A Low-Profile Vertically Polarized Antenna With Conical Radiation Pattern for Indoor Micro Base Station Application

A novel low-profile vertically polarized wideband monopole antenna is proposed. A central-fed circular patch antenna, which is shorted concentrically by three metal pins, is initially adopted to excite TM01 and TM02 modes. Then, a fan-shaped clearance area is cut out in the angular area between each two shorting pins. Finally, three mushroomlike structures are placed in the clearance area, which, together with the feeding probe, form three split ring resonators (SRRs) that introduce an extra resonance, thereby substantially expanding the antenna operation bandwidth. All the three modes have radiation patterns similar to the conventional monopole. The proposed antenna has a very low profile of 0.06 λmin and a lateral dimension of π × (0.176 λmin)
²
, where λmin is the free-space wavelength at the lowest frequency of operation. A simulated impedance bandwidth for |S11| <; -10 dB of about 48.5% ranging from 1.7 to 2.79 GHz is achieved, which fully covers the 4G LTE band, while the measured result shows a wider fractional bandwidth of 66%.