Frequency Control of a Varactor-Loaded Dual-Band Single-layer Shorted Microstrip Antenna Fed by an L-probe with Reduced Cross Polarization

This paper presents a frequency-tunable varactor-loaded dual-band single-layer shorted microstrip antenna (MSA) fed by an L-probe with reduced cross polarization. The proposed antenna consists of two L-shaped patches on both sides of a feeding L-probe arranged on a dielectric substrate. In order to miniaturize the antenna, the two patches with approximately a quarter wavelength in length are shorted at the opposite side to the L-probe with a via hole. A varactor diode is mounted on each shorted patch in the vicinity of the via hole. The resonant frequencies of the two patches can be controlled by the DC bias voltages applied to the varactor diodes independently. In order to reduce cross polarization radiated from the L-shaped patches, a varactor-loaded frequency-tunable dual-band shorted MSA with modified L-shaped patches is proposed. Although the fractional frequency-tunable ranges of the two patches are almost unchanged in comparison with the conventional MSA with L-shaped patches, measured cross-polarization of the proposed MSA with the modified L-shaped patches is improved by around 5 to 10 dB in the broadside direction.