Coupled Microstrip Filters: Simple Methodologies for Improved Characteristics

This paper presents improved characteristics of the hairpin filter topology. Standard hairpin configuration has the drawback of broader bandwidth, more insertion loss along with poor skirt rate. This paper demonstrates the approach to overcome the limitation inherent in hairpin as well as suppression of the harmonic which is prominent in the microstrip coupled filter topology. This has been achieved using the concept of the Q involved along with the compensation of the phase velocity. The modified topologies of the hairpin along with the concept of transmission zeros for better skirt rate has been explained in this paper. Furthermore, presented topologies are insensitive to parameter variations and standard design equations can be used. The band pass filter topologies were designed at the center frequency of 1.24 GHz, aimed to be part of the multiplier chain, in satellite communications.