Summary
International Symposium on Antennas and Propagation
2010
Session Number:4FD4
Session:
Number:4FD4-5
Wideband Dual Mode Bandpass Filter with Wide Spurious Response Suppression
Surin Ahonnom, Somsin Wangkhuntod, Prayoot Akkaraekthalin,
pp.-
Publication Date:2010/11/23
Online ISSN:2188-5079
Summary:
The dual mode is mostly applied in the planar microwave bandpass filters (BPFs) for all narrow bands and wide band bandpass filters because of compact size, low cost and easy fabrication. Therefore, the dual mode bandpass filters are highly popular to apply in wireless communication system and measurement instrument. The method of an asymmetrical coupling line and notched on the conductor of substrate of the ring resonator was designed to dual mode [1]. In order to excite a dual mode, many methods placed the different types of perturbation at different positions on the ring resonators.To use the small patch and notch perturbations attract at the corners of the square loop [2]. In [3], they have been used the stepped impedance perturbation on the ring resonator for degenerate into the dual mode characteristic. Which the results have narrow band characteristics and high insertion loss affected from coupled feed lines. Much research proposed the wideband dual mode square ring resonator bandpass filters. The direct connecting orthogonal feed lines are used in designing filters to reduce insertion losses. A square stub perturbation and two tuning stubs connected to square ring resonators produced two sharp stopband [4]. It has been found that changing direct feed lines to be tapped feeds at input/output port results in suppression of harmonics in out off band about 2.5 fo , where o f is the fundamental frequency [5]. In [6], they used a piece of aperture by enhancing a parallel-coupled line with length of λ / 2 connected at output port, which it could control the transmission zero to appear at o 2f . In this paper, we present a new configuration of the wideband dual mode bandpass filters using the properties of microstrip open loop resonator combined a novel perturbation by notching rectangular slots. The properties of microstrip open loop resonator is miniaturized the filter structure, and the perturbation is enhancing the attenuation rates for the sharp cutoff frequency and coupling on square ring resonator structure. To reduce the harmonics in out off band, the interdigital coupled line is used to control the transmission zeros appeared at DC (lower stopband) and at o 2f (higher stopband) for suppression of the first harmonics. The higher harmonics at more than o 2 can be suppressed by adding the quarter wavele f ngth open stubs are used at the input and output feed lines to control multiple transmission zeros, resulting in wide suppressed harmonics.