A dual-band two-section and tri-band three-section impedance transformers are designed
in which the characteristic impedance discontinuities of the corresponding transmission line is involved.Based on the transmission line model and microstrip line theory
design equations of the proposed transformers are derived
and the effect of the microstrip "step" is included.By the method of genetic algorithm
the design parameters of the proposed transformers are obtained for the purely resistive source and load impedances
as well as the frequency-dependent source and load impedances
respectively.Finally
electromagnetic simulations of the microstrip circuit based on the above design parameters are implemented with the commercial software ADS
and the numerical examples prove the validity of the proposed design.