Ultra compact filters for ultra-wideband (UWB) applications using multilayer ring resonators

Novel compact ultra-wideband (UWB) bandpass filters are proposed. It is based on multilayer ring resonators (MRR). The ring is applied to any loop shape. The filter has a simple structure for fabrication and the design technique can be adapted in order to realize both narrowband and ultra-wideband filters. With the MRR, filters of bandwidths in excess of 10 GHz while enjoying a wide stop-band can be designed. The fractional bandwidth of more than 143% and a group delay of less than 0.2 ns are achieved with this class of filters. Also, in this class of filters, it is easy to place the attenuation poles in order to fit a requirement. Due to its small circuit size (around 2 mm in each dimension), this filter can be used in hybrid integration with small UWB, WLAN and radar devices. Since the filter is located within two ground planes, no radiation affects its characteristics. Two types of the proposed UWB filters were fabricated and the measurement verified the theory and simulation.