Designing Low Cost Wideband Microstrip Bandpass Filters

The design of RF filters where the bandwidth is much greater than 10% of the centre frequency is difficult to implement, since conventional filter design techniques such as those for coupled line or interdigital filters are applicable to filters with less than 10% bandwidth. This paper describes a design technique for designing wideband RF filters and illustrates this with the design of a 5 resonator filter with a 50% bandwidth at a centre frequency of 1 GHz. The design technique produces filters with a remarkable accuracy, so that one-iteration filter designs can be produced reliably.