Reconfigurable monopole antenna with polarization and pattern diversity

Abstract

A planar monopole antenna capable of reconfiguring both the polarization and radiation pattern is presented for MIMO systems. A star shape patch is used as the radiator. Four PIN diodes are inserted to control the polarization and radiation pattern. The antenna can operate over two frequency bands. A prototype antenna is designed and fabricated for radiation at 5.5 GHz and 8.4 GHz. The first switching state provides left-hand circular polarization (LHCP) in the first band with the main beam at ϕ = +60° and right-hand circular polarization (RHCP) at 8.4 GHz at ϕ = +140°. For the second switching state, the sense of polarizations changes with the main beam at ϕ = +120° and + 40°, respectively. Measured results show that overlapped bandwidths are obtained from 5.17 to 5.85 GHz at lower band and 8.35 to 8.49 GHz at upper band for both the first and second switching states. For the third switching state, it generates an omnidirectional radiation pattern with linear polarization (LP) over 3.78–5.87 GHz. The antenna possesses the measured peak gain values of 0.65 dBi at lower band and 1.15 dBi at upper band for first and second switching states and an average gain value of 1.1 dBi is obtained for the third switching state. The overall size of the prototype is 24 mm × 23.5 mm on a 1.6 mm thick FR4 substrate. The CP band positions, as well as beam tilt, are tunable. Design guidelines are provided. The demerit of the proposed antenna is that it has achieved lower gain values at dual bands.