A new procedure to measure the apparent reflection coefficient of differential patch antennas at 60 GHz is described. The measurement method makes use of two WR15/microstrip-line (MSL) transitions which are simple to realise. The experimental results are compared with simulated results. This comparison emphasises the limited effect of transition losses on measurement accuracy.

A novel and simple approach to adjust the polarisation properties of a microstrip patch antenna in the entire axial ratio (AR) range is proposed. The proposed antenna consists of a radiating patch and a parasitic strip separated into two parts, and the separated strip is placed at the outer perimeter of the patch for capacitive coupling. This structure enables the antenna to induce opposite-direction currents on the strip, which allows flexible polarisation adjustment by moving the separated positions of the strip. For evaluation, two antennas with linear and circular polarisations are fabricated, and their performance is measured in a full anechoic chamber. The results prove that the proposed approach is suitable for flexible AR adjustment without a significant degradation of the matching characteristics and the design complexity.

A compact planar UWB-MIMO antenna array with WLAN band rejection is presented. The array consists of four monopole radiators and a common ground plane. These monopoles are placed in such a way that the polarisation diversity of nearly placed radiators is exploited, resulting in high isolation. The proposed MIMO antenna array is electrically small (50 × 39.8 mm²), printed on a low loss 1.524 mm thick Rogers TMM4 laminate with a dielectric constant of 4.5 and a loss tangent of 0.002. A band-stop design was inserted on the ground plane to behave similar to a LC band-stop filter and reject the WLAN band. Simulation and measurement results satisfy the return loss requirement of better than 10 dB and isolation better than 17 dB over the entire 2.7–5.1 and 5.9–12 GHz bandwidths.

Three different metamaterial absorbers based on ultra-thin multi-layer structures, with different bandwidth characteristics, are presented. The proposed structure is composed of three vertically stacked metal-dielectric layers backed by a metal ground. All the metallic patches are of crossed dipole shape and have different geometrical dimensions, which can be manipulated to design triple-band, 3 dB and 10 dB absorbers separately. The designed structures are polarisation-insensitive as well as wide-angle absorptive for both TE and TM polarisations. The 10 dB broadband structure, exhibiting an absorption bandwidth of 7.5% at 10 GHz, has been fabricated and the absorption performance has been verified with the simulated response. The proposed absorber has the advantages of ultra-thin thickness (λ ₀/50 corresponding to the centre frequency), compact size, simpler design, tunable absorption bandwidth and experimental validation, which makes it a promising candidate for many potential applications.

An energy-efficient successive approximation register (SAR) analogue-to-digital converter (ADC) switching scheme is proposed for low-power biomedical applications. By dramatically reducing energy consumption in the first three bit-cycles, the average switching energy of the proposed scheme is reduced by 98.8% compared with the conventional architecture. The number of capacitors in the capacitor array of this proposed scheme is also reduced by 75.5% over the conventional approach.

A column-level two-step analogue-to-digital converter (ADC) structure for infrared focal-plane array (IRFPA) is proposed. The first step adopts a 16-column-shared 6-bit flash ADC to accomplish the coarse conversion of 16 columns one by one. Owing to the staggered code and correction, a dynamic comparator is adopted in the flash ADC and the power dissipation of a flash ADC averaged to one column in period is only 0.386 μW. The second step is SAR conversion of which the cycle time is prolonged. The input voltage variation of the comparator in the charge redistribution structure is decreased to tens of millivolts; so a 1.8 V power supply is adequate in spite of 5 V V _FS. The power dissipation of this comparator is reduced to 5.966 μW. Also, the lower clock frequency of the SAR logic reduces the dynamic power. A 14-bit two-step ADC is designed in 0.18 μm process and the equivalent power dissipation of the proposed ADC structure for one column is <20 μW.

A new switching method for the stabilisation of a one-dimensional capacitor array tank for the stepwise charging of a load capacitor is presented. In this method, the tank capacitor configuration is rearranged in a circular manner once the charging process of a load capacitor finishes and before the charging process of a new load capacitor begins. Unlike previously reported methods, this method does not require backward switching for the stabilisation of tank capacitor voltages. Hence, the proposed method reduces the number of charging process steps by a factor of up to 2 compared with the conventional method. Moreover, since the tank recycles its charge inherently, the capacitive load can retain its charge after the charging process finishes without the problem of instability. Systematic MATLAB simulation, post-layout simulation in 0.18 μm technology and a fabricated printed circuit board prove the benefits of the proposed method and the provided analytical derivations.

A concurrent 10.5/25 GHz power amplifier (PA) is designed and implemented in a 0.18 μm CMOS technology. This PA employs dual-band matching networks that can suppress harmonics, inter-modulation products, and out-of-band signals so as to improve linearity performances. Moreover, the driver stage of the PA utilises a current-reused topology which increases the gain without increase of the power dissipation. The chip size of the PA is 0.95 × 0.91 mm² including testing pads, and its power consumption is 150 mW. The PA exhibits a measured gain of 15.2 and 6.8 dB, output P _1dB of 10.5 and 9 dBm, P _out,max of 11.4 and 10 dBm and power added efficiency of 9 and 4.8% at 10.5 (f ₁) and 25 GHz (f ₂), respectively. The measured rejection of signals at 4 GHz (f ₂–2f ₁), 14.5 GHz (f ₂ − f ₁) and 21 GHz (2f ₁) is 43, 16.5 and 10.8 dB, respectively.

An all-digital phase frequency detector design capable of accepting an infinite range of input frequency differences and [0 2π] radians input phase difference is presented. The proposed phase frequency detector design minimises the dead zone, supresses unwanted output glitches, achieves a high maximum operating frequency, can drive high-capacitive loads and avoids differential outputs. The proposed phase frequency detector takes advantage of a fast reset operation from modified tristate inverters acting as a D flip-flop. Simulation results indicate that the design can detect input phase differences as small as 750 fs apart for all process corners at input operating frequencies of 38 kHz–2.5 GHz in 1.2 V, 90 nm CMOS technology.

A resolution-enhanced sturdy multi-stage noise shaping (MASH) delta–sigma modulator is presented. By employing the Leslie-Singh architecture in the first stage and an appropriate second stage digital filtering, the proposed structure could achieve much higher resolution [>80 dB signal-to-quantisation noise ratio] when compared with a traditional sturdy MASH, at a lower oversampling ratio (e.g. 8X). Interestingly, the mismatch between digital and analogue transfer functions is inherently shaped so that the structure is not sensitive to opamp finite gain error. Both these properties make the proposed structure suitable for wideband low-voltage applications. Behavioural simulations are presented to demonstrate the effectiveness of the proposed structure when compared with the prior art of its high performance delta–sigma counterparts.

A digital-based, process-supply-and-temperature independent voltage reference suitable to nanoscale CMOS technologies, which exploits the recently proposed ‘virtual reference’ concept to achieve a very low thermal drift, is presented. Its performance is assessed on the basis of simulations and experiments carried out on a microcontroller-based, proof-of-concept prototype and is compared with state-of-the-art integrated analogue and digital voltage references. A simulated (measured) thermal drift as low as 1 ppm/°C (5 ppm/°C) in the temperature range −40/+140°C (−10/+100°C) is reported.

A hardware design capable of supporting high-efficiency video coding (HEVC) inverse transform (IDCT) is developed for a 32-point transform unit using a single one-dimensional (1D) transform core with two transposed memories to reduce area overhead. The proposed 1D core employs two calculation paths to obtain high throughput and is able to calculate first-dimensional (1st-D) and second-dimensional (2nd-D) transformations simultaneously along two parallel paths. The results from a practical implementation of the chip demonstrate that the proposed design presents the smallest circuit area among existing 2D transform cores.

Each pixel in a full-colour image has three colour values, and warping of the colour image requires three times the computational load of a greyscale image. A new colour image warping is proposed for enhancing computational efficiency in real-time video applications. Considering that a colour filter array (CFA) is commonly utilised in an image sensor, the raw CFA image obtained from the image sensor is warped before colour reconstruction. The computational load is only one third of the conventional colour image warping.

Fully transparent dual-layer Ga-doped zinc oxide (GZO) thin-film transistors (TFTs) were fabricated on flexible plastic substrate by room temperature processes. The GZO thin films are deposited by radio-frequency sputtering according to the variation of the depositing time in order to optimise the performance of GZO TFTs. The results show that dual-layer GZO TFTs exhibit excellent electrical properties, mechanical flexibility and optical transparency. A saturation mobility μ _s of 350 cm²/V.s, a linear field effect mobility of 281 cm²/V.s, a threshold voltage V _TH of 3.2 V, a steep subthreshold swing of 268 mV/decade, a low off-state current value (I _OFF) of 1.5 × 10⁻¹¹ A and a high on/off ratio of about 10⁸ were extracted. The TFTs also have admirable transparency with an average visible transmittance of 87.2%. These results indicate that GZO material is suitable for the next generation flexible displays.

A robust fitting algorithm for geometric computer vision problems under the L_∞ -norm optimisation framework is presented. It is essentially based on the maximum feasible subsystem (MaxFS) but it overcomes the computational limitation of the MaxFS for large data by finding only a quasi-maximum feasible subset. Experimental results demonstrate that the algorithm removes outliers more effectively than the other parameter estimation methods recently developed when the outlier-to-inlier ratio in a data set is high.

Visual saliency estimation through label propagation is proposed. Since salient regions are generally distinctive from the background, visual saliency is estimated in an image by the similarity to salient and non-salient seeds. First, salient and non-salient seeds from the initial saliency map estimated by superpixel segmentation and three common priors are obtained. Then, labels of seeds are propagated to unlabelled superpixels based on label propagation to obtain the visual saliency map. Experimental results demonstrate that the proposed method is very effective in estimating salient regions in images compared with existing state-of-the-art methods.

Support vector data description (SVDD) is a data description method which gives the target data set a hypersphere-shaped description and can be used for one-class classification or outlier detection. To further improve its performance, a novel SVDD called SVDD+ which introduces the privileged information to the traditional SVDD is proposed. This privileged information, which is ignored by the classical SVDD but often exists in human learning, will optimise the training phase by constructing a set of correcting functions. The performance of SVDD+ on data sets from the UCI machine learning repository and radar emitter recognition is demonstrated. The experimental results indicate the validity and advantage of this method.

Multilevel coding (MLC) provides a low-complexity encoding scheme for lattices obtained via construction D. On the other hand, multistage decoding is also a practical decoding scheme for MLC provided that the underlying error correcting codes are capacity achieving, which requires using a powerful soft decoder for each code. Proposed is an approximation of the log-likelihood ratio (LLR) which used for the soft decoding of the different error correcting codes employed in the lattice construction. This approximation is based on the von Mises distribution and achieves, with lower complexity, the same error rate performance obtained with the exact LLR calculation.

A novel magic-T with bandpass filtering response using substrate integrated waveguide (SIW) technology is presented. The basic design concept is based on properly locating the two power-division ports in a dual-mode circular SIW cavity, whose field distributions are even or odd symmetric. Not only in-phase and out-of-phase operations can be achieved in the magic-T, but also filtering responses for the two operations can be obtained. This magic-T is fabricated in a single-layer PCB and measured results show that it is centred at 9 GHz with 70 MHz 3 dB bandwidth. Good measured performance of balance for magnitude (±0.35 dB) as well as phase (0°–5°) is also obtained within the passband.

A novel substrate integrated waveguide (SIW) highpass filter with sharp attenuation characteristics using shunt SIW resonant stubs is proposed. The highpass filter consists of a main SIW transmission line loaded with three shunt SIW resonant stubs. The three shunt SIW resonant stubs are used to realise the band-stop filter, whose stopband is designed to coincide with the transition band of the SIW highpass filter. Therefore, the sharp attenuation of the stopband filter contributes to the attenuation of the entire filter. To verify the concept, a filter prototype with a cutoff frequency of 16 GHz is designed, fabricated and measured. Another hybrid filter with the same specifications is fabricated and compared. The measured results show that the proposed filter has sharper attenuation characteristics than the hybrid filter.

A novel ultra-compact wide-band microwave cross-over using lumped components is presented for the first time. The proposed cross-over is composed by inductors and capacitors, and the explicit design equations are derived based on the even–odd mode method. The size of the proposed cross-over is 1 × 1 cm², and the bandwidth is 20–30%. Full-wave electromagnetic simulations are performed and an experimental prototype is fabricated to demonstrate the novel design concept. The measurement results match well with the theoretical and numerical results.

A compact microstrip ultra-wide stopband low pass filter using multimode resonators is presented. It consists of a narrow width microstrip line with high impedance and three multimode resonators. The characteristics and equivalent circuits of the multimode resonator are investigated. Owing to the strong slow-wave and bandstop effects, the multimode resonator can be implemented to achieve an ultra-wide stopband and size reduction. At the 3 dB cut off frequency of 1.8 GHz, the measured stopband of the low pass filter with 15 dB suppression is from 2.83 to 24 GHz. The physical size of the proposed low pass filter is 0.09λ _g × 0.11λ _g. The presented simulation and measurement results are in good agreement.

A compact microstrip diplexer for UMTS and WCDMA systems is presented. The size of the diplexer can be reduced by using capacitance loaded square meander loop resonators. Owing to the capacitance loaded arms, the resonator has the advantages of compact size and harmonic suppression. The two degenerate-mode resonances are used to form the lower and upper channel of the diplexer, respectively, which generate two transmission zeroes so as to obtain high frequency selectivity. Simulated and measured results are presented and show good agreement.

A new approach is proposed to act as an efficient design technique for the implementation of ultra-wideband (UWB) bandpass filters in integrated passive device technology. The proposed design is based on two major original contributions. First, the use of hourglass filter theory which, to the best of authors knowledge, has not been applied yet to such technology. Then, the minimisation of the number of inductors involved in the filter circuit through the zigzag technique. Implemented in 0.18 µm CMOS technology, the designed filter exhibits excellent performances such as two finite tunable transmission zeros, enhanced selectivity, a bandwidth covering the entire UWB spectrum of 3.1–10.6 GHz, a stopband rejection better than 15 dB throughout frequencies below 2.7 GHz and above 11 GHz, a good matching better than 11 dB, a minimum mid-band insertion loss of 1.8 dB and, finally, a sufficiently constant group delay. With these features and only 10 lumped elements, the proposed filter is one of the most promising compact filters for UWB applications.

A novel substrate integrated waveguide to rectangular waveguide (RWG) transition for effective power transfer is proposed. The substrate taper is inserted into a conventional height-stepped impedance transformer of the RWG region to improve transmission loss and bandwidth. The transition is designed to cover the entire K-band (18–26 GHz), showing a return loss of 20 dB. A back-to-back transition has been fabricated to verify the proposed transition. The experimental results show good agreement with the analysis. The transmission loss of the stand-alone transition is 0.22 dB at 21.7 GHz with a usable bandwidth of 36%.

The use of microplasma discharges as power-induced limiter elements in microstrip devices is proposed to protect receivers against high-power microwave threats. A microstrip bandpass filter integrating such a microplasma-based active microwave power limiter has been designed and measured. Power limitation is observed when the input power exceeds 19 dBm with a leakage power of 14 dBm. Due to the gaseous properties of the active medium, the proposed structure exhibits a very low additional insertion loss of 0.06 dB.

A novel method is employed for the derivation of an analytical model for a carbon-dioxide (CO₂) gas sensor based on graphene nanoribbon (GNR) conductance variation. The capacitance gradient created between the channel and the gate of a field effect transistor device is employed as an important property in the interpretation. Gas concentration and its effect on capacitance are incorporated as a modelling platform. In another attempt to model the electrical conductance in GNRs, an intelligent artificial neural network scheme is used in the modelling stage. A satisfactory agreement is presented by comparison between the empirical data extracted from a study conducted by Yoon et al. and the proposed models.

The trade-off between transmission performance and hardware implementation in application-specific integrated circuits of digital backpropagation (DBP) in coherent 32 GBd polarisation-division multiplexing 16 quadrature amplitude modulation is analysed. The reach is optimised for different DBP implementations under constraints of 16 and 28 nm complementary metal–oxide–semiconductor (CMOS) technology digital signal processing (DSP) area.

A high-speed and energy-efficient oxide-confined 850 nm vertical-cavity surface-emitting laser (VCSEL) for optical interconnects is presented. A record-high modulation bandwidth of 30 GHz is reached for a 3.5 µm oxide aperture VCSEL, with 25 GHz bandwidth already at a bias current of 1.8 mA. The high bandwidth at low currents enables energy-efficient transmission with a dissipated heat energy in the VCSEL of <100 fJ/bit at 25, 40 and 50 Gbit/s.

A novel fabrication method of buried-heterostructure (BH) mid-infrared quantum cascade lasers (QCLs) by using non-selective regrowth of iron-doped indium phosphide (InP) (Fe:InP), around deeply etched laser ridges, via metal-organic chemical vapour deposition (MOCVD) and planarisation via chemical polishing is reported. Owing to better heat dissipation, the fabricated 4.75 μm emitting QCLs exhibit about three-fold enhancement in maximum output power under continuous-wave operation at room temperature (T = 20°C) compared with that from lasers without the regrown InP. The demonstrated fabrication method provides a more flexible route to realising BH QCLs by removing strict requirements on the etched-ridge sidewall profile, as well as on the physical dimensions of the dielectric mask for the regrowth via MOCVD. The method can be further employed for making large-emitting aperture, closely packed arrays of QCLs, with planarised geometry, for coherent-power scaling.

Laser Doppler vibrometers (LDVs) both in a bulk optics and fibre optic format have been available for more than 30 years. Calibration of the vibrometer at fixed frequencies varies from counting fringes at low frequencies to measuring the displacement from the Doppler velocity. The proposed method for calibration exploits the properties of the optical vibration spectrum which can be described by Bessel functions of the first kind making it intrinsic to the vibrometer itself and not requiring any additional optical equipment. Calibration was achieved using an electric shaker to generate the vibration signal over a range of frequencies. Ideally the shaker should be calibrated but this is not required in the proposed system. This approach enables the maximum vibration amplitude and the minimum amplitude to be determined. In addition, an example of the calibration of a LDV is presented in which a minimum displacement of 1.6 nm at 4 kHz was achieved.

The fabrication of orange-emitting semiconductor laser on interdiffused InGaP/InAlGaP structure is reported. The lasers lased at 22°C at a wavelength as short as 608 nm with threshold current density of 3.4 KAcm⁻² and a maximum output power of ∼46 mW. This is the shortest wavelength electrically pumped semiconductor laser emission from the InGaP/InAlGaP structure.

An Nd:YVO₄ laser with intracavity frequency doubling exhibits two mode-locked states with different repetition rates. The two states may coexist, interact and transform from one to the other as the cavity length is varied. The transition from one dominant state to the other takes place continuously. The proposed effect is evidence of a bifurcation phenomenon.

An AlGaAs/GaAs quantum well (QW) laser is fabricated with GaInP and AlGaInAs asymmetric barrier layers (ABLs) and its light–current characteristic (LCC) is compared with that of a reference conventional QW laser without ABLs. It was found that the use of the ABLs suppresses the sublinearity of the LCC at high current densities. As a result, the maximum lasing power of 9.2 W, being limited by catastrophic optical mirror damage, is achieved at a considerably lower operating current in the laser with ABLs as compared to the reference laser (12.5 against 20.2 A). The ABL effect is associated with the suppression of the parasitic recombination in the optical confinement layer, as confirmed by a decrease of the intensity of the spontaneous emission from the layer.

Airborne synthetic aperture radar (SAR) image quality considerably degrades because of motion errors. High-precision motion compensation (MOCO) is necessary in an advanced SAR data processing scheme. In the case of ultra-high resolution, the conventional two-step MOCO algorithm introduces significant range cell migration correction (RCMC) error which causes a loss to resolution. Another method named one-step MOCO can avoid RCMC error, improving image quality obviously. Meanwhile, one-step MOCO can well integrate with the standard Omega-K algorithm succinctly. A comparison of the two MOCO algorithms is demonstrated by analysing the RCMC error. Point targets simulation has validated the proposed research.

The polarisation characteristics of a high-voltage power-line radar cross-section (RCS) at 76 GHz are experimentally evaluated to improve the detection conditions of the helicopter obstacle detection radar system. Vertical polarisation transmission and reception (V–V) are normally used to detect power lines. In addition to V–V polarisation, horizontal transmission and reception (H–H) polarisation characteristics are measured for the two types of high-voltage power lines. For V–V polarisation, the measured RCS characteristics of the power lines agree well with those previously reported at 35 and 94 GHz. However, the measured results of the H–H polarisation are almost the same as, or higher than, those of the V–V polarisation.

The results of recent measurements taken with two radar systems to measure the simultaneous monostatic and bistatic signature of wind turbines, at S-band and X-band are presented. Coherent monostatic and bistatic data was collected with the University College London (UCL) NetRAD 2.4 GHz radar, and the Cranfield University CW radar operating at X-band. Initial analysis shows the bistatic Doppler signature of wind turbines and informs on the key differences seen at modest bistatic angles. Polarimetric variations are also analysed via data gathered from using co-polarised VV and HH and cross-polarised VH components.

A fast I/Q imbalance compensation algorithm is presented. It is demonstrated through MATLAB simulations that with a few samples an image-to-signal ratio (ISR) lower than −25 dB was achieved. On the basis of digital processing of the received signal, this algorithm is compliant with low-cost and low-complexity wireless receivers because it does not require extra time and resources for calibration. Moreover, its fast convergence allows reaching a high enough image rejection ratio by adapting the compensation weight during the reception of a known preamble such as defined by the IEEE 802.15.4 or the Bluetooth low energy standards.

Massive multiple-input–multiple-output (MIMO) can significantly outperform conventional MIMO in terms of spectrum efficiency and link reliability. For massive MIMO, there are still theoretical and practical issues that have to be addressed. The capacity of the massive MIMO-orthogonal frequency division multiplexing (OFDM) downlink system is derived and analysed and the duality of antennas and subcarriers in such system is demonstrated analytically and by simulation. A detailed comparison between massive MIMO, massive MIMO-OFDM and MIMO-OFDM with large subcarriers is presented.

A multi-cell joint optimisation problem is analysed to maximise the energy efficiency of the cellular and device-to-device (D2D) transmission, subject to a maximum power and signal-to-interference-plus-noise ratio constraint, under the scenario considering both intra-cell and inter-cell interference. On this basis, a multi-cell joint power control (MCJPC) algorithm is proposed. For simpler implementation and lower coordination overhead, a single-cell independent power control (SCIPC) algorithm is further proposed. The theoretical analysis and simulation results indicate that the proposed MCJPC and SCIPC algorithms can not only achieve higher energy efficiency compared with other typical power control algorithms, but also have good scalability.

Knowledge of the refractive index profile at radio frequencies in the surface layer of the atmosphere is required to predict the performance of terrestrial radio systems, and although a constant gradient of refractivity with height is often assumed, both measurements and theory suggest that gradients in the lowest 20 m of the atmosphere may often be greater than those above this level. For the special case of evaporation ducts over water in a neutral atmosphere, a logarithmic refractivity profile is normally assumed, but a general model that includes both this case and the linear profile as special cases is proposed, which may also be used to approximately model stable and unstable surface atmospheres. This new model may be particularly suited to predicting sub-refractive fading.

For multi-user MIMO downlink transmission, a block-diagonal zero-forcing (BD-ZF) precoder is usually used to suppress multi-user interference. In the case of a large number of transmitted antennas installed at the base station, there exists a larger nullspace than the precoder requires. An optimal BD-ZF precoder is developed to maximise throughput using the determinant maximisation technique. It helps to gather all gain for the transmission of each user. Numerical results validate that the precoder obtains throughput improvement.