14.1 INTRODUCTION AND ADVANTAGES OF CW

The usual concept of radar is a pulse of energy being transmitted and its roundtrip time being measured to determine target range. Fairly early it was recognized that a continuous wave (CW) would have advantages in the measurement of the doppler effect and that, by some sort of coding, it could measure range as well.

Among the advantages of CW radar are its apparent simplicity and the potential minimal spread in the transmitted spectrum. The latter reduces the radio interference problem and simplifies all microwave preselection, filtering, etc. A corollary is the ease in the handling of the received waveform, as minimum bandwidth is required in the IF circuitry. Also, with solid-state components peak power is usually little greater than average power; CW then becomes additionally attractive, particularly if the required average power is within the capability of a single solid-state component.

Another very apparent advantage of CW (unmodulated) radar is its ability to handle, without velocity ambiguity, targets at any range and with nearly any conceivable velocity. With pulse doppler or moving-target indication (MTI) radar this advantage is bought only with considerable complexity. An unmodulated CW radar is, of course, fundamentally incapable of measuring range itself. A modulated CW radar has all the unwanted compromises, such as between ambiguous range and ambiguous doppler, that are the bane of coherent pulsed radars. (See Chaps. 15 to 17.)

Since CW radar generates its required average power with...