The Open University ’ s repository of research publications and other research outputs Diode - switched thermal - transfer printed antenna on flexible substrate

Copyright and Moral Rights for the articles on this site are retained by the individual authors and/or other copyright owners. For more information on Open Research Online's data policy on reuse of materials please consult the policies page. 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). Introduction: Rapid and inexpensive antenna manufacturing is required to support the burgeoning interest in the Internet of Things (IoT). IoT is heavily reliant upon wireless communications between, ultimately, trillions of devices [1]. For any IoT antenna, it is important to be able to handle a dynamic frequency allocation, at least in part determined by regulatory authorities according to location [2] but also influenced by the local propagation environment favouring some channels over others due to fading mechanisms associated with building geometry e.g. [3] and other radio noise sources. Hence, reconfigurable antennas are attractive both for prototyping IoT communications networks in new locations, but also during deployment for responding to changes in the optimal channel choice. Reconfigurable antennas often require less non-returnable engineering effort compared to designing multi-band antennas, and can go further than frequency agility to include polarisation diversity [4] or beamforming capability [5]. Switching is known to introduce frequency [6] and polarisation [7] agility into planar antennas produced using conventional printed circuit board techniques on a variety of dielectric substrates. However, these manufacturing techniques are relatively slow compared to thermal transfer printing of metallic films, which prints at a rate of approximately 5cm/s and requires no curing to reach minimum sheet resistance [8]. Flexible substrates give IoT system designers more options for integrating nodes unobtrusively into built environments [9].