An equivalent circuit model for a compact OLRR based notch filter

In this paper, a simple, equivalent circuit model for characterizing an open loop rectangular resonator (OLRR) based notch filter is proposed. The OLRR is placed within a U-shaped microstrip line assuring effective coupling between the OLRR and the transmission line. OLRR exhibits electric and magnetic coupling, when placed in close proximity to microstrip line. If the electric and magnetic coupling could be modelled using inductors and capacitors, a more accurate model considering the effect of coupling gap and width of the feed line could be developed. The circuit model is based on methods used to model spiral inductors in monolithic microwave integrated circuits. The S parameters of the filter and the equivalent circuit model are simulated. The simulation results are compared with that of measured results and the results are in good agreement in the frequency range 2 GHz to 6 GHz. The geometric parameters are varied and the resonant frequency of the filter (f
_r
) is compared with that predicted by the equivalent circuit model (f
_eq
). The average deviation Δf, the difference of f
_r
and f
_eq
is a few 100 MHz. Results reveal that the proposed equivalent model can be used to predict the notch frequency of the filter accurately.