The chief use of the simple, unmodulated CW radar is fro the measurement of the relative velocity of a moving target, an in the police speed monitor or in the previously mentioned rate -of-climb meter for vertical -take-off aircraft.In support of automobile traffic,CW radar has been suggested for the control of traffic light, regulation of toll booths, vehicle counting as a replacement for the "fifth-wheel"speedometer in vehicle testing as a sensor in anti lock braking systems, and for collision avoidance. For railway. CW radar can be used as a speedometer to replace the conventional axle driven tachometer.In such an application it would be unaffected by errors caused by wheelslip on accelerating or wheelslide when braking. It has been used for the measurement of railroad-freight-car velocity during humping operations in marshalling yards,and as a detection device to give track maintenance personnel advance warning of approaching trains. CW radar is also employed for monitoring the docking speed of the velocity of missiles, ammunition,and baseballs.
The principal advantage of a CW doppler radar over ( non radar) methods of measuring speed is that there need not be any physical contact with the object whose speed is being measured. Most of the above applications can be satisfied with a simple, solid-state CW source with powers in the tens of milliwatts. High-power CW radar for the detection of aircraft and other targets have been developed and have used in such systems as the Hawk missile systems.However, the difficulty of eliminating the leakage of the transmitter signal into the receiver has limited the utility of unmodulated CW radar fro many long-range applications.A notable exception is the space Surveillance system. The CW radar, when used for short or moderate ranges, is characterized by simpler equipment than a pulse radar. The amount of power that can be used with a CW radar is dependent on the isolation that con be achieved between the transmitter and receiver since the transmitter noise that finds its way into the receiver sensitivity.
Perhaps one of the greatest shortcomings of the simple CW radar is its inability to obtain a measurement of range.This limitation can be overcome by modulating the CW carrier, as in the frequency-modulated radar described in the next section.Some anti-air-warfare guided missile systems activeness homing guidance which a receiver in the missile receives energy from the target,the energy having been transmitted from an "illuminator" external to the missile. The illuminator,for example,might be at the launch plat from. CW illumination has been used in many successful systems.It is a tracking radar as well as an illuminator since it must be able to follow the target as it travels through space. the doppler discrimination of a CW radar allows operation in the presence of clutter and has been well suited for low altitude missile defense systems. A block diagram of a CW tracking illuminator. Note that following the wide-diagram amplifier is a speed gate, which is a narrow-band tracking filter that acquires the target's doppler and tracks its changing doppler frequency shift.
No comments:
Post a Comment