Microwave ablation (MWA) is a minimally invasive therapy that kills cancer cells by exploiting the cytotoxicity of heat. In MWA, an interstitial antenna delivers electromagnetic (EM) energy to the tumor. The deposited EM energy heats the tumor and induces coagulation necrosis. Most of the current MWA antenna designs generate axisymmetric ablation zones, meaning the antenna needs to be placed in the center of the tumor for successful ablation of the tumor. This, however, may become challenging in cases where direct access route is blocked by a vital organ and only the periphery of the tumor is accessible by the MWA antenna. In these cases, having an antenna that can be placed on the periphery of the tumor and generate a directional ablation zone may be useful. I have developed two minimally invasive antenna designs capable of generating directional heating patterns. One is a coaxial-based hybrid slot/monopole antenna, and the other is a non-coaxial-based parallel-wire antenna. The ex vivo experimental results in the laboratory testbed of egg white as the coagulation medium confirmed that the ablation zones generated by these antennas were asymmetric. Moreover, the overall performance of the proposed antennas remained robust throughout the ablation procedure as the dielectric properties of the coagulation medium were changing. Another characteristic of most of the current MWA antenna designs is that they are implemented with rigid coaxial cables. The rigidity of the cable and the percutaneous nature of the antenna's insertion may increase the invasiveness of the MWA procedure when applied to treat tumors deep-seated inside the body. If the rigid antenna is replaced by a flexible one, those tumors can be accessed less invasively through natural ductal pathways, decreasing the potential contraindications of the ablation procedure. I developed a minimally invasive flexible helical dipole antenna that can generate substantial ablation zones in the presence of significant perfusion in perfused ex vivo pig liver. The proposed antenna maintained its good impedance matching and ablation performance while bent.