Wireless data communication could improve the performance and reliability of biomedical implants used in fundamental neuroscience research by removing infection-prone transcutaneous cabling. The small size of common research animals like mice and rodents, however, presents an additional challenge in the design of implantable antennas due to the resonance effects of the host body. In this work, we demonstrate how the far-field radiation performance of an antenna implanted in a rat cadaver is impacted by the electrically small size of the rat’s body. We further discuss design strategies for developing implantable antennas in small animals to obtain robust wireless link budgets for the considered size- and energy-constrained wireless implantable systems.