Design of a Dual-Band Microstrip Loop Antenna With Frequency-Insensitive Reactance Variations for an Extremely Small Array

This paper proposes a design for a dual-band microstrip loop antenna with an electromagnetically coupled feed for frequency-insensitive reactance variations. The antenna consists of two microstrip loops that are coupled to each other, and the ratio of the electric and magnetic coupling strengths is adjusted to lower the reactance slope. To demonstrate the suitability of the proposed feeding mechanism, antenna characteristics are measured in a full-anechoic chamber, and its operating principle is interpreted from a circuit standpoint. The results prove that the proposed structure exhibits a frequency-insensitive behavior without a significant gain reduction in the presence of strong mutual coupling.