Microwave Filters for Communication Systems: Fundamentals, Design and Applications

CHAPTER 13

WAVEGUIDE REALIZATION OF SINGLE- AND DUAL-MODE RESONATOR FILTERS

In the preceding chapters, we have studied methods for generation of the polynomials for filtering functions that have the widest practical application in today's microwave systems for terrestrial and airborne telecommunications, radar, and earth Observation and scientific systems. In the great majority of cases the Chebyshev equiripple filtering function is employed, as it has the optimal balance between in-band linearity, close-to-band selectivity, and far out-of-band rejection. Specialist variants are available where high Performance is required—asymmetric, group delay equalized, prescribed transmission zeros, and combinations of the fore-going. Other classes of filtering function were briefly touched on—including elliptic Butterworth, where very linear group delay Performance is required, and predistorted for linear amplitude and compact size.

From the generation of transfer and reflection polynomials, attention was then focused on exact synthesis techniques for the electrical networks corresponding to the original filtering function polynomials, concentrating on those configurations that may be realized with a microwave structure of some kind, such as the coaxial resonator or waveguide cavity resonator. From the electrical network, or directly from the transfer and electrical polynomials themselves, a coupling matrix may be generated for most configurations. Having a direct correspondence with individual ...