Various electrodynamic models of a combustion chamber, in which an initiated subcritical streamer discharge is used to ignite a combustible mixture, are considered. To localize the discharge in the working chamber, discharge initiators are used based on half-wave electromagnetic vibrators with resonant properties. The dependences of the structure of the electric fields that form the discharge on the geometric parameters of the discharge initiator are obtained on the basis of numerical calculations, and the issues of matching the chamber with the radiation generator are considered. Comparison of the calculation options for different positions of the initiator of the discharge in relation to the optical centreline of the camera. Possibilities for further enhancement of the field in the working zone at the poles of the microwave discharge initiator, which is required for the formation of discharges with a developed streamer structure at elevated gas pressures in the combustion chamber, are discussed. The ways of increasing the resulting electromagnetic field in the area of vibrators for the formation of discharges with a volumetric structure have been determined.