chapter  3
Active Millimetre-Wave Sensor Using Direct Detection Approach
WithBoris Y. Kapilevich, Stuart W. Harmer, Nicholas J. Bowring
Pages 40

A direct detection receiver can be used to realize a very simple radar system. The signal from a direct detection radar gives a series of pulses which are separated only by the difference between any one scattering object and all other objects, while the radar cross section terms are also irrevocably mixed with each other. In a direct detection radar sensor, the transmitted pulse is swept, linearly with time, over its entire operating frequency range, and the received waveform is synchronized to that transmitted by, a priori, knowledge of the sweep time, allowing the appropriate frequency channels, or bins, to be allocated. Because of the simplicity of the direct detection radar, ultra-wide band radar systems can be simply constructed using a direct detection approach, as there is no need for the expensive intermediate frequency stages that are employed in conventional heterodyne radar systems.