Recent experimental and theoretical works on coherent radiowave transition radiation (CRTR) of short particle bunches have shown that CRTR intensity is proportional to the square of the number of particles in the bunches and it can be used for detection of very high energy particles. CRTR is convenient for the study of transition radiation pre-wave zone and radiator transversal size effects. In this connection the angular and spectral distribution of CRTR produced by periodic bunches are investigated with the purpose to carry out new experiments devoted to CRTR.