In-body bioelectronics relies on antennas to interface with external on- or off-body equipment. In this paper, we address the impedance detuning of in-body antennas caused by nondeterministic electromagnetic properties of biological tissues. The impedance robustness can be improved in two ways. First, by using wideband and multiresonance antennas with an added benefit of higher achievable data rates. Second, by applying specific dielectric-loaded narrow-band microstrip designs that additionally show enhanced radiation performance and robustness to inner components. Fully tissue-independent characteristics can be realized using hybrid slot-patch designs.