Compact ultra-wideband bandpass filter using broadside-coupled microstrip/coplanar waveguide composition structure

In this paper, a compact UWB bandpass filter based on broadside-coupled microstrip/CPW composition structure has been presented. The performance of the proposed filter can be optimized accordingly by varying gaps among three parallel microstrip stubs. The measured filter exhibits good in-band performance, including a low insertion loss of < 0.8 dB in the midband, a good return loss of < -9.7 dB, and a very small group delay variation of < 0.15 ns within its whole passband. In addition, the proposed UWB bandpass filter has the merit of compact size (0.309 by 0.145 guided wavelength at the center frequency of 7.2 GHz) comparing to most of the published UWB bandpass filters.