Classes of reconfigurable band-reject filters realising constant absolute bandwidth in two distinct states

This study presents the synthesis and design of novel band-reject filters whose frequency characteristics can be reconfigured between two distinct states, each of which is centred at a different resonant frequency. The absolute bandwidth of the reconfigurable filters in the two distinct states is maintained constant by virtue of introducing two new resonator types which are thoroughly studied and analysed in this work. The synthesis of two prototype networks realising a common electrical specification is illustrated and each network is subsequently transformed into two types of band-reject filters comprising novel coupled-line sections. The presented circuit concepts are then validated through the simulation of a suspended-substrate stripline filter modelled utilising high frequency structure simulator (HFSS) which realises an absolute bandwidth of 200 MHz in the two distinct states centred at 1180 and 1485 MHz. The HFSS filter model is manually reconfigured between the two distinct states upon terminating stubs within each of its resonator structures as either open circuit or short circuit. The performance of the HFSS filter model shows close correspondence to the performance of the synthesised prototype network, thus demonstrating the validity of the proposed circuit principles.