Overview

From APPLIED MICROWAVE & WIRELESS, VOL. 3, NO. 3, FALL 1991

Dual mode cavity and dielectric resonator filters are the mainstay of satellite communications. All currently used filter designs, such as elliptic function, self-equalized, and other common types can be implemented in microstrip using this new concept. The proposed filter structures are ideally suited for implementation using the recently discovered high-temperature superconductors. Basic dual mode resonator and filter structures are discussed, and experimental data for proof of concept filters implemented using both normal and superconducting microstrip are presented.

Design techniques for single mode microstrip filters (see Figure 1) have long been established. However, these filters are of limited utility for most high performance microwave applications due to their typically high insertion loss and impracticality for filter pass bands of less than 5 percent. It is also very difficult, if not impractical, to realize self equalized, elliptic function responses using these single mode structures. Figure 2 illustrates the superior selectivity and insertion loss performance of an elliptic function filter as compared to a Tchebyscheff filter with the same number of poles, and equivalent bandwidths and quality factors.

Figure 1: Illustration of commonly used, single mode mirostrip filter configuration. On the left is the broadside edge coupled configuration, and the interdigital configuration is on the right.

Figure 2: Plots contrasting the performance of Tschebysheff...