A new microstrip diplexer with very high output isolation and low insertion losses is presented in this letter. With the adoption of the spiral compact microstrip resonant cell (SCMRC) form into the dual behavior resonator (DBR) microstrip filter design, a bandpass filter with high rejection in the upper stopband can be achieved. Therefore, very high output isolation for the diplexer can be realized. Furthermore, the proposed diplexer also has a property of low insertion loss in the passband. To validate the design theory, one demonstrator diplexer has been designed and fabricated; the results indicate that the proposed diplexer has good performance of simple structure, better than 65 dB output isolation in the stopband, and less than 1.2 dB insertion losses in the passband.

Rubber tire dust-rice husk is an innovation in improving the design of pyramidal microwave absorbers to be used in radio frequency (RF) anechoic chambers. An RF anechoic chamber is a shielded room covered with absorbers to eliminate unwanted reflection signals. To design the pyramidal microwave absorber, rice husk will be added to rubber tire dust since the study shows that both have high percentages of carbon. This innovative material combination will be investigated to determine the best reflectivity or reflection loss performance of pyramidal microwave absorbers. Carbon is the most important element that must be in the absorber in order to help the absorption of unwanted microwave signals. In the commercial market, polyurethane and polystyrene are the most popular foam-based material that has been used in pyramidal microwave absorber fabrication. Instead of using chemical material, this study shows that agricultural waste is more environmentally friendly and has much lower cost. In this paper, three combinations of rubber tire dust and rice husk are fabricated to investigate the performance of microwave absorber reflection loss in operating in the frequency range from 7 GHz to 12 GHz.

In this paper, a two-dimensional (2D) diffraction tomographic algorithm based on the first order Born approximation is proposed for the imaging of hidden targets behind the wall. The spectral expansion of the three layered background medium Green's function is employed to derive a linear relationship between the spatial Fourier transforms of the image and the received scattered field. Then the image can be efficiently reconstructed with inverse Fast Fourier Transform (IFFT). The linearization of the inversion scheme and the easy implementation of the algorithm with FFT/IFFT make the diffraction tomographic algorithm suitable in through-the-wall radar imaging (TWRI) applications concerning the diagnostics of large probed domain and allow real-time processing. Numerical and experimental results are provided to show the effectiveness and high efficiency of the proposed diffraction tomographic algorithm for TWRI.

In this letter, the design and measurement of a new ring power divider exhibiting wideband high isolation is presented. Coplanar techniques are used to achieve a compact and truly uniplanar design. The design is demonstrated by a prototype, operating at K-band, that has been monolithically fabricated using a GaAs MMIC process with airbridge technology. The measured insertion loss is 0.6 dB at the center design frequency of 25 GHz. The output port isolation is better than 20 dB across a wide bandwidth from 10 MHz to 50 GHz. The output amplitude and phase balance is within ±0.5 dB and ±2°, respectively, in the bandwidth from 10 MHz to 43 GHz.

An improved multipactor dynamic model is proposed for studying the multipactor phenomenon on a dielectric surface existing longitudinal RF electric field using Monte Carlo method. The susceptibility curves of the electric field on the surface and the temporal evolution images of the multipactor discharge were obtained and discussed. The power deposited on the dielectric surface by the multipactor was also investigated in terms of an S-band RF dielectric window. The results show that, the longitudinal RF electric field may intensify the single-surface multipactor effect, which is likely detrimental to RF transmission and to result in the dielectric crack.

In this letter, a new miniaturized broadband 3-dB branch-line coupler at the center frequency of 880 MHz is proposed. The proposed coupler is designed by means of integrated miniaturization method, which consists of shunt capacitors, fractal geometry and equivalent miniaturized stubs, to achieve 82% size reduction compared with the referenced coupler. The return loss and isolation are both under -20 dB over a 19% relative bandwidth. The proposed coupler is simulated, fabricated and measured. The measured results agree well with the simulated ones.

An iterative hybrid method combining the Kirchhoff approximation (KA) and the multilevel fast multipole algorithm (MLFMA) is studied for electromagnetic scattering from a three-dimensional (3-D) object above a two-dimensional (2-D) random dielectric rough surface. In order to reduce the computational costs, some treatments have been studied. Firstly, the fast far-field approximation (FAFFA) is utilized to speed up the electromagnetic coupling interaction process between the rough surface and the object. Secondly, based on the scattering mechanism of the rough surface, a truncation rule on moderate rough surface for bi-static scattering is proposed under the plane wave illumination, which can further speed up the iteration. Compared with the conventional methods, the hybrid method with the above treatments is very efficient to analyze the scattering of a 3-D object above random rough surfaces. Simulation results validate the effectiveness and accuracy of the iterative hybrid method.

The design of a simple microstrip fed folded strip monopole antenna (FSMA) with a protruding stub in the ground plane for the application in WLAN and RFID is presented. The antenna has two resonant paths, one in the radiating element (folded strip) and the other in the protruding stub of the ground plane. It supports two resonances at 2.4 GHz and 5.81 GHz, which are the center frequencies of WLAN and RFID. Effectively consistent radiation pattern and large percentage bandwidth have been observed. The measured percentage fractional bandwidth at 2.4 GHz (2.05 GHz to 2.86 GHz) is 32.99, and the percentage fractional bandwidth at 5.81 GHz (5.55 GHz to 6.14 GHz) is 10.11. The proposed antenna is simple and compact in size, providing broadband impedance matching, consistent radiation pattern and appropriate gain characteristics in the WLAN and RFID frequency regions.

A novel 21-35 GHz single-balanced quadruple subharmonic monolithic passive mixer is fabricated using the 0.15 μm GaAs pHEMT process. This mixer consists of a local oscillation (LO) spiral balun and a radio frequency (RF) band pass filter which has an intermediate frequency (IF) extracted feature utilizing a pair of anti-parallel Schottky barrier diode to achieve quadruple subharmonic mixing mechanism. The RF band pass filter formed with an interdigital coupler and a low-pass network is used to reduce the chip dimension while operating at a low frequency band and to improve the isolation between the RF and IF ports with a broadband operation. From the measured results, the mixer exhibits 11.3-15.1 dB conversion loss, 28.8 dB-high RF-to-IF isolation, 40 dB-high LO-to-RF isolation, 60 dB-high 3LO-to-RF isolation over a 21-35 GHz RF bandwidth, and an input 1 dB compression power of 4 dBm. The compact IF extraction circuit supports an IF frequency ranging from DC to 3.1 GHz. The core chip size is only 0.67 × 0.75 mm².

A compact microstrip ultra-wideband (UWB) bandpass filter (BPF) including a narrow notched band within the UWB passband is proposed. The proposed filter is constructed by combination of two highly compact wideband bandpass filters (BPFs) with different physical dimensions which are designed on the basis of a folded-T-shaped stepped impedance resonator (SIR) and parallel-coupling feed structure. The wideband BPFs can be designed separately, and the design procedure is described. The narrow notched band with 3.8% 3 dB fractional bandwidth (FBW) from 5.15 to 5.35 GHz (IEEE 802.11a lower band) is created in order to eliminate interference from wireless local area network (WLAN) with the determined UWB passband. The center frequency and bandwidth of the notched band can be controlled by tuning the structural parameters. The full-wave EM simulated and measured results are in good agreement, showing that the proposed filter possesses good characteristics including wide passband, high selectivity, low insertion loss, large notch deep and sharp rejection.

A printed dipole antenna with back to back asymmetric dual-C-shape uniform strips capable of generating a wide operating band for digital television (DTV) signal reception in the 470-862 MHz band is presented. This antenna is associated with C-shape strips and asymmetric structure, and it operates band in 455-865 MHz. By proper adjusting some parameters, it is possible to achieve a broadband response. Measured results have been compared with simulation and found in a good agreement. The antenna with back to back asymmetric dual-C-shape uniform strips can generate two adjacent resonant modes to form a wide operating band of larger than 62% in 2.5:1 VSWR bandwidth, which is much wider than that of the corresponding back to back symmetric dual-C-shape strips dipole antenna. The experimental results show that stable radiation pattern is similar to a dipole antenna. The measured peak gains are 3.2 dBi and 2.3 dBi, at 620 MHz and 780 MHz, respectively. The radiation efficiencies are all larger than 60% for an entire DTV band.

The integration of the Iterative Multi-Scaling Multi-Region (IMSMR) procedure and the Inexact-Newton method (INM) is proposed within the contrast-field formulation of the inverse scattering problem. Thanks to its features, such an implementation is expected to effectively deal with the reconstruction of separated objects. A selected set of numerical results is presented to assess the potentialities of the IMSMR-INM method also in comparison with previous INM-based inversions.

The Kelvin image theory for a conducting sphere is extended to the case of a conducting oblate spheroid in uniform motion along its axis of revolution (a Heaviside ellipsoid) using the well-known method provided by Special Relativity. The results derived are checked in various ways.

The downlink beamforiming technology plays a key role in a cognitive radio network (CR-Net). It can be used to reduce transmission power and interference to other users, etc. This paper presents a robust downlink beamforming method with power control for a multiuser multiple-input-single-output (MISO) CR-Net. In this proposed approach, the beamforming optimization problem is formulated as the second-order cone programming (SOCP). The presented method can not only minimize the transmitted power but also guarantee that the received signal-to-interference-plus-noise ratio (SINR) is strictly above the prescribed quality-of-service (Qos)-constrained threshold at each secondary user (SU) and the the interference power (IP) is strictly below the prescribed threshold at the primary user (PU). Simulation results are presented to verify the efficiency of the proposed method.

The relationship between the immittance inverter coefficients and the coupling coefficients is obtained under the non-resonating coupling condition. With the relationship and the determinant properties of the transformation matrix, the coupling matrix could be decomposed to many sub-matrixes for filter designs. The physical significance of the decomposition is discussed. Using this idea, a filter can be decomposed to a number of sub-filters, which could be connected by sections of transmission lines with the same characteristics kept.

In this paper, a novel compact quasi-elliptic waveguide low-pass transmit reject filter (TRF) by using T-shape units is proposed for Ku-band very small aperture terminal (VSAT) transceivers. The equivalent circuit model of the T-shape unit is investigated and shows a topology similar to that of the elliptic low-pass filter. In order to reduce the difficulty in physical realization, which is commonly encountered with a standard elliptic low-pass filter, an approximate elliptic low-pass filter prototype is presented. Accordingly, a synthesis approach is developed to obtain the initial dimensions of the filter. To optimize the performance of the filter, full-wave electromagnetic simulation is used to fine-tune the dimensions of the filter. An eleven-order Ku-band low-pass TRF is designed and fabricated using a WR-75 waveguide. Measured results show it has a low insertion loss of less than 0.3\,dB in the pass band and a high attenuation slope of 78 dB/GHz. Moreover, the miniaturized size of the filter is only 38 mm × 38 mm × 42 mm (WR-75 flange size is 38 mm × 38 mm).

ℜOptical filtering properties in a multichanneled transmission filter based on one-dimensional photonic crystal containing the coupled defects are theoretically investigated. The resonant transmission peaks are designed to be located within the photonic band gap of a defect-free photonic crystal. The number of peaks is directly equal to the number of the coupled defects. The positions of resonant peaks can be tuned by varying the refractive index of the defect layer. In addition, extremely resonant peaks can be produced by adding the Bragg mirrors at the front and rear sides of the structure.

Photoinductive (PI) field mapping for eddy-current (EC) probes above a thin metal film was performed by multiphysics analysis with two-dimensional finite element method (FEM). The FEM model of PI method was used to observe how metal film properties affect the field-mapping signals of EC probes. The PI signal was tested for effects of resistivity, temperature coefficient of the resistivity, thermal conductivity, heat capacity, and thin film density The applicability of actual thin film materials for mapping the field of EC probe when using PI method was discussed. Field-mapping signals of EC probe coils with tilt angles of 0^o, 5^o, 10^o, 15^o, and 20^o were also examined with appropriate metal film material. These experiments showed that the higher-resolution field-mapping signals of EC probes can be obtained by given a titanium thin film The resolution of field-mapping signals of EC probes correlated positively with resistivity, heat capacity, and density of thin film and correlated negatively with its thermal conductivity. Improved understanding of distinct field distribution of EC probes enables selection of optimal probes for EC inspection.

We investigate the propagation characteristics of super-Gaussian beam in highly nonlocal nonlinear media. The optical beam propagation has been modeled by well known nonlocal nonlinear Schrődinger equation. The variational method is employed to find the initial beam propagation parameters and then split step Fourier method is used for numerical simulations. A generalized exact analytical solution of the model is obtained and critical power of soliton is determined. The evolution of super-Gaussian beam has shown oscillatory propagation.

In this paper, the simulation and experimental studies of SAR distribution in a bio-medium situated very close to a rectangular dielectric resonator antenna (RDRA) in C-band of microwave frequencies are reported. The simulation study has been carried out using CST Microwave Studio simulation software. The experimental distribution has been obtained using two 50Ω L-shaped and straight probes and Agilent make 3 Hz-50 GHz spectrum analyzer. The experimental results for SAR distribution are compared with simulated results.