Compact, meandered-line microstrip bandpass filter

A size reduction technique based on meander-lines for microwave filters is presented for designs employing Signal Interference Techniques. These filters exhibit low insertion loss, high selectivity and sharp rejection. Also, these are suitable for microstrip structure with fractional bandwidths ranging from 10 to 45%. Absence of any form of coupling structures render the filters suitable for meandering technique. From fabrication point of view, dielectric constant variations in the substrate effects the production repeatability of coupled-line structures. Unlike those, filters mentioned in this paper are relatively tolerant of such variations and are thus, repeatable in production. For frequencies around 1 GHz, meandering technique is especially useful as filter can be reduced to about one-third of its original size. It is demonstrated by designing a filter at center frequency of 1.09 GHz with fractional bandwidth of 33%. A guideline for matching meandered-line sections to their straight-line counterparts is presented in detail. The meandered-line filter is compared with its straight-line version of similar specifications in terms of response and physical size. A good agreement between simulated and measured results is observed between both straight and meandered-line filter with more than 30% size reduction in the latter version.