A balun-free coax-fed helical antenna for minimally invasive microwave ablation

We present a coax-fed helical antenna for microwave ablation of tumors. In contrast to previously reported coaxial antenna designs, the proposed antenna achieves a localized specific absorption rate pattern at the desired frequency of operation without using a coaxial balun. Such baluns increase the outer diameter, and thus the invasiveness, of the antenna. Balun-free operation in the proposed antenna is achieved by operating the helical antenna at a frequency where its feed point impedance is intrinsically high. This efficiently chokes the currents excited on the outer surface of the feeding cable. Using a compact impedance matching network at the antenna feed point, we achieve an excellent impedance match between the antenna and the main feeding transmission line as demonstrated by the simulation and measurement results. This balun-free antenna design offers a promising solution for reducing the invasiveness of interstitial devices in microwave ablation.