On-Glass Omnidirectional Loop Antenna Using Open-End Subloops for Dominant Magnetic Dipole Moment

This letter develops an on-glass omnidirectional loop antenna using electrically small open-end subloops to achieve a dominant magnetic dipole moment. The open-end loop geometry facilitates the excitation of a magnetic dipole moment. The three subloops are arranged in a circular array with 120° spacing and connected by three arc-shaped strips, forming a large loop. For in-phase magnetic dipole excitation, the circumference of each strip is designed to be a half guided wavelength (0.5λg) at the operating frequency. Moreover, the split gap of the subloop is adjusted to maintain current along the large loop in phase by introducing a serie s capacitance. Thus, a dominant magnetic dipole moment is achieved, enabling omnidirectional radiation even in a large loop with 1.5λ_g. The developed antenna is fabricated on a 2-mm quartz substrate. The antenna shows a −10-dB impedance bandwidth of 0.26 GHz (5.3−5.56 GHz) and a maximum gain of 4.17 dBi at 5.4 GHz in the azimuth plane.