An ablation probe having a ground plane is disclosed. The disclosed probe includes an inner conductor coaxially disposed within an outer shield. One or more ground plane(s) oriented substantially transversely to a longitudinal axis of the probe are joined to the outer shield. One or more dielectric(s) may be disposed around the inner conductor or upon a surface of a ground plane. The probe may include a rigid or flexible catheter disposed around the outer shield to define a conduit therebetween to enable the delivery of pressurized fluid to an inflatable balloon disposed around a ground plane. A semicylindrical housing having a circumferential surface and a distal surface may be included. A proximal edge of the circumferential surface of the semicylindrical housing may be joined to a circumferential edge of a ground plane. An opening may be defined in the distal surface of the semicylindrical housing, through which the inner conductor may extend distally.