Circularly Polarized Beam-Scanning Microstrip Antenna Using a Reconfigurable Parasitic Patch of Tunable Electrical Size

A reconfigurable microstrip antenna with a circularly polarized (CP) beam-scanning feature is proposed in this paper. Such feature is attained using a novel methodology that effectively tunes the electrical size of a patch antenna. The proposed antenna is a microstrip Yagi-Uda antenna consisting of two square patches. One patch is driven with two orthogonal feeds for CP operation, whereas the other patch is a parasitic one of tunable electrical size for beam scanning. The parasitic patch is loaded with a narrow square slot and four lumped varactors along with their dc biasing network to effectively tune its electrical size. Because the main beam direction is determined by the electrical size of the parasitic patch, electronic beam scanning is allowed by changing the capacitance value through the applied reverse dc biasing voltage. An antenna prototype has been fabricated for experimental validation. Operating at 2.45 GHz, the antenna performance shows a monotonic CP beam scanning that ranges from -36 degrees to 32 degrees with a 0.48-6.64 pF tuning capacitance. The achieved peak value for the realized gain is 8.1 dBic with 2.4-dB variation along the entire scanning range.