Antennas with Two Shorted Rectangular-ring Slots Coupled by Microstrip Line for the Opposite Sense CP in the Wide-Band Operations

Abstract

The two shorted rectangular-ring slots antenna fed by a microstrip line is presented to achieve the novel characteristic of wide impedance bandwidth with the opposite sense circular polarizations (CP). If the two rectangular-ring slots are arranged to be shorted in the opposite direction, reversely circular polarization will be obtained in the different frequency band. A microstrip line is used to feed power and to couple to the two shorted rectangular-ring slots. Meanwhile, the impedance and axial-ratio (AR) matching are done by adjusting line's parameters. An antenna example is given to result in the lower and upper bands in the 1575 MHz and 1.8 GHz bands. The measured impedance bandwidth is 27.54% which covers the 1575 MHz and 1.8 GHz band. But the polarization for the lower and upper bands is right- and left-hand CP, respectively. The frequency ratio of opposite sense CP band can be lowered to 1.13 and then, give a good choice to design the low frequency ratio with opposite sense CP. The measured AR's center frequency and bandwidth for the lower band is 1.602 GHz and 2.81% respectively, and the minimum AR and antenna gain is 0.987 dB and 3.8 dBic for RHCP, respectively. Meanwhile, the AR's center frequency, bandwidth, antenna gain for the upper band are 1.820 GHz, 3.24%, and 2.43 dBic for LHCP, respectively. Radiation patterns in both bands are broadside radiations and similar to each other except the opposite sense CP characteristic.