Study of rectangular open loop resonators with groundings for low and high coupling

High performance bandpass filters are essential components in advanced communication systems, which require low insertion loss, high return loss and small dimensions. In this work, simple rectangular open loop resonators with groundings are observed. Compared to the similar resonators but without groundings, these resonators are smaller with about factor 2. We studied twenty possible coupling configurations, and revealed that the same coupling configurations but with different groundings positions could show different coupling types (electric or magnetic coupling) and could possess high or low coupling factors. An example of filter design with high and low coupling resonators was shown.