Investigation of a Via-Loaded Microstrip Magnetic Dipole Antenna With Enhanced Bandwidth and Gain

A via-loaded microstrip magnetic dipole antenna with enhanced bandwidth and gain is proposed and investigated. The antenna is constructed on a long microstrip antenna with three edges shorted and one edge opened. The open aperture is equivalent to a magnetic dipole, which serves as the radiation source. In the long cavity, two modes are generated, in which the lower one is half-TE110 mode and the higher one is half-TE310 mode. By loading two sets of shorting vias around the null voltage points of the half-TE310 mode, the resonant frequency of the half-TE110 mode is shifted upward. Then, the two modes are merged to achieve an enhanced bandwidth. Moreover, the superposition of the far fields of the two modes results in a narrowed unidirectional beam, a reduced sidelobe level (SLL), and therefore, an improved gain. The theoretical investigation is validated with simulation results. A prototype of the antenna is fabricated and measured. Measured results show that the proposed antenna with a low profile of 0.027 lambda(0) (lambda(0) is the wavelength in free space) has an impedance bandwidth of 9.1%, and a peak gain of 10.2 dBi.