A Hybrid Slot/Monopole Antenna With Directional Heating Patterns for Microwave Ablation

We present a new coax-fed interstitial antenna for generating directional heating patterns during microwave ablation. The antenna comprises a base-fed monopole wherein, a portion of the outer conductor is extended to create a reflector that directs the fields toward the opposing direction. To further direct the fields away from the reflector, we etched a semicylindrical slot in the outer conductor. The electric field produced by the slot constructively interferes with the field generated by the monopole in the desired radiation direction, while destructively interfering with the monopole's field behind the reflector. This creates directional specific absorption rate and heating patterns. In addition, the reflector and slot suppress the unwanted currents along the antennas feeding cable. This eliminates the need for a balun and reduces the overall antenna diameter. The antenna is impedance matched using an internal π-matching network. A prototype of this antenna, designed to operate at 7 GHz in egg white, was fabricated and used to perform ablation experiments at a power level of 20 W for 5 min. Experimental results agree well with simulations and confirm the capability of the antenna for generating directional heating patterns.