A Compact Wide-Band Shorted Folded Antenna

Planar monopole antennas are easy to construct from a single metal plate and able to offer attractive performance in terms of impedance bandwidth and radiation properties [1]. However, the necessity of compactness has induced the research community to investigate folded radiation elements [2 and 3]. But, at the same time, by reducing the overall dimensions of planar monopole antennas distortions in the radiation pattern and drawbacks in the impedance bandwidth can be introduced. Special feeding techniques and particular grounding systems have to be designed in order to obtain an acceptable compromise between compact dimensions and interesting performance [4, 5 and 6]. The novel and compact wide-band shorted folded antenna presented in this paper offers a working bandwidth of 4.6GHz between 1.6GHz and 7.2GHz (IBR=4.5;1). Good radiation properties and acceptable omni-directionality are obtained throughout the operating bandwidth. The use of a vertical ground plane and a microstrip feeding system permit a dramatic reduction of dimensions when compared to a planar monopole antenna with same characteristics. In this paper, we present another promising bandwidth-enhancement technique, which consists of grounding the radiating element with the vertical ground plane. This solution is shown to only moderately disturb the radiation properties of the antenna. As a consequence of performance and reduced dimensions, this antenna represents a significant candidate for in-door, mobile and vehicular applications where the coverage of different communication protocols is required. Numerical simulation have been obtained by CST Microwave Studio and compared to experimental results of the constructed prototype. A good agreement is achieved.