What Is a Tracking Radar?
Tracking radar is a radar that can continuously track a target and measure target coordinates. It can also provide the trajectory of the target.
Radar tracking
discuss
- Chinese name
- Radar tracking
- English name
- radar tracking
- definition
- The movement of a specific aircraft is tracked by a manual or computer of the radar to ensure continuous indication of the aircraft's identification, position, track and altitude.
- Applied discipline
- Aeronautical technology (level 1 discipline), navigation and air traffic management (level 2 discipline)
- Chinese name
- radar
- Foreign name
- radar
- Tracking radar is a radar that can continuously track a target and measure target coordinates. It can also provide the trajectory of the target.
- The above content was published by the National Science and Technology Terminology Examination Committee.
- A radar that continuously tracks a target and measures its coordinates. It can also provide the trajectory of the target. Tracking radar generally consists of a range tracking branch, an azimuth tracking branch and an elevation tracking branch. They each complete the automatic tracking of the distance, azimuth, and elevation of the target, and continuously measure the distance, azimuth, and elevation of the target. The coherent pulse Doppler tracking radar also has the capability of Doppler frequency tracking and can measure the radial velocity of the target. The tracking radar's automatic tracking of the target's azimuth and elevation angle means that the radar antenna continuously changes its direction following the movement of the target, so that the electrical axis of the antenna always points at the target. To achieve this follow-up process, a closed-loop feedback control needs to be established between the radar and the target. When the radar automatically tracks a target, the instantaneous movement of the target to a new position deviates from the electrical axis of the antenna, and an angle is generated between the target and the antenna's electrical axis, which is called an angular error. The angular error causes the antenna system to have an error signal output. The receiver amplifies and transforms the error signal and sends it to the input of the antenna's azimuth and elevation drive amplifiers. After power amplification, the azimuth and elevation drive motors are controlled to change the antenna electrical axis orientation Aim the antenna axis to the target. This is the automatic tracking process of the radar's angular coordinates of the target, including the extraction of angular error information, error signal processing, and control of the antenna's electrical axis pointing. Tracking radars have different angle measurement systems or types due to different methods of extracting angle error information. Automatic distance tracking is based on the principle of comparing the time difference between the target echo pulse and the ranging gate (the time difference has a strict correspondence with the distance difference). After comparing the time difference, the ranging gate can be controlled to move to the target echo distance, that is, the distance tracking of the target is completed. The development of tracking radar originated from the need for artillery aiming control. The earliest radar used for artillery targeting was the hand-controlled tracking radar SCR-268 developed by the US Army Communications Team in 1938. It uses the beam conversion method to measure the angle, and the angle measurement error is about 1 °. This radar was used until the end of World War II. In 1944, the United States' new microwave gun sighting automatic tracking radar SCR-584 was put into use, using a conical scanning angle measurement system, and the angular tracking error (root mean square) was about 2 dense bits. Improving the accuracy of angular tracking is the main subject of research on tracking radar. As early as 1940, the U.S. Naval Laboratory has begun to study a new angle measurement system-the simultaneous lobe method, later known as the single pulse method. The single pulse method can completely determine the angular position of the target in an echo pulse, and it can also eliminate the angle measurement error caused by the change of the target cross-sectional area. From 1947 to 1948, the monopulse tracking radar was used in the control of ground missiles and airborne artillery. However, the representative single-pulse precision tracking radar is AN / FPS-16, a range measurement radar developed by the American Radio Corporation in 1956. Its angular tracking error (root mean square) is 0.1 to 0.2 mils. In the late 1960s, some countries began to study coaxial tracking technology. Coaxial tracking technology uses accurate static and dynamic calibration, advanced data processing methods and adaptive tracking technology to improve radar measurement accuracy. In 1980, the United States built a re-entry multi-station measurement system at the Kwajalein shooting range, improving the position accuracy of the re-entry measurement to better than 4 meters, and the accuracy of 3D Doppler velocity measurement was better than 0.1 meters / second. The development of China's tracking radar technology is roughly divided into two phases. In the 1950s, gun-sight radars and airborne interception radars, which were modeled after the conical scanning system, began to study monopulse technology in the late 1950s. The first microwave composite comparator was developed from 1960 to 1961, which promoted the realization of the single-pulse antenna. In 1963, the first single-pulse system test radar was successfully developed, and subsequently single-pulse tracking radars for various purposes were successively developed. The application of tracking radar is increasing. Not only is it used in various artillery control, missile guidance, external ballistic measurement, satellite tracking, penetration technology research and other military departments; moreover, it is increasingly used in meteorology, transportation, scientific research and other fields. Types of tracking radars are classified according to the angle-measuring system. There are three types of beam-shifting methods, cone scanning methods, and monopulse methods. The main difference between them is the method of extracting angular error information. Beam conversion method: The principle of angle measurement is to change the position of the spatial beam and compare the amplitudes of the corresponding echo pulses received at the two beam positions (Figure 1) in the same coordinate plane to extract the angular error of the target. The magnitude of the amplitude difference between the two echo pulses is proportional to the angular error, and the sign of the amplitude difference indicates the direction in which the target deviates. The position of the spatial beam is generally controlled by the beam switching switch turning on the four feed sources of the antenna one by one in a certain order. The four feed sources are arranged up and down and left and right, and four beams are formed at different times, and each beam position completes the transmission and reception of signals. The upper and lower beams extract the elevation error information of the target; the left and right beams extract the azimuth error information. Some radars use five antenna feeds. At this time, the middle feed completes the signal transmission, and the four surrounding feeds receive the time-sharing signal. The advantage of the beam conversion method is that the beam conversion switch can not withstand high power. Cone scanning method: Generate a continuously rotating scanning beam to extract the angular error information of the target. There is a fixed angle between the maximum direction of this scanning beam and the axis of rotation. The scanning trajectory of the beam centerline (maximum direction) is a conical surface, so it is called conical scanning. If the target position deviates from the rotation axis (electrical axis of the antenna), the amplitude of the received echo signal is modulated by the beam scan to form an amplitude-modulated error signal. The modulation frequency is the cone scanning frequency. The degree of modulation is proportional to the angular error, and the phase is determined by the target deviation direction. Therefore, the amplitude modulation error signal formed during beam scanning includes all the information of the target angle error. The error signal output from the antenna of the cone scanning tracking radar (Figure 2) is amplified and detected by the receiver and sent to the azimuth and elevation angle error phase detectors. The reference signals of the error phase detectors are the same frequency (cone scan frequency) and phase. Quadrature sine and cosine signals. The output of the phase detector is the azimuth and elevation angle error signals. After the power is amplified, the antenna is controlled to rotate, so that the electrical axis of the antenna moves in the direction of reducing the angle error. The function of the automatic gain control circuit is to complete the normalization of the error signal, so that the magnitude of the azimuth and elevation angle error signals output by the error detector is proportional to the angular error of the target, and has nothing to do with the distance of the target and the size of the reflection section. Single-pulse method: According to different methods of extracting angular error information, it can be divided into two kinds of phase comparison method and amplitude comparison method. The more widely used are the amplitude comparison method and differential single pulse proposed by RM Becky. In this method, two pairs of interlaced beams are simultaneously formed on two coordinate planes of azimuth and elevation, one pair measures the azimuth error, and the other measures the elevation angle error. This staggered four beams can be achieved by four feed horns shining on the same reflector (or lens). The input ends of the feed horn are respectively connected to the input arms of the double T network, and the difference arms of the double T network form an azimuth difference beam and an elevation angle difference beam, respectively. The difference beam is obtained by subtracting two interlaced beams, so it has an oddly symmetric pattern. The intersection of two beams of equal amplitude forms the zero point of the difference beam. No error signal is output when the target is in the direction of the zero point of the differential beam, and an error signal is output when the target is in the direction of the zero point. The magnitude of the error signal is proportional to the angular error of the target deviation, and the polarity depends on the direction of the deviation. The pattern of the differential beam is the error voltage characteristic curve. Figure 3 is a block diagram of the monopulse radar angle measurement principle. The antenna adopts the five-speaker Cassegrain type (see reflective surface antenna), the middle horn is formed and the beam, and the echo signal that emits RF energy to illuminate the target and receive the target is sent to the distance tracking branch, and the phase detector for the angle tracking branch Provide a reference signal. The four horns around each form an azimuth difference beam and an elevation angle difference beam, respectively. There are three receivers: He branch, elevation difference branch, and azimuth difference branch. In order to ensure the phase consistency between the branch and the branch, the three paths share a local oscillator. The elevation and azimuth error signals output by the phase detector control the servo drive motor to make the antenna point to follow the target movement. The three receive channels of a monopulse radar greatly increase the complexity. To simplify the system structure, the receiver uses single or dual receive channels. The disadvantage of this system is that there is cross coupling between the azimuth and elevation branches, which reduces the accuracy of radar angle measurement. The angular tracking accuracy of a tracking radar is limited by many error factors, among which are mainly tracking noise errors, including target noise, servo noise, and receiver thermal noise. Target noise includes target amplitude fluctuation noise and angular flicker noise. In the range auto-tracking radar, almost all of the range auto-tracking adopts the split gate method. The ranging gate is a pair of adjacent gates. When the center of the video pulse of the target echo signal does not coincide with the center of the split gate, the comparison circuit in the ranging system, the time discriminator, will output an error signal, control the delay of the split gate, and make the center of the split gate Quasi-target echo video pulse center. At this time, the distance corresponding to the center of the split gate is the distance of the target. The distance tracking system is divided into electromechanical, electronic analog and digital according to its physical structure. With the development of digital technology, digital distance tracking systems are showing more and more advantages. Speed tracking In tracking radar, the principle of speed tracking is the same as pulse Doppler radar, which detects the frequency difference between the transmitted signal and the target echo signal. Speed tracking can not only measure the radial speed of the target in real time, but also perform coherent accumulation processing on the distance and angle tracking branches to extend the radar tracking distance and increase the radar's speed resolution capability.