Simulation of platform tolerance characteristics of RFID tag antennas

The platform tolerance of two types of tags have been investigated in this paper by using a novel simulation technique, described herein, which yields reliable and physically acceptable results for the input impedance, free of higher-order mode effects that are excited in the vicinity of the feed. We have found that when the meander tag which is without a ground plane, is placed on 10 mm thick sheets of cardboard (epsiv_r=2.5), glass (epsiv_r=3.8), and plastic (epsiv_r=4.7), is, it performs reasonably well, and its return loss remains below -3dB. However, this is no longer true when the same tag is placed on a metallic object. The tag performance is found to deteriorate significantly in this case. In contrast to this, the PIFA tag continues to work well not only when it is placed atop the three materials mentioned above, namely cardboard, glass and plastic, but also when it is located above a metallic object, and its return loss remains better than -3dB for all of these scenaios. Two reasons why the PIFA exhibits a superior platform tolerance as compared to the Meander antenna are: the PIFA has its own built-in gound; it is wider than the PIFA itself by about 5*5*10 mm. However, despite the width, its improved performance justifies its use in preference to the meander tag, in situations where the platform tolerance is important.