This paper presents a novel filter design technique for the compact microstrip dual-mode filters. An equivalent circuit for the single dual-mode filter section is derived to show that a single unit behaves as a pair of coupled synchronously tuned single-mode resonators. The equivalent circuit was linked to the inverter-coupled bandpass prototype network to allow higher order filters to be realized. A complete design example (from design to realization) of a fourth-order Chebyshev bandpass filter is presented. It is shown that the dual-mode resonator may be employed to design cross-coupled filters with finite frequency zeros. Two filters are designed using optimized coupling matrix method, fabricated and tested. Experimental and simulation results are presented to validate the argument. Finally, it is shown that more compactness may be achieved with narrowband filters by employing folded resonators.

A compact, low loss and mass producible antenna filter is proposed. The radiating element consists of a microstrip patch. Waveguide feeding ensures low loss. Coupling with the antenna is achieved via a slot in the ground plane, maintaining the simplicity of the structure. In order to avoid any complicated transitions, an E-plane filter is integrated in the waveguide. Simulated and experimental results at X-band are presented to validate the argument.

A novel highly selective compact reconfigurable filter with a switchable notched band for ultrawideband (UWB) systems is presented. The proposed filter exhibits two distinct features by altering switching device such as PIN diode (BAP65-02) in this case. First, a switchable notched band is generated which facilitates a rejection at 3.5 GHz to avoid interferences from the WiMAX systems. Later, a reconfigurable filter is developed which changes from bandpass to bandstop at the same UWB (3.1-5.2 GHz) spectrum. The filter shows very low pass-band insertion loss and five transmission zeros are created between passband edges to enhance the signal selectivity and broad rejection at the stopband. A filter sample is fabricated to provide an experimental verification on the proposed filter. The proposed filter is able to achieve significant size reduction as compared to an conventional reconfigurable filters and bandpass filters with notched band.

A novel digital baseband predistorter with improved reduction of spectral regrowth is proposed and investigated. The improvements are achieved by using a proposed predistortion technique and extended power amplifier (PA) fundamental-frequency modeling. The digital baseband predistortion (DPD), known for its simplicity of realization, low cost and integrability; however, it suffers from poor linearizing performances. We incorporate baseband iterative injection of in-band distortion components into the baseband DPD to enhance the nonlinearity compensation. General formulas for the fundamental-frequency output of a PA with n-order nonlinearity and recursive formulas for calculating the injected components for different number of iterations are developed. The proposed iterative digital baseband predistorter is verified experimentally with a wireless PA and measured results are presented to demonstrate feasibility of the proposed concept. The spectral regrowth suppression of 20 dB is achieved for a 3.5 MHz digitally modulated signal. © 2009 Wiley Periodicals, Inc. Int J RF and Microwave CAE, 2009.

This paper presents novel ultracompact waveguide bandpass filters that exhibit pseudoelliptic responses with the ability to place transmission zeros on both sides of the passband to form sharp rolloffs. The filters contain E-plane extracted pole sections (EPSs) cascaded with cross-coupled filtering blocks. Compactness is achieved by the use of evanescent mode sections and closer arranged resonators modified to shrink in size. The filters containing nonresonating nodes are designed by means of the generalized coupling coefficients' extraction procedure for the cross-coupled filtering blocks and EPSs. We illustrate the performance of the proposed structures through the design examples of third- and fourth-order filters with center frequencies of 9.2 and 10 GHz, respectively. The sizes of the proposed structures suitable for fabricating using the low-cost E-plane waveguide technology are 38% smaller than ones of the E-plane extracted pole filter of the same order.

This paper presents the design of compact second-order bandpass filters based on dual-mode open-loop resonator. A filter design procedure is provided to facilitate the design process. The paper also describes the nature of the inherent transmission zero associated with the structure and presents a method of generating two additional zeros for improving stop-band performance. Finally, a filter design example is presented to validate the argument.