An Improved Dual-Mode Microstrip Ring Resonator Filter with Simple Geometry

An improved dual-mode microstrip ring resonator bandpass filter is presented. The new technique has a very simple geometry which leads to lower insertion loss, and makes the design less sensitive to fabrication tolerances and easier for accurate computer simulations. It allows the implementation of two transmission poles and two transmission zeros by using only one ring resonator. The measured results show excellent performance with 300 MHz 3dB bandwidth centred at 5.4 GHz and only 1dB insertion loss.