Electrically Small, Planar, Complementary Antenna With Reconfigurable Frequency

An electrically small, planar, complementary antenna with endfire radiation patterns is investigated in this paper. It mainly consists of an electric dipole and a segmented loop that functions as an equivalent magnetic dipole. There is also an additional stub used to adjust the maximum radiation direction and a slotted circular patch for impedance matching. Two modes of the electric dipole and magnetic-dipole loop are excited and combined, realizing an impedance bandwidth of 6.1%, a gain of 4.85 dBi, a front-to-back ratio (FTBR) of 18.5 dB, and an efficiency of over 90%. Furthermore, it is found that the resonance frequency of the loop relies on the length of its small segments. Therefore, two p-i-n diodes are introduced to the loop to manipulate its resonance frequency. Also, two extra p-i-n diodes are added to adjust the resonance frequency of the electric dipole. Consequently, two reconfigurable bands (1.5 and 2.4 GHz) with consistent endfire radiation patterns are achieved for the first time in a complementary antenna.