A Non-reflecting Branching Filter for Microwaves

Abstract

Microwave branching filters are required as integral parts of multi‐channel microwave radio relay systems. These filters must have characteristics which are difficult to attain if one attempts to extend familiar lower frequency techniques to the microwave region. A novel network configuration, through which currently anticipated requirements can be met without excessive difficulty, is described in this paper. In this configuration individual constant resistance channel dropping units are formed of appropriate assemblies of two hybrid circuits, two band reflection filters and two quarter wavelengths of line. An assembly of N channel dropping units in cascade then forms an N channel constant resistance branching network. The mechanical and electrical characteristics of a practical five channel branching filter of this type are described. As a result of experience with this prototype filter it can be stated with some safety that these requirements can be fulfilled with a network of this type. Experimentally observed impedance, insertion loss and phase characteristics were fully satisfactory. In addition the circuit appears to be flexible enough both electrically and mechanically to fulfill the various types of systems needs which may be encountered at branch points or when channels must be added or interchanged.

TD-3 System: Networks

“…The basic configuration selected for the channel-combining and sepa ration networks is the constant-resistance one originally described by Lewis and Tillotson, 4 and used successfully in the TD-2, TH and TJ radio systems. However, instead of the rod-and-disc resonators used in Lewis and Tillotson's filters, the resonators of the band rejec tion filters which form the selective elements of the networks for the TD-3 system consist of rectangular waveguide cavities, spaced along the main waveguide at three-quarter wavelength intervals, and coupled to it by circular irises.…”

High-Order Dual-Port Quasi-Absorptive Microstrip Coupled-Line Bandpass Filters

“…The idea of absorptive filters was first introduced in [4] as a "non-reflecting branching filter". The filter consists of two hybrid junctions, two identical reflective-type bandpass filters (BPFs) tuned to the absorption band, and two quarter-wavelength waveguides.…”