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.

This paper presents some theoretical and experimental analyses of the rotating-magnet based mechanical antenna (RMBMA), a promising portable transmitting antenna for ELF-ULF (3-3000 Hz) wireless communication. Based on the Amperian current model, a theoretical model is developed to analyze the electromagnetic fields generated by RMBMA. A prototype is manufactured and measured, and the measurements coincide well with the calculations based on the established theoretical model. The results reveal that this new technique can create a constant channel condition in complex propagation environment, and an RMBMA with a small size can produce an AC magnetic field of 1 pT at hundreds of meters across lossy media, such as soil and sea water.

A novel broadband ±45° dual-polarized magneto-electric (ME) dipole antenna is proposed for 2G/3G/LTE/5G (3.3-3.6 GHz)/WiMAX applications. The proposed antenna has Γ-shaped feeding strips to impart a wide impedance bandwidth for its special structure. Stable antenna gain and radiation pattern are realized by using a rectangular box-shaped reflector instead of planar one. The antenna is fabricated and measured. The measured results show that a common impedance bandwidth is 83% with standing-wave ratio (SWR) ≤ 1.5 from 1.59 to 3.83 GHz and port-to-port isolation larger than 25 dB within the bandwidth. The measured antenna gains vary from 8 to 10.8 dBi and from 8 to 10.6 dBi for port 1 and port 2, respectively. The antenna has nearly symmetrical radiation patterns with low back lobe radiation both in horizontal and vertical planes, and broadside radiation patterns with narrow beam can also be obtained. The proposed antenna can be used for multiband base stations in next generation communication systems.

This paper presents a dual-band Multi-Input Multi-Output (MIMO) antenna design with acceptable isolation and compact size for wireless applications. The proposed antenna operates at two frequencies (2.75 GHz-5.3 GHz) and consists of two symmetrical monopoles with a T-shaped junction that is added on the upper layer of the substrate and used to connect the two monopoles and the ground plane. The T-shaped junction is added to enhance the isolation between the two antennas. Different forms of slots have been etched on the ground plane to adapt the frequency bands to the desired frequencies. The simulations and measurement are used to examine the performance of the antenna in terms of S parameters, radiation patterns and the envelope of correlation coefficient. The results show that the MIMO antenna has two resonance frequencies (2.75 GHz and 5.3 GHz), is suitable for WLAN applications and comes with a mutual coupling that is less than 12 dB. As a result, an envelope correlation coefficient lower than 0.001 and a diversity gain higher than 9.98 dB are obtained, which means that the antenna has a remarkable diversity gain at operating bands.

In this paper, design and development of a novel electromagnetics band gap cell is presented. The EBG cell is designed aiming its use at relatively low frequencies. It is designed as a uni-planar structure to simplify the fabrication processes. It consists of multiple parallel combinations of L and C. These components are realized using planar microwave integrated circuit technology. The components L & C are designed as a meander-line inductor and inter-digital capacitors, respectively. The cell is perfectly symmetrical along x and y-axes to have uniform performance along two orthogonal directions. It is evaluated for its S-parameters and reflection phase. Simulated and measured results are presented for frequency range of 0.885 GHz to 3.1 GHz.

In this article, a negative index metamaterial (NIM) superstrate is designed and cooperated with the filtenna to produce miniaturize communication front end for gain enhancement without any substantial increase in the profile of the whole structure. A finite array Double H Split Ring (DHSR) of 11x9 unit cells has been designed on a dielectric substrate to form the NIM metamaterial superstrate. The proposed superstrates and filtenna have an overall dimension of 0.67λ_ox0.54λ_ox1.19λ_o at 10.16 GHz with 10.6 dB total broadside gain in simulation and 9.8 dB in measurement at 10.22 GHz (λ_o = 30 mm). This miniaturized communication front end which consists of a filter, an antenna and a gain enhancer affords smaller size with the overall volume of 0.43λ_o³ in the context of using metamaterial superstrate for gain enhancement reported in the earlier literatures.

This paper proposes a composite right/left-handed cylindrical waveguide. Negative permeability is realized by the cutoff TM₀₁-mode in a hollow waveguide, and negative permittivity is realized by the cutoff dominant TE-mode in a sector waveguide with a ridge. Usefulness of the proposed cylindrical waveguide is verified from the numerical computations of both the dispersion diagrams and the transmission characteristics of the structure with finite-number unit cells. Finally, measurement of the fabricated waveguides is performed for the experimental verification.

A simple broadband and wide stopband half-mode substrate integrated waveguide (HMSIW) filter is proposed. Symmetrical complementary split ring resonators (CSRRs) and metallized holes are loaded on the surface of the HMSIW resonator. Metallized holes placed in the center of the CSRRs are used to create two passbands. CSRRs can reduce the return loss of the first passband, and a transmission zero is introduced to suppress the performance of the second passband, thus generating broadband covering the entire X-band. The simulated results show that the center frequency and fractional bandwidth of the filter are 9.26 GHz and 60.7%. There is a transmission zero at 13.18 GHz, and the insertion loss in the range of 12.30 to 21.46 GHz is better than -10 dB, which means that the out-of-band suppression performance is good. The measured results are in good agreement with the simulated ones. This new combination not only obtains broadband frequency, but also makes the filter more compact. The filter has some practical and application significance.

In this paper, a novel multi-physics parametric modeling approach using artificial neural networks (ANNs) for microwave passive components is proposed. In the proposed approach, the ANN is used to learn the nonlinear relationships between electromagnetic (EM) behaviors and multi-physics design variables. The trained model can accurately represent the EM responses of the passive components with respect to the multi-physics input parameters. Therefore, the proposed model can provide accurate and fast prediction of EM responses using low computational cost and little time for multi-physics design. The advantage of the proposed model is demonstrated by two microwave examples: the proposed model can save about 98% computational cost compared with the EM model, and the CPU time of the proposed model is less than 0.1 s while that of the EM model needs many minutes.