Coplanar-Waveguide Ultra-Wideband Bandpass Filter Based on Interdigital Structure

Abstract

Abstract-In this paper, a novel ultra wideband (UWB) bandpass filter based on interdigital structure is proposed. The proposed UWB bandpass filter is designed on coplanar waveguide (CPW) with the passband obtained by interdigital structure on the step-change center strip of CPW. The rectangular curling slots are adopted to improve the stopband characteristics and the normal slots are used to restrain the insertion loss of the filter in passband. The interdigital structure and all slots are on the same side of a circuit board which makes the UWB bandpass filter compact and easily realized. Simulations and measurements verify the design idea and the proposed filter has a more than 150% -3dB fractional bandwidth centered at 5.56 GHz as well as sharp skirt selectivity at the upper passband edge.

Design, analysis and fabrication of the CPW resonator loaded by DGS and MEMS capacitors

“…In the planar radio frequency circuits and systems, the coplanar waveguide (CPW), periodically loaded by defected ground structure (DGS) [1,2], have attracted much attention, owing to its attractive features such as compact structure [3], easy insertion of shunt or series active devices, and low substrate dependence [4]. CPW loaded by DGS has been studied in many aspects such as resonant frequency and equivalent circuit and been widely employed in filter design [5][6][7][8][9][10][11]. Microstrip bandstop filters (BSFs) also often use DGS and stepped impedance resonators to obtain the stopband [12].…”

“…MEMS capacitive devices have demonstrated some superiorities [16,17], such as lower loss, lower parasitics and high linearity, in comparison to other varactor devices [18][19][20], it can be used in tuned filter [21] and reconfigurable antenna design [8,[22][23][24]. Bandstop DGS resonator is usually studied by using equivalent circuit model due to its slow-wave effect and band resistance characteristics [25,26], which is obtained by fitting resonant response curve [10,27]. In literature [11], the bandstop resonant characteristic of CPW with DGS was modeled by a parallel RLC resonator in parallel connection, but this characteristic is contradictorily described by a series connection of a parallel RLC resonator in [6,9].…”