Direct Synthesis of Passband Impedance Matching With Nonuniform Transmission Lines

An analytical technique is used in this paper to achieve a direct synthesis of passband impedance matching under the Wentzel-Kramers-Brillouin approximation with nonuniform transmission lines. The input reflected power over a required frequency band is minimized using a least squares method, and the characteristic impedance function is constructed in terms of a Fourier series. General properties are observed as a result of this analysis, and a table covering all normalized design parameters of the single passband case is given. Results from two independent methods, the ABCD-matrix method and the High Frequency Structure Simulator full-wave analysis, are used to compare to this theory. Sensitivity analysis of this design is also given and compared with Klopfenstein´s taper. A linear property of this theory provides more freedom to extend it to multiband applications. In the end, one measurement result using microstrip line is compared with numerical theories to confirm this theory.