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I recently bought an FM antenna for a receiver like this.

enter image description here

I've flattened it out a good bit on my windowsill but it's far from straight and is fairly wavy/curled from being bundled like this for who knows how long after manufacturing.

How does this still work as an antenna? I was under the impression antennas were (when practical) designed to be straight and some nice fraction of a wavelength.

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  • \$\begingroup\$ Are both arms of the dipole stretched out? If so, it doesn't matter if the feeder has bends in it. \$\endgroup\$ – Leon Heller Jul 17 '19 at 17:46
  • \$\begingroup\$ Yes, they're stretched out as much as I could reasonably do. I was afraid to damage the wire if I attempted to fold out the bends, though, so while stretched they're far from flat. \$\endgroup\$ – brenzo Jul 17 '19 at 17:52
  • \$\begingroup\$ You might think of an antenna as 1) needing to have an impedance that ensures some power can be taken from it, and 2) needing to have a shape that intercepts the incoming EM wave (especially from a particular direction) well. Having the dipole not straight screws up both of these desirable characteristics. I would guess that its impedance is not as messed up as it's directionality though. If you want to know the real answer, get the program "NEC". It allows you to experiment with different shapes of wire antennas and find out how they work. It is free. \$\endgroup\$ – user69795 Jul 19 '19 at 4:13
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I think this could be compared to meandered dipole antenna, a technique commonly found in UHF RFID tag antennas. But here is one article for research of VHF dipole antenna. So, if you keep the length l (dipole length) the same and add meanders, the frequency goes down because the electrical length of the antenna is longer:

Meander dipole1

In your situation the dipole length is reduced, but the electrical length of the dipole is the same:

Meander dipole 2

Even though the "meanders" are a bit different, I suspect it could be working quite close to the intended frequency.

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