Synthetic transmit aperture focusing (STAF) has the problem of high computational complexity. An STAF scheme with greatly reduced computational complexity by using an optimal periodic sparse receive array (SRA) is proposed. An analytic method to design optimal SRAs that provide minimum main lobe width and grating lobe levels for a given number of active receive elements is also suggested. The experiment results show that the proposed STAF method can reduce computational complexity by up to 66.67% compared with conventional STAF.

A practical method to achieve both decoupling and six polarisation states by employing the mode-based approach for a four-element antenna is presented. The eigenmode theory as well as a practical implementation scheme are presented. The resulting approach can operate with vertical, horizontal, slant +45°, slant −45°, right-hand circular polarisation, or left-hand circular polarisation. A prototype has been manufactured and measured results show good agreement with simulations.

A broadband circularly-polarised monopole antenna is proposed. The broadband property of the antenna is basically achieved not only by the chifre-shaped monopole radiator, but also its asymmetric feed. The circular-polarisation characteristics are greatly enhanced by adjusting the location of the monopole microstrip-feed. The antenna delivers good performance on impedance matching and circular polarisation. The measured results demonstrate that the impedance bandwidth is 72% and the 3-dB axial-ratio bandwidth reaches 41.6% with a central frequency of 2.5 GHz.

Diode-switching that can be used to introduce frequency agility into antennas produced by thermal transfer printing is demonstrated. The particular example is a triangular Sierpinski fractal pattern with two PIN diodes to switch between operation optimised for the 800 MHz ultra-high frequency (UHF) band (diodes on) and 2400 MHz ISM band (diodes off). Our measured results show an improvement in S ₁₁ in the UHF band from −2 to −28 dB and from −7 to −30 dB at 2400 MHz, when switching the diodes appropriately. The measured bandwidth is 200 (1000) MHz, and the measured directivity is 3.1 dB (5.2 dB) while the measured gain is −5.2 dB (6.7 dB) for the diodes on (off).

An experimental study of the conditions for negative energy refraction and negative phase refraction in lossy metamaterials is provided. In hypothetical non-lossy metamaterials, the angles of phase and energy refraction are one and the same. Using measured S-parameters of split ring resonator–wire metamaterial samples, it is shown that negative refractive index is not a requirement for negative energy refraction in lossy metamaterials. It was assumed that the sample is effectively homogeneous and isotropic in the direction of wave propagation. For transverse-electric polarisation, negative energy refraction with a positive refractive index was demonstrated.

A new off-grid direction-of-arrival (DOA) estimation method based on a parametric sparse representation model is addressed for incoherently distributed non-circular sources. The parametric sparse representation model exploits the signal non-circularity to double the number of measurements, and is parameterised by the angular spread and the quantisation error. On the basis of this model, an improved generalised approximate message passing technique is utilised to estimate the central DOA. Numerical simulations are provided to illustrate the excellent performance of the proposed method.

A novel energy efficiency (EE) is introduced, which is defined as the ratio of the average transmission rate to the total consumed power. On the basis of this, a suboptimal energy efficient power allocation (PA) scheme is developed for the distributed antenna system with antenna selection over the composite fading channel. A Newton's method-based practical iterative algorithm is presented to find the solution of PA in this scheme. Compared with the conventional energy efficient PA scheme, which requires the instantaneous channel state information (CSI), the developed scheme only needs the statistic CSI, and thus it has good robustness and low overhead. Moreover, it can obtain an EE performance very close to that of the optimal scheme. Simulation results verify the effectiveness of the proposed scheme.

A simple method is proposed to significantly enhance the broadside directivity of a simple slot antenna over a wide bandwidth. This improvement is achieved by introducing a simple optimised dielectric superstructure with an axial variation of permittivity. In this antenna, both the superstructure and ground plane are cylindrical in shape with an area of 1.62λ₀ ². The antenna has a measured peak directivity of 18.1 dBi and an extremely wide 3 dB directivity bandwidth of 51.1%. A WR-75 waveguide is used to feed the slot antenna. The antenna is well matched over the entire directivity bandwidth, which extends from 8.75 to 14.75 GHz. The measured average aperture efficiency is ∼88% over the 3 dB directivity bandwidth.

A very simple ring-oscillator voltage-controlled oscillator (VCO) structure for use in VCO-ADC applications is presented. It has a greatly improved linearity compared with previously published VCOs. Measurement results of a 1 V, 65 nm CMOS prototype confirm the effectiveness of the proposed approach.

Novel simplified merged processing element (SMPE) architectures to design a low-complexity successive-cancellation (SC) polar decoder are presented. The proposed SMPE architectures reduce the number of sign-magnitude conversions and switch networks, relative to those of the conventional merged processing element. Synthesis results show that the (1024, 512) SC polar decoder using the proposed SMPE architectures significantly decreases hardware complexity and improves technology scaled normalised throughput, as compared to those of the previously reported architectures.

A chattering free adaptive integral sliding mode control (AISMC) for a nuclear research reactor system in the presence of system uncertainties and input perturbation is presented. The proposed control method ensures finite time stability and also eliminates the chattering phenomenon. Also, using a deadzone technique, the upper bound of unknown system uncertainty can be estimated. The proposed AISMC can compensate for a reactivity feedback term significantly affecting the reactor system in the form of input perturbation, which is not possible in the case of integral sliding mode control (ISMC). Through simulation results, the effectiveness of the proposed controller is compared with the ISMC method for a nuclear research reactor system, and the effectiveness of the proposed control method is confirmed.

Speeded up robust features (SURF) is one of the most popular feature extraction algorithms used for detecting, recognising, and tracking objects in various applications. However, it is not suitable for real-time implementation because its operating speed does not satisfy real-time constraints. In this Letter, operating speed is highly dependent on the amount of computations required for the Haar wavelet response (HWR) step, and present a fast descriptor extraction method that eliminates repeated operations in the HWR step is shown. Experimental results show that the proposed method (PM) can achieve operation time-savings of approximately 27% without using additional resources, while the descriptor extraction performance of the PM is exactly identical to that of the original reference software.

How to represent an image is an essential problem of the image retrieval task. To build a powerful image representation, a novel method named cross-regions-pooling (CRP) combining two key ingredients is proposed: (i) region proposals detected by objectness detection technique; (ii) deep attributes (DA), i.e. the outputs of the softmax layer of off-the-shelf convolutional neural network pre-trained on a large-scale dataset. The ultimate representation of an image is the aggregation (e.g. max-pooling) of DA extracted from all the regions. In addition, a multi-scale orderless pooling strategy considering layout of contexts of an image is proposed to integrate with CRP to improve the image representation. Experimental results on standard benchmarks demonstrate superiority of the proposed method over state-of-the-arts.

A novel iterative equaliser, the 2-dimensional iterative soft decision interference cancellation (ISDIC) (2D ISDIC) equaliser, is introduced. The 2D ISDIC is the first equaliser that bridges the gap between the low-complexity ISDIC equaliser which has poor performance, and the high-complexity inverse-channel equalising methods, such as the LMMSE and the MMSE ISDIC equalisers, which have better performances. The 2D ISDIC will be incorporated into the turbo equalisation scheme, resulting in an enhanced turbo equaliser, that performs better than the conventional, state of the art, linear turbo equaliser, with lower complexity and lower amount of iterations.

A new reflectometry-based wire diagnosis method using chaotic signals is presented. It shows excellent potential for the diagnosis of live wires (i.e. during their operational usage) and complex topology networks. The use of chaotic signals for distributed diagnosis and the detection of defects in wires is investigated. Chaos time-domain Reflectometry (CTDR) using low auto-correlation sidelobes signals, shows high performances in very noisy environment: the detection and location of hard defects are possible, even if several reflectometers inject their signals concurrently with the diagnosis and the normal operation of the cable. This enables using CTDR for distributed diagnosis of complex topology networks.

Runs distribution test is an important statistical test based on Golomb's randomness postulates. It is an important randomness test included in some famous evaluation standards and statistical test suites such as Application Notes and Interpretation of the Scheme (AIS20), the Federal Information Processing Standards (FIPS140), CryptX, and so on. However, when it is applied on some well-known good Deterministic Random Bit Generators (DRBGs), the test results show apparent bias from randomness. This shows that there exist some inaccuracies in the runs distribution test. The problem is solved and the runs distribution test through two ways is corrected. First, the degree of freedom of statistical value V is adjusted. Secondly, the expected number of different lengths runs is modified. The experiment results show that the corrected runs distribution test is more accurate under two-level evaluation approach proposed by National Institute of Standards and Technology (NIST) Special Publication (SP) 800–22.

Biomedical signals transmitted over the internet are usually tagged with patient information. Data hiding techniques such as steganography ensures the security of such data by hiding the data into signals. However, data hiding results in signal deterioration that might affect diagnosability. A novel technique which uses curvelet transforms to hide patient information into their ECG signal is presented. Curvelet transform decomposes the ECG signal into frequency sub-bands. A quantisation approach is used to embed patient data into coefficients whose values are around zero, in the high-frequency sub-band. Performance metrics provide the measure of watermark imperceptibility of the proposed approach. BER is used to measure the ability to extract patient data. The proposed approach is demonstrated on the MIT-BIH database and the observations validate that its performance is superior compared with the random locations approach. Although the performance of the proposed approach decreases as patient information size increases, the peak signal-to-noise ratio values are high. Therefore, the proposed approach can be used for the safe transfer of patient data.

It has been shown that input queued (IQ) switches have throughput limitations when loaded with multicast traffic. However, if circulation of packets is allowed, the IQ switches can be non-blocking for any admissible multicast traffic scenario using only a speedup of two. The non-blocking frame based algorithm for scheduling the multicast traffic is proposed.

A two-stage iterative method is proposed to design prototype filters for a fast filter bank with low complexity, which is aimed at controlling the optimum ripple magnitude tolerance of each filter according to the overall specifications. This problem is formulated as an optimisation problem for which the total number of multiplications is to be minimised subject to the constrained ripple in the passband and stopband. A two-stage iterative solution is proposed to solve this optimisation problem for the purpose of obtaining impulse response coefficients with low complexity at each stage. Simulations have been conducted to verify the performance of the proposed scheme and show that compared with the original method the proposed scheme can reduce the number of multiplications by about 20.02%.

A new technique to measure a capacitor or a capacitive sensor by means of a direct sensor-to-microcontroller interface circuit that does not need a calibration capacitor is proposed. Basically, the measurement process consists of three consecutive steps of charge, discharge and charge of the capacitor under test. A non-linear equation is obtained and solved that is dependent only on known circuit parameters. Experimental results show that it is possible to measure a wide range of capacitor values with a maximum deviation of 2% from the reference value, and that temperature changes from 18 to 70°C yield relative errors below 0.1%. For the lowest measured capacitor range (33 pF–4.7 nF) the uncertainty holds below 1 pF which enables measurement of commercially available capacitive sensors. The main advantage of the proposed technique is cost and space reduction of the final design.

A 67–80 GHz double-balanced Gilbert-cell mixer fabricated in 0.1 μm gallium arsenide pseudomorphic high-electron-mobility transistor technology is presented. Two Marchand baluns were placed in RF and local oscillator (LO) input ports to convert single-ended signals to differential signals for wideband use. A differential amplifier between the switch and output stages was used to enhance the conversion gain (CG). The mixer demonstrated an average CG of 14.1 ± 2.1 dB at an LO power of 0 dBm from 67 to 80 GHz. The measured intermediate frequency 3 dB bandwidth was 3 GHz and the input 1 dB compression point was −4.8 dBm.

A generalised two-box cascaded Hammerstein-like (GTBC-H) digital predistorter is proposed for linearising wide-band RF power amplifiers (PAs). The GTBC-H predistorter is composed of a static nonlinearity block for countervailing the strong static nonlinearities and a dynamic nonlinearity block for compensating the memory effects of RF PAs. The proposed predistorter adds extended cross-terms of the leading terms and some lagging envelope terms in the dynamic nonlinearity block to compensate the memory effects of wide-band RF PAs more effectively. A 460 MHz and a 1.94 GHz Doherty RF PA are utilised to validate the performance of the proposed predistorter when a three-carrier wide-band CDMA and a single-carrier long-term evaluation signal are applied separately. The validation results illustrate that the proposed GTBC-H predistorter can further suppress the residual out-of-band emission over the augmented Hammerstein, the enhanced Hammerstein and the parallel-LUT-MP-EMP predistorter.

A miniature CMOS dual balun which can be applied to a star mixer or a power amplifier for four-way equal power dividing is reported. Compared with the four output coupled lines, the input coupled line has two-fold metal width to achieve ideal coupling coefficient of 0.408. This is the way to achieve nearly perfect input-port impedance matching and output-port transmission properties. The dual balun occupies a small chip area of 0.0252 mm² and achieves S ₁₁ smaller than −12 dB for frequencies of 50–110 GHz. For frequencies of 55–65 GHz, the dual balun achieves excellent S ₂₁ of −7.6∼−7.9 dB, S ₃₁ of −7.9∼−9 dB, S ₄₁ of −7.5∼−7.9 dB, S ₅₁ of −7.8∼−8.9 dB, magnitude of amplitude imbalance (MAI) of 0.34–1.1 dB and phase difference (PD) of 179.22°–180.78° for ports 2–3 and MAI of 0.3–1 dB and PD of 178.83°–180.48° for ports 4–5. The state-of-the-art results of the dual balun indicate that it is suitable for millimetre-wave systems.

A novel package integrated solution for gallium nitride high-electron-mobility transistors with an electronically two-dimensional reconfigurable L-section matching network is presented. Thick-film barium-strontium-titanate (BST) varactors are used to realise a tunability of the load impedance of 1:2 in resistive and 1:1.5 in reactive parts, respectively, applying tuning voltages of up to 200 V. The tuneable module achieves a peak output power of 43.2 dBm (20.9 W). Comparison with simulated results using field simulations and a large-signal model shows good agreement in terms of output power and power added efficiency and thus proves the concept of using metal–insulator–metal BST varactors for reconfigurability.

An underwater optical wireless communication (UOWC) system is considered. For such system, a zero-padding (ZP) block-transmission scheme is presented to reduce the influence of inter-symbol-interference. Simulation results, which are based on the existing experimental data of channel pulse response, show that ZP system is effective especially for serious dispersive channel with high data rates and thus, potentially applicable to the high data rate UOWC systems.

In this reported work, the analogy between parallel electrical arcs and memristors is extended to high-impedance faults such as carbonised paths and circuit openings. First, it is demonstrated that the conductance from the high-impedance Mayr model behaves like a particular memductance sensitive to the integral of the squared current. Then, the current–voltage plot confirms the memristive behaviour of high-impedance faults, both by simulation and with experimental results.

Bottom gate, top contact thin-film transistors (TFTs) with transparent Sn-doped zinc oxide as the active layer have been fabricated on glass substrate at room temperature. Indium tin oxide, alumni zinc oxide (AZO) and Al thin films serve as the source/drain (S/D) electrode. It turns out that devices with AZO S/D electrodes exhibit preferable properties such as a saturation mobility of 13.6 cm²/Vs, a subthreshold slope of 381 mV/decade, a Vth of 3.47 V and an on/off current ratio of 3.1 × 10⁷. Moreover, the superior output characteristic and lower parasitic resistance demonstrate the excellent contact performance of the tin-zinc oxide TFTs with AZO S/D electrodes.

The performance of LEDs with Ga-doped ZnO (Ga:ZnO) and Sn-doped In₂O₃ (ITO) current-spreading layers (CSLs) has been evaluated at high injection current densities. LEDs with electron beam-hydrothermally deposited Ga:ZnO transparent CSLs showed improved performance compared to electron beam deposited ITO at all current densities. External quantum efficiency and wall plug efficiency were both higher for blue emitting LEDs with ZnO. Luminous efficacy increased greatly for the ZnO-based CSL with a peak value of 113 lm/W compared to 82 lm/W for the ITO-based CSL, a 37% improvement.

An active add-on option for 208 V_LL/60 Hz passive three-phase rectifiers is presented. The active optional circuit is implemented as ‘centre-tapped’ full-bridge stage and guarantees low-harmonic input currents and unity power factor. The active unit is able to operate for a wide frequency range and therefore applicable for high- (e.g. >100 kW) and low-power applications. Some basic considerations such as principle operation, duty cycles, voltage/current stress of switches and design of inductors are discussed and additionally supported by simulation results. Applicability of emerging wide bandgap power devices such as silicon carbide MOSFETs, which improve converter efficiency and power density, is furthermore briefly discussed.

A potential approach for designing and fabricating igniter for compact fluorescent lamp is introduced using high-voltage DC (HVDC) source which is controlled by gate pulse obtained from TRIAC-based firing circuit. The Cockroft–Walton voltage multiplier circuit is used to design HVDC (2 kV) source where initially optimal rating of capacitance for each stage was considered based on experimental analysis. This design was further simulated by Multisim 11 and characterised experimentally. The response obtained by this method reveals that the HVDC source is able to ignite the fluorescence lamp potentially than the conventional available ignition processes. The major advantages of using HVDC are lower power to ignite fluorescence lamp, longer life and cost effective.

The highest power transfer efficiency (PTE) of the magnetic resonance wireless power transfer (WPT) system with two transmitters (TXs) and a single receiver located at an arbitrary position can be obtained by adjusting the amplitude ratio and the phase difference (PD) of the signals of two adjacent TXs. The coupling coefficient between two coils is calculated, and is used to establish an equivalent circuit model for a WPT system with two TXs. Using the circuit model, the PTE of the WPT system (which is a function of the amplitude ratio and PD) is extracted. The optimum conditions of these values to achieve the highest power efficiency can be analytically determined. The experimental results agree well with the simulated results based on the analysis. The result shows that the suggested optimised transmit scheme can achieve the highest PTE for a magnetic resonance WPT system with two TXs.

An analytical method for calculation of total coupling coefficient between two helical resonators is presented. The ratio of electric to magnetic (EMR) coupling coefficient is calculated by approximating the electric and magnetic fields of the resonator with TE₁₀ and TM₁₀ spherical modes. A helical resonator is wounded to verify the analysis and simulation results.

A rapid design approach to achieve the optimal efficiency in a magnetic resonant wireless power transfer (MR-WPT) system is presented. A concise design guideline is provided to determine the optimal efficiency condition and related coupling coefficients. Experimental validations are demonstrated by both simulation and measurement results of a 6.78 MHz MR-WPT system prototype with the maximum efficiency of 76.1% at a 50 mm distance between transmitter and receiver.

People tracking is a key building block in many applications such as surveillance, abnormal activity detection and the monitoring of elderly persons or persons with restricted mobility. In this reported work, the problem of multipath signals, which is one of the main challenges in indoor and urban environments, is addressed. The proposed method integrates the aspect dependence feature of multipath signals into the tracking framework which allows making full use of more potentially useful information in the time domain in order to make more accurate decisions and to relax some constraints in the space domain such as the large number of antennas that are placed over a large area. An important feature of the proposed method is that it can suppress/mark the entire multipath track; furthermore, it does not assume any prior knowledge of the environment.

A 45 nm high In component metamorphic In_0.7Ga_0.3As/In_0.6Ga_0.4As composite-channel high electron-mobility transistor (mHEMT) on GaAs substrate with good DC and RF performance has been developed. The structure was grown by molecular beam epitaxy and exhibits a superior electron mobility of 10200 cm²/(V.s) and a sheet density of 3.5 × 1012 cm⁻² at a room temperature. A combined optical and e-beam lithography technology was used to achieve the nanometre mHEMT device. The mHEMT device shows an extrinsic transconductance of up to 990 mS/mm and a maximum current density of 910 mA/mm. The unity current gain cutoff frequency f_T and the maximum oscillation frequency f _max are 187.94 and 258.62 GHz, respectively. These performances make the device well suited for millimetre-wave applications.

The design of unimodular sequences of even length N that possess impulse-like periodic correlation and non-zero complementary correlation coefficients at lags l = −N/2 and l = N/2, is addressed. The parameters that define the sequences are determined by minimising the integrated side lobe using the limited-memory Broyden-Fletcher-Goldfarb-Shanno optimisation method. It is shown that the objective function and its gradient can be efficiently evaluated using the fast Fourier transform.

Although the state-of-the-art i-vector-based probabilistic linear discriminant analysis systems resulted in promising performances in the National Institute of Standards and Technology speaker recognition evaluations, the impact of domain mismatch when the system development data and the evaluation data are collected from different sources remains a challenging problem. This issue was a focus of the Johns Hopkins University 2013 speaker recognition workshop where a domain adaptation challenge (DAC13) corpus was created to address it. The cross-domain variation compensation (CDVC) approach has been recently proposed to address it when in-domain development data are available. The work reported by the present authors addresses this issue when in-domain development data are unavailable using a library of CDVC transforms. This approach is evaluated on the DAC13 corpus and is shown to be more powerful than nuisance attribute projection-based inter-dataset variability compensation and the whitening library.

An Alamouti-type orthogonal space–time-block-code transmission over a relay-based cooperative-diversity system under the influence of the cooperating nodes’ mobility is considered. It is shown that the high nodes' mobility destroys the optimality of the conventional Alamouit's decoder (ALD) employed at the system's destination, which causes severely degraded error performance. A zero-forcing-space–time-decoder is proposed, to be applied instead of the ALD, and its capability of mitigating this severe impact of the nodes' mobility is shown.

A one-pin crystal oscillator (XO) employing a one-pin startup and self-charged architecture is proposed to reduce power consumption. The self-charged circuit, replacing a constant-current opamp, recharges crystal to save significant power. The proposed 32.768 kHz one-pin XO, fabricated in a 0.18 μm CMOS technology, consumes 2.89 nW from a 0.25 V supply.

The booming of user groups challenges the flexibility of satellite communication systems. A unified modulation and demodulation design for satellite communication systems based on a mathematical mapping and basis expansion model is proposed. The phase shift keying, quadrature amplitude modulation and continuous phase modulation are implemented via the setting of two model structures, the mapping table which unifies mapping processes with and without memory, and the basis expansion coefficient matrix which consistently represents different waveforms. Simulations show that the communication performance of the system with unified design equals and even overmatches classical separated systems.