Microwave filters based on coupled MSW resonators and their applications

A novel and simple technique for realizing tunable and planar microwave bandpass filters has been investigated. The use of coupled magnetostatic wave (MSW) resonators for realizing these filters is demonstrated. Due to their low magnetic losses, epitaxially grown single-crystal yttrium iron garnet (YIG) films are used for the MSW propagation. The individual resonators are rectangular YIG films. The microwave signals are coupled to and from resonators using microstrip structures. The MSW resonators are magnetically coupled to realize multiple filters. Experimental results demonstrate the enhancement of the bandwidth and the improvement in the out-of-band rejection. Using two-coupled resonators the 3-dB bandwidth increased from 4-7 MHz (for single resonators) to more than 10 MHz. The out-of-band rejection was improved by 10 dB using the coupled resonators for realizing the filters. Since this technique is based on microstrip circuitry it can be easily integrated with other microwave integrated circuits in a system. The utilization of IC fabrication techniques ensures the potential for high degree of yield and reproducibility at reasonable cost. Applications for FW systems, such as tunable integrated channelizers, using the MSW coupled resonators are discussed