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Difference between DC/AC coupling (Antennas)

  1. Dec 13, 2016 #1
    Good evening everyone!
    Given that I have no experience in antenna physics or related areas, I'm studying a paper for a project I will be involved. It is an image sensor for THz e.m. waves and exploits micro-bowtie antennas to "capture" the signal and convert it through a standard CMOS imager.
    Now, some clever guys developed a sensor where at each pixel they engraved 2 bowtie antennas; one orthogonal to the other (like a cross) and in two different planes within a special substrate.
    According to what they wrote in the paper:

    For one polarization of the THz impinging radiation, the incident wave directly excites the longer bowtie antenna named “DC (direct coupling) Antenna”. For the crossed polarization, radiation is coupled via a lower stack level antenna: “CC (capacitive coupling antenna)”.

    I didn't find any explanation for this thing so I'm a little bit puzzled. If someone has familiarity with antenna-related stuff, please, I need you. ;)

    Enjoy your day! Bye
     
  2. jcsd
  3. Dec 13, 2016 #2

    tech99

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    It sounds as if the bow tie called DC is connected to the detector directly whilst the other one is coupled via some capacitance existing in the arrangement. This might be a cleaner physical layout than connecting both directly. The capacitive coupling might also be used to introduce some phase shift, which will be needed if it is desired to obtain circular polarisation.
     
  4. Dec 13, 2016 #3
    Mmm..very interesting..thank you so much. You helped me in understanding a little bit. For the DC coupling so far so good. For the other one, what do you mean that it could be a cleaner layout solution and that a phase shift could provide circular polarization? I don't see that thing of phase shift that you have in mind..
    In any case thank you a lot. I really appreciate.
     
  5. Dec 13, 2016 #4

    Merlin3189

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    I wonder if you could give a few more clues?
    A link to the paper would be great, but assuming that is not possible, the names of the authors and full title would help us to search for references.
     
  6. Dec 14, 2016 #5

    tech99

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    Regarding a cleaner layout. If you try to connect two bow ties together, it is very crowded and the effect on performance is unknown. On the other hand, if If one of the bow ties is just positioned nearby and coupled via capacitance, that is easy to do.
    Regarding phase shift. Suppose the DC bow tie is vertical, so it responds to vertical polarisation. Now suppose the other is horizontal - it responds to horizontal polarisation. But I imagine you would like something which responds to linear polarisation at any angle. If you connect the two bow ties together, it now responds to polarisation at 45 degrees. But if you give one of them a 90 degree phase shift, it gives circular polarisation and the array responds to any plane of linear polarisation.
     
  7. Dec 14, 2016 #6
    This is a link to the paper, but unfortunately it is not readable unless you have access to SPIE library:
    http://doi:10.1117/12.974970 [Broken]
     
    Last edited by a moderator: May 8, 2017
  8. Dec 14, 2016 #7
    @Merlin3189 here also is a snapshot from the article. Hope it could help!
     

    Attached Files:

  9. Dec 14, 2016 #8

    tech99

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    Very hard to work out the various layers.
     
  10. Dec 14, 2016 #9

    Tom.G

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  11. Dec 15, 2016 #10

    tech99

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    This seems to describe a detector having a resistive bolometer film above a reflector but with no dipoles.
     
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