In order to realize bandpass filter with Chebyshev and elliptic function responses using a single resonator only, a dual-mode square resonant structure is proposed. Four small square loops are added into a large loop. One of small loops is defined a perturbation element, other small ones are references. By changing the thickness of the perturbation element with respect to that of a reference element, the resonator can produce a capacitive or inductive coupling between two degenerate modes. The capacitive coupling can acquire an elliptic function characteristic since it can create the transmission zeros on both the lower and upper sides of the passband, while the inductive coupling cancels them which exhibits a Chebyshev characteristic. Therefore, both Chebyshev and elliptic function responses can be obtained in a filter. The proposed bandpass filter is with a wider stopband and more compact in size. Experiment results have been verified this design.

This work presents a novel broadband monopole antenna for digital video broadcasting-terrestrial (DVB-T) application. The proposed antenna consists of a grating zigzag patch and a concave rectangular ground plane. The zigzag patch is used to enable the antenna height reduction for fixed ranges of operating frequency. The proposed antenna can operate from 420 MHz to 1050 MHz frequency range corresponding to 85% of impedance bandwidth for |S₁₁| better than -10 dB. This covers the working frequency band (470-862 MHz ) of DVB-T system. The radiation pattern of the proposed antenna is omnidirectional across the desired operating frequency band. Details of the proposed antenna design and experimental results of the constructed prototypes are presented and discussed. Furthermore than the bandwidth enhancement, we have also arranged the structure for network antennas application.

A closely-packed (4 mm) diversity slot antennas operating in the UWB frequency is proposed. High isolation (S₂₁ < -20 dB) of two closely-packed slot antennas can be easily achieved in a broad band by taking advantage of the directional radiation characteristics of slot antenna. Quarter-wavelength slot resonator is adopted to improve the isolation in the low-band of the UWB. The simulated current distribution and the radiation patterns of the single antenna element with and without slots are also presented to explain the mechanism of decoupling in the diversity system. Furthermore, the diversity performance of correlation coefficient, mean effective gains (MEGs), diversity gain (DG) are also studied.

A compact, parasitic array antenna printed on both sides of the substrate to generate dual Notches is introduced. The antenna is composed of one driver and two directors. Both directors are discretely segmented and are twisted with each other to minimize the radiation interference from one director to the other at each resonance. The antenna is optimized for realized gains in the director direction at the two resonant frequencies. The optimized antenna has been fabricated and measured to verify the simulated results. At both resonances, the measured realized gains in the director direction are greater than 8.5 dBi, and the front-to-back ratios are more than 10 dB.

In this paper, a K-band ground-based hyperspectral microwave radiometer for atmospheric sounding is proposed, which improves the profile error and vertical resolution of moisture profiling under the high water vapor condition. The hyperspectral microwave radiometer (80 K-band spectral channels) can observe the rapidly changing weather with high sensitivity and accuracy of brightness temperature by using a stable high-speed receiver and an improved tipping calibration method. By combining several advantages of traditional microwave receiver, the MMIC receiver has good ultra-wideband performance, high linearity, and short measuring time. Moreover, through correcting the calibration parameters of traditional tipping calibration, the proposed calibration method can increase calibration accuracy based on the radiative transfer equation in the atmosphere. Measurement results demonstrate that the radiometer achieves a sensitivity of 0.1 K for 2 s of integration time and an accuracy of better than 0.77 K. For the water vapor profile, the variational retrievals method is used to extract the redundant information under the microwave hyperspectral condition. Preliminary comparisons of measured water vapor profiles with traditional results show good improvement of the profile error and vertical resolution.

In this paper, a multilevel time domain fast dipole method (TD-FDM) is proposed for solving time-domain magnetic field integral equations. It is the extension of TD-FDM to the multilevel. This proposed scheme starts by multilevel grouping. At each level, the far-field interaction can be expanded through the Taylor series and reconstructed via aggregation-translation-disaggregation procedure, which reduces the memory requirement and the computational cost of the marching-on in-time (MOT) method. Numerical results about the electromagnetic scattering from perfect electric conductor (PEC) objects are given to demonstrate the validity and efficiency of the proposed scheme.

In this paper, a novel tunable antenna using graphene-based artificial magnetic conductor (AMC) is proposed and investigated. The resonance frequency of the AMC ground plane can be electrically tuned by applying a gate voltage. A bowtie-shaped antenna is mounted above the 15×15 AMC units. It is observed that the operating frequency of the antenna system shifts in a large range when varying the external electric field. The bandwidth of the antenna system can reach as high as 47% with a gain higher than 9 dB.

A novel miniaturized composite right/left-handed (CRLH) transmission line based on the structure of spiral inter-digital is proposed and analyzed in this article. Compared with the conventional inter-digital CRLH, the proposed CRLH realizes a 25% resonace frequency shift, and the miniaturization is realized. Then, a compact bandpass filter centered at 1.00 GHz with minimum insertion loss 0.42 dB was designed, fabricated and measured. The measured results show that the band width is 61.6% and that the sharpness at the two edges of passband is 212.5 dB/GHz and 607.1 dB/GHz. This designed filter has very high selectivity. Besides, the whole size of the designed filter is 0.114λ×0.054λ. The filter realizes the miniaturization effectively, and this designed bandpass filter has good performances and smaller size than the same works in references.

Microwave induced thermo-acoustic tomography (MITAT) has great potential in early breast cancer detection because it utilizes the advantages of both microwave imaging and ultrasound imaging. In this paper, we develop a fast and efficient simulation approach based on a hybrid method which combines finite integration time domain (FITD) method and pseudo-spectral time domain (PSTD) method is developed. By using this approach, energy deposition of biology tissue illuminated by electromagnetic fields can be accurately simulated. Meanwhile, acoustic properties of the tissue can be efficiently simulated as well. Compared to traditional methods, such as finite difference time domain (FDTD), et al, the developed method can well process real 3-D electromagnetic-acoustic complex models. Based on this approach, a MITAT model is created and some simulated results are analyzed. Furthermore, some real breast tissues are adopted to perform the thermo-acoustic imaging experiment. Comparisons between experimental and simulated results are made. The feasibility and effectiveness of the proposed approach are demonstrated by both numerical simulations and experimental results.

The influence of beam convergence on the photonic band-gaps, or stop-bands (SBs), of onedimensional photonic crystals (1D PCs) is investigated. The investigation is based on an analysis of the gap map obtained from reflection spectra, calculated by the transfer matrix method for various angles of light incidence, φ, The calculated data is compared with reflection spectra taken using Fourier Transform Infrared microspectroscopy. It was found that the introduction of the parameter, Δφ to account for the focused light beam, for angles up to 20°, has little effect on the first, or lowest SB and the SBs adjacent to it. However, an increase in the order of the SB causes an increase in the influence of this parameter.

This study presents a novel wideband absorber for radar cross section (RCS) reduction. Unlike previous absorber designs that use multilayer lossy materials, this study proposes a design based on a planar antenna array that adopts a bowtie dipole structure as the unit cell. The complete design procedure was investigated by using examples for single- and dual-polarized incident wave designs. The measurement results show that the bandwidth of both designs exceeded 81% of 10 dB RCS reduction when the thickness is less than 12% of the free space wavelength at the lowest operating frequency. The high RCS reduction of the proposed absorbers was demonstrated using commercial ground-penetrating radar. Results show that the proposed absorber is invisible to radar.

A nonlinear electrical transmission line with an intersite circuit element acting as a nonlinear resistance is introduced and investigated. In the continuum limit, the dynamics of localized signals is described by a non-linear evolution equation belonging to the family of nonlinear diffusive Burgers' equations. This equation admits compact pulse solutions and shares some symmetry properties with the Rosenau-Hyman K(2,2) equation. An exact discrete compactly-supported signal voltage is found for the network and the dissipative effects on the pulse motion analytically studied. Numerical simulations confirm the validity of analytical results and the robustness of these compact pulse signals which may have important applications in signal processing systems.

An investigation of dual-band balanced-to-unbalanced (blaun) bandpass filters (BPFs) is presented in this letter. Two types of balun BPFs named Type-A and Type-B filters based on coupled ring resonators are discussed and fabricated. Both the simulated and measured results show that these balun-BPFs have not only good amplitude performances but also excellent phase difference performances. The center frequencies of these balun BPFs are set at 2.4 GHz/5.6 GHz for Type-A and 1.57/4.65 GHz for Type-B balun filters. The differences are 180° ± 5° in phase and within 0.6 dB in magnitude of type A and 0.73 dB of type B, respectively. Thus, these balun BPFs can be used in many wireless communication systems.

A rectangular dielectric resonator antenna (DRA) with a square spiral microstrip feedline is investigated in this paper. The design utilizes a feeding structure to excite two resonant modes (TE_δ11 and TE_1δ1 modes) of the rectangular DRA that are spatially orthogonal in polarization and in phase. The antenna with the proposed feeding structure has provided a measured circular polarization(CP) over a bandwidth of ~15.5% in conjunction with an impedance-matching bandwidth of ~31.25% at the same frequency range. The gain of the dielectric resonator antenna varies between 6.8 and 7.2 dBi across the bandwidth (7.5~8.75 GHz). Reasonable agreement between the simulated and measured results is obtained.

A frequency dependent model of sheet resistance of transparent conductive mesh coatings is proposed based on transmission line theory and vilified by experiments. And the effect on shielding effectiveness of frequency dependent sheet resistance is analyzed. Simulation results of shielding effectiveness are compared with the experimental data of a mesh-coated window sample with equivalent parameters fabricated and measured by Exotic Electro-Optics. The agreement between experiment and simulated proves the validity of the proposed sheet resistance model. So it can be therefore concluded that the frequency dependent model can be used to reasonably evaluate sheet resistance and shielding effectiveness of transparent conductive mesh coated windows.

Adaptive beamforming methods degrade in the presence of model mismatch. In this paper, we develop a modified interference covariance matrix reconstruction based beamformer that is robust against large array calibration errors. The calibration errors can come from the element position errors, and/or amplitude and phase errors, etc. The proposed method is based on the fact that the sample covariance matrix can approximate the interference covariance matrix properly when the desired signal is small, and a reconstructed covariance matrix based on the Capon spectral will be better than the sample covariance matrix when the desired signal is large. A weighted summation of two covariance matrices in references is used to reconstruct the interference covariance matrix. Moreover, a computationally efficient convex optimization-based algorithm is used to estimate the mismatch of the steering vector associated with the desired signal. Several simulation cases are applied to show the superiority of the proposed method over other robust adaptive beamformers.

We investigate the design of Concentric Circular Antenna Arrays (CCAAs) with λ/2 uniform inter-element spacing, non-uniform radial separation, and non-uniform excitation across different rings, from the perspective of Multi-objective Optimization (MO). Unlike the existing single-objective design approaches that try to minimize a weighted sum of the design objectives like Maximum Side Lobe Level (MSLL) and principal lobe Beam-Width (BW), we treat these two objectives individually and use Multiobjective Evolutionary Algorithm based on Decomposition (MOEA/D) with Differential Evolution (DE), called MOEA/D-DE, to achieve the best tradeoff between the two objectives. Unlike the single-objective approaches, the MO approach provides greater flexibility in the design by yielding a set of equivalent final (non-dominated) solutions, from which the user can choose one that attains a suitable trade-off margin as per requirements. We illustrate that the best compromise solution attained by MOEA/D-DE can comfortably outperform state-of-the-art variants of single-objective algorithms like Particle Swarm Optimization (PSO) and Differential Evolution. In addition, we compared the results obtained by MOEA/D-DE with those obtained by one of the most widely used MO algorithm called NSGA-2 and a multi-objective DE variant, on the basis of the R-indicator, hypervolume indicator, and quality of the best trade-off solutions obtained. Our simulation results clearly indicate the superiority of the design based on MOEA/D-DE.

This paper presents a stable grounding technique for the inner conductor of a coaxial resonator in vacuum and high-power condition applications, where the inner and outer conductors of the coaxial resonator are connected by a flange plate. When this novel technique is applied, the stable and unified microwave grounding ability is increased by making the stress on the contact surface uniform, the reliability of space products is improved by reducing the deformation of the rod-end at a transverse vibration load of 10 g by 75%, and the unstable tiny cracks of the high-power component are fully eliminated.

This letter presents the design of a novel wideband omnidirectional antenna with the usable bandwidth enhanced. The antenna is designed for wireless applications and proposed to operate within WLAN (2.4 GHz-2.484 GHz) and WiMAX (2.3 GHz, 2.5 GHz and 3.5 GHz) frequency bands. The bandwidth is enhanced through the use of balun, while the radiation patterns remain stable. This antenna has a much wider VSWR band (47.5% for VSWR < 2) with high radiation pattern stability compared with printed dipole antennas. Details of design, simulated and experimental results of this omnidirectional antenna are presented and discussed. The measured results confirm the validity of this design which meet the requirement of wireless applications.

Properties of wave transmission in a photonic quantum well (PQW) structure containing superconducting materials are theoretically investigated. We consider two possible PQW structures, (AB)^P(CD)^Q(AB)^P-asymmetric and (AB)^P(CD)^Q(BA)^P-symmetric, where the host photonic crystal (PC) (AB)^P is made of dielectrics, A = SrTiO₃, B = Al₂O₃, and the PQW (CD)^Q contains C = A and superconducting layer D = YBa₂Cu₃O_7-x, a typical high-temperature superconducting thin film. Multiple transmission peaks can be seen within the photonic band gap (PBG) of (AB)^P and the number of peaks is directly determined by the stack number of PQW, i.e., it equals Q-1. Additionally, the results show that symmetric PQW structure is preferable to the design of a multichannel transmission filter. The effect of stack number of photonic barrier is also illustrated. Such a filter operating at terahertz with feature of multiple channels is of technical use in superconducting optoelectronic applications.