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A novel dual-band printed diversity antenna is proposed and studied. The antenna, which consists of two back-to-back monopoles with symmetric configuration, is printed on a printed circuit board (PCB). The effects of some important parameters of the proposed antenna are deeply studied and the design methodology is given. A prototype of the proposed antenna operating at UMTS (1920 ~ 2170 MHz) and 2.4-GHz WLAN (2400 ~ 2484 MHz) bands is provided to demonstrate the usability of the methodology in dual-band diversity antenna for mobile terminals. In the above two bands, the isolations of the prototype are larger than 13 dB and 16 dB, respectively. The measured radiation patterns of the two monopoles in general cover complementary space regions. The diversity performance is also evaluated by calculating the envelope correlation coefficient, the mean effective gains (MEGs) of the antenna elements and the diversity gain. It is proved that the proposed antenna can provide spatial and pattern diversity to combat multi-path fading. Index Terms-Diversity antenna, diversity gain, dual-band antenna, envelope correlation coefficient, mean effective gain (MEG). I. INTRODUCTION ntenna diversity is a well-known technique to enhance the performance of wireless communication systems by reducing the multi-path fading and co-channel interference [1]. Nowadays, in a cellular communication system, it is easy to be implemented at the base station where antenna separations of many wavelengths are readily available. However, in order to improve the quality of wireless downlink signal, more than one antenna is necessary for the terminal side. In this kind of mobile terminal, two or more antenna elements are envisaged and the restricted space available for antenna is an open issue [2]. Most designs of diversity antenna in mobile terminals are for WLAN operation [3][4], and they are applied in the PCMCIA

An orthogonal vector approach is proposed for the synthesis of multi-beam directional modulation (DM) transmitters. These systems have the capability of concurrently projecting independent data streams into different specified spatial directions while simultaneously distorting signal constellations in all other directions. Simulated bit error rate (BER) spatial distributions are presented for various multi-beam system configurations in order to illustrate representative examples of physical layer security performance enhancement that can be achieved.

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Directional modulation (DM) is