"Meandered Split Ring Resonators SRRs Based Reconfigurable Band Pass Filter Design for Cognitive Radio Applications "

Abstract

In this paper, a reconfigurable bandpass filter based on meander open loop resonators called split ring resonators (SRRs) in square shapes is proposed. The proposed filter is able to tune its centre frequency and bandwidth by changing DC voltages applied to varactor diodes loaded on SRRs simultaneously. Two groups of varactor diodes are placed where the equivalent electrical length and electrical coupling can be effectively influenced. The first group of varactor diodes is attached to open ends of SRRs to obtain variable electrical lengths, leading to a tunable resonant frequency, while the second group is inserted between the two SRRs as a step to store more electrical energy which in turn leads to govern the required bandwidth freely. Consequently, the proposed filter can vary its centre frequency and bandwidth independently. All diodes utilized in the proposed design are reverse biased to get a wide range of variable capacitance. The microstrip technology is adopted in all simulation and fabrication. The substrate used in the fabrication is a FR4 with dielectric constant 4.5 and thickness 1.5mm. The filter response has two transmission zeros located below and above the passband to improve the filter selectivity due to asymmetrical locations of feeding lines. The proposed filter has been designed, simulated, fabricated, and measured where both the measured and simulated results are in good agreement. However, only a filter with static response is manufactured because the required equipment is not available. The two coupled SRRs generate second order responses. The tuning range of bandwidth from 404MHz to 960MHz has been achieved, while the centre resonant frequency is widely changed from 0.92GHz to 2.06GHz to cover the most important wireless applications.