The advantage of our proposals comes from the inherent properties of our synthesis approach and from the good performance achieved by structures with smooth (nonabrupt) profiles in terms of flexibility in the design, robustness in the implementation, spurious-multimode-excitation avoidance, and high-power handling capability. The theoretical background rests on the knowledge of the coupled-mode theory, the field of periodic structures (PS), the electromagnetic band-gap (EBG) concepts, and the one-dimensional (1D) inverse scattering (IS) principles. The rigorous study of nonuniform microwave structures has been the starting point of the novel synthesis techniques of passive microwave components presented in this paper.
A myriad of examples has been presented by our group in many different technologies for very relevant applications such as harmonic control of amplifiers, directional coupler with enhanced directivity and coupling, transmission-type dispersive delay lines for phase engineering, compact design of high-power spurious free low-pass waveguide filters for satellite payloads, pulse shapers for advanced UWB radar and communications and for novel breast cancer detection systems, transmission-type th-order differentiators for tunable pulse generation, and a robust filter design tool. (c) They are flexible, because they are valid for any causal, stable, and passive transfer function only inviolable physical principles must be guaranteed. (b) They are exact, as there is neither spurious bands nor degradation in the frequency response hence, there is no bandwidth limitation. (a) They are direct, because it is not necessary to use lumped-element circuit models just the target frequency response is the starting point. The main characteristics of these synthesis methods are as follows. We provide the theoretical foundations based on inverse scattering and coupled-mode theory as well as several applications where the devices designed following those techniques have been successfully tested.
We briefly review different synthesis techniques for the design of passive microwave components with arbitrary frequency response, developed by our group during the last decade.