Simple Matching Strategy for Surface Acoustic Wave (SAW) Delay Lines in Radio Frequency (RF) Applications

To achieve best performance in radio frequency (RF) circuits it is necessary to match each active component to the characteristic system impedance. This requirement is also valid for passive surface acoustic wave (SAW) filters and, as used in this application, delay line elements. Matching circuits are commonly built up by inductors and capacitors, arranged as L-type, PI-type or tee-type network. In addition to component losses also the layer setup of the printed circuit board (PCB) and also the routed traces influence the overall performance of the system. Nowadays several free matching tool software programs available in the internet help to calculate the matching network at a given frequency for a desired complex load, but nevertheless also other edge conditions have to be taken into account. This paper shows how it is possible to achieve the best matching result for the given delay line element and also how real components influence different parameters like the group delay, the insert losses and the pass band ripple. Briefly also the advantages and disadvantages of the L-structured matching network are discussed and simple rules are presented to reduce the number of design iterations.