A planar filtering crossover utilizing full-wavelength ring resonators

This paper proposes a planar filtering crossover which consists of four coupled full-wavelength ring resonators to improve the frequency selectivity of a conventional crossover. The proposed crossover has a simple structure and favorable impedance of coupled lines. No slots on the ground plane is required. Theoretical analysis is presented and validated by simulation and measurement. The fabricated 2-GHz prototype shows an 18-dB in-band return loss and has a fractional bandwidth of 14.5% for 3-dB insertion loss. Measured results also show good frequency selectivity and validate the bandpass characteristic of the proposed crossover.