A simple expression for the maximum data rate that can be reliably communicated (i.e., capacity) through a narrowband, resonant antenna with a Lorentzian frequency response is derived. Both transmit and receive cases are considered. In general, resonant antennas handle different data rates on receive than transmit because receive antennas filter out some of the external noise, but they also add their own loss related noise. It is also shown how adding loss, an impedance mismatch, or a matching network can increase the channel capacity by widening the resonant bandwidth at the expense of a reduced signal strength. A baseband simulation of communication between a narrowband transmitter and wideband receiver employing single-carrier quadrature amplitude modulation (QAM) is developed. The simulated data rates closely approach the derived theoretical limit. Finally, the simulation is experimentally validated by transmitting a quadrature phase shift keyed (QPSK) modulated signal through a single-resonant narrowband filter.