Efficient area reduction in microstrip cross-coupled resonator filters by using split rings resonators and spiral resonators

In this work, it is demonstrated that microstrip band pass filters with a pair of attenuation poles at finite frequencies can be implemented by introducing cross coupling between non-adjacent split ring resonators (SRRs) or spiral resonators (SRs). As compared to filter implementations that use conventional open loop resonators, a reduction of layout area by a factor of 4 is demonstrated in the SR-based filter implementation. The filter synthesis method is based on the calculation of the coupling coefficients of intercoupled resonators and external quality factors of the input and output resonators, as reported in previous realizations based on open loop resonators. This reduction in device dimensions is related to the sub-wavelength operation of SRRs and SRs. It is believed that the approach proposed in this work can be of interest to optimize the size of microstrip band pass filters.