A compact microstrip two-layers bandpass filter using improved interdigital-loop resonators

In this paper we present a new compact two-layers microstrip bandpass filter using multilayer cross-coupled improved interdigital-loop resonators. The filter structure consists of four resonators placed on two microstrip stack layers. The coupling between the resonators on the upper layer and the lower layer is obtained by using three coupling apertures on the common ground plane. The full-wave simulator IE3D has been employed to design the interdigital-loop resonators and to calculate the coupling coefficients between resonators of the filter. Finally, the filter has been optimized, resulting to low passband insertion loss (less than 3 dB) and high return loss (higher than 20 dB) at the center frequency. By using this two-layer technique in the microwave filter design, a filter size reduction of about 50% is obtained. These features make the proposed structure suitable for compact and high-performance circuit component designs in microwave integrated circuit (MMIC).