In railway networks, metal objects near the balise transmission system can affect the performance of antennas in the system operating at 27.095 MHz and 4.23 MHz. In this paper, the performance of the antennas in the proximity of steel rails and metal plates are simulated and tested in terms of resonant frequency, magnetic field distribution. The results show that the metal effect is dependent on the distance between the metal and the antenna. They shift the resonant frequency and change the magnetic field distribution. In order to solve the problem, we find that the antennas should keep specified distance with the steel rails. Also, a metal plate is fixed on the back of on-board antenna unit to reduce the sensitivity to metal. These methods increase the robustness and reliability of balise transmission system antennas in railway signalling.