Resonant Frequency Control of a Varactor-Loaded Single-Layer Triple-Band Miniaturized Microstrip Antenna Fed by an L-probe with Straight Shorted Elements

This paper presents a frequency-tunable varactor-loaded single-layer triple-band miniaturized microstrip antenna (MSA) fed by an L-probe with straight shorted elements. The proposed antenna consists of three shorted patches with different sizes and a feeding L-probe arranged on a single-layer dielectric substrate. In order to change resonant frequencies of the three patches, a varactor diode is mounted on each patch near the shorted via hole and a bias circuit to apply a DC voltage to the varactor diode for each patch is placed on the back side of the ground plane. Therefore, three resonant frequencies of the patches are controlled independently by the bias voltages in different frequency bands. In this paper, measured performance of the proposed miniaturized varactor-loaded frequency-tunable triple-band MSA is presented. Measured resonant frequency ranges of the three bands are 2.608 to 3.416 GHz, 3.509 to 4.783 GHz, and 5.038 to 6.008 GHz, respectively, when the DC voltages applied to the varactor diodes are changed from 0 to 8 V.