Direct Coupled Spiral Resonator for Band Stop Filter Applications

This paper presents a direct coupled open ended spiral resonator (OESR) on a microstrip line for band stop filter applications. Using the insertion loss method, a band stop of third order with Butterworth response is realized. Using Kuroda's identity LC filter transformation to open and closed stubs is carried out. This filter is modified as a direct coupled open ended spiral resonator (OESR) for achieving same response. Design equations for OESR configuration is provided based on the analytical study using ANSYS HFSS. Design equations predict the resonance of the filter with less than 3 % error. Testing the resultant prototype provided results identical with simulations. A size reduction of 98.4 % is achieved for the OESR compared to standard filters realized using open/short circuited stub microstrip lines. Thus, a miniaturized version of a planar band stop filter is realized with a size of 0.33 λ
₀
× 0.17 λ
₀
for different communication gadgets.