Tradeoff Between Antenna Efficiency and Q-Factor

Abstract

The tradeoff between radiation efficiency and antenna bandwidth, expressed in terms of Q-factor for small antennas, is formulated as a multiobjective optimization problem in current distributions of predefined support. Variants on the problem are constructed to demonstrate the consequences of requiring a self-resonant current as opposed to the one tuned by an external reactance. The tradeoffs are evaluated for sample problems and the resulting Pareto-optimal sets reveal the relative cost of valuing low radiation Q-factor over high efficiency, the cost in efficiency to require a self-resonant current, the effects of lossy parasitic loading, and other insights. Observations are drawn from the sample problems selected, though the tradeoff evaluation method is valid for studying arbitrary antenna geometries. In the examples considered here, we observe that small increases in Q-factor away from its lower bound allow for dramatic increases in efficiency toward its upper bound.