عنوان مقاله [English]
In this paper, a four-arm spiral antenna at 2-4 GHz frequency band with desirable radiation characteristics for use in direction finder and airborne targets mono-pulse tracking systems is presented. The designed antenna consists of three main parts, four-arm Archimedean spiral radiator, four-arm balun, and cylindrical metallic cavity. The four-arm balun contains four microstrip lines with linear tapering, and convert the input impedance of the spiral radiator to the 50Ω standard impedance at the antenna feeding ports, linearly. Role of the cylindrical metallic cavity is uni-directing, and consequently increasing the antenna gain. The simulation results of the antenna obtained via HFSS and CST software packages show that by using the received waves from the four ports of this antenna, much appropriate sum and difference radiation patterns with circular polarization are achieved. The average value of the isolation between the different ports of the antenna is nearly 28dB and the return loss of the four input ports at the entire frequency band is lower than 10dB. Also, the antenna gain of sum mode and null depth of difference mode at the center frequency, 3GHz, are 6.58 and 35.18dB, respectively.