A novel sleeve monopole with broad bandwidth

Owing to simplicity, polarization purity, power capacity, good match, and low cost, the use of a coaxially fed monopole in a parallel plate waveguide is an attractive option as an adapter or a feed and has been extensively investigated for years. However, a simple coaxially fed linear monopole particularly offers a narrow impedance bandwidth. So some modified monopoles have been often applied to wireless communication antennas in the past decades. The input impedance performance has been significantly improved by means of the various loading techniques, such as dielectric coatings, attached dielectric resonator structures, and disc-ended or top-hat structures. Previously, an alternative is a leaky-mode aperture-coupled dielectric resonator, which has been successfully used as a feed of a class of omnidirectional antennas suitable for wireless communication systems. In this article, a novel sleeve monopole type is proposed to further improve the impedance performance of a monopole. This structure simply consists of a second sleeve and a sleeve monopole vertically put between a parallel plate waveguide. Compared to traditional structures used in a parallel plate waveguide, this modified sleeve monopole has the merit of noticeably broad impedance bandwidth and still maintains the feature of simple structure, low cost, and pure polarization. Because of simple manufacture, broad bandwidth, and good match, this novel structure has shown a promising potential application in various microwave applications and wireless/satellite communications.