the underground mm-Wave measured channel in which the architecture is tested.