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Here is an image of a WiFi yagi antenna I bought recently (and opened up for I could see no spectrum out of my SDR)Yagi Antenna Image

I see that the coax has been connected to two plates, which I think act as dipoles. But they are insulated from the rest of the frame. Is this normal (shouldn't the dipole be in contact with the rest of the frame), or is it just dismal construction?

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  • \$\begingroup\$ Your photo doesn't show what's under the plastic cover. I'd expect another element (like the rest with black plastic endcaps). If so, then these brass dipole elements couple to that (hidden) element mounted in the frame. \$\endgroup\$
    – glen_geek
    Commented Dec 13, 2016 at 18:21
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    \$\begingroup\$ The driven element, i.e. the two plates connected to the coax, is a half-wave dipole and neither of these plates need to be connected electrically to the remainder of the antenna. The other elements, parallel to the driven half-wave dipole, are passive directors and a reflector. They may, or may not, be connected to the central supporting member, it makes no difference to the operation of the antenna. \$\endgroup\$
    – Chu
    Commented Dec 13, 2016 at 22:50
  • \$\begingroup\$ The brass plates are not connected to the rest of the frame. The mounting screws that hold the plates in position are embedded in the plastic casing itself. But, I think @Chu has answered my query that they don't have to be connected to the feed. \$\endgroup\$
    – Anshul
    Commented Dec 14, 2016 at 1:48

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A Yagi–Uda antenna, commonly known as a Yagi antenna, is a directional antenna consisting of multiple parallel elements in a line, usually half-wave dipoles made of metal rods. Yagi–Uda antennas consist of a single driven element connected to the transmitter or receiver with a transmission line, and additional "parasitic elements" which are not connected to the transmitter or receiver: a so-called reflector and one or more directors. It was invented in 1926 by Shintaro Uda of Tohoku Imperial University, Japan, and (with a lesser role played by his colleague) Hidetsugu Yagi.

-- Wikipedia

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