In this Letter, a compact dual-band dual-mode microstrip-fed dipole-loop (MDL) element is proposed, which consists of a rectangular loop-structure embedded in the feed-line of a printed dipole. This MDL element exhibits an additional one-wavelength loop resonance at a lower frequency (1.55 GHz) with omnidirectional pattern, along with the conventional reflector-backed half-wavelength dipole mode (2.55 GHz) having end-fire radiation. Thus, electrical size reduction and dual-band frequency-dependent pattern diversity characteristics are obtained simultaneously in the MDL element. Furthermore, the proposed MDL element is used to construct a 1 × 2 array which operates at 1.45 and 2.59 GHz with impedance bandwidths of 14.33 and 12.92%, respectively. Bi-directional broadside radiation (peak gain of 4.42 dBi) is achieved at the lower band, whereas the higher band exhibits high-gain end-fire radiation with peak gain of 7.46 dBi. The proposed design concepts are validated by Ansys HFSS simulations as well as measurements carried out on fabricated array prototypes.

A simple and cheap solution is proposed to transform a wideband and linearly polarised horn antenna in a dual-band circularly polarised horn filtenna. The filtering and polarisation transformation capabilities are achieved by inserting inside the throat of the horn a complementary electrically small resonator etched on a thin metallic sheet. In this way, the overall structure is well matched in two frequency ranges (13–14 and 16.4–17 GHz) and radiates left-handed and right-handed circularly polarised fields in the lower and upper frequency bands, respectively. The measurements performed on a realised prototype confirm the good performance of the proposed structure, which may be employed in satellite communication systems requiring different circular polarisation for the up- and down-link frequency ranges.

A novel frequency selective surface (FSS) based on quasi-lumped inductor and capacitor is proposed to miniaturise FSS unit cell size. The quasi-lumped inductor and capacitor, implemented by meander line and parallel-plate capacitor, respectively, are connected in series to achieve a bandstop filtering response. This FSS provides the advantages of small unit cell size, independent control of the filtering response for different polarisations, and easy optimal design of desired resonant frequency and bandwidth. To validate the proposed design concept, a bandstop FSS operating at 2.42 GHz was designed, fabricated, and measured. Its unit cell size is only (λ ₀/28) × (λ ₀/28), where λ ₀ refers to the resonant wavelength in free space. Both the simulated and measured results exhibit stable filtering performance under different polarisations and incident angles (up to 60°).

In this Letter, a mu-negative metamaterial (MTM) filter-based novel decoupling technique is presented for multiple input multiple output (MIMO) antennas. The design process has been described in a systematic manner, starting with the basic two port monopole antenna and then adding cancellation network and finally the proposed MIMO antenna by adding the matching network. Since the presented decoupling network is developed using MTM structure, good isolation between the antennas is achieved by maintaining compactness. The presented isolation technique can be used in different applications like in developing circularly polarized and multi-band MIMO antennas. As an example, two port circularly polarised MIMO antenna design is also presented. The proposed designs have been fabricated and the simulation results are experimentally verified.

A resonant cavity-based dielectric lens antenna has been presented for 60 GHz-band (57.24–65.88 GHz) wireless applications. The feeding element is a patch antenna designed with size improvement method for laboratory based fabrication with printed circuit board etching process. A semi-sphere dielectric lens is placed in front of the feeding antenna at a distance equal to about half-wavelength of the operating central frequency of 61 GHz. Simulation analysis has been performed on the cavity height and lens radius to obtain an optimised antenna design for its best performance in term of gain (20.1 dBi) and return loss (S ₁₁) bandwidth (6.14 GHz).

A cylindrical spiral liquid antenna and a tapered helical water antenna are presented. Saline water with a concentration of 3.5% is injected into a flexible tube to form the radiation structure. Thresholds for changes of the radiation direction are calculated to be 0.1 and 0.4 for the ratio between the spiral diameter and the wavelength. Resonance frequency increases when the probe length or the radius of the vertical liquid decreases. The quantity of the water could be changed with the help of a syringe to enable the reconfigurability. Measurement results show fairly good agreements with that simulated.

Design approach of a novel wideband slotline antenna is proposed. An offset-fed structure is applied to simultaneously excite the first three radiation modes within a slotline radiator, without introducing external less-radiative resonant modes. By controlling the excitation of its full-wavelength radiation mode, the proposed slotline antenna exhibits a frequency-spatial steerable notch-band characteristic in radiation gain within a wide-impedance bandwidth.

An analytic approach is proposed for estimation of electromagnetic interference (EMI)-induced phase noise and jitter. The radiated susceptibility of an oscillator implemented on the PCB is defined based on its fundamental specification. Closed-form expressions are derived for EMI-added phase noise and jitter on the oscillator output signal. A simple oscillator board is designed and implemented to verify the derivations. The measurement results confirm the accuracy of the proposed method.

UAV rendezvous is a necessary precondition for formation flight. Fixed-wing rendezvous is complex by nature because of its velocity constraints and uncertainties during flight. This Letter presents a rendezvous method for fixed-wing UAVs, in which velocity tuning and online trajectory adjustment are combined. Time-varying vector fields are designed to adjust the trajectories according to the estimated flight time, therefore the UAVs can reach the rendezvous position at the same time. This method can be applied in real time without complex communication topology. It is verified by the non-linear mathematical model of a fixed-wing UAV, and the simulated results confirm that it works effectively.

Projection of omnidirectional videos in the spherical domain onto the planar domain is required to utilise existing video compression techniques. Due to its simplicity, the equirectangular projection (ERP) method has been widely adopted for sphere-to-plane mapping. However, the coding efficiency of the ERP method is inefficient because the ERP video includes visual redundancies in the high latitude areas of the sphere. To solve this problem, this Letter presents an efficient data compression scheme that employs latitude adaptive down-sampling followed by pixel rearrangement. Experimental results show that the proposed method can achieve a bitrate reduction of up to 28.9%, as compared with the ERP.

A new multiple-input multiple-output system, referred to as transceive spatial modulation (TRSM), which integrates transmit spatial modulation (SM) and receive SM. In the TRSM system, information bits are carried by the conventional amplitude–phase modulation as well as by the indices of both the transmit and the receive antennas. To improve the bit-error-rate performance, block Markov superposition transmission (BMST) is applied to the TRSM, resulting in BMST-TRSM, where BMST is a recently proposed coding scheme and can be easily designed according to the spectral efficiency requirement. To reduce the computational complexity, a layered (suboptimal) soft detection algorithm is presented, which delivers a list of candidate spatial points (antenna combinations) first. Numerical results show that the proposed TRSM system performs well over the Rayleigh fading channels.

In a very interesting recent paper, the authors proposed a least support denoising-orthogonal matching pursuit (LSD-OMP) algorithm and gave a sufficient condition for LSD-OMP algorithm in terms of restricted isometry constant of the measurement matrix. According to Dai and Milenkovic (2009), Wang et al. (2012) and Needell and Tropp (2009), this comment will point out that there are some errors in Tawfic and Kayhan (2015).

The comment of Haifeng Li is acknowledged. In response, it is argued that by establishing the complete comment response, the conclusions in the original Letter are appropriate. The authors have studied the comments carefully and revised their response accordingly.

A compact flexible filter based on 0° feed structure with ultrathin liquid crystal polymer substrate is proposed firstly. An open-ended stub is introduced to improve the out-band rejection. The presented flexible filter with dimension of 6.48 × 9.89 × 0.086 mm³ is operating at WLAN of 5.15–5.875 GHz, which will alleviate the channel congestion of 2.4 GHz. In the case of flat, the measured minimum insertion loss is 1.9 dB at 5.61 GHz and the return loss is better than 16.45 dB. The bending behaviour of the compact flexible filter is also analysed. Compared with the flat case, the return loss is optimised by 0.45 dB, the maximum deterioration of insertion loss is 0.13 dB in case of R = 10 mm, and the transmission zeros position are invariant. Good agreement is obtained between the flat and the bending situation, which shows that the presented flexible filter is promising for the wearable applications.

A miniaturised frequency selective surface (FSS) with λ₀/7 × λ₀/7 unit cell at the pass band centre frequency is presented for millimetre wave remote sensing. A resonant corner convoluted square ring (CCSR) is loaded with non-resonant cross dipole (CD) for tri-band spectral response. Rectangular patches integrated in the CCSR are used to optimise the coupling between the CD and CCSR to reject 50–60 GHz (B₁) and 170–195 GHz (B₃), and transmit 87–91 GHz (B₂). The FSS fabricated on 175 μm thick quartz with 3721 unit cells indicates polarisation and angle stable transmission response.

Silicon arrayed-waveguide grating using rib-waveguide multimode interference coupler at the array and slab waveguide interface is reported. A 100 GHz channel spacing 8ch device showing 2.8 dB insertion loss is obtained. The insertion loss was improved compared with a device using simple width taper.

For the first time, a rare-earth-doped GaN nanocolumn light-emitting diode is fabricated on an n-type (111) Si substrate, grown by rf-plasma-assisted molecular beam epitaxy. The nanocolumn structure remained in the n-GaN and europium-doped GaN active regions, but the lateral growth was enhanced in the p-GaN region such that a continuous film was obtained. Clear diode characteristics and a sharp red luminescence with two dominant peaks at 620.3 and 633.8 nm were observed at room temperature. The shift in the wavelength with an increase in the injected current was <0.2 nm. Thus, this device has the potential for application as a stable-wavelength optical device.

A single-impedance network consists of two inductors and capacitors connected in an X-shape to provide single-stage energy conversion. This structure eliminates the need for two-stage energy conversion that is currently employed in traditional converters. A dual-impedance network includes two individual sets of inductors and capacitors connected in parallel. This network possesses the flexibility of using two different sources as inputs to meet the load demand. In order to provide voltage boosting, the switching must be performed selectively to shoot-through (ST) the power sources. A modified modulation method has been implemented to introduce the ST for switching. The modified modulation method shares the operating principle with the in-phase disposition modulation method for multilevel inverters. However, the reference signals are dispositioned via the modified modulation method rather than employing carrier disposition via the traditional modulation methods. Therefore, the circuit analysis of a dual-impedance network is evaluated whose switching is achieved by a modified modulation method for an ideal condition. The simulations are carried out using the MATLAB/PSIM environment and the results are presented.

An innovative nonlinear (IN) H _∞ control for static synchronous compensator (STATCOM) to improve voltage stability of power system is proposed. Taking the parameter deviations, external disturbances and unmodelled dynamics into account, the nonlinear dynamic model of STATCOM can be transformed into a standard Hamiltonian structure with the help of coordinate transformation. Using the Hamiltonian structure of STATCOM, an IN H _∞ control is designed for STATCOM. A two-area four-machine power system is used to testify the robustness and effectiveness of the proposed IN H _∞ control in comparison with the feedback linearisation (FL) control. The numerical simulation results indicate that the IN H _∞ control has better performance than the FL control.

Harmonic magnetic fluxes in transformer's core and harmonic currents in grid-side winding can be restrained via the inductive filtering technology, and running noise of the transformer is reduced at the source. The A-weighted sound levels of the measuring points are measured under DC bias. The noise test results verify this theory. When the fully-tuned filters matched with the new converter transformer are inputted and not inputted, the noise response curves of the measured points are compared. The fitting coefficients of the noise values at 1250 and 1600 Hz with the unbalance degrees of the trigger angle are obtained.

A sliding-mode direct power control (SMDPC) strategy using second-order generalised integrator (SOGI) for doubly fed induction generator is proposed, which can achieve various objectives without the decomposition process of negative and positive sequence components when the grid voltage is unbalanced. The impact of the non-ideal grid voltage to the SM controller is studied, and an improved strategy is proposed by combining an SOGI-based compensator with the SMDPC strategy. Different control targets can be achieved by selecting different variables as the compensation. Experimental studies based on the proposed and traditional SMDPC are implemented to verify that the proposed strategy is effective when the grid voltage is unbalanced.

The relationship between common-mode voltages (CMVs) and switching states in the post-fault reconfigured topology of the three-level neutral-point-clamped inverter with open-circuit fault in a leg, which is named eight-switch three-phase inverter (ESTPI), is revealed, and based on that, two modified space vector pulse-width modulation (M-SVPWM) algorithms for the CMV reduction in the ESTPI are proposed. The maximum CMV of the ESTPI with two proposed M-SVPWM algorithms is only half of that with two conventional SVPWM algorithms. Experimental results have shown the effectiveness of two proposed M-SVPWM algorithms.

Harmonic magnetic fluxes in transformer's core and harmonic currents in grid-side winding can be restrained via the inductive filtering technology. Vibration and abating noise of the core caused by the harmonic magnetic fluxes are controlled at the source, and has a good effect in reducing vibration and abating noise of the grid-side winding. Vibration and noise characteristics of the inductive filtering converter transformer are tested under load. The experimental results verify this theory.

In the active echo cancellation (AEC), the jammer can suppress the true target by superimposing on it a false target with the same amplitude and inverted phase. Under certain conditions, the interrupted-sampling repeater jammer (ISRJ) performs a kind of partial AEC against chirp radars. A novel technique that not only eliminates the effect of a self-protection ISRJ is proposed, but also the jamming signal power to augment the power of the true target is exploited. The theoretical analysis of this technique is presented and its effectiveness is verified by simulation.

Drone platform for synthetic aperture radar (SAR) operation has been little publicised due to the technical constraint of the payload implementation. Multi-rotor drone based SAR is distinguished from the conventional airborne system by the increased sensitivity to turbulences and poor motion stability. Extremely limited power and mass budgets may prevent the use of extra hardware for motion compensation and the difficulty of SAR focusing is aggravated. Feasibility of micro-SAR drone operation is investigated through field tests, where experimental SAR images are acquired over ground targets. Attempts have been made to implement near-real-time compensation for non-uniform motion disturbance. Finally, experimental drone SAR operation is validated through calibrated SAR images.

A novel phase unwrapping method is proposed that can be used in digital holograms, magnetic resonance imaging and synthetic aperture radar interferometry. Phase unwrapping is often an essential task for images with periodic phases, and its result directly affects the measurement precision. However, the path-independent unwrapped results generally cannot be obtained owing to the inconsistencies of phase gradients, i.e. residues. A simple and efficient approach is provided to determine the connections of opposite-sign residues by analysing the relationship between the phase gradients and the residues’ generation. After the determination of the connections, integrated the phase map and obtained the path-independent phase unwrapping result by not crossing the connections and residues. The proposed method has efficiently reduced the computational complexity when compared with the traditional phase unwrapping methods. The effectiveness of the proposed method was proved by experimental results based on real and simulated data.

A series of novel continuous inverse modes based on current element is proposed. The series of novel continuous inverse mode is extended by increasing the coefficient in the current equation of traditional inverse class F power amplifier (PA). The theoretical analysis shows that new current equation can provide a wide matching space for the design of broadband high efficiency PAs. To prove this theory, a wideband high efficiency PA is designed and fabricated. The experimental test results show that the drain efficiency is 65–78% in the 1.8–3G frequency range. The designed PA can obtain output power from 12.9 to 21 W and gain is from 10 to 13.3 dB in the interesting frequency range.

We propose a direction of arrival (DoA) estimation technique, which is enabled by a single printed patch antenna capable of four reconfigurable beams at the operative frequency of 2.45 GHz. The direction of the messages sent by a nomadic wireless node is estimated and stored without the need of lengthy offline measurements, by correlating the real-time received signal strength actual data and the expected antenna beams. The comparison is implemented with a least square technique with an extremely reduced computational cost. Experimental validations demonstrate the DoA estimation capability, with a mean error <2.3° with a variance of 1.9° within a domain of 90°.

Two size-reduced dual-band half-mode substrate integrated waveguide (HMSIW) cavity filters double-side-loaded with the conventional and stepped-impedance complementary split-ring resonators (SICSRRs) are presented. The SICSRR can exhibit larger equivalent electrical length than the conventional CSRR and thus provides a method to implement size-miniaturisation. By loading both CSRR and SICSRR into the two sides of the HMSIW cavity, a dual-band resonator is formed. Since sizes of the CSRR and SICSRR on the two sides are controlled independently, the two passbands of the proposed resonator can be tuned flexibly. With the proposed HMSIW–DS–SICSRR cavity resonators, two dual-band filters are realised. Compared to other dual-band SIW filters, the two proposed dual-band filters can achieve sized-reduction about 48.5 and 50%, with the measured results in good agreement with the simulated ones.

A new channel access scheme to improve the throughput in the medium access control layer is proposed to support the high data rate of multiple users. The proposed scheme is based on access point-coordinated multiuser transmission via the adoption of a trigger frame. The total throughput of the proposed scheme is improved by up to 30% compared with the uplink-multiuser channel access scheme based on the request to send/clear to send exchange. Moreover, as the number of stations increases, the degree of improvement in performance increases.