A compact dual-band switchable bandpass filter is designed using two centrally-loaded open-loop resonators and six pin blocks. The pin diodes are loaded at the zero-voltage points of odd and even modes along the microstrip resonators, such that the two passbands operating at odd and even modes can be individually switched on or off. The isolations for the two passbands are greater than 20 dB.Introduction: Microstrip filters are important components in wireless communication systems. The bandpass filter (BPF), the most important kind, has been a research focus in recent years [1][2][3]. The microwave switch is another key building block in an RF system. Most existing switches are wideband and devoid of frequency selectivity. In a traditional microwave system, bandpass filters are cascaded with switches to implement the switch and frequency preference separately. The circuit area is large and the loss is high. To overcome this problem, switchable bandpass filters that integrate filters and switches are desired. Recently, piezoelectric and pin diode controlled switchable bandpass filters have been investigated, which have sharp cutoff, good selectivity and small circuit sizes [4][5]. These proposed switchable bandpass filters operated at single-band. In this Letter, a compact dual-band switchable bandpass filter is constructed using two centrally-loaded open-loop resonators and six pin blocks. By observation that the zero-voltage points along the microstrip resonators are separate for odd and even modes, pin diodes may be loaded at these zero-voltage points. Loading lumped elements at the zero-voltage points of odd modes has no effect on odd-mode operating, but has great effect on even-mode operating, and vice versa. This principle permits us to design a compact dual-band switchable filter. The two passbands can be controlled independently.

An efficient algorithm for wave scattering from two-dimensional lossy rough surfaces is proposed. It entails the use of a single magnetic field integral equation (SMFIE) in conjunction with a multilevel sparse-matrix canonical-grid (MSMCG) method. The Rao-Wilton-Glisson (RWG) triangular discretization is adopted to better model the rough surface than the pulse basis functions used in the well-established SMCG method. Using the SMFIE formulation, only one unknown per interior edge of the triangular mesh approximating the rough surface is required, and the iterative solution to the moment equation converges more rapidly than that of the conventional coupled equations for dielectric rough surfaces. The MSMCG method extends the applicability of the SMCG method to rougher surfaces. Parallel implementation of the proposed method enables us to model dielectric surfaces up to a few thousand square wavelengths. Simulation results are presented as bistatic scattering coefficients for Gaussian randomly rough surfaces.Index Terms-Multilevel sparse-matrix canonical-grid method (MSMCG), Rao-Wilton-Glisson (RWG) triangular basis, rough surface scattering, single magnetic field integral equation (SMFIE).

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A novel numerical scheme that employs quadratic B‐spline functions as temporal basis functions is proposed for solving time‐domain integral equations (TDIE) of electromagnetic scattering. Because of the compact support of these new temporal basis functions, the resulting time‐domain integral equations solution is efficient in terms of memory usage and computation time. Numerical examples of scattering by both conducting and dielectric objects show that the solution is also stable and accurate. Compared with the Lagrange interpolating functions of the same order, the quadratic B‐spline functions, being complete to the second order, yield a better accuracy in the time‐domain integral equations solution of scattering problems. © 2007 Wiley Periodicals, Inc. Microwave Opt Technol Lett 49: 1154–1159, 2007; Published online in Wiley InterScience (www.interscience.wiley.com). DOI 10.1002/mop.22385