A simple, planar, electrically small antenna with both wide bandwidth and good out-of-band filtering selectivity is presented. The proposed filtering antenna is mainly composed of a small driven patch and a slotted ground plane. Two slots are etched in the ground plane to form two square ring patches that can generate a new resonant mode and two radiation zeros, and a T-shaped stub is loaded not only to enhance the impedance bandwidth but also to increase the out-of-band rejection level. A prototype is fabricated and measured. The measured −10 dB fractional impedance bandwidth is 23.05% (2.61–3.29 GHz) centred at 2.95 GHz with the realised gain values 2.95 ± 0.34 dBi in the operational band, with two radiation zeros located at 2.27 and 3.62 GHz, respectively, even with electrically small size ka = 0.98. The experimental results are in good agreement with the simulated values.

Antenna selection is a promising solution to reduce the high cost of multiple RF chains in multiple-input multiple-output (MIMO) systems while maintaining the benefits of spatial diversity and multiplexing gain. By modelling the problem of transmit antenna selection as a multi-class classification and/or decision-making task, this Letter proposed a multi-class import vector machine (IVM) based approach to maximise the average received signal-to-noise ratio (SNR). Simulation results prove that IVM outperforms the conventional optimisation driven algorithm and the state-of-the-art learning-based scheme of support vector machine in terms of average received SNR performance with feasible complexity and sparsity.

As the dimensions of neural implants are miniaturised to mm-scale, wireless powering becomes more challenging. Antenna sizes become smaller, and so does the amplitudes of the received RF signal. More importantly, a meticulous effort is required when multiple implants are placed on the brain under a transmitter, as each implant has a different spatial position from the transmitter coil. In addition, RF power may fluctuate over time. These factors, both effects the coupling coefficient. In this case, rectifiers with a fixed number of stages are limited to a rather narrow operational voltage range, and cannot accommodate such variations. To address this, the authors propose an adaptive-stage rectifier that changes the number of connected stages by monitoring the final rectifier output voltage using two comparators and a digital block. By doing so, it can generate an output voltage within the targeted voltage range for a much wider RF input voltage range. The authors' design and simulations in 180-nm CMOS SOI process show that the proposed rectifier is capable of keeping the output voltage within 1–1.7 V for an RF input range from 0.73 to 2 V, which is five times wider than that of conventional rectifiers with three fixed stages.

A 4:1 multiplexer (MUX) circuit in SiGe BiCMOS technology intended to directly drive a plasmonic Mach–Zehnder modulator for transmitter applications is presented. To achieve the highest data rates at a high output voltage swing, a power MUX concept is applied that maps the high-speed performance of the final clock signal onto the output data. In the clock tree a novel wideband clock phase shifter circuit is utilised for timing adjustment and frequency doubling. Electrical measurements of the chip demonstrate open eye diagrams for non-return-to-zero on-off-keying (NRZ-OOK) signals up to 180 Gbit/s, which is record speed for Si-based technologies. A differential output voltage swing of was measured that corresponds to an output voltage swing of more than without the bandwidth limit of the measurement equipment.

A third-order complex delta-sigma modulation (CDSM) structure with cross-coupling paths is proposed and analysed. Although the conventional CDSM can reduce circuits complexity in digital transmitter systems, it suffers from other shortcomings like increasing algorithm complexity. This structure imports cross-coupling paths both at output and interstage, which realises decorrelation between zeros and poles. The advantage is that complex zeros can be arbitrarily placed, and thus, the reconfigurable digital wireless transmitter application can be satisfied; and the poles are not affected by zeros placement, which improves the flatness of signal transfer function.

Capacitive coupling is a well-established principle in isolated signalling. A major challenge esp. in power electronics is common-mode transient immunity caused by the displacement currents at the coupling capacitors. Digital isolator integrated circuits (ICs) employ modulated signalling, the authors propose an active filter circuit to remove common-mode components from baseband signals. This allows for reliable data transmission during transients in power semiconductor control, AC-coupled RS-485 or transformer-less Ethernet. The filter structure is simple and consists of two current mirrors, one for positive transients, and one for the negative. A current on one differential signal line is ‘mirrored’ onto the other, common-mode currents are conducted to ground. Differential signals are minimally affected. The proposed filter is verified in simulation and experiment: baseband signalling with 50 Mbps in presence of 30 kV/ burst transients is achieved using discrete semiconductors. Even better results are expected when monolithically embedding the filter in an integrated circuit.

A low-phase noise ring voltage-controlled oscillator (VCO) employing input-coupled dynamic current source is presented. By simply coupling the input signal to the gate node of the current source transistor, the proposed inverter has a larger output swing and steeper maximum slope than conventional structures, which directly results in phase noise improvement. Under the same conditions, compared to the conventional structure, the proposed ring VCO achieves 7.5 and 11 dB of phase noise improvement at 100 kHz and 1 MHz offset frequencies, respectively. The proposed ring VCO has a tuning range of 823–1300 MHz and post-layout simulation shows a figure-of-merit of 159–162 dBc/Hz in the entire oscillation frequency range. In the measurement results,the authors recorded a phase noise of −106 dBc/Hz and figure-of-merit reaching 165 dBc/Hz at 1 MHz offset frequency, consuming 1.2 mW from a 1.8 V supply at 1 GHz oscillation frequency. The proposed ring VCO is implemented in 180 nm CMOS process and occupies a size of 0.0024 mm².

A novel memristive chaotic system with tiny perturbation is proposed in this Letter. Particularly, by adjusting tiny perturbation properly, this system can generate a novel compound chaotic attractor (including one stable chaotic attractor and one periodic-2 attractor). Furthermore, transient mixed-mode oscillations (MMOs) and attractor inversion behaviour are also observed. The numerically observed transient MMOs are demonstrated by Multisim experiment. As a result, the simulation results verify the feasibility and effectiveness of the tiny perturbation method.

The analysis of the interior scattering from open cavities with small modifications is an important task in designing a stealthy jet engine. Previous research has shown the magnetic field integral equation with the Kirchhoff approximation can be used to calculate the cavity interior scattering. However, it must repeat the expensive method of moments (MoM) solution even when the cavity is modified only slightly. In this Letter, the efficient method based on the partitioned-inverse formula and the Sherman–Morrison–Woodbury formula is employed to address this problem. It can avoid the repeated MoM direct solution. We only need to solve the lower-upper (LU) decomposition of the impedance matrix of the original cavity, and can efficiently derive the solution of the modified cavities via matrix identities without loss of accuracy. Numerical results are given to demonstrate the performance of the proposed approach.

Detection of double JPEG compression is essential in the field of digital image forensics. Although double JPEG compression detection methods have greatly improved with the development of convolutional neural networks (CNNs), they rely on handcrafted features such as discrete cosine transform (DCT) histograms. In this Letter, the authors propose an end-to-end trainable 3D CNN in the DCT domain for double JPEG compression detection. Moreover, they also propose a new type of module, called feature rescaling, to insert the quantisation table into the network suitably. The experiments show that the proposed method outperforms state-of-the-art methods.

In this Letter, the authors present a novel tracking system, in which tracking accuracy can be enhanced by trajectory simulation. They generate synthetic trajectories based on observed trajectories by adopting the hidden semi-Markov model (HSMM). In the course of trajectory simulation, HSMM can encode representative states and speeds of the targets. The simulated trajectories enforce the proposed tracker to focus on the areas where targets will move at following frames. Experimental results demonstrate that it is easy to integrate the proposed trajectory simulation into traditional visual tracking methods and the trajectory simulation can considerably improve the accuracy of visual trackers.

In this Letter, the channel capacity under different transmission policies is analysed using a mixture gamma distribution. Specifically, the capacity of the channel with inversion and fixed rate, optimum power and rate adaptation, and truncated inversion and fixed rate IS derived in unified exact simple closed-form expressions. The composite /gamma fading channel which includes most of the well-known fading distributions as special cases, has been employed in this work. Moreover, a comparison between numerical and simulation results has been carried out to verify the validation of the derived expressions.

The vital signal extraction remains an on-going challenge due to the low signal-to-noise ratio (SNR) of vital signals in real tests. In this Letter, the authors propose a novel vital signal enhancement method using spectral gain instead of the traditional singular value decomposition (SVD) method, which shows excellent performance in the elimination of noise that is in the same frequency band as the vital signal and reducing calculation time. The simulation and experiment have been conducted, and the results indicate that the proposed extraction method outperforms the traditional SVD in output SNR and processing time.

In this Letter, the authors present the construction of three-dimensional microstructures by two-photon polymerisation induced by ultrashort pulses of a mode-locked diode laser. The ultrafast light source is based on a diode laser with segmented metallisation to realise a waveguide integrated saturable absorber. It is subsequently amplified and compressed resulting in ultrashort laser pulses of 440 fs length and average output power of 160 mW at a fundamental repetition rate of 383.1 MHz. These pulses are coupled into a customised two-photon polymerisation setup. A series of suspended lines were fabricated between support cuboids for testing the process behaviour. A 3D structure with complex features was polymerised to demonstrate the high potential for mode-locked diode lasers in the field of direct laser writing.

The authors experimentally demonstrate a modulating retro-reflector based on electro-optical in-phase quadrature modulator and test it in an atmospheric cell simulated atmosphere environment by using 80 Gb/s polarisation-multiplexing quadrature phase-shift keying (Pol-MUX QPSK) signals. At the BER of 1 × 10⁻³, the power penalties of the x- and y-polarisation signals are both <1.1 dB when the temperature difference in the atmospheric cell is <250°C.

The authors report buried-heterostructure long-wavelength VCSELs with GaAs/AlGaAs metamorphic DBRs, which has a potential for low thermal resistance and operation in the single transverse mode with a large emission area. In spite of their being upside-up and unmounted, they achieve CW operation at 17°C, and VCSELs with a 15-µm mesa exhibit single-mode operation.

The frequency-modulated continuous wave (FMCW) radar will play a more important role in future intelligent traffic systems due to low cost and high adaptability to complex environments. Generally, a 2D array is utilised to measure range, speed and azimuth and elevation angles (4D) for multiple vehicles simultaneously. However, a traffic radar utilising a 2D array will enhance its system complexity; therefore, the increased cost would make it less superior to LiDAR. In this Letter, an azimuth and elevation angles estimation method of FMCW radar utilising only 1D array is proposed. Thus, it can provide 4D parameters to multiple vehicles simultaneously. The feasibility of the proposed approach is verified by on-road measurement data.

In multiple-input multiple-output (MIMO) radar system, timely array diagnosis method is needed for transmit and receive arrays. To avoid using extra probes or measurements, a novel signal subspace clustering-based array diagnosis method is proposed. By exploiting the relationship between the signal subspace extracted from the covariance matrix and the steering matrix in MIMO radar, the feature of the anomalous data points in signal subspace caused by faulty elements is examined. Consequently, the anomalies are grouped into one cluster by density peaks clustering algorithm, and the faulty antennas in transmit and receive arrays can be identified based on the clustering results. Numerical simulation results demonstrate the superiority of the proposed approach in array diagnosis problem for MIMO radar.

In this Letter, the authors investigate the electrical characteristics of amorphous indium-tin-gallium-zinc-oxide (a-ITGZO) thin-film transistors (TFTs) under positive gate bias stress (PBS). An as-prepared a-ITGZO TFT exhibits a mobility of 26.05 cm²/V⋅s, subthreshold swing of 183 mV, threshold voltage of −0.33 V, and on/off ratio of 1.34 × 10⁸. These electrical characteristics deteriorate upon the application of PBS. The proposed experiments and simulations reveal that this deterioration can be attributed to the increase in the density of acceptor-like conduction band-tail states and donor-like Gaussian states within the bandgap of the a-ITGZO channel material.

A new uniform shallow trenches termination (ST²) with field plate for high-voltage VDMOS transistor is proposed in this Letter. In ST² structure, the electric field near the source is decreased and the depletion region is extended by the field plate, besides, many electric field peaks are introduced in shallow trenches under the field plate and the average electric field strength is increased, both improve the characteristic of the breakdown voltage (BV). Simulation results show the BV of ST² VDMOS is 706 V with a termination length L _d = 132 μm, which reaches 97% of that of the parallel-plane junction, and the influence of the edge curvature effect is almost entirely eliminated. The ST² structure is compatible with conventional CMOS process with only one additional mask and its fabrication is low-cost.

The analysis of dense small-cell networks has largely relied on the use of either unbounded path loss models that may violate the conservation of energy at very short distances, or bounded path loss models that are not tractable. In this Letter, the authors derive the coverage probability and area spectral efficiency (ASE) in closed-forms for dense small-cell networks by using a novel bounded path loss model. Their analytical results demonstrate that the coverage probability will monotonically decrease with the increase of base station (BS) density, and the ASE will first increase with the BS density and then reduce to zero when the network becomes ultra dense. They also give the closed-form expression of the optimal BS density that maximises the ASE.

In this Letter, the authors propose a novel low-density parity-check (LDPC) coding scheme to transmit extra bits aided by rotated signal constellations without any additional cost in transmission power or bandwidth. In the proposed scheme, the LDPC coded data are modulated by a rotated two-dimensional signal constellation, in which the rotation angle is specified by the given extra bits. At the receiver, the rotation angle is estimated with the aid of the statistical learning of the syndrome of the LDPC code. After recovering the rotation angle, the coded payload data can be decoded by the LDPC decoder. The simulation results show that, for an LDPC code of length 2304, up to four extra bits can be transmitted with negligible influence on the reliability of the LDPC coded data.