Fundamental Bandwidth Limitation for Small Antennas on a Platform

Abstract

Classical theory on fundamental gain bandwidth limitation for antennas constrained by their electrical size has been extensively examined, and is collectively referred to here as the Chu theory [1]. However, there are major shortcomings and ambiguities in the Chu theory when applied to real world problems, as pointed out recently by this author [2]. One problem is the case of an antenna on a platform, as depicted in Fig. 1, where the antenna is generally inseparable from the transceiver/platform. In fact, in some designs the main radiator is the platform or transceiver, not the antenna per se. Thus, the extent and size of the antenna become ambiguous. Also, the Chu theory is valid only for high Q (Quality factor). With the platform becoming part of it, the antenna’s effective size is increased and its Q can be lowered beyond the realm of the Chu theory.