Design, Optimization and Realization of Two Compact C-band Microstrip BPF Structures

In last two decades, several microstrip BPF topologies have been investigated to meet more than 100% fractional bandwidth requirement of Ultra-Wideband (UWB) systems with pass-band from 3.1-10.6 GHz. This paper presents two compact C-band microstrip BPF structures inspired from design techniques of UWB BPF. These C-band BPF are designed for center frequency f0 of 6 GHz and fractional bandwidth around 67% covering complete C-band (4-8 GHz). The first proposed BPF is realized by using a combination of step impedance low pass filter (LPF) and the optimum distributed short-circuited stubs high pass filter (HPF). The second filter is designed using pseudo-interdigital stepped impedance resonators (PIDT-SIRS. Both filters have been implemented on commercial printed circuit board (PCB) of RO4350B substrate and each occupy an area less than 20 mil × 10 mil. These filters require minimum pass band variation so that they can be integrated with a gain equalizer circuit (4-8 GHz) without significant degradation of overall gain treatment by later circuit. Measured results observe close agreement to simulated results. Insertion loss of first BPF is 0.85dB ±0.2 dB and second BPF is 1 dB±0.3 dB.