A metal horn antenna fed by a co-planner waveguide with ground (CPWG) is designed and fabricated. To integrate and connect other active elements of the system, the CPWG is designed by multi-substrate PCB technology. A transition in the PCB layer concatenating the CPWG and the microstrip line has provided a continuous structure to lead the electric field from RF circuit into the horn. A ridge waveguide is used to widen the bandwidth. The simulated and measured results show that the proposed antenna has a broad impedance bandwidth of 33.1% (from 20.5 to 28.6 GHz) for |S ₁₁|<–10 dB and the radiation patterns also satisfy the requirements over the bandwidth.

The effects of the wrapped bow-tie antenna with and without resistive loading are explored for pulsed radar applications. The antenna characteristics such as voltage standing wave ratio, input impedance, reflected pulse of the antennas and radiated electric field are investigated by fully wrapping the planar bow-tie antenna. The antenna characteristics of the loaded antennas are shown to be robust with respect to the deformation of the planar bow-tie antenna. The peak-to-peak antenna reflected voltages of the conventional bow-tie planar antenna (PA) and bow-tie wrapped antenna (WA) are 0.24 and 0.49 V, respectively, whereas those of the resistor-loaded PA (RPA) and the resistor-loaded WA (RWA) are 0.23 and 0.25 V, respectively. The calculated figure of merit of the PA and WA are −4.58 and −7.92 dB, respectively, whereas those of the RPA and RWA are −20 and −18.42 dB, respectively. On the basis of the performance evaluation, the pulse radiating performance of the resistively loaded antennas is shown to be stable with respect to the deformation of the planar bow-tie antenna.

In this Letter, a new polarising grid for a folded reflectarray is proposed to improve the aperture efficiency of the antenna. This polarising grid is designed using a partial grid and a director which can improve the antenna radiation characteristic. Consequently, the measured aperture efficiency of the proposed antenna with the new polarising grid is 60.49% at 77 GHz.

A previous investigation of a modified circle-like slot antenna with dual-band-notched properties is extended. Frequency-domain characteristics have proved that the proposed antenna has very wide impedance bandwidth and shows good radiation characteristics. In this Letter, time-domain properties in terms of the antenna pulse response and power spectral density are investigated. Moreover, a study of indoor propagation channel characteristics when the proposed antenna is applied as transmitter and the receiver antenna is presented. A frequency-domain measurement setup and a sub-band divided ray tracing method are applied to measure and simulate the ultra-wideband indoor channel characteristics. The results show that the proposed antenna has also good time-domain characteristics and it is suitable for indoor and short range applications.

Here is demonstrated Rivener, a mask-less oral and nasal audio recorder and air flow estimation system. This system records audio and low-frequency pseudo-sound from the nares and mouth. The system does not interfere with speech intelligibility, and minimally interferes with visual observation of the speaker. From these recordings, nasalance (a ratio of oral and nasal sound energy), oral air flow, and nasal air flow patterns may be estimated, all while allowing effective clinical observation. The first demonstration is a case-study comparison of the difference between hearing-impaired (HI) speech and non-impaired (NI) speech. Rivener records standard features of HI speech such as: (i) Atypically high or low speech amplitude; (ii) fundamental frequency (pitch) making individual words into intonational phrases; (iii) speech segment substitution; (iv) hypernasalance; (v) atypical air flow in HI speech, including low air flow during plosive release. The second demonstration is a comparison of Rivener and the Rothenberg NAS-1's ability to record nasalance among 26 New Zealand English speakers. The NAS-1 can differentiate low, medium, and high nasalance passages, whereas Rivener differentiates only medium and high nasalance passages consistently.

Herein, the authors experimentally characterise the dynamics of voltage edges oscillating in a transmission line with regularly spaced two series-connected tunnel diodes (TDs). They clearly observe the mutually synchronised behaviour of the edges supported by each TD, which can be utilised to generate large-amplitude and low-phase-noise oscillatory voltages. They establish the fact that the response time of the device for state-transition is the key to qualitatively determine the edge oscillation, i.e. a single large-amplitude edge develops for sufficiently a large response time, whereas two larger and smaller edges coexist and are synchronised for short response time.

This Letter describes an innovative interactive evolutionary computational tool to optimise robust analogue complementary metal-oxide-semiconductor (CMOS) integrated circuits (ICs), by using genetic algorithm, entitled iMTGSPICE. The main results demonstrate that the iMTGSPICE is able to reduce the optimisation cycle times of designs of robust single-ended single-stage and Miller operational transconductance amplifiers (OTAs) in up to 93.9% in comparison to the non-interactive optimisation process. Moreover, the iMTGSPICE is capable of reducing the influence of the knowledge levels of the analogue CMOS ICs designers (experts and non-experts) to obtain robust potential solutions (maximum error of 0.5% for the Miller OTA).

A new structure and an improved control method of the three-axis gimbal for hexacopter unmanned aerial vehicle (UAV) are presented. By optimising the structure of the three-axis gimbal and establishing the mathematical model with the maximum stability, the improved structure of three-axis gimbal is proposed, which two groups of virtual reality (VR) camera arrays are mounted on the top and bottom of the frame to meet requirements of the 720-degree panoramic shot. The redundant design of five motors in the structure could realise the stabilisation of three-axis linkage of the gimbal that will ensure the optimal performance of the independent stable cameras all the time. At the same time, the attitude of the gimbal could be controlled by the complementary filter and proportional, integral and derivative algorithms. Furthermore, the closed-loop controls of angle, speed and current of Brushless DC motor are realised by the non-contact magnetic encoder, which improves the anti-shake performance of the system. The experiments in the prototype are designed to prove the anti-shake performance of the proposed gimbal and stability of the hexacopter UAV.

Systems for counting vehicles should be fast enough to be implemented in real-time situations. Most of the related work uses two stages for vehicle counting, vehicle detection and tracking, which increase the computational complexity. In this Letter, a fast and efficient approach for vehicle counting is proposed, where there is no need for the vehicle tracking step. A background model is created only for a narrow region, a line, in the video frames. The moving vehicles are detected as foreground objects while passing this narrow region. Morphological processes are applied to the extracted objects to enhance them and decrease the effects of vehicle occlusions. Finally, an efficient counting vehicles method is introduced employing only the extracted detection information. The experimental results performed on diverse videos show that the proposed method is fast and accurate. The average execution time per frame is 7.78 ms.

The key issue for facial expression recognition (FER) is to concentrate on the prominent expression feature regions where the expression changes. In this Letter, the authors propose a novel and effective FER framework jointing prominent expression feature regions in an auxiliary task learning network (ATLN). The proposed approach consists of two deep learning neural networks, one of which is the main network whose inputs are complete face images, and the other is the auxiliary learning network whose inputs are pre-processed face images containing prominent expression feature regions. The main network structure of the ATLN improves its ability to focus on regions with prominent expressions changing by sharing parameters with their auxiliary network structure. They carry out experiments on two public facial expression databases, namely, CK+ and MMI. Experimental results demonstrate the superior performance of proposed method.

A method which simply generates evaluation data for scene flow testing is presented, in which most algorithms for scene flow estimation require a pair of depth and colour images. We scanned the 3D geometry of a real object and rendered it in graphical space to acquire its depth and colour information. Next, surface deformation to generate natural motion for the scene flow is employed. The surface deformation enabled the generation of non-rigid as well as rigid motion. Next, barycentric coefficients were exploited to compute the ground truth scene flow. The coefficients enabled the acquired dense scene to flow accurately without dense point tracking and colour information. On the other hand, each flow vector was computed per pixel and a pixel could come from more than one point due to occlusion. We compute the flow maps dividing the geometry into the front area and the occluded area by modifying a z-buffer algorithm. Experimental results showed that the proposed method reliably provided evaluation data (a pair of depth and colour images and a scene flow map) based on a scanned model with occlusion.

Non-data-aided (NDA) carrier phase recovery (CPR) is one of simple CPR algorithms which simply rotates received symbols to the nearest constellation point. Unfortunately, when the NDA CPR is used with M-ary phase shift keying, it suffers inherent M-fold phase ambiguity and thus the phase ambiguity must be resolved. On the other hand, the generator matrix of polar code can be obtained with the Kronecker product of a lower triangular matrix. Hence, the Hamming weights of all columns of are given by non-negative integer powers of 2. Based on this observation, an rotationally invariant polar code suitable for digital communication systems employing binary phase shift keying and NDA CPR is proposed. The proposed polar code offers virtually identical performance under both and carrier phase offsets to that of conventional polar code with perfect CPR with identical encoding and decoding complexities.

Finite field multiplier is a very important operation for realising elliptic curve cryptography. Dickson basis is a recently developed basis for representing finite elements in GF(2 ^m ). This study will propose a unidirectional systolic multiplier for such Dickson basis. The unidirectional systolic structure offers low space and time complexities and can be easily modified to have error detection capability which can resist side-channel attacks.

Air pollution is a crucial environmental problem, especially the fine particulate matter (PM2.5) which has become one of the focal points. PM2.5 is a complex pollutant which can intrude the lungs and threaten people's health during the whole lives. In order to enable people to know the PM2.5 index of their surroundings at any time, an image-based PM2.5 predictor with saliency detection (IPPS) is proposed. The proposed predictor first obtains the non-salient regions based on saliency detection technologies. Then, the authors extract two features of the entropy and intensity values of non-salient image saturation map. Finally, they multiply these two features into the approximation of PM2.5 concentration. Experiments show that the proposed IPPS is superior in accuracy and efficiency.

For the first time, a novel bandwidth-tunable filtering balun based on compact 3D configuration is presented. The overall design is basically composed of a two-layer horizontal feeding plane, a three-layer vertically mounted plane, and the transmission-line circuits disposed on both. Implementing the ring resonator in vertical double-sided parallel-strip line, the complete horizontal ground and frequency-independent phase difference are subtly combined. Connecting the shunt varactor diodes with the inserted vertical ground, the desirable filtering property and flexible bandwidth tunability are splendidly fulfilled. A prototype balun centred at 1.53 GHz is fabricated. The measured operating bandwidth is dynamically tuned from 0.87 to 1.23 GHz with a return loss <−10 dB, forcefully validating the design concept.

In this Letter, a differentially fed impedance-transforming directional coupler is considered. The utilisation of recently introduced unequal-width differentially fed coupled conductors allows for setting independently terminating impedances for each of coupled lines as well as for coupling control in a chosen dielectric stack-up. The theoretical analysis is confirmed by experimental verification, in which an impedance transforming 70–50 Ω 3 dB single-section directional coupler has been designed and measured.

This Letter presents a four-way hybrid substrate integrated waveguide/microstrip-line power divider circuit based on the double microstrip-slot coupling. By slotting between T branch and loading isolation resistance, the isolation and output voltage standing wave ratio between non-adjacent ports is improved. By putting four output ports on the same side, the practicability of the circuit is improved. The test results show that the input return loss is >17.5 dB and insertion loss is <2 dB in 9–10.5 GHz.

A modified quarter-wavelength (λ/4) stepped-impedance resonator (SIR) is proposed to design a miniature dual-band bandpass filter (BPF). The proposed λ/4 SIR has two individually controllable resonances for constructing dual passbands. Moreover, two independent geometrical parameters are adopted to realise individual adjustment of the coupling strengths between two adjacent λ/4 SIRs at the dual passbands. As a result, both the centre frequencies and bandwidths of the two passbands of the filter can be individually designed. Furthermore, multiple transmission zeros are created by the introduced source-load coupling, which improves highly the selectivity of both passbands. The dual-band BPF is designed at 2.35 and 5.8 GHz, and its simulated and measured responses are presented and show good agreement.

A passive microfluidically tunable power divider (PD) with a wide-frequency-agile range based on substrate integrated waveguide (SIW) has been presented. The proposed structure consists of two SIW resonators loaded on the same complementary split-ring resonator and five identical filling-water tubes placed on the top plane. By injecting water into five tubes, the effective permittivity of the substrate can be controlled, and thus the operating frequency of the PD can be precisely tuned. For demonstration, the proposed PD is designed and fabricated. The measured and simulated results are given, showing good agreement.

A novel filtering power divider (FPWD) with a quasi-elliptic response based on the multilayer substrate integrated waveguide is presented. The odd-symmetric fact of the TE₁₀₂ mode is applied to accomplish two contrary couplings with equal strengths. On the basis of the specially coupling topology, the FPWD can realise quasi-elliptic response. An experimental sample is measured to verify the design methods, and the measured results account with the simulated ones well.

A novel scheme for the generation of an optical frequency comb with exceptionally high flatness for a large number of spectral lines is proposed. The scheme consists of a dual-parallel Mach–Zehnder modulator (DP-MZM) with which to carve the narrow intensity pulse and phase modulators for the application of high chirp. The experimental results show perfect spectral profiles with 35 lines with <1 dB flatness and 54 lines at 1.6 dB flatness when a DP-MZM is combined with two and three phase modulators, respectively.

An ultra-low-power oscillator with 0.24 pJ/cycle energy efficiency is presented, suitable for nanowatt-level energy harvesters. The sub-pJ/cycle energy efficiency is comparable with the lowest energy per cycle costs of prior arts and is achieved by minimising short-circuit current with a leakage-based delay cell and minimising dynamic power consumption with a capacitively coupled stacked structure. The proposed oscillator is fabricated in 180 nm CMOS process. Under 2.2 V supply voltage, the energy per cycle is 0.24 pJ/cycle over a frequency range of 18.2–226 kHz.

This Letter proposes an improved repetitive controller based on Lagrangian interpolation method to suppress harmonic current in the permanent magnet synchronous motor. Harmonic current suppression performance is degraded drastically if the ratio of the sampling rate to the fundamental frequency of harmonic current is fractional. The fractional-order delay link based on Lagrange interpolation is used to approximate the delay link which is composed of the fractional part of the frequency ratio. In order to further reduce the tracking error of the current harmonics, the low-pass filter located inside the traditional repetitive controller is removed and the stability of the system is ensured by adding a phase compensator. Finally, the experimental results demonstrate the effectiveness of the proposed scheme.

Multiple-input multiple-output (MIMO) radar recently has attracted the attention of engineers and researchers. MIMO radar performance is based on the orthogonality of the transmitted waveforms. A receiver optimisation method is proposed to suppress cross-correlation rather than finding orthogonal waveforms. The method considers two transmitters and is based on the minimum variance distorsionless response (MVDR) algorithm to minimise cross-correlation while maintaining the level of auto-correlation. Performance is evaluated by simulation using random phase code sequences. The proposed method is well suited for single target tracking, or slow moving target detection.

The effects of complicated motion error on synthetic aperture radar have been analysed. A precise frequency-division is proposed based on the precise angle-frequency relation. The proposed method completely compensates the residual aperture-variant motion and can be integrated into the traditional image formation algorithms directly. Both the simulated data and real airborne data have been applied to validate this method.

Through-the-wall radar is widely used in civil and military applications. However, the echo from the target behind the wall is often buried in the wall reflections and other clutter waves. An effective subspace selection method based on singular value decomposition for wall clutter mitigation is presented. Furthermore, the Akaike information criterion method is employed for noise clutter mitigation. Experimental results with real data demonstrate the correctness and effectiveness of the proposed algorithm.

A wideband low-phase noise VCO is proposed for multi-standard wireless communication system. An 8-shaped high-Q inductor is employed to enhance the performance of the VCO. The frequency pulling is reduced by using the 8-shaped coil. Implemented in a 180 nm CMOS process, the VCO can provide a very wide tuning range of 65.4% from 2.49 to 4.91 GHz. A phase noise lower than −121.25 dBc/Hz is obtained at 1 MHz offset over the whole working band while the current consumed varies from 3.5 to 8.7 mA.

In this Letter, a product concatenation scheme of systematic polar codes with irregular low-density parity check (LDPC) codes is proposed. The proposed scheme may take advantage of the good error-correction capability of irregular LDPC codes and superior error floor performance of polar codes. The joint belief propagation algorithm is employed, where scaling factors are introduced to manipulate the belief messages exchanged between constituent decoders, such that a fast convergence and a low BER performance may be achieved. Simulations are presented to validate its effectiveness.