The time-domain response of coupled-resonator filters with applications to tuning
This thesis develops a new theory of tuning filters based on the time-domain response of the filter. These methods are shown to work very well for all-pole coupledresonator filters in particular, and may be applied to automated tuning of filters. Numerous filter-tuning methods are reviewed, and the attributes and limitations of each are discussed. Key results about transfer functions, filter theory and Laplace transform theory are reviewed as applied to all-pole filters. The Fourier Transform theory is reviewed and a new, detailed analysis of the Vector Network Analyzer (VNA) time-domain transform, including gating and windowing is presented, including new work in area of the compensation for the masking effects of time-domain gating. A complete description of the time-domain tuning method is presented, which includes experimental and empirical results from simulations and measurements on filters. The theoretical underpinning supporting the novel method of time-domain tuning is developed, along with a rigorous mathematical relationship between VNA timedomain response of a simple filter, and the analytic impulse response. The timedomain results observed in experiments are shown to be directly correlated to the filter transfer functions and the specific effects that differentiate the VNA time-domain transform from the analytically derived impulse response. This thesis includes previously unpublished work that is the basis for two U.S. patents, as well as the development of a commercial filter tuning software program. An improved method for filter tuning, which uses time-domain gating on the S 11 response of the filter is introduced, and shown to be a key improvement for developing automated tuning techniques. The details of a software application for filter tuning are presented, along with methods for determining and compensating the interactions from other resonators. A case study of applying the FTS method to a complex duplex filter is described. Areas for extension into other filter types are discussed. General guidelines for the successful application of the new tuning method to various filter types are presented, along with other conclusions of this thesis.