Microwave Filters for Communication Systems: Fundamentals, Design and Applications

CHAPTER 14

DESIGN AND PHYSICAL REALIZATION OF COUPLED RESONATOR FILTERS

This chapter addresses the physical realization of microwave filters illustrating how one can combine filter circuit models with electromagnetic (EM) simulation tools to determine the filter physical dimensions. The techniques illustrate a direct approach to synthesis filter physical dimensions from the elements of the coupling matrix model, the K-impedance inverter model, or the J-admittance inverter model. The approach is fast, yet it provides reasonably accurate results. Numerical examples are given in this chapter to demonstrate, step by step, the application of the approach to the design of dielectric resonator, waveguide, and microstrip filters.

Bandpass filters typically consist of resonators coupled to each other's by induetive or capacitive coupling elements. Figure 14.1 shows some of the common microwave filter structures. In waveguide, coaxial, and dielectric resonator filters, interresonator coupling is achieved with the use of an iris, whereas input/output coupling is realized with the use of a probe or an iris. In microstrip filters, interresonator and input/output coupling can take various forms depending on the circuit layout. The objective is to determine the physical dimensions of the individual resonators, interresonator couplings, and input/output couplings. The filter design process usually involves the following four main steps:

Step 1. Identification of the filter order and filter function ...