Abstract: A compact system and method are provided for implementing the generation of electromagnetic radiation extending over mm-wavelength to sub-mm-wavelength or terahertz range. The generated electromagnetic radiation can be broadband or have a variable bandwidth. Electrons are accelerated to a chosen energy and undergo subsequent or simultaneous temporal or spatial compression. The degree of compression is chosen such that the electron beam pulse length is near to or less than that of the terahertz wavelength desired to be generated. The radiation is produced by one or combination of methods of synchrotron radiation or transition radiation.