Basic composition of radar

The last article described some basic contents of radar , Here we go on to talk about , The components of a radar system .
The diagram is the basic frame diagram of a radar system ：

Transmitter , Power amplifier in the figure , Generate appropriate waveforms for specific tasks performed by the radar . Its average power may be as small as milliwatts or as large as megawatts ( The average power is better than the peak power to indicate the performance index of radar ). Most radars use short pulse waveforms , So that an antenna can be used to transmit and receive on the basis of time sharing .
Duplexer The function of allows the use of a single antenna to protect the sensitive receiver from being burnt out when the transmitter is working and to guide the received echo signal to the receiver instead of the transmitter .
The antenna It is a device that radiates the transmitted energy into space and then collects the echo energy when receiving . The antenna is almost always directional , Radiate energy into a narrow beam , The direction of the target can be determined at the same time of gathering power . An antenna that produces a narrow directional beam when transmitting , It usually has a large area when receiving , So as to collect weak echo signal from the target . The antenna not only gathers energy when transmitting, but also collects echo energy when receiving , It can also be used as a spatial filter , Provide angular resolution and other capabilities .
The receiver amplifies the received weak signal to a level that can detect its presence . Because of the final restriction that the radar makes a reliable detection decision and extracts the target information in case of noise , Pay attention to ensure that the receiver generates very low internal noise . Most radars work in the microwave band , The noise affecting radar performance usually comes from the first stage of the receiver , In the picture is Low noise amplifier . The limitation of detection in many radar applications is the unwanted environmental echo ( be called Clutter ), At this time, the receiver should have a large enough dynamic range , To avoid clutter saturating the receiver , So it seriously affects the detection of moving targets . The receiver's Dynamic range , Usually expressed in decibels , It is defined as the level ratio of the maximum and minimum input power that the receiver can operate with certain specified performance . The maximum signal level can be set by the corresponding nonlinear effect of the allowable receiver , The minimum signal level may be the minimum detectable signal . Signal processor , It is usually located in the if part of the receiver , It can be described as that the receiver separates the part of the required signal from the unwanted signal that will degrade the detection performance . Signal processing includes the process of maximizing the output signal-to-noise ratio Matched filter , It also includes Doppler processing that maximizes the signal to clutter ratio of moving targets when the clutter ratio noise is large. Doppler processing can separate different moving targets or separate moving targets from clutter . The detection decision is made at the output of the receiver , When the receiver output exceeds a predetermined threshold, the presence of a target is declared . If the threshold setting is too low , The receiver noise will cause too many false alarms . If the threshold is set too high , It is possible that the detected target will be missed . The criterion for determining the decision threshold level is to set the threshold as follows , It produces an acceptable predetermined average false alarm rate generated by the noise of the receiver .
stay Detection decision After making , You can determine the trajectory of the target , That is, the trajectory of the target position measured over a period of time . This is an example of data processing . The processed target detection information or track can be displayed to the operator ; Or used to automatically guide the missile to the target ; Or the radar output can be further processed to provide other information about the nature of the target . The radar controller ensures that different parts of the radar work together , For example, it gives different parts of the radar , Provide timing signals as required .
It is possible for radar engineers to provide good Doppler processing time 、 Provide bandwidth with good range resolution 、 External factors that affect radar performance include target characteristics, which provide space for large antennas and provide long-distance performance and accurately measured energy and other resources , External noise that may enter through the antenna , From the earth 、 ocean 、 Unwanted clutter echoes such as birds or rain , Interference from other electromagnetic radiation ; Propagation effects caused by the earth's surface and atmosphere . The volume factor here is to emphasize that they are very important in the design and application of radar .
notes ： The article is excerpted from 《 Radar manual 》 Volume 3