We present an improved model for antennas in a reverberation chamber. The derivation of this model is more rigorous than previous derivations and models, but is still, admittedly, overly simplistic. However, this model should be applicable for a special class of antennas (those that can be modeled as an unknown 2-port network between the test port and an ideal antenna). For more realistic antennas, these models should still provide valuable insight into the possible behavior of any antenna. Using these models, we show that some previous assumptions regarding receiving characteristics (mismatch and efficiency) of an antenna are invalid: most significantly we show that there can be differences between the transmitting and receiving efficiency of an antenna, and also between the transmitting and receiving mismatch factors. However, we show that the errors are unimportant for most measurements. We also give justification for the assumption that the average reflection coefficient of an antenna in a reverberation chamber is simply the free-space reflection coefficient of the antenna.