A reconfigurable bandpass to bandstop filter using PIN diodes based on the square ring resonator

This paper presents a reconfigurable, bandpass to bandstop switchable filter, based on the square ring resonator topology with two tuning stubs, which control the filter's response. In the proposed design, switching between the bandpass and bandstop response is achieved by strategically placing two PIN diodes, at locations where the diodes do not affect the resonating response of the overall design. Skyworks SMP1345-079LF RF PIN diodes are used in order to allow switching between bandpass to bandstop responses. The operating frequency of the filter is at 2.4 GHz. The -3 dB bandwidth for the bandpass filter ranges from 1.9 GHz to 3.2 GHz, with an average insertion loss of 0.8 dB. For the bandstop filter the loss is 0.3 dB and the -10 dB rejection bandwidth is from 2.2 GHz to 2.7 GHz. DC bias lines of A/4 overall length are integrated with radial matching stubs, to ensure compact overall size of the circuit. The key advantage of this type of filter is the efficient switching ability between the two different operational states, the bandpass and bandstop. The proposed filter is simulated on a commercially available, low cost Roger 4003C substrate having ε_r = 3.55 and tan δ = 0.0027 and substrate thickness 0.813 mm. The proposed filter can be a good candidate for transceivers operating in strong interference environments, for reconfigurable radios, or for alternating transmission and reception schemes, in the highly congested, 2.4 GHz frequency band.