DESIGN AND PERFORMANCE OF NOVEL SHORTED SMALL MICROSTRIP ANTENNAS Reda S.Ghoname Ashraf S. Mohra Electronics Research Institute Electronics Research Institute Microstrip Department Microstrip Department Dokki, Cairo, Egypt Dokki, Cairo, Egypt reda@eri.sci.eg mohra@eri.sci.eg Esmat A.F.Abdallah Hadia S. El-Henawy Electronics Research Institute Electronics &Comm. Department Microstrip Department Faculty of Engineering, Dokki, Cairo, Egypt Ain Shams University, esmat@eri.sci.eg Cairo 11517, Egypt. Abstract In this paper two novel shorted microstrip antennas are proposed to achieve reduction in antenna size and at the same time work at a broadband frequency of operation. They are designed to operate at the Bluetooth range of frequency(ISM band). The performance of these antennas is obtained by using the ready-made IE3D (Zeland) software package. The area of the antennas are much smaller as compared to the conventional rectangular microstrip antenna (only 6.7% of it), while its bandwidth is larger. 1. Introduction The rapid growth of wireless communications resulted in the production of a large variety of wireless devices ranging from mobile phones to PDAs to GPS receivers. Currently satellite radios and other entertainment systems are also making entrance to the marketplace. Each communication system needs an antenna. It is crucial that such antennas be small, conformal, low profile and has the ability to communicate effectively. The importance of miniaturization is enormous since it opens up more space to accommodate other components inside the device. Broad impedance bandwidth is greatly desired. Good angular coverage and polarization diversity are also very important. The most noticeable among conformal low-profile antennas for mobile communication is the microstrip patch antennas since they can provide advantages over traditional whip and helix antennas. However, there are several applications where even the physically small size of a conventional microstrip patch antenna is still too large. Bluetooth frequency (2.4-2.485GHz) or even low requires conventional patches too large to be readily installed on typical dimensions of a mobile communications handset. Several techniques have been proposed to reduce the size of the patch such as using high dielectric constant materials, however, only poor efficiency due to surface wave excitation and narrow bandwidth have been achieved [1]. Also, the limited availability of low cost, low loss, and high dielectric constant material is another problem with this method. Shorting posts were used in different arrangements to reduce the overall size of the microstrip antenna. However, there are critical drawbacks with this form of printed antenna due to the strong dependence of the input impedance on the close positioning of the shorting post with respect to the feed and once again the narrow impedance bandwidth. To date, the recoded bandwidths of the proposed shorted patches are significantly less than that required for typical cordless systems such as DECT (Digital European Cordless Telephones)[2], [3]. Regarding the bandwidth enhancement of patch antennas, several techniques have been proposed, including the use of impedance matching network, the use of multiple resonators and the use of thick substrates. For an electrically thick substrate, coaxial feed is typically used, however, the increased inductance introduced by the long probe will limit the achievable bandwidth [4]. For this reason several other methods have been proposed to solve this problem, including etching a small circular slot, cutting a U-slot on a patch and the use of an L-probe feed. In this paper two novel shorted microstrip antennas are proposed to achieve reduction in antenna size and at the same time work at a broadband frequency operation. Fig.1 shows the proposed geometries together with the conventional rectangular