Broad band microwave filters

Abstract

A band-pass filter is an important component of any microwave front-end receiver for use in the area of military, civil, space and astronomical applications. Most of these applications require specified passband having low insertion loss with sharp rejection on either side of the passband region. In this paper, we discuss the design and fabrication of a broadband band-pass filter having a fractional bandwidth of more than 70 percent. The design in this paper incorporates design for Optimum Distributed High pass filter in microstrip and stepped impedance low pass filter in coaxial structure. The design issues in realizing the high pass filter and low pass filter for obtaining multi octave bandwidth are considered. Both the simulated and measured results for both low pass and high pass filter have been presented. The combination of the two had resulted in getting a band pass filter in the frequency range of 8 to 18 GHz. The main characteristic of this filter is that we could achieve a fractional bandwidth of more than 70 percent in the microwave frequency. The performance of coaxial structure decides the sharp rejection outside the band of interest. This type of multi octave bandwidth is important in astronomical receivers to realise large instantaneous noise equivalent bandwidths that increases continuum sensitivity and supports simultaneous multi-line spectroscopy.