http://defensetech.org/2006/08/03/undetectable-radar-probably-not/ The Future of the Military, Law Enforcement and National Security Fri, 10 Feb 2012 10:25:29 +0000 hourly 1 http://wordpress.org/?v=3.3.1 http://defensetech.org/2006/08/03/undetectable-radar-probably-not/#comment-134810 Dr. Renato D'Antonio Thu, 31 Jan 2008 17:39:04 +0000 http://deftech.usmilblog.com/?p=2076#comment-134810 rutty comments that "Noise, by definition, has infinite bandwidth". This is only true for "white" noise which does not exist. Non-white noise is called "Pink" noise and is band-limited. The basic problem with Pink noise is that it has high correlation sidelobes when compared to, say, "chirp" pulses. If there are any large companies in the Radar or Sonar business, I have solved the problem of turning Pink noise into Almost White noise having correlation sidelobes of -100 dB. Please contact me at radson@verizon.com for licensing information. rutty comments that “Noise, by definition, has infinite bandwidth”. This is only true for “white” noise which does not exist. Non-white noise is called “Pink” noise and is band-limited.
The basic problem with Pink noise is that it has high correlation sidelobes when compared to, say, “chirp” pulses. If there are any large companies in the Radar or Sonar business, I have solved the problem of turning Pink noise into Almost White noise having correlation sidelobes of –100 dB. Please contact me at radson@verizon.com for licensing information.

]]> http://defensetech.org/2006/08/03/undetectable-radar-probably-not/#comment-134809 rutty Fri, 04 Aug 2006 00:31:45 +0000 http://deftech.usmilblog.com/?p=2076#comment-134809 "Typical radar signals are high-power, narrowly focused "chirps;" not because they sound like birds, but because each signal is extremely short" Actually, they are called chirp signals because they are linearly frequncy modulated just like a chirp you would here from a bird. LFM signals are popular because they have a high pulse compression ratio, meaning that you can compress a long duration signal into a 'short duration' signal, typically using a matched filter or what is known as 'deramping'. The width to which a pulse compress is a direct function of its RF bandwidth (0.886 * speedOfLight / 2 / bandwidth to be exact). Transmitted bandwidth, however, in LFM systems is a function of two things: the chirp rate and the pulse length. So the short pulse asumtpion is not correct either. It may sound counter intuitive, but the a longer pulse will have a finer resolution than on half as long if the chirp rates are equal. (Google 'chirp matched filters' for more easy-to-find info.) The length of the chirp chose for a given system, like all things in engineering, depends on many things (SNR requirements and transmit power, for example) and will be tradeoff to meet design requirements. "To detect these radar signals, an adversary can simply sweep his field of view searching for high-powered pulses that are narrowly focused at a single frequency." Single frequency radars (most likely continuous wave) are not the most common. Most have bandwidth for the reason outlined above. I'm not sure what you mena by 'leak sideways'. The beampatern is function of the shape of the antenna amongst other things. Noise, by definition, has infinite bandwidth. "The wide band of frequencies has several advantages. Different frequencies interact with different materials in different ways “Typical radar signals are high-power, narrowly focused “chirps;” not because they sound like birds, but because each signal is extremely short“
Actually, they are called chirp signals because they are linearly frequncy modulated just like a chirp you would here from a bird. LFM signals are popular because they have a high pulse compression ratio, meaning that you can compress a long duration signal into a ‘short duration’ signal, typically using a matched filter or what is known as ‘deramping’. The width to which a pulse compress is a direct function of its RF bandwidth (0.886 * speedOfLight / 2 / bandwidth to be exact). Transmitted bandwidth, however, in LFM systems is a function of two things: the chirp rate and the pulse length. So the short pulse asumtpion is not correct either. It may sound counter intuitive, but the a longer pulse will have a finer resolution than on half as long if the chirp rates are equal. (Google ‘chirp matched filters’ for more easy-to-find info.) The length of the chirp chose for a given system, like all things in engineering, depends on many things (SNR requirements and transmit power, for example) and will be tradeoff to meet design requirements.
“To detect these radar signals, an adversary can simply sweep his field of view searching for high-powered pulses that are narrowly focused at a single frequency.“
Single frequency radars (most likely continuous wave) are not the most common. Most have bandwidth for the reason outlined above. I’m not sure what you mena by ‘leak sideways’. The beampatern is function of the shape of the antenna amongst other things.
Noise, by definition, has infinite bandwidth.
“The wide band of frequencies has several advantages. Different frequencies interact with different materials in different ways

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