Design of a compact C-band microstrip bandpass filter for satellite communications applications

A novel and compact microstrip wideband bandpass filter is proposed in this paper for C-band applications. The filter consists of only one section of three parallel-coupled lines which is a quarter wavelength long at the midband frequency. In addition, a quarter wavelength short-circuited stub is added at each end of the central line. As a result, the filter exhibits two new symmetric transmission zeros around the passband which increases the selectivity of both edges of the passband significantly. The transmission zeros can be located at any desired frequency by adjusting the width of the additional stubs. Hence, different bandwidths can be obtained where the bandwidth is reversely proportional to the width of the stubs. The filter with fractional bandwidth of about 66% is successfully realized on microstrip lines. The filter is simulated, and fabricated to demonstrate the proposed technique where excellent agreement is obtained. The filter shows low insertion loss of less than 1 dB and a flat group delay of about 0.25 n at the center frequency.