Abstract
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. 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. The main characteristics of these synthesis methods are as follows. (a) They are direct, because it is not necessary to use lumped-element circuit models; just the target frequency response is the starting point. (b) They are exact, as there is neither spurious bands nor degradation in the frequency response; hence, there is no bandwidth limitation. (c) They are flexible, because they are valid for any causal, stable, and passive transfer function; only inviolable physical principles must be guaranteed. 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-typeNth-order differentiators for tunable pulse generation, and a robust filter design tool.
Highlights
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
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
∂H⃗ + ∂z dN−, dz being Ê⃗, Ĥ⃗ the total electric and magnetic field present in the structure; E⃗+, H⃗ +, E⃗−, and H⃗ − the vector mode patterns of the forward (+) and backward (−) traveling waves corresponding to the mode of operation in the auxiliary uniform waveguide associated with the crosssection of interest; N+, N− the normalizations taken for the fields of the mode; β the phase constant of the mode; K the coupling coefficient between the forward and backward traveling waves; z the direction of propagation; and a+, a−, the complex amplitudes of the forward (+) and backward (−) traveling waves along the nonuniform waveguide
Summary
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. Very useful to enrich the variety of target frequency responses attainable was the well-known Fourier transform relationship [12] This is only accurate enough for devices with very low reflectivity. International Journal of Antennas and Propagation a generic frequency response and the physical dimensions of a device in the form of an infinite series is shown. Another exact and automatic alternative, valid when the target specifications can be expressed in terms of an arbitrary rational function, is proposed.
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