An Automatic Design Approach for Microstrip Line Impedance Transformer for Triple-Band Application

In this paper, a novel automatic design approach of the microstrip line impedance transformer for triple-band application is presented. The cross-shaped line and two series transmission lines are employed to allow matching between source impedance and a given load impedances at three different operating frequencies. The required circuit parameters of the proposed structure are computed using the derived analytical equations. A simple synthesis approach is provided to develop triple-band impedance transformer. To validate the analytical derivation, two prototypes of triple-band impedance transformer are designed, simulated and tested for smaller (10 Ω) as well as larger (400 Ω) load impedances. The simulated and measured return loss are greater than 20 dB at three operating frequencies. The prototypes exhibit good performance between measured and simulated results.