Abstract
A design of parallel-coupled microstrip bandpass filters without spurious resonance is presented. Two different techniques are used to eliminate this response at twice the passband frequency (2fo). The first one is based on usage of suspended substrate, while the second is carried out by shorting the parallel-coupled lines to the ground plane through two shorting walls. The numerical results show that a broadband filter can be obtained by the suppression of the spurious response. The finite difference time domain (FDTD) with the perfect matched layer (PML) is used in the present analysis. The obtained results are compared with the available published data and good agreements are found.
Highlights
In microwave and millimeter-wave systems, parallel-coupled microstrip bandpass filters are widely used
Two different techniques are used to eliminate this response at twice the passband frequency (2 fo )
The first one is based on usage of suspended substrate, while the second is carried out by shorting the parallel-coupled lines to the ground plane through two shorting walls
Summary
In microwave and millimeter-wave systems, parallel-coupled microstrip bandpass filters are widely used. The conventional design of these filters suffers from the spurious response at twice the passband frequency (2 fo ) [1, 2]. This is because the inequality of the velocities of the even and odd modes of each coupled sections [1]. This problem could greatly limit the filter applications. A defected ground plane is effective in suppressing the spurious response [3]. Microstip filters with ground grooves are used for implementation of harmonic suppression in [4]. Shorting walls are used to get a broadband antenna [5]
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