A dualband quasi-isotropic antenna is presented. It is based on the split-ring-resonators (SRRs), which provide a quasi-isotropic radiation pattern with an electrically small size. For the dualband operation, the SRRs are placed orthogonally to reduce the mutual coupling between the elements. A folded dipole structure is applied to the SRR, therefore, the input impedance at each band can be easily tuned. Both simulated and measured results are presented. The results show dualband operation (792 and 1124 MHz), high efficiency (higher than 86 and 85.5%), compact size (ka = 0.47 at 792 MHz), moderate gain deviation (4.42 and 5.76 dB) with simple direct feed.

A new approach to suppress mutual coupling of spatial electromagnetic fields between two circularly polarised (CP) antennas using frequency selective surface (FSS) technique around 30 GHz is presented. The transmission-type FSS layer with the CP capability is placed on the top of two closely multiple-input, multiple-output (MIMO) antennas. The study shows that the FSS layer can suppress an average of 10 dB mutual coupling between two adjacent CP-MIMO antennas. The proposed technique does not degrade the impedance and radiation performance of the antenna in comparison with the antenna without FSS layer. The two-port CP antennas are fabricated and measured to validate the simulation results. Good agreement is achieved between simulated and measured results in terms of the reflection coefficient, mutual coupling, and axial ratio.

In this Letter, three ports proximity coupled microstrip patch antenna with linear co-polarisation and linear dual polarisation characteristics has been presented for in-band full duplex and active antenna applications. Depending upon the excitation ports, antenna can perform transmit and receive operation either with dual linear polarisation or linear co-polarisation at same carrier frequency with dc isolated ports in both cases. It provides >10 dB interport isolation with linear co-polarisation when compared with around 2.5 dB port-to-port isolation of simple linear co-polarised antenna with two anti-parallel feeds. With dual polarisation, interport isolation is >43 dB at centre frequency when compared with 36 dB port isolation provided by dual polarised antenna with two orthogonal feeds. Proposed antenna has been implemented on FR4 substrate to compare its simulated and measured input matching and port-to-port isolation performances.

A microstrip antenna array (MAA) loading with metasurface is designed and fabricated for ultra-wideband radar cross-section (RCS) reduction while preserving its radiation characteristics. A new physical mechanism based on size adjustment of the multiple basic unit cells is proposed for ultra-wideband manipulation of electromagnetic waves. To obtain the excellent RCS performance, the selection of the basic unit cells is optimised by the hybrid optimisation algorithm. Both simulated and measured results indicate that the proposed MAA can reduce the RCS significantly in an ultra-wide frequency band from 6.2 to 27.3 GHz under x- and y-polarised normal incidence. The radiation characteristics of the MAA are well preserved simultaneously.

A polarisation rotation reflective surface (PRRS) is proposed to achieve radar cross-section (RCS) reduction of a patch antenna at a broadband. The PRRS consists of two pairs of L-shaped patches, which are printed on a substrate backed by a metallic ground. By arranging the PRRS around the patch antenna in four orthogonal directions, a wideband RCS reduction can be obtained in the frequency band of 10–18 GHz. The proposed low-RCS patch antenna is fabricated and measured in an anechoic chamber. The experimental results show that the designed PRRS makes the antenna RCS dramatically reduced. What is more, the introduction of PRRS has little influence on the antenna performance.

A user-driven treadmill is a walking platform that is put into motion by the action of a user. The estimation of walking speed plays an important role in controlling the treadmill, especially the ones with a small walking area. Plantar pressure potentially has a significant relationship with walking speed. A new walking speed estimation and treadmill control algorithm using plantar data, which is measured using wearable insole pressure sensors is proposed. After capturing the best pressure parameters and developing an appropriate feedforward control scheme, the user experiment and analysis results are analysed to verify the performance and effectiveness of the proposed method.

An approach is presented for the determination of the 4 × 4 transmission matrix of differential transmission line interfaces on a microchip fixture. Different settings of a simple calibration structure that extends the already available 50-Ω on-chip termination excite different transmission modes, which are used for the determination of the transmission matrix in mixed mode parameter form. Only reflection measurements at the two easily accessible connectors of the fixture are required, which enables an in-situ deembedding of the chip performance while mounted.

In this Letter, an opamp-free noise shaping successive-approximation register (SAR) ADC is proposed. Third-order noise shaping is achieved by implementing a second-order passive filter and a passive error feedback topology. In the proposed scheme, the SAR error signals (including quantisation noise, comparator thermal noise, DAC thermal noise and settling error) are subjected to third-order noise shaping. Therefore, the thermal noise specifications of the comparator can be relaxed. Also, since no active element is used, the proposed scheme achieves a higher power efficiency than earlier SAR ADCs.

Traditional solutions for Ethernet transmission of data acquisition systems (DAQ) are mainly based on software transmission control protocol/internet protocol (TCP/IP) stack while its throughput is relatively low and hard to improve. A hardware TCP/IP stack that can greatly promote the Ethernet throughput for generic DAQ is presented. To reduce the memory overhead of FPGA in DAQ, a shared memory method based on parallel and pipeline operations is proposed so that it can realise multiple protocols with just 2 Kb RAM for receiving and sending respectively. Unlike software system, hardware stack is difficult to realise multiple data source transmission simultaneously since it is realised totally by logic circuits. Therefore, a data manage module is designed specially to manage the internal, software and hardware data and it can enhance the flexibility and practicability remarkably. Functional simulation shows that, under 50 MHz system clock, the maximum throughput is near 800 Mbps. A common Megabit Ethernet controller chip is applied in the board test. The results show that the maximum throughput of the whole system is 82.2 Mbps which is much better than designs based on the same or similar network controllers.

A novel cascade ΔΣ modulator, which combines the benefits of sturdy MASH (SMASH) topology and feed-forward loop filter, is presented. The proposed ΔΣ architecture is based on moving the power-hungry adder block from the quantiser input to the first integrator output. The proposed architecture shows a better operational transconductance amplifier (OTA) linearity and relaxed OTA DC-gain compared with conventional MASH and SMASH topologies. This feature makes the modulator topology more suitable than conventional MASH and SMASH topologies for low-voltage applications.

A novel training algorithm called geometric AdaBoost learning, which integrates the local-appearance models with the explicit shape model is proposed. The proposed algorithm employs a two-stage AdaBoost learning algorithm. The first-stage learning is performed to learn the local texture model within local image patches and to produce a confidence map. Based on the confidence values, the high-discriminative local patches are selected, and then the global context models between them are trained in the later stage using AdaBoost learning. The proposed algorithm is applied to wheelchair navigation, and the results demonstrate that it outperforms the state-of-the-art algorithms with improvements of 23.3 and 49% in terms of accuracy and speed.

A spatial modulation (SM) using double multi-strata space–time codes (MSSTC) is proposed, which will be called D-MSSTC-SM. Uneven transmit power and phase are allocated to layers of each MSSTC and rotation angles are assigned to SM codebooks to maximise the minimum coding gain distance of D-MSSTC-SM. It is observed that the proposed D-MSSTC-SM enables higher spectral efficiency and lower error probability than other conventional schemes.

A novel and low-cost solution to improve the radiation patterns of the on-chip patch antenna at 220 GHz is proposed. The radiation performances are enhanced by mounting the lens on the patch. The air cavity in the lens not only reduces the focal length, but also provides space for chip integration. The imaging chip and antenna are fabricated and an experimental platform is built. The responsivity and radiation patterns are measured. The 3 dB beamwidths of the with-lens detector in the E and H planes are 8° and 7°, respectively. Good agreement between the simulated and measured results is obtained.

A quad-band microstrip bandpass filter (BPF) based on stub-loaded resonators (SLRs) with improved skirt selectivity is presented. A single metallic via hole in microstrip is utilised to introduce a compact inductive source–load coupling, with which two pairs of SLRs generate eight controllable transmission zeros at each side of all the quadruple passbands. As an example, a quad-band BPF with measured centre frequencies of 1.88, 2.55, 3.55 and 5.15 GHz as well as insertion losses of 1.53, 1.64, 1.79 and 2.55 dB, and respective fractional bandwidths of 4.38, 3.84, 3.44 and 2.9% is designed and fabricated. The measured response shows a good concordance with the simulated one.

An improved millimetre wave microstrip power divider is presented. This circuit enhanced the conventional Wilkinson power divider (WPD) performance by adding transmission lines between the transformer arms and the resistor to reduce inherent undesirable mutual coupling. The proposed power divider design parameters show more stability over a wider frequency band compared to other valid design solutions. For comparison purposes, the proposed power divider along with the WPD are designed at 61 GHz using high permittivity thin ceramic substrate. The measurement results of the proposed circuit demonstrate improved bandwidth with high input/output matching and isolation of −15 and −24 dB, respectively, in the whole frequency band of 10 GHz. Furthermore, the excess insertion loss is reduced by 20% compared to the conventional one.

A microwave method has been proposed to retrieve the complex permittivity and thickness of lossy dielectric liquids, which result in at least 10 dB attenuation, using reference-plane-invariant reflection scattering (S-) parameters. The CST Microwave Studio simulation program was first used to validate the method. Then, the permittivity and thickness of lossy distilled water sample poured over a polyethylene sample holder were measured from reference-invariant reflection-only S-parameter measurements at the X-band. The method was compared with other methods in the literature to analyse its accuracy.

A novel sixteenth-mode substrate integrated waveguide (SMSIW) bandpass filter loaded with complementary split-ring resonator (CSRR) is proposed. The filter size is reduced by introducing the SMSIW circular cavity loaded with CSRR. The SMSIW occupies only 6.25% of the conventional substrate integrated waveguide with same resonant frequency. Further miniaturisation is achieved by loading the SMSIW circular cavities with CSRRs. The designed filter is centred at 2.45 GHz with a bandwidth of 8.2%. The measured minimum insertion loss is 0.9 dB and passband return loss is below 10 dB. Good agreement is achieved between simulated and measured results.

Superluminal wave propagation phenomenon achieved from a periodic structure in which a transmission line (TL) is loaded with non-Foster negative capacitors is presented. The loading decreases the effective capacitance and the effective permittivity of the dielectric substrate of the TL. An experimental investigation of the superluminal phase and group velocity in the non-Foster loaded TL is reported. The phase and group velocities are extracted from measured S-parameters. To do so, three non-Foster negative capacitors operating over [50–350 MHz] frequency band are integrated in a TL. Superluminal broadband effects are obtained from 50 to 220 MHz. The negative capacitors loaded TL paves the way to innovative broadband leaky wave antennas, active metamaterial surfaces and cloaking devices.

A low power-consumption distributed feedback quantum cascade laser (DFB-QCL) is developed for gas-sensing in 7 μm wavelength region. The threshold power-consumption was as low as 0.93 W with the sufficient output power of 20 mW at 20°C under continuous-wave condition. In addition, it maintained a single-mode operation between −40 and 50°C without a mode-hopping, leading to a total wavelength shift of 66 nm. This DFB-QCL would be suitable for gas-sensing application.

A low-power 0.18 µm CMOS capacitor-less low-dropout voltage regulator for battery-operated portable devices is presented. A high-gain telescopic cascode-compensated amplifier is used to attain a stable topology with good static performances, while a very simple dynamic biasing circuit significantly enhances transient performances with no quiescent current penalty. Post-layout results show a 1.8 V output voltage from a 3.6 to 1.9 V battery input voltage, delivering a 50 mA load current over a 100 pF load. The quiescent current is only 7 µA, the line and load regulations are, respectively, 0.039 mV/V and 0.17 mV/mA, and settling times are lower than 3.9 µs at full load transient.

A compact low-loss microstrip diplexer that forms by two band-stop filters using interdigital capacitor and a stepped-impedance resonator structure when joined by a miniature T-junction is introduced. The diplexer operates at global system for mobile communication frequency 1800 MHz and 2.45 GHz WLAN frequency which are the most available frequency bands for RF energy harvesting applications. Simulated and measured results are in very good agreement with low insertion loss of 0.4 dB and high selectivity characteristics.

A flexible traction power system is proposed for AC-fed railway due to its benefits in power flow optimisation, online catenary anti-icing and power quality improvement. In this system, an energy optimisation controller in section post is adopted to provide reactive anti-icing current and control the energy flow in regenerative braking of the locomotives. The energy optimisation controller in traction substations is adopted to eliminate three-phase unbalance in power grid and perform reactive power compensation. The mathematic model of the proposed system is built based on a power transformation analysis and the validity of compensation algorithms is verified by case studies.

The model predictive control (MPC) technique for a solar-based series-resonant inverter conventionally used in domestic heating is explored. The photovoltaic energy system (PVES) converts the solar energy into electrical energy where DC voltages of different cells are linked at a common bus. A Cuk-converter is used to interface the PVES with the DC load bus and the heating inverter. These heating inverters are replacing gas cookers in restaurants, guest rooms, and domestic- and commercial-kitchens for cooking of various foods. A number of control algorithms have been employed to control the power of the heating inverter but they have certain limitations; especially they do not predict the future response of the circuit. The MPC, an advanced control approach, has the potential to estimate the future behaviour of the model in a predictive manner. Hence, to control the power of the resonant inverter connected with a 3.36 kW heating load, MPC is applied. The simulation results verify the validity of the power control of a solar-based series-resonant inverter using the MPC algorithm.

The design problem of radar waveform to enhance target delectability while ensuring spectral compatibility is considered. Precisely, an iterative sequential optimisation algorithm is developed to jointly optimise signal-to-interference-plus-noise ratio and stopband frequency energy. In each iteration of the proposed algorithm, the multidimensional optimisation problem is turned into multiple one-dimensional optimisation problems with closed-form solutions. Finally, the computational cost and objective value of the proposed algorithm in comparison with the existing method is assessed.

A knowledge-aided space–time adaptive processing (STAP) is a quite useful technique to suppress non-stationary and heterogeneous clutter. It estimates a covariance matrix by combining a conventional covariance matrix based on secondary data with a synthesised one by prior information. A new combining method is presented, where weight vectors, rather than constant weights, are used to combine two covariance matrices. In this method, the weight vectors are derived in a way to maximise clutter-to-noise ratio of the combined covariance matrix. A numerical simulation is conducted for a bistatic radar scenario where clutter non-stationarity and heterogeneity can be assumed and the performance of the proposed method is demonstrated in terms of clutter suppression and target detection.

The problem of estimating the direction-of-arrivals (DOAs) of multiple groups of coherent signals with uniformly linear array (ULA) is addressed. An iterative root-MUSIC method is proposed to refine a given coarse DOA estimation by investigating the information carried by the coherency structure among incident signals. The refinement processes for the DOAs associated with distinct sources are implemented in a parallel fashion. Meanwhile, the proposed method is search-free and maintains the effective array aperture. Compared with several representative DOA estimators, numerical examples have verified the effectiveness of the proposed method.

A block filtering method to reduce sidelobes in random noise and linear frequency modulated signals is investigated. Brief theoretical methodology for this method is reviewed. Simulation and experimental results are discussed.

A knowledge-aided mono-pulse forward-looking imaging algorithm to enhance the performance of airborne radar is proposed. Firstly, the ideal mono-pulse imaging model based on the dual-channel radar system is analysed and the mismatch model of the receiving channel is constructed. Then the mismatch phase error and a modified mono-pulse curve (MPC) are derived based on the least square (LS) method by taking advantage of a prior antenna pattern information. Finally, the modified MPC is utilised to perform the direction-of-arrival (DOA) estimation of each scattering centres in mono-pulse imaging. Real airborne radar data experiments are given to verify the effectiveness of the proposed algorithm.

To tackle the problem of the uncertainty of EM wave propagation velocity in the subsurface medium, a novel sparsity-based autofocusing imaging method for stepped frequency continuous wave ground penetrating radar system is proposed. On the basis of the parametric sparse recovery method, the proposed imaging method exploits the sequential L ₀ and L ₂ norms minimisation strategy to simultaneously retrieve the EM wave propagation velocity information and the high-quality focused image. Experimental results demonstrate the validity and effectiveness of the proposed imaging method.

This Letter presents a technique for implementing circuits with multiple subthreshold swings. Such circuits are of particular interest to large-area and flexible electronics, including active matrix displays and sensors. In these circuits, devices with large swings may be used for high-precision analogue driving, whereas steep subthreshold devices may be used for fast and low-power switching. This Letter demonstrates that large swings may be obtained by the series connection of diode structures to the source terminals of steep subthreshold devices. In principle, this technique is applicable to a wide range of thin-film transistors, but it is particularly well suited for heterojunction field-effect transistors where the gate heterojunctions may be readily utilised as diodes without altering the fabrication process or increasing the number of mask steps. Implementation of multiple subthreshold swings is demonstrated experimentally and described by a first-order model.