A Method for Improving Stopband Characteristics of a Dual-Band Filter

Abstract

This paper presents a simple and effective method for improving stopband rejection characteristics of previously studied dual-band filters. Small electric couplings were applied to the symmetrically positioned shunt resonators, which divided each transmission zero into two transmission zeros without any effect on passbands. We were able to achieve improved stopband rejection characteristics by these additional transmission zeros. For the filter application, we designed a dual-band filter with improved stopband characteristics using microstrip quasi-lumped elements. The electric couplings that control the location of transmission zeros are controlled by the distance between symmetric open stubs of the filter. The filter was fabricated with a relative dielectric constant of 3.5 and a thickness of 0.76 mm. The fabricated filter has a small size (14.6×13.2×0.76 mm) and a low insertion loss when compared with conventional filters.

Design of a Switchplexer Based on a Microstrip Ring Resonator with Single-Switch Operation

“…However, these previous diplexers have all had fixed frequency bands. As multiband communication systems have been developed, multiband filters and tunable filters have been proposed [5][6][7]. The technique for multi-band and multi-functional capabilities using the diode and switch has also been found to be useful in other microwave applications, such as for use with reconfigurable antennas [8,9].…”