INVESTIGATIONS INTO A LOADED RING TYPE MONOPOLE ANTENNA

The paper presents an investigation into a loaded ring type monopole antenna with an objective of developing a compact and low-cost antenna for ultra-wideband applications. A planar monopole antenna is well known for its ultra wide impedance bandwidth performance [1-2]. Several configurations have been proposed in [2-4], which exhibit wide bandwidth. However, these structures fail to exhibit good impedance match at lower frequency bands. The lower frequency limit of bandwidth depends primarily on height of antenna, for example, a typical value of the lower frequency band (for VSWR ≤ 2) of a planar monopole antenna of 75 mm height is about 1.5 GHz. Extending the lower end of frequency band without making any changes to antenna dimensions has been a challenge to many antenna designers. In this paper we investigate a ring shape planar monopole antenna loaded with a metal disc (brass) for ultra-wide band applications. The structure is shown in Fig 1. The outer ring diameter is fixed to 75 mm. Brass post diameter is assumed to be 1.27 mm. The antenna is positioned vertically using a 50-Ohm SMA receptacle. A finite ground plane (200 mm x 200 mm) is used to support the monopole. The gap between the ground plane and the antenna is chosen to be 0.8 mm. In order to validate the response of this antenna in terms of impedance bandwidth, radiatio