Radar detects the moving object’s presence, distance, direction, and speed; as well as things that are stationary. In radar, the transmitter sends out microwaves, which are then reflected off the object and received by the receiver. As a result, the radar is able to detect the object.
Microwaves are electrical radiation with a frequency of 1GHz to 300GHz.The microwaves have a small wavelength, so they can be transmitted as a beam signal in the desired directions.
Microwaves, like other electromagnetic waves, travel in a straight line. When they collide with anything else, their path does not alter. The microwaves may reflect off of the thing, but they will not be altered in any way.
Why does Radar Use Radio Waves?
Microwaves are a form of electromagnetic waves that travel at the speed of light and have no mass. The high speed of electromagnetic waves is ideal for quickly travelling long distances to assess distant objects with minimal delay.
There are numerous various kinds of electromagnetic waves, such as infrared, X-rays, and visible light. For a variety of purposes, radio waves are utilized in radar:
- It is easy and inexpensive to construct radio waves using modern technology.
- The radio waves can penetrate fog, rain, mist, snow, and smoke..
- They cannot be confused with infrared energy produced by fire, heated surfaces, warm things, hot gas, or the sun.
- Radar does not require light to operate, thus it can be used in total darkness as well as intense sunlight without losing efficacy.
- Unlike X-rays or gamma rays, microwaves are non-ionizing, making them completely safe.
How are Radar Waves Generated?
Radio waves that are used by radar are created by a piece of equipment called a magnetron. The magnetron is a very high-powered vacuum tube and works as a self-excited microwave oscillator. The magnetron uses crossed electric and magnetic fields to generate the high-power output required in radar equipment.
In essence, typical radar is as follows: A Magnetron creates high-frequency radio waves. The magnetron is switched to the antenna via a duplexer. The antenna functions as a transmitter, sending out a narrow beam of radio waves through the air.
Radar Frequency Bands
Radars are instruments that use electromagnetic, or radio, waves to detect objects. Most objects reflect radio waves, which can be detected by a radar system. The radiated frequency of a radar system is determined by the purpose for which it’s being used. The wavelength or frequency band in which a radar system works is usually indicated using the band names shown in the table below.
| Radar Band Frequency (GHz) | Wavelength (cm) | Millimeter |
|---|---|---|
| Ka | 26.5–40 | 0.75–1.1 |
| K | 18–26.5 | 1.1–1.7 |
| Ku | 12.5–18 | 1.7–2.4 |
| X | 8–12.5 | 2.4–3.75 |
| C | 4–8 | 3.75–7.5 |
| S | 2–4 | 7.5–15 |
| L | 1–2 | 15–30 |
| UHF | 0.3–1 | 30–100 |
The frequency of an antenna is determined by the demands of the application. The smallest antenna size is inversely proportional to wavelength and directly proportional to frequency.
Airborne applications typically require a smaller antenna because of the small size of electronics within. A smaller antenna necessitates a higher frequency and lower wavelength choice.
Beamwidth, or the ability of a radar to concentrate radiated and received energy in a small area, is also determined by both antenna size and frequency selection. Larger antennas enable the beam to be more precisely focused. As a result, for a given antenna size, a higher frequency allows the beam to be more effectively concentrated.
The antenna’s “focusing” ability is frequently portrayed using an antenna lobe chart, which displays the directional gain of an antenna over the azimuth (side to side) and elevation (up and down).
The frequency of the radar system also has an impact. Because of electronic circuit limitations, higher-frequency systems are generally lower power and have greater atmospheric attenuation. In addition to the direct electrical noise that may harm the functioning of analog circuitry, higher frequencies produce greater ambient electrical noise. The majority of radar signal absorption and scattering is caused by oxygen and water vapor.
Water vapor has a high absorption in the “K” band. The frequency range where radar operations are limited by water vapor absorption was divided into Ka and Ku, with “above” and “under,” respectively, for the frequencies where radio waves would be absorbed by water. Oxygen has the same effect at higher frequencies in the millimeter band, causing absorption and scattering.
Another point to consider is the influence of the radar operating frequency on Doppler frequency measurements. The relative velocity and radar frequency have an inverse relationship, which means that Doppler frequency changes are proportional to both the relative speed and the radar frequency. Doppler frequencies may be used by radars to acquire important data.
Almost all airborne radars operate in the L and Ka bands, also known as the microwave region. Many short-range targeting radars, such as those on a tank or aircraft, use the millimeter band.
Long-range ground-based radars operate at higher frequencies, due to the use of large antennas and low atmospheric attenuation and ambient noise. The ionosphere may become reflective at even lower frequencies, allowing over-the-horizon radar operation up to hundreds or thousands of kilometers long.