High frequency electromagnetic (EM) scattering analysis from the electrically large scatterers is important to the computational electromagnetics community. Meanwhile, the high frequency diffraction technique, like the uniform geometrical theory of diffraction (UTD), is very important when the observation point lies in the transition, shadow and deep shadow regions of the considered scatterer. Furthermore, the diffracted fields arising from the electrically large scatterers via the UTD technique are usually highly oscillatory in nature, which is named as the Fock type integrals with the Airy function and its derivative involved. In this work, we propose a Fourier quadrature method to calculate the Pekeris integrals. Moreover, we first adopt the Fourier quadrature technique to calculate the diffracted fields from the dielectric convex cylinder with impedance boundary conditions, like the creeping wave fields and NU-diffracted wave fields. On invoking the Fourier quadrature method, the results of total scattered fields at the fixed observation points could achieve 1 dB relative errors. Moreover, numerical results demonstrate that the computational efforts for the oscillatory Pekeris-integrals are independent of wave frequency with the fixed sampling density and integration limit.

In this letter a four-port multi-input-multi-output (MIMO) antenna for 5G applications is proposed. This antenna is compact with a size of 11.3 mm×31 mm excluding feed lines. The radiation patterns of the antenna show pattern diversity in the azimuthal plane, and each antenna element has an end-fire gain about 10 dBi by employing an array of metamaterial unit cells. The isolation between the antenna elements with edge to edge separation <λ₀/5.5 at 28 GHz is enhanced by trimming the corners of the rectangular high refractive index metamaterial region along with a ground stub between antennas. The proposed antenna is fabricated, and each antenna element has return loss, S_nn<-10 dB with isolation, S_nm>21 dB in the frequency range 26 GHz to 31 GHz, which makes this antenna potential candidate for MIMO application at 28 GHz band enabling 5G cellular communications.

This paper presents a compact high-isolation dual-polarized dipole antenna with an artificial magnetic conductor (AMC) reflector. The proposed antenna is composed of a radiating element, two short pins and a 7×7 AMC array. By introducing two short pins, the port isolation is lower than -33 dB in the whole band on two ports. With the ring and AMC reflector, the dimension of the proposed antenna is only 0.36λ₀×0.36λ₀×0.16λ₀ at 2.2 GHz. The antenna also achieves a 10-dB return loss bandwidth from 1.6 to 2.78 GHz (54%) for both ports. The gain of the proposed antenna is around 8 dBi, and the cross-polarization is about 30 dB. Due to these properties, the proposed antenna can be applied to 2G/3G/long term evolution (LTE) base station and WLAN/WiMAX applications.

This piece of work replicates on the antenna array thinning exploring the benefits of known Fourier Analysis. In this communication Fourier transform is applied to the synthesis of periodic arrays for minimizing the Peak Side Lobe (PSL) level and thereby enhancing the directivity. Furthermore, the concept of Fill Factor(degree of thinning) i.e, reduction in the number of active elements is experimented for the above said objective. The proposed methodology is workedout on periodic linear and planar arrays. Numerical study and simulation results are composed with array thinning designs from literature. The analysis demonstrates the superiority of the illustrated Fourier technique.

In this paper, an ultrathin egg-shaped microbubble was proposed and analyzed for pressure sensing firstly, which was fabricated by utilizing an improved pressure-assisted arc discharge technique. By tailoring the arc parameters and the position of glass tube during the fabrication process, the thinnest wall of the fabricated microbubble could reach 873 nm. Such an ultrathin film structure is very suitable for pressure sensing. Especially, as only a commercial fusion splitter and pressure pump were utilized to achieve such functions, the fabrication cost was very cheap. The fiber Fabry-Perot (FP) interference technique was used to analyze its pressure sensitivity by filling the inner wall of the microbubble with different air pressures. The experiment results depicted that the end face of microbubble expands with the increase of the filling pressure. The pressure sensitivity of such an egg-shaped microbubble could reach up to 14.3 pm/kPa in terms of interference spectrum shift, while the maximum cavity deformation sensitivity of the microbubble vs. pressure could reach up to 0.334 nm/kPa in terms of cavity length change. Besides, the maximum sensitivity vs. temperature was only 27.83 pm/˚C. Results of this study could be good reference for developing new pressure sensors with low cost, high sensitivity and good anti-temperature interference abilities.

In this letter, a new wideband circularly polarized antenna for Radio Frequency Identification (RFID) readers is proposed. A prototype operating in the Ultra-High Frequency (UHF) band is successfully realized and tested using a defected Ground Structure (DGS). This antenna consists of an L-shaped metal strip and a DGS with four tuning stubs. The overall size covers 90*90*1.6 mm³. The measured -10 dB reflection coefficient S₁₁ bandwidth is 27% (800-1020 MHz) and a good radiation pattern and suitable gain coefficient about 3.7 dB have been achieved. Also, an excellent agreement was noticed between simulation and measurement results demonstrating the good performance of the proposed antenna.

In this paper, a simple and compact tri-band multiple-input-multiple-output (MIMO) antenna for wireless applications is proposed. The antenna is composed of two symmetric monopoles placed a distance of 0.106λ₀ and occupies 0.26λ₀×0.25λ₀ board area. The tri-arm monopole offers operation over 2.1-2.7 GHz, 3.3-3.7 GHz and 4.9-5.35 GHz with percentage impedance bandwidth of 25%, 11.4% and 8.7%, respectively. An isolation greater than 20 dB is achieved by integrating a stub in the ground plane and adding a stub in the feed line. The structure exhibits stable gain and radiation patterns. Various performance metrics including envelope correlation coefficient (ECC), diversity gain (DG) and mean effective gain (MEG) are measured.

A new miniaturized microstrip lowpass filter with compact size and a wide spurious-free stopband is investigated. To achieve compact design and ultra-wide band rejection, both triangular patch resonators and trapezoid patch resonators are introduced in the filter. To further reduce the circuit size of the filter, the meander transmission line is also adopted in the design. A demonstration filter with 3 dB cutoff frequency at 0.76 GHz has been designed, fabricated and measured. Results indicate that the proposed filter is able to suppress the 16th harmonic response referred to a suppression degree of 15 dB. Furthermore, the proposed filter exhibits a small size of 0.080λ_g×0.072λ_g, where λ_g is the guided wavelength at 0.76 GHz.

Space-time adaptive processing (STAP) for airborne radar employs training samples to estimate clutter covariance matrix (CCM). However, the target-like signals contained in the training samples severely corrupt the accuracy of the CCM. This paper proposes a novel non-homogeneous STAP algorithm for target-like signal elimination based on reduced-dimension sparse reconstruction (RDSR) to overcome this issue. The proposed algorithm exploits the high-resolution angle-Doppler spectrum obtained by RDSR to estimate and eliminate target-like signals. Theoretical analysis and simulation results show that the proposed algorithm effectively suppresses clutter and improves the performance of STAP in non-homogeneous environments.

A main defect of far-field (FF) measurement techniques is long measurement time, which often leads to the problem of inefficient use of measurement facilities that is a strong limiting factor in many measurements. To solve this problem, in this study, we propose a technique to accelerate the antenna measurement that is achieved by sparse test results in the FF measurement system. In the data processing part of the measurement, the concept of the quadrature analog-to-information conversion (QAIC), which make the approach both efficient and easy to implement in existing FF measurement facilities, is discussed. Simulations are provided to show this low-speed uniform sampling approach. The proposed strategy is then applied to measure the pattern of a standard rectangular horn antenna in an anechoic chamber. The experimental results demonstrate that our technique can reduce the measuring time by at least 34.4% while guaranteeing the measurement accuracy. These results demonstrate the potentials of the method.

In this paper, a stub-loaded penta-mode resonator (PMR) with its analysis, characterization and applications for bandpass filter (BPF) is presented. Even-/odd-mode analysis method is employed to analyze the PMR which exhibits five transmission poles (TPs) and three inherent transmission zeros (TZs). By changing the dimension parameters of the resonator, TPs and TZs can be flexibly controlled, and wideband/dual-wideband/tri-band BPF has been designed successfully utilizing the same configuration. For validation, all these three filters are fabricated and measured, and the measured results are in good agreement with the simulated ones.

Minimum variance distortionless response (MVDR) beamformer is an adaptive beamforming technique that provides a method for separating the desired signal from interfering signals. Unfortunately, the MVDR beamformer may have unacceptably low nulling level and high sidelobes, which may lead to significant performance degradation in the case of unexpected interfering signals such as the rapidly moving jammer environments. Via support vector machine regression (SVR), a novel beamforming algorithm (named as SVR-CMT algorithm) is presented for controlling the sidelobes and the nullling level. In the proposed method, firstly, the covariance matrix is tapered based on Mailloux covariance matrix taper (CMT) procedure to broaden the width of nulls for interference signals. Secondly, the equality constraints are modified into inequality constraints to control the sidelobe level. By the ε-insensitive loss function for the sidelobe controller, the modified beamforming optimization problem is formulated as a standard SVR problem so that the weight vector can be obtained effectively. Compared with the previous works, the proposed SVR-CMT method provides better beamforming performance. For instance, (1) it can effectively control the sidelobe and nullling level. (2) it can improve the output signal-to-interference-and-noise ratio (SINR) performance even if the direction-of-arrival (DOA) errors exist. Simulation results demonstrate the efficiency of the presented approach.

This paper presents two novel substrate integrated waveguide (SIW) diplexers with transmission zeros placed below and above the passband. Diplexer I is based on two bandpass filters (BPFs) using eighth mode SIW (EMSIW) cavities with Rx and Tx frequencies at 3.68 GHz and 6.09 GHz. The second one is operated at 2.37 GHz and 6.04 GHz using EMSIW and thirty-second SIW (TMSIW) cavity. The diplexers are all combined through a T-junction by carefully choosing the length and width of two branches to allow each filter to match the antenna, while maintaining an open circuit at the middle band of the other. The proposed diplexers possess compact size, because of the EMSIW and TMSIW cavity. The diplexers are fabricated in SIW technology. The minimum insertion losses including SMA connectors are measured to be 1.39/1.61 dB and 0.38/0.85 dB. Meanwhile, the diplexers exhibit 37 dB and 42 dB isolations between the channels, respectively. Good agreement is achieved between simulated and measured results.

This paper presents a direct matrix synthesis for in-line diplexers constructed by general Chebyshev channel filters. The finite transmission zeros of the channel filters are generated and independently controlled by a set of frequency-variant couplings (FVC) sections. The network only involves resonators cascaded one by one without any auxiliary elements (such as cross-coupled or extracted-pole structures), and this paper provides the best synthesis solution in configuration simplicity for narrowband contiguous diplexers. For the channel filters, considering both the couplings and capacitances matrices of a traditional low-pass prototype, a generalized transformation on the admittance matrix is introduced as the basis of the synthesis, which allows more than one cross-coupling to be annihilated in a single step, while generating an FVC section simultaneously. Two examples of diplexer are synthesized to show the validation of the method presented in this paper.

In a recently published report, Sen and Das [5] proposed a frequency tunable low-cost microwave absorber to obtain tunable absorption spectra. In this paper, we justify that the proposed device is not an absorber. It is observed that the total absorption rates merely reach 2% and 14.85% for the air gaps of 3.5 mm and 7.5 mm, respectively, when the co- and cross-polarization reflections are taken into account in the reported device. Obviously, The original authors erroneously consider a polarization converter as an absorber, and the obvious errors can be found in their paper.

In this paper, B₂-spline interpolation technique for Overset Grid Generation (OGG) and Finite-Difference Time-Domain (FDTD) method is developed. B₂-spline or biquadratic spline interpolation offers better accuracy compared to the bilinear interpolation. The two-dimensional (2-D) numerical simulations are carried out for electromagnetic (EM) field analysis to measure the scattered fields for an unknown object in a free space and a dielectric medium. There are 2 antennas utilized in this work, each antenna will become transmitter sequentially to transmit a microwave pulses while another acts as receiver to collect the scattered fields in the OGG-FDTD lattice. In order to analyse the efficiency of proposed method, the scattered fields that collected by receiver antenna will be investigated with relative error. The results show that OGG-FDTD method with B₂-spline interpolation gives lower relative error than bilinear interpolation with 0.0009% differences in a free space and 0.0033% differences in a dielectric medium. Hence, it proves that OGG-FDTD method with B₂-spline interpolation has ability to measure the scattered fields around the unknown object efficiently. For future work, the proposed method can be applied to inverse scattering for detection and reconstruction of the buried objects with arbitrary shapes in a complex media.

A novel triple-mode bandpass filter (BPF) using half-wavelength-resonator-coupled square-loop resonator is developed in this letter. The half wavelength resonator is applied to add an additional path, which increases a pole in the passband and a transmission zero in the stopband. Furthermore, the coupling scheme is used to accurately predict its desired performance. Compared to the conventional square-loop dual-mode filter, higher frequency selectivity and wider bandwidth are achieved. Finally, this filter is designed, fabricated and measured. Good agreement is achieved among the theoretical, simulated and measured results. All of these results validate our design idea.

In this paper, we propose a novel method for wideband direction of arrival (DOA) estimation. By calculating the largest principal angle between the signal subspace and the subspace spanned by the augmented array manifold, the proposed method can estimate direction of arrival of wideband signals. Unlike conventional wideband methods, it adopts a new augmented array manifold and constructs the augmented matrix entirely by processing the received signals in frequency domain. It does not require any preliminary DOA estimates or focusing matrices. Simulation results show that the proposed method exhibits satisfactory performance at medium and high signal-to-noise ratio (SNR) conditions in comparison to the existing wideband DOA estimation methods.

A transmitting lens antenna using Huygens matematerials is proposed. The type of metamaterial has a 100% transmission. For obtaining a high gain antenna, a patch antenna is placed at the focal point of the metasurface as a feed source, and then quasi-spherical wave can be transformed to plane wave. As demonstration of the concept, a lens antenna, working at frequency of 10 GHz is designed, fabricated and measured. Numerical and experimental results agree well with each other. The measured results show that the gain has been enhanced about 11.2 dB.

Recent research has shown that the Pareto family of distributions provides suitable intensity models for high resolution X-band maritime surveillance radar clutter. In particular, the two parameter Pareto Type II model has been shown to fit the Australian Defence Science and Technology Group's medium to high grazing angle clutter returns very well. The Pareto Type II model is a special case of a Burr distributional model, which is a three parameter power law statistical model. Hence this paper begins by investigating the fitting of the Burr model to real data. Based upon these results a detailed study of the development of non-coherent sliding window detectors is justified, for operation in such clutter. Several different approaches will be applied to construct the decision rules. These include a transformation approach and direct adaptation of such detectors, designed for operation in exponentially distributed clutter, to the Burr clutter setting. In addition to this, the fact that the Burr distribution is invariant with respect to two of its distributional parameters allows specication of detection processes which have the constant false alarm rate property with respect to these model parameters. Performance analysis, in simulated clutter, of the derived detectors is then examined. This includes performance in the presence of interference and false alarm regulation during clutter power transitions. This is complemented by an application of the decision rules to target detection in real high resolution X-band maritime surveillance radar clutter.