Design of Microwave Active Devices

Appendix 4

Wideband Impedance Matching: Reactive Two-Port Networks

A4.1. Use of filters’ theory

Let us assume the load impedance is resistance R_L, we can use the filters’ theory and get a ladder structure. The ripple is imposed by the maximum reflection coefficient and the order is decided a priori with a likely value. This order is directly related to the feasibility conditions of the impedance-matching circuit (Figure A4.1).

Figure A4.1. Ladder topology

In the bandwidth of the filter, the input impedance is close to R_norm.

The values of the elements in the case of a bandpass structure are obtained from denormalization relations:

– series-element g_i : series-LC circuit

– Parallel-element g_i : parallel-LC circuit

The resistance value depends on the load resistance value as well as on the value of g_n+1. We may come across two cases depending on whether the filter’s last element is in series or parallel:

– series-element

– parallel-element

In the instances where we use Butterworth and ...