A Wideband Low-Profile Antenna Composed of a Conducting Body of Revolution and a Shorted Parasitic Ring

An antenna composed of a conducting body of revolution (BOR) and a parasitic ring shorted to a finite-sized ground plate, designated as the BOR-SPR, is designed for realizing a low-profile base station antenna with a wideband voltage standing wave ratio (VSWR) characteristic. The design of the BOR-SPR starts with a center-fed patch antenna. To match the antenna input impedance to a 50-ohm feed line, as a first step, a slot is cut into the patch (this antenna is designated as Ant-I), and as a second step, shorted parasitic conducting pins are added to the periphery of Ant-I (this antenna is designated as Ant-II). Ant-II has a VSWR bandwidth of approximately 28%. Further increase in the VSWR bandwidth is achieved by replacing the inner feed region of Ant-II with a conducting BOR. It is found that this replacement, creating the BOR-SPR, yields an extremely wide VSWR bandwidth of approximately 147%, where the electrical antenna height at the lower edge frequency of the bandwidth is small: approximately 0.07 wavelength. It is also found that the radiation pattern of the BOR-SPR is similar to that of a monopole above a finite-sized ground plate. The beam direction thetas (measured from the direction normal to the surface of the BOR) varies between approximately 30deg and 60deg. The gain at thetas = 60deg is approximately 2 dBi near the lower edge frequency of the VSWR bandwidth and approximately 8 dBi near the upper edge frequency.