Narrowband microwave suppression filters

A theoretical and experimental investigation into narrow-bandwidth microwave rejection filters, which can be constructed from simple, standard microwave components, is described. Suppression factors of at least 50dB at resonance are possible, and the bandwidth can be easily controlled. A simple form of analysis, which indicates clearly the effects of variation in the parameters, gives good agreement with experimental measurements. The possibility of using a 2-cavity system to obtain a slightly broader frequency response and a very low insertion loss, at the expense of a lower suppression factor at the centre frequency, is indicated.