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a log periodic antenna shown In the diagram shown bellow. As you can see there are reflective region and non radiative region. there are phase shift of 180 degrees between neighbor "wings". I have read that the not radiative region is not radiative because it hase capcitative profile. I can see why it has capacitate profile? And why a capacitative profile doesnt allow us to radiate? Same this for the reflecting region,its says that its reflective because its an inductive profile. why inductive profile reflects the wave? Thanks.

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These are "parasitic reflectors" or "parasitic elements." They receive and reradiate the emissions from the active elements. This does not add to the power output, of course, but the 360 degree round trip between elements causes them to reinforce and concentrate along the length of the antenna. (The same thing happens on receive, but the power is coming from the remote antenna.)

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  • \$\begingroup\$ Hello, The question is why its capacitave? and not allowing to radiate? why the other side it inductive and reflects. I am trying to understand the physical intuition for this words. \$\endgroup\$
    – rocko445
    Mar 30, 2021 at 19:50
  • \$\begingroup\$ Hello,Can i have an intuition regarding how exactly we get a constructive sum in the main direction? capacitative part make -90 degrees phase inductive part make +90 degrees phase so how they make 360 degrees in phase? Thanks. \$\endgroup\$
    – rocko445
    Mar 31, 2021 at 14:29
  • \$\begingroup\$ They're spaced about half a wavelength apart in the target band. The variable width is so there's parasitic elements tuned across the band...the narrower the band, the more rectangular the antenna...and you'll probably see the spacings follow suit. The distance to the active elements will be n*180 degrees at the target frequency. Therefore the signal to the active element(s) will induce a signal in the passive elements which is either in phase or 180 degrees out of phase with itself. When you look at all these elements as (re)radiators, they are all in phase in the direction of the axis. \$\endgroup\$ Apr 6, 2021 at 15:30

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