Diode-switched thermal-transfer printed antenna on flexible substrate

We demonstrate that diode-switching can be used to introduce frequency agility into antennas produced by thermal transfer printing. Our particular example is a triangular Sierpinski fractal pattern with two PIN diodes to switch between operation optimised for the 800 MHz UHF band (diodes on) and the 2400 MHz ISM band (diodes off). Our measured results show an improvement in S11 in the UHF band from -2 dB to -28 dB, and from -7 dB to -30 dB at 2400 MHz, when switching the diodes appropriately. The measured bandwidth is 200 (1000) MHz, and the measured directivity is 3.1 dB (5.2 dB) while the measured gain is -5.2 dB (6.7 dB) for the diodes on(off).