Description
Primary radar operation is based on the principle of echolocation. Electromagnetic pulses of high power emitted by the radar antenna are converted into a narrow wavefront which propagates at the speed of light (300 000 km/s). This is reflected by the aircraft and then picked up again by the rotating antenna on its own axis. A primary radar detects all aircraft without selection, regardless of whether or not they possess a transponder. [1]
The operator hears the echoes from any reflection. Therefore, it performs transmission/listening continuously, which covers the space 360 °. The primary radar functions, therefore, results in detection and measurements of position if there is the presence of a target by the recognition of the useful signal.
A primary radar measurement include:
- the distance D based on the wave transit time on the path to / from;
- an angle θ based on the position of a directional antenna in azimuth;
- radial velocity using the Doppler effect.
It can be said that a radar locates a flying object on a quarter circle in the vertical plane, but cannot know exactly its altitude if it is using a fan-beam antenna. This information must be obtained by triangulation of several radars in that case. However, with a 3D radar this data is obtained by using either a cosecant squared pattern [2] or a scanning on multiple angles with a pencil beam. [3]
Usage
The rapid wartime development of radar had obvious applications for air traffic control (ATC) as a means of providing continuous surveillance of air traffic disposition. Precise knowledge of the positions of aircraft would permit a reduction in the normal procedural separation standards, which in turn promised considerable increases in the efficiency of the airways system.
This type of radar (now called a primary radar) can detect and report the position of anything that reflects its transmitted radio signals including, depending on its design, aircraft, birds, weather and land features. For air traffic control purposes this is both an advantage and a disadvantage. Its targets do not have to co-operate, they only have to be within its coverage and be able to reflect radio waves, but it only indicates the position of the targets, it does not identify them.
When primary radar was the only type of radar available, the correlation of individual radar returns with specific aircraft typically was achieved by the controller observing a directed turn by the aircraft. Primary radar is still used by ATC today as a backup/complementary system to secondary radar, although its coverage and information is more limited. [4] [5] [6]
Radar is a system that uses radio waves to determine the distance (ranging), direction, and radial velocity of objects relative to the site. It is a radiodetermination method used to detect and track aircraft, ships, spacecraft, guided missiles, motor vehicles, map weather formations, and terrain.
Radio navigation or radionavigation is the application of radio frequencies to determine a position of an object on the Earth, either the vessel or an obstruction. Like radiolocation, it is a type of radiodetermination.
A pulse-Doppler radar is a radar system that determines the range to a target using pulse-timing techniques, and uses the Doppler effect of the returned signal to determine the target object's velocity. It combines the features of pulse radars and continuous-wave radars, which were formerly separate due to the complexity of the electronics.
As defined by FS-1037C and ITU Radio Regulations, radiodetermination is:
the determination of the position, velocity or other characteristics of an object, or the obtaining of information relating to these parameters, by means of the propagation properties of radio waves
Radiolocation, also known as radiolocating or radiopositioning, is the process of finding the location of something through the use of radio waves. It generally refers to passive uses, particularly radar—as well as detecting buried cables, water mains, and other public utilities. It is similar to radionavigation, but radiolocation usually refers to passively seeking a distant object rather than actively finding one's own position; both are types of radiodetermination. Radiolocation is also used in real-time locating systems (RTLS) for tracking valuable assets.
Secondary surveillance radar (SSR) is a radar system used in air traffic control (ATC), that unlike primary radar systems that measure the bearing and distance of targets using the detected reflections of radio signals, relies on targets equipped with a radar transponder, that reply to each interrogation signal by transmitting encoded data such as an identity code, the aircraft's altitude and further information depending on its chosen mode. SSR is based on the military identification friend or foe (IFF) technology originally developed during World War II; therefore, the two systems are still compatible. Monopulse secondary surveillance radar (MSSR), Mode S, TCAS and ADS-B are similar modern methods of secondary surveillance.
Precision approach radar orPAR is a type of radar guidance system designed to provide lateral and vertical guidance to an aircraft pilot for landing, until the landing threshold is reached. Controllers monitoring the PAR displays observe each aircraft's position and issue instructions to the pilot that keep the aircraft on course and glidepath during final approach. After the aircraft reaches the decision height (DH) or decision altitude (DA), further guidance is advisory only. The overall concept is known as ground-controlled approach (GCA), and this name was also used to refer to the radar systems in the early days of its development.
The air traffic control radar beacon system (ATCRBS) is a system used in air traffic control (ATC) to enhance surveillance radar monitoring and separation of air traffic. It consists of a rotating ground antenna and transponders in aircraft. The ground antenna sweeps a narrow vertical beam of microwaves around the airspace. When the beam strikes an aircraft, the transponder transmits a return signal back giving information such as altitude and the Squawk Code, a four digit code assigned to each aircraft that enters a region. Information about this aircraft is then entered into the system and subsequently added to the controller's screen to display this information when queried. This information can include flight number designation and altitude of the aircraft. ATCRBS assists air traffic control (ATC) surveillance radars by acquiring information about the aircraft being monitored, and providing this information to the radar controllers. The controllers can use the information to identify radar returns from aircraft and to distinguish those returns from ground clutter.
A transponder landing system (TLS) is an all-weather, precision landing system that uses existing airborne transponder and instrument landing system (ILS) equipment to create a precision approach at a location where an ILS would normally not be available.
An airport surveillance radar (ASR) is a radar system used at airports to detect and display the presence and position of aircraft in the terminal area, the airspace around airports. It is the main air traffic control system for the airspace around airports. At large airports it typically controls traffic within a radius of 60 miles (96 km) of the airport below an elevation of 25,000 feet. The sophisticated systems at large airports consist of two different radar systems, the primary and secondary surveillance radar. The primary radar typically consists of a large rotating parabolic antenna dish that sweeps a vertical fan-shaped beam of microwaves around the airspace surrounding the airport. It detects the position and range of aircraft by microwaves reflected back to the antenna from the aircraft's surface. The secondary surveillance radar consists of a second rotating antenna, often mounted on the primary antenna, which interrogates the transponders of aircraft, which transmits a radio signal back containing the aircraft's identification, barometric altitude, and an emergency status code, which is displayed on the radar screen next to the return from the primary radar.
A transponder is an electronic device that produces a response when it receives a radio-frequency interrogation. Aircraft have transponders to assist in identifying them on air traffic control radar. Collision avoidance systems have been developed to use transponder transmissions as a means of detecting aircraft at risk of colliding with each other.
Sensitivity time control (STC), also known as swept-gain control, is a system used to attenuate the very strong signals returned from nearby ground clutter targets in the first few range gates of a radar receiver. Without this attenuation, the receiver would routinely saturate due to the strong signals. This is used in air traffic control systems and has an influence on the shape of the elevation pattern of the surveillance antenna. It is represented in terms of numerical value typically expressed in decibels (dB), starting from zero, indicating that there is no muting and that the radar system is accepting all returns.
Squitter refers to random pulses, pulse-pairs and other non-solicited messages used in various aviation radio systems' signal maintenance. Squitter pulses were originally, and are still, used in the DME/TACAN air navigation systems. Squitter pulses, because of their randomness and identical appearance to standard reply pulse-pairs, appear the same as unsolicited/unsynchronised replies to other interrogating aircraft.
Radio is the technology of communicating using radio waves. Radio waves are electromagnetic waves of frequency between 3 hertz (Hz) and 300 gigahertz (GHz). They are generated by an electronic device called a transmitter connected to an antenna which radiates oscillating electrical energy, often characterized as a wave. They can be received by other antennas connected to a radio receiver, this is the fundamental principle of radio communication. In addition to communication, radio is used for radar, radio navigation, remote control, remote sensing, and other applications.
ASR-11 is a Digital Airport Surveillance Radar (DASR,) an advanced radar system utilized by the United States as the next generation of terminal air traffic control. The ASR-11 is an upgraded, advanced version of the previous ASR-9 radar. This next generation radar system has been developed through a joint effort by the Federal Aviation Administration, the Department of Defense and the United States Air Force, who took most of the lead development tasks.
Automatic Dependent Surveillance–Broadcast (ADS-B) is an aviation surveillance technology and form of electronic conspicuity in which an aircraft determines its position via satellite navigation or other sensors and periodically broadcasts its position and other related data, enabling it to be tracked. The information can be received by air traffic control ground-based or satellite-based receivers as a replacement for secondary surveillance radar (SSR). Unlike SSR, ADS-B does not require an interrogation signal from the ground or from other aircraft to activate its transmissions. ADS-B can also receive point-to-point by other nearby equipped ADS-B equipped aircraft to provide traffic situational awareness and support self-separation.
ASR-9 is an airport surveillance radar system admitted into the National Airspace System (NAS), to be utilized by the Federal Aviation Administration to monitor civilian and commercial air traffic within the United States. Developed by Westinghouse, ASR-9 was the first radar system to display air traffic, and weather conditions simultaneously. The ASR-9 is mainly intended to monitor and track aircraft below 25,000 ft and within forty to sixty nautical miles from the airport of operation. The ASR radar systems were widely used where an advanced radar system was needed, consisting of 135 different ASR-9 operating locations around the U.S. The FAA is currently working to upgrade the remaining ASR-9 radar sites to a modernized digital version known as the ASR-11.
The AMES Type 82, also widely known by its rainbow codename Orange Yeoman, was an S-band 3D radar built by the Marconi Company and used by the Royal Air Force (RAF), initially for tactical control and later for air traffic control (ATC).
The AR-3D was a military air traffic control and early warning radar developed by Plessey and first produced in 1975. It used a pencil beam and simple frequency scanning system known as "squint scan" to produce a low-cost 3D radar system that was also relatively mobile. About 23 were produced in total and found sales around the world into the early 1980s.
