A Minimally Invasive Coax-Fed Microwave Ablation Antenna With a Tapered Balun

We present a minimally invasive coax-fed dipole antenna with a tapered slot balun for microwave ablation (MWA) applications. The balun is created by gradually tapering the outer conductor of the coaxial feed line into two parallel strips, leaving two tapered slots on the outer conductor. Implementing the balun within the outer conductor of the coax itself helps reduce the overall diameter of the antenna compared to interstitial antennas that use conventional coaxial baluns. The tapered-slot balun connects the dipole antenna comprised of three active segments to the coaxial feed line. One active segment is defined by an extension of the inner conductor of the coaxial cable, acting as one arm of the dipole. The other two active segments are located in the two slots created by tapering the outer conductor and connected to its distal end to constitute the second arm of the dipole. We designed the antenna to operate at 6 GHz in ex vivo bovine liver and fabricated a prototype to conduct ablation experiments. Simulation and experiment results show that the tapered balun provides good impedance matching between the coaxial feed line and the dipole and helps the antenna achieve localized ablation zones. The proposed antenna offers a promising solution for reducing the overall diameter, and the invasiveness, of coax-fed interstitial antennas used for MWA.