In this paper, a wide band ridge gap waveguide (RGW) fan beam antenna with low side lobe level (SLL) is presented making use of parabolic offset reflector concept in antenna geometry. In the proposed topology, in contrast to TEM based RGW horn, the amplitude distribution across the antenna aperture can be easily controlled. Furthermore, thanks to intrinsic feature of parabolic reflector in generating plane wave front, the phase distribution uniformity across the proposed antenna aperture is better than that of the RGW horn. These two facts allow the proposed topology to provide lower SLL compared to the RGW horn. A prototype of the proposed structure is designed and fabricated. Simulation and measurement results also show that wider operating bandwidth compared to the RGW horn can also be achieved using this topology. For the designed sample, the impedance bandwidth of 41% with −20 dB ≤ SLL ≤ − 15 dB and gain of 11.8–15.5 dBi is achieved. Results show that the proposed topology can be a good candidate for realization of high gain wide band RGW fan beam antennas with low SLL.

Synthesis of planar continuous current sources (planar CCSs) with arbitrary shapes is developed for the generation of specified radiation patterns by method of moments (MoM) and method of least squares (MLS). First, an integral equation is expressed, which relates planar CCS current distribution to its radiation pattern. Second, the planar CCS region is divided into several segments and its current distribution is expressed in terms of the pulse expansion functions to discretise the integral equation. Third, the resulting discretised integral equation is converted to a linear equations system by MoM and MLS. Fourth, the resulting linear equations system is solved to determine unknown coefficients of planar CCS current distribution. To evaluate and compare the efficacy of proposed methods, two parameters of synthesis error (SE) and superdirectivity ratio (SR) are used. It is shown that the number of segments should be properly determined to achieve specified SE and SR. If resulting radiation pattern does not meet design goal, a perturbation procedure is applied to current distribution in order to improve the characteristics of radiation patterns of the planar CCS, such as side-lobe level and pattern ripple. Several examples are given to validate the efficacy of the proposed methods.

A low-profile microstrip patch antenna (MPA) with wide bandwidth, wide beamwidth, and reduced cross-polarisation is proposed here. Firstly, the far-zone radiated fields of the MPA are deeply studied to improve its radiation performance. It demonstrates that the E-plane half-power beamwidth (HPBW) of the antenna could be progressively widened by using a single equivalent slot instead of two equivalent slots. Meanwhile, its high cross-polarisation of the H-plane radiation patterns could be successfully decreased down by enlarging the width of the rectangular patch and loading the shorting pins. Secondly, the input impedance of the MPA operating in the fundamental mode is extensively investigated. The results illustrate that the resonant frequencies of its dual modes could be reallocated in proximity to each other for bandwidth enhancement by properly selecting the dimension of radiating patches. Finally, the proposed antenna is fabricated and tested. Experimental results show that the antenna has gained an improved bandwidth (|S ₁₁|<–10 dB) of about 12% ranging from 2.70 to 3.03 GHz, while keeping a thin thickness of about 0.029 free-space wavelength. Besides, its H-plane cross-polarisation is kept below −20 dB. Most importantly, the E-plane HPBW of the antenna is extended to around 140° over the wide band.

An analogue modulation-type independent feed-forward carrier recovery approach for broadband wireless communication systems is introduced in this work. The focus is on the deliberately increased local oscillator (LO) signal feed-through to the radio frequency (RF) port of the up-converter in a direct conversion transmitter (TX). The strong LO feed-through is used at the receiver (RX) side to demodulate the RF signal. The heart of the carrier recovery block is a narrowband bandpass filter (BPF) and a frequency divider-by-n operated in injection-locking mode to the strong LO feed-through. The proposed method is investigated through circuit level simulations; while its feasibility is examined via the successful demodulation of complex data with various modulation types up to 8 Gbps for an E-band front-end. This method can be used for transceivers working at high carrier frequencies as far as the realisation of frequency divider circuits and narrowband BPFs is technically feasible.

A design methodology for a small-size multifunctional quad-band bandpass filter (BPF) exhibiting high selectivity is proposed in this study. In this design, the resulting BPF would comprise a dual-band split-type BPF, wideband BPF and narrowband BPF, and it can execute narrowband/wideband operation and provide close/wideband spacing. Since each passband can be formed by respective filters, the design methodology has high flexibility in that it can achieve different filter functions and can be compatible with various communication systems. In addition, because of the source–load coupling, four additional transmission zeros could be created over the stopband, thus enhancing the selectivity. A quad-band BPF operating at 1.45/1.65/4/6 GHz with fractional bandwidths of 6.6/5.8/35/3% was implemented to verify the design methodology. The fabricated BPF was determined to have a compact circuit size of 0.3 λ _g × 0.44 λ_g (λ _g is the guided wavelength at the central frequency of the first passband) and it exhibited an in-band insertion loss of no more than 2.8 dB. The experimental and simulation results were determined to be in good agreement.

Four-way single-/dual-band operation integrated filtering power divider (FPD) with new design topology is presented in this study. For either single- or dual-passband response, it involves only one same-type pair of multi-mode resonators and three isolation resistors, comparing with other existing four-way FPDs. By adopting the even-/odd-mode analysis method to flexibly control the resonant modes of the designed resonator and select isolation resistances, both single- and dual-band four-way filtering power division responses are specified and derived with the same one configuration. The proposed four-way FPD designs stand out from the reported ones by both nice operation performance, flexible topology with reduced number of resonators, and no additional feeding network at input port. For demonstration, two prototypes for four-way single- and dual-band FPDs are implemented following the given design procedure, respectively. Both simulated and measured results are exhibited to verify the theoretical design concept.

In this study, the authors present three different metamaterial absorbers (MMAs) namely, T, split-I (SI) and split-Jerusalem cross (SJC) with different dimensions and geometrical configurations. The absorption rates of T-, SI- and SJC-shaped absorbers are studied at microwave frequencies. T-shaped absorber demonstrates perfect absorption at 10.19 GHz, making it suitable for single band operation, whereas SI-shaped absorber exhibits two perfect absorption peaks at 9.32 and 10.75 GHz finding its application in dual band operation. However, novel SJC-shaped absorber demonstrates multiple absorption peaks at 9.92, 10.42, 10.93, 11.75 and 13.25 GHz with absorption of 99.5, 91, 99.9, 91.8 and 99.6%, respectively, making it suitable for X- and Ku-band operations. The proposed MMAs have a thickness of around 0.8 mm (i.e. <λ/37) with respect to the lowest frequency of operation. Furthermore, the absorbers are analysed for different angles of polarisation and incidence for transverse electric polarised wave with a step size of 15°. The proposed absorbers have been fabricated and experimentally demonstrated at X-band verifying the results obtained from simulations and implementing an equivalent circuit method. Further, SJC-shaped absorber is demonstrated for multi-and wide-band terahertz applications exhibiting four perfect absorption peaks at 2.76, 2.89, 3.02 and 3.31 THz.

A new design of the double dielectric resonator antenna (DRA) fed by a printed ridge gap waveguide for beam-switching applications based on frequency selective surfaces (FSSs) is presented here. The dual-sided printed FSS element works in its reflection mode and comprises a slotted square C-shaped patch on the top layer and a square strip on the back plane. Therefore, the beam switching can be implemented by loading the proposed FSS array over and in the middle of DRAs. Loading the antenna with two layers of 3 × 3 FSS unit cells results in ±77° beam switching and a 3.16 dBi gain enhancement at 28 GHz. Simulation and measurements confirm the operation of the proposed antenna, with good matching and gain observed.

An efficient electronic beam steering technique in time modulated linear array (TMLA) is proposed, where the first positive and negative sidebands are utilised to implement the electronic steering process. In this technique, new periodic time sequences are used, in which a positive-ON, negative-ON, and OFF durations are utilised to obtain high sufficient steering in TMLA. Furthermore, it is shown that by using these time sequences, the non-steerable array pattern at the fundamental frequency and also the even sidebands can be eliminated and nulled to zero. In addition, the radiation power and the directivity of this proposed steered-TMLA are formulated in their closed form. The genetic algorithm is implemented to optimise the steered-TMLA by suppressing the remaining odd sidebands and increasing the power radiation at the first positive and negative sidebands.

The aim of this study is to disclose how the performance of a gallium nitride (GaN)-based X-band low-noise amplifier is modified by applying a blue-ray (404 nm) laser beam. The tested amplifier employs an aluminium gallium nitride/GaN (AlGaN/GaN) high electron mobility transistor on silicon carbide whose dc and noise behaviour have been first analysed with and without optical illumination. Mild improvement of the gain together with severe degradation of the noise figure has occurred during light exposure with the amplifier operating according to the recommended bias condition. Conversely, pronounced improvement of the performance has taken place when the amplifier has been biased close to the transistor pinch-off point. The results presented in this work follow a previous intense activity carried out on devices and amplifiers based on gallium arsenide technology.

In this study, a corrugated substrate-integrated waveguide (CSIW) is used to design a passive microwave displacement sensor. Hence, one of the electric walls of the proposed structure is formed by open-circuited quarter guided wavelength stubs and the other walls are made by metal vias and moveable copper metal is placed on the stubs. By displacing the moveable metal layer along with the stubs, the length of the stubs is changed and therefore the resonant frequency is shifted. An analytical model that relates the variation of the resonant frequency and the displacement has been formulated. The proposed sensor seems like a simple structure and it is operated at 2.4–2.9 GHz. There is a good agreement between the measured results and those obtained by simulation. The measured results indicate that the sensor provides a high dynamic range of displacement of 15 mm and high sensitivity of 25.16 MHz/mm.

In this study, dual-port dual-frequency tuneable MIMO planar inverted-F antenna (PIFA) is presented for mobile hand-held device applications. The proposed MIMO antenna consists of two symmetrical PIFAs with the centre-to-centre distance of 43.0 mm (0.1906). The dual-band tunability is achieved by changing the capacitance ( and ) of 4.15 pF (0 V)–0.72 pF (15 V). The impedance bandwidth of  dB is realised from 0.8 to 0.98 GHz for the lower band and 1.65 to 2.2 GHz for the higher band. The proposed antenna provides the independent frequency tunability without disturbing the frequency bands. It shows the good isolation for both the tuneable bands 20 dB without using any coupling element between the antenna structure. It has a peak realised gain of 3.44  dBi, good efficiency of and envelope correlation coefficient of 0.007. In addition, the proposed PIFA performance is analysed with total active reflection coefficient, channel capacity, diversity gain, multiplexing efficiency, mean effective gain and specific absorption ratio for the tuneable range of frequencies. The good agreement is obtained between simulation and experimental performances to validate the antenna parameters.

The contribution of this study is to develop a miniaturised substrate integrated waveguide (SIW) cavity resonator with two evanescent-mode resonances. The circuit area of the developed dual-frequency SIW cavity is only 9.2% that of its conventional SIW cavity counterpart. A dual-band filter is implemented from using two miniaturised SIW cavity resonators. The two-passband frequencies can be independently controlled. Two transmission zeros are created by the two sides of each passband for enhancing the signal selectivity. A diplexer is also designed from using the proposed SIW cavities. A dual-band filter and a diplexer are built for experimental verification. Agreements between measured and simulated data are observed. To the best of the authors’ knowledge, the designed dual-band filter and diplexer have achieved the best circuit area efficiency in the categories of dual-band SIW cavity filters and diplexers.

A dual-band rectangular dielectric resonator (DR) antenna is implemented with a multi-frequency circularly polarised (CP) response. The wide dual-band response is achieved by inserting the slots in the DR. The insertion of slots in the DR in a specific manner generates the orthogonal degenerate modes. Consequently, the multi-frequency CP response is obtained. The antenna provides the total overlapping CP bandwidth of 4.96% (13.36–14.04 GHz) in the lower band and 3.28% (14.95–15.45 GHz), 9.624% (17.11–18.84 GHz) and 0.517% (19.28–19.38 GHz) in the upper band. The antenna provides the 10 dB impedance bandwidth of 6.44% (13.36–14.25 GHz) and 28.89% (14.95–20 GHz) in the lower and upper bands, respectively. The peak gain of antenna remains >3 dBic in the passbands.

A generalised nested array (GNA) configuration with large minimum inter-element spacing is attractive to alleviate mutual coupling. In this study, by decomposing and rearranging the sub-arrays of GNA, the authors propose a new nested array configuration named as widened nested array (WNA). The WNA enables to provide the reduced mutual coupling, enhanced degrees of freedom (DOFs), extended array aperture and improved direction of arrival (DOA) estimation performance compared to GNA. The closed-form expressions for sensor positions of WNA are given and the optimal array configuration for largest DOFs is derived. Meanwhile, the authors propose a partial angular compressed sensing(CS) based DOA estimation algorithm for WNA. Specifically, discrete Fourier transform method is first derived for consecutive DOFs of WNA to obtain initial DOA estimates. Subsequently, the initial estimates are utilised to compress the angular range of overcomplete dictionary of the CS algorithm, which is exploited to obtain the fine DOA estimates. Extensive simulation results testify that the proposed algorithm has the same estimation accuracy as CS algorithm with lower complexity.

This study presents a compact transmission line topology to reduce the circuit size of single- and two-section branch line couplers (BLCs). The proposed transmission line is composed of a high impedance series line and one coupled line section. The coupled line section consists of two high impedance series lines and one coupled line. The proposed line is analysed with even–odd mode analysis to derive closed-form design equations. To validate the equations, a compact single- and two-section BLCs are designed at 0.85 GHz based on the proposed line. The physical size occupied by the proposed single- and two-section BLCs is 23 and 19.5%, respectively, compared to conventional BLCs. Moreover, the proposed transmission line demonstrates the harmonic suppression characteristic due to the coupled line section. As a result of which, the second- and third-order harmonic of the proposed BLCs are suppressed. The proposed BLCs are designed, fabricated, and tested.