Question about RF absorbers and radar

  1. Hi everyone , new to forum, but not new to forums. I am a radar detector hobbyist and have some knowledge of how radar works. Specifically and to be on point and productive, here's my question(s):

    First, are there any materials readily available to general consumers that will readily absorb X, K and Ka band radar? For example, I am looking for a material such as a flexible foam or sheet material that will absorb 33.8, 34.7 and 35.5 ghz radar ? Ka is considered wide band and X and K are less wide. I have searched and done my homework, but many of the foams only absorb a certain band of K Or Ka radar. They don't do the whole spectrum. Eccosorb is one such material.

    Second, regarding a radar horn ( receiver) , would it be possible and/or beneficial to either polish the interior of the horn with a Dremel to reduce attenuation of the signal the horn receives OR gold plate the interior of the horn to retain the signal captured. Thoughts? I am not an EE and just a hobbyist with some questions. Thanks in advance.
     
  2. jcsd
  3. Student100

    Student100 764
    Education Advisor
    Gold Member

    Hey, how does this look?

    I wouldn't mess with the horn.
     
  4. davenn

    davenn 3,981
    Science Advisor
    Gold Member
    2014 Award

    nice stuff
    I dread to think what the price per metre2 would be tho

    cheers
    Dave
     
  5. Thanks for the link, looks good. I wonder if it'll absorb higher Ghz such as Ka 33 .8/34.7/35.5?

    The reason I ask is nearly 30 years ago a guy from CO developed a car bra that absorbed radar and I was wondering if it would work. He covered the mirrors and the front of the car.

    As far as the horn, from the factory they are not terribly polished/finished . I understand that a smooth surface transfers RF better than an unfinished one. Is this accurate?
     
  6. Baluncore

    Baluncore 3,040
    Science Advisor

    You will also need to install a thick radar absorbent windscreen to hide the seats and your head.

    As an anarchist, you might consider driving more slowly to save fuel and speeding tickets.
    That will bring the Government down by reducing revenue from speeding fines.
     

  7. Seemed to work for this guy:http://youtu.be/9E-14fIoa7A
     
  8. Baluncore

    Baluncore 3,040
    Science Advisor

    Sorry, but I do not have bandwidth sufficient for youtube at my end of the Earth.
     
  9. sophiecentaur

    sophiecentaur 14,170
    Science Advisor
    Gold Member

    Absolutely. Speed is a decision we make.
     

  10. More on topic, any thoughts from an experienced EE about the horn and polishing it to make it smoother and can it possibly make a difference?
     
  11. Baluncore

    Baluncore 3,040
    Science Advisor

    Polishing is quite unnecessary.

    If the surface errors are less than one tenth of the wavelength, then they will not be visible to the radiation, so at that wavelength it will appear to be a mirror.
     
  12. marcusl

    marcusl 2,138
    Science Advisor
    Gold Member

    Do not touch the horn. Assuming it is from a commercial supplier, it will have been designed and tested to work properly. At Ka band, removing just 0.5 mm from each wall changes the dimensions by 0.1 wavelength--enough to change the performance. Nothing a non-pro (hobbyist) has the skills for will improve performance, while many many things will degrade it.

    If you want to maximize performance, use a high-gain horn (which, however, will have a smalll field of view) and choose a receiver/detector with lowest noise figure and best sensitivity. These are often traded off against cost for products like radar detectors where competition is fierce and selling price is important.

    BTW, your horn will reflect microwaves back to the transmitter, defeating much of the benefit of foam. This is a general property of antennas. Your vehicle will be stealthier with no radar receiver at all...
     
  13. Baluncore

    Baluncore 3,040
    Science Advisor

    This is quite true. Any mismatch at the mixer's RF port will reflect incident RF.

    But there is another way to use a horn, and it takes advantage of the reflection feature. If instead of driving the mixer diode with RF you drive it with a square-wave audio frequency, then the horn can be made to switch between reflect and absorb and so modulate the reflected wave with that audio frequency. When that frequency enters the observers receiver it will be detected and interpreted as a strong doppler component, masking your real speed. The receiver will search for the maximum doppler frequency present in-band and find your generated audio doppler frequency. If you calculate it right, to give say 250 km/h, it will be obvious that something is wrong with their equipment. If that audio was moved every two seconds by say 50 km/h then it will confuse the operator even more. Don't forget that you will need to select different audio frequencies for different microwave bands, which will require multiple tuned cavities, or multiple horns.

    As it does not involve actively transmitting microwave radiation it would be undetectable. It may even be legal in some places. It explains why the police here now measure differential reflection time from speeding vehicles with an infra-red laser.
     
  14. sophiecentaur

    sophiecentaur 14,170
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    Tricky li'l devil, ain't you MrB?
     
  15. marcusl

    marcusl 2,138
    Science Advisor
    Gold Member

    It is actually true regardless of match. A matched antenna will reflect no less than 50% of the power incident on it. A well-designed and perfectly matched antenna achieves 50% and is called a "minimally scattering antenna," while a more poorly designed but perfectly matched antenna will reflect more than 50%.

    This will not, of course, adversely affect your clever spoofer. This device modulates the reflection with a chirp to confuse the police radar
    http://www.radarscramblers.com/faq.htm
     
  16. Baluncore

    Baluncore 3,040
    Science Advisor

    I do not believe that is true of all antennas.

    Full article is at: http://vbn.aau.dk/files/19704710/absorption_efficiency.pdf
     
  17. marcusl

    marcusl 2,138
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    Gold Member

    Thank you for that reference, Baluncore. I was familiar only with the older literature that this article refutes.
     
  18. berkeman

    Staff: Mentor

    Welcome to the PF.

    Unfortunately, we do not allow discussions of illegal activities. What you are asking about is illegal in many places. Thread is closed.
     
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