Design and optimization of amplitude-modulated microwave backscatter transponders

In the current paper design rules and exemplary optimized designs for microwave backscatter transponders are presented. The overall goal of the proposed transponder design is to achieve a maximum signal to noise ratio in the radar signal of a given base-station that interrogates the transponder. To accomplish this task, it is important not only to consider the transponder modulation factor, i.e. the values of modulated/switched antenna loads, but also the resulting radar cross-section of the loaded transponder antenna. Unfortunately, both aspects are partly opposing and optimization is not straightforward. The design method presented and applied in this paper allows selecting the optimal relation between the antenna parameters and the load parameters. To prove the proposed method, exemplary designs and measurement results of 5.8 GHz backscatter transponders are shown.