Empirical design of multiband loop antenna ?

[Externet]

Good day.

Multiband dipoles like this do work well, I use one for 7; 14; 21 MHz

Can the same principle be applied for magnetic loops to receive ~70; ~200, ~600 MHz ?

What would happen if made with more than the 3 loops pictured above ?

 

[PlanarMetamaterials]

I don't see why such a design couldn't *work*, but it would probably be difficult to impedance match all of the loops simultaneously. Also, the coupling between the elements would be high.

But, maybe your system can tolerate these.

 

[volker@muehlhaus]

I doubt that this will work. Unlike the resonant dipole where current varies along the length, the requirement for length of a magnetic loop is to keep it short, so that current along the loop is almost constant. In my opinion these loops will behave like inductors connected in parallel, resulting in a single resonance.

 

[G4BCH]

A 200Mhz full wave loop should work at 600MHz in the same way as a 7MHz dipole or quad also works at 21MHz. Radiation pattern may not be what you want though. It will also work after a fashion at 70MHz.
If you need a wide band antenna you could do worse than use something like a discone.

 

[FvM]

I'd like to see the "working" 7/14/21 MHz multiband-dipole drawn to scale along with an impedance curve. No doubt that the individual dipoles are strongly coupled, less clear if the shorter segments have a big effect at all. The working of parallel connected loops is different, unlike dipoles, the smaller one is not hidden by the larger.

I understand that you are talking about electrically large loops. I'd consider LC circuits as multiplexers if you are stuck to the multiple loop concept, otherwise go for proven wideband antenna designs as already suggested.

 

[vfone]

See the attached antenna pattern for a tri-band dipole antenna you posted.
As you see, is not "working" in all bands the same, and is not working as 3 separate dipole antennas.

I think that you can connect 3 circular loop antennas as you want, but have to make each of them resonant using series capacitors.

VHF TX Loop

But even then, may be possible to get the same situation as in tri-band dipole antenna.