Shipborne Applications. Physical size becomes a limiting factor aboard ships for many applications including radar systems. While at the same time, the ship's requirement to operate in various types of weather conditions puts a constraint on the upper portions of the radio frequency spectrum that may be used.
This limit is eased somewhat where extremely long ranges are not required. Higher frequencies are usually employed when operating against surface targets and targets at low elevation angles, such as sea-skimming missiles.
The radar return received directly from targets at very low elevation angles are very nearly canceled by the return from the same target reflected off the water multipath propagation.
This cancellation is due to a phase reversal occurring when the return is reflected. As the elevation angle increases, this multipath propagation problem decreases. This multipath problem decreases at higher frequencies. For this reason, the short wavelengths of the 2. Airborne Applications. In an aircraft, the housing limitations of radars are more severe than on ships. Frequencies in the MHz and GHz bands are the lowest frequency bands where aircraft radars operate. These bands provide the long detection ranges required by military airborne early warning aircraft and their antennas are very large to provide the desired angular resolution.
Above these bands, the next application are radar altimeters using the MHz band. Airborne weather radars, which require greater directivity, operate in 5. If there is too much scattering, the radar will not penetrate deeply enough into the storm to see its full extent.
However, if too little energy is scattered back to the radar, the storm will not be visible on the radar scope. The larger aircraft use 5. The majority of smaller aircraft employ lighter weight 8. The majority of military fighter aircraft have attack and reconnaissance radars operating in the 8. This upper portion of the 8. Frequencies above the 8. Aircraft radars operating in the GHz band are used for ground search functions and for terrain following and terrain avoidance.
Spaceborne Applications. In a space platform, the power and space limitations for radar systems are most severe. Considering the limited power available on space platforms and the availability of small radar components make radars operating in the UHF and above frequency ranges a better choice. For spaceborne surveillance radars, the frequencies from GHz would be good choices.
Spaceborne altimeters generally use frequencies in the GHz band while scatterometers generally use frequencies between GHz. Frequencies around the GHz band is where precipitation radars generally operate. Endnotes: Chapter 3. Its band boundaries are adapted to the technologies and measurement possibilities in the different frequency ranges.
They are almost logarithmically distributed and the system is open to the high frequencies. In this system, further frequency bands up to the terahertz range can easily be defined in the future. This designation system is also of military origin and is a band division for the electronic war, in which radar equipment finally occupies an essential place.
Since an assignment into the new frequency bands is not always possible without the exact frequency being known, I made use of the traditional band names without comment where they were mentioned in the manufacturer's publications. But be careful! In Germany, for example, companies still use old band names. The frequencies of radar sets today range from about 5 megahertz to about gigahertz ,,, oscillations per second!
However, certain frequencies are also preferred for certain radar applications. Very long-range radar systems usually operate at lower frequencies below and including the D-band. These radar bands below MHz have a long tradition, as the first radar sets were developed here before and during the 2nd World War.
The frequency range corresponded to the high-frequency technologies mastered at that time. Since the accuracy of angle determination and the angular resolution depends on the ratio of wavelength to antenna size, these radars cannot meet high accuracy requirements. The antennas of these radar sets are nevertheless extremely large and can even be several kilometers long.
Here special abnormal propagation conditions act, which increase the range of the radar again at the expense of the accuracy. Since these frequency bands are densely occupied by communication radio services, the bandwidth of these radar sets is relatively small.
These frequency bands are currently experiencing a comeback, while the actually used Stealth technologies don't have the desired effect at extremely low frequencies. These frequencies are damped only very slightly by weather phenomena and thus allow a long-range. Newer methods, so-called ultrawideband radars , transmit with very low pulse power from the A to the C band and are mostly used for technical material investigation or partly in archaeology as Ground Penetrating Radar GPR. Relatively low interference from civil radio communication services enables broadband radiation with very high power.
They transmit pulses with high power, wide bandwidth and an intrapulse modulation to achieve even longer ranges. Due to the curvature of the earth, however, the range that can be practically achieved with these radar sets is much smaller at low altitudes, since these targets are then obscured by the radar horizon.
L-band: like large antenna and long-range. The designator L -Band is good as mnemonic rhyme as l arge antenna or l ong range. In the frequency band from 2 to 4 GHz the atmospheric attenuation is higher than in the D-band.
Radar sets require a much higher pulse power to achieve long-ranges. In this frequency band, considerable impairments due to weather phenomena are already beginning to occur. An ASR detects aircraft position and weather conditions in the vicinity of civilian and military airfields. For example, a Doppler radar transmits a signal that gets reflected off raindrops within a storm.
The reflected radar signal is measured by the radar's receiver with a change in frequency. That frequency shift is directly related to the motion of the raindrops. When a storm is moving towards the radar, the transmitted wavelength's frequency will be lower than the reflected wavelength frequency. Atmospheric scientists use different types of ground-based and aircraft-mounted radar to study weather and climate.
Radar can be used to help study severe weather events such tornadoes and hurricanes, or long-term climate processes in the atmosphere. Continuously modified and improved, this state-of-the-art radar system now includes dual-wavelength capability. When the Ka-band is added, a 0. Airborne Research Radar In the air, research aircraft can be outfitted with an array of radars.
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