Automated computer-controlled tuning of waveguide filters using adaptive network models

This paper describes a method for computer-controlled tuning of waveguide filters. The tuning algorithm is based on approximate filter network models, which take into account the effects of input/output coupling. Based on measurements of an initial filter design, the approximate network model is then corrected by optimizing the element values such that they minimize the mean square error between the measured and simulated response. The sensitivities of the tuning screws are determined directly from the sensitivities of the element values. Filter tuning is accomplished by gradient optimization of the corrected computer model rather than its physical realization. Only as a final step are the tuning screws of the physical model turned to the position determined by the optimization process.

I. Introduction

THE explosive growth of satellite and terrestrial communication systems has significantly increased the market for microwave and millimeter-wave filters. To satisfy the high demand for short-term availability of filters at different mid-band frequencies, bandwidth, skirt selectivity, etc., a suitable set of standard filters is the key to fast production. In addition, these filters must be tunable and their tuning process must be automated to minimize labor cost. Depending on the filter topology, the basic three tuning techniques are: 1) mechanically; 2) magnetically; and 3) electronically.