Design and Construction of Ultrawideband Spiral Antenna for Microwave Imaging

Recently, circular polarization ultrawideband (CP UWB) antennas have received significant attention in microwave imaging. In this paper, the use of a UWB logarithmic spiral antenna with circular polarization for tumor detection is proposed. One of the main advantages of UWB antennas to narrow-band (NB) antennas is its higher resolution. The absorption of more scattered fields is also the advantages of circular polarization antennas to linear polarization antennas. Compared with the conventional spiral antenna that uses coaxial cable for feed structure, to improve the performance of radiation characteristics, tapered microstrip to stripline balun is used to feed the two arms of spiral antenna. The measured results show that the return loss is better than 10 dB from 3/1 to 10/6 GHz. Also the radiation pattern is bidirectional with circular polarization in the entire bandwidth. The time-domain characteristic of the transmitting and receiving system using the proposed spiral antenna with studying two parameters fidelity factor and group delay is investigated. Results show that for proposed antenna, the fidelity factor is higher than 0/91 and group delay less than 1/0 5 nsec. Construction and measurement of the proposed spiral antenna for use in tumor detection are presented.