A New Chu Formula for Q

Abstract

The Chu fundamental limitation on Q for electrically small antennas is well known and widely used. However, Chu did not include energy stored inside the hypothetical enveloping sphere. Exact calculation of total stored energy by Thal gives a new Q, which should better match well-designed electrically small antennas. The TM- and TE-mode Q formulas are derived, and a simple approximate form for the lowest-order TM mode is presented.