Experimental Investigation of Reconfigurable Harmonic Suppressed Fractal Dipole Antenna

Cognitive radio (CR) is a very promising technology of future wireless communications that has greater demands for antenna designs. One practical antenna is a reconfigurable antenna that has dual mode operations, i.e. scanning a free RF spectrum and transmitting or receiving information data via a CR link. One possible compact antenna configuration is based on the dipole or monopole that has narrow or wideband frequency features for handheld or base station terminal. A typical technique is to create two antennas with wideband and narrow band features of omni-directional and directional patterns for sensing and frequency agile purposes [1]-[3]. A three L-shaped monopole antennas designed on the same substrate with the inter-band frequency being changed using a PIN diode while a DC supply is used to control the reactance of a varactor diode for frequency tuning purposes that covers UHF band, mobile radio and wireless LAN [4]. A single patch antenna integrated with parasitic elements via RF switches to create a tunable feature from 550 MHz to 1500 MHz has been proposed [5]. In [6], a single band antenna is connected via a harmonic filter. Similar approach has been employed in earlier works on a dipole, aimed as a reconfigurable antenna [7]-[8]. In this paper, an experimental investigation of a tunable fractal dipole antenna is presented. It is aimed for CR handheld unit with wideband features such as hand phone or personal digital assistant (PDA) [9]. In addition, this paper proposed an alternative implementation using low loss material showing better performances. The structure is formed from the integration of Koch fractal dipole antenna, stubs-filter and wide-band taper balun as will be explained in the next section (section 2). The experimental results are explained in section 3 while the concluding remarks are given in section 4.