The radar principle
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The radar principle
I know that radars work on the principle that send out pulses in a particular direction with the pulses being reflected back towards the antenna and the receiver by the aircraft. From what i have read, as only a fraction of the signal will be reflected the receiver it has to be very sensitive and therefore, frequency bands with as little noise as possible will be chosen (the region of 1-10 GHz is quite common).
Could anyone tell me what are the noisiest frequency bands? and are they the least sensitive?
Could anyone tell me what are the noisiest frequency bands? and are they the least sensitive?
Join Date: Aug 1999
Location: England
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Not really my area of expertise but I'll have ago until someone better comes along:
Same considerations as any other radio application:
What do you want to the signal to bounce off?
What do you want the signal to penetrate?
Do you want the signal to refract over the horizon / around objects or not?
Is the antenna size an issue? (antenna size, wavelength and beamwidth are related)
For weather radar we need to be able to paint droplets and have reasonable resolution / bearing accuracy. We need to be able to get a reasonably narrow beam from an antenna that will fit in the nose of an aircraft. We don't need to see over the horizon. We don't want the signal to be attenuated just by passing through atmosphere.
Put all those considerations together and a few gigahertz is the place to be. Go much higher and atmospheric attenuation starts kicking in. Go much lower and you need an unfeasibly large antenna.
I might be wrong, but I'm not sure noisy frequencies are too much of an issue. Modern signal processing is capable of dealing with tiny signal to noise ratios.
(finally as an aside radars are not exclusively pulse based. For some application (e.g. altimetry) continuous waves are more suitable).
Hope that's a starting point.
pb
Same considerations as any other radio application:
What do you want to the signal to bounce off?
What do you want the signal to penetrate?
Do you want the signal to refract over the horizon / around objects or not?
Is the antenna size an issue? (antenna size, wavelength and beamwidth are related)
For weather radar we need to be able to paint droplets and have reasonable resolution / bearing accuracy. We need to be able to get a reasonably narrow beam from an antenna that will fit in the nose of an aircraft. We don't need to see over the horizon. We don't want the signal to be attenuated just by passing through atmosphere.
Put all those considerations together and a few gigahertz is the place to be. Go much higher and atmospheric attenuation starts kicking in. Go much lower and you need an unfeasibly large antenna.
I might be wrong, but I'm not sure noisy frequencies are too much of an issue. Modern signal processing is capable of dealing with tiny signal to noise ratios.
(finally as an aside radars are not exclusively pulse based. For some application (e.g. altimetry) continuous waves are more suitable).
Hope that's a starting point.
pb
