This chapter introduces compact antenna systems designed for implantation in biomedical settings, particularly for placement on the scalp. The proposed antenna designs are characterized by dual-band functionality operating at the industrial, scientific, and medical (ISM) frequencies of 915 and 2450 MHz. The IMDs are remarkably compact, with volumes of 344 mm \(^{3}\) for System A and 406 mm \(^{3}\) for System B. Each system incorporates microelectronic components and a battery, with the antenna itself designed as an ideal electric conductor. A notable aspect of these devices is the antenna with its minimal dimensions, measuring just 8 \(\times \) 6 \(\times \) 0.5 mm \(^{3}\) , and its innovative slotless and vialess ground plane, which simplifies the overall design. The antenna achieves peak gain values of 28.5 dBi at the lower resonant frequency and 22.8 dBi at the higher frequency. Performance assessments are conducted using both the finite-element method and finite-difference time-domain simulations. Validation of the antenna performance is achieved through measurements in a saline solution, demonstrating strong agreement with the simulated results. Additionally, a link budget analysis is performed to evaluate the range of data transmission capabilities.