20m Delta Loop.
This antenna is fed for vertical polarisation, to give a low angle of radiation for DX and also a nearly omni-directional radiation pattern (broadside is the best direction by about 3 dB).
I have built two versions of this antenna; one using coax as a monoband antenna for 20m as simulated below, and the second as presently used with 450 Ohm slotted ladder-line feeder for multiband use (20 and 15m).
In the monoband application, the impedance at resonance on 14.2 MHz of about 100 Ohms is transformed by a quarter wavelength of 75 Ohm cable (3.5m long) to give a good match ( better than 2 : 1) across the whole band. The 75 Ohm coax braid is connected to the lower side of the loop element. I don't use a balun as the antenna is not balanced, due to the offset side feedpoint, but do implement a coaxial choke at the 50 Ohm cable connection to the matching stub of 10 turns, 20cm diameter. The antenna is 7.71m per side, with the feed point 3/4 of the way down one side (5.78 m from the top) note; 3/4 * 1/3 wavelength = 1/4 wave, this is important to obtain vertical polarisation.
This antenna is also effective on 15m provided open wire feeder is used up to the antenna instead of coax. I have found 10m DX performance to be rubbish! Simulation confirms this.The pattern is rather directional on both the higher bands.
Photo of the antenna
Drawing of antenna
The NEC4WIN95 design file;
CM Equilateral Delta loop for 20 meters, apex up.
CM Feed point 0.25 lambda from top corner for vertical polarisation
CM 2:1 75 ohm coax quarter wave-length match assumed.
CM G4EZT Tree supported antenna.
Over Ground 13 5 (Diel. - Cond. ÁSiemens)
GW 0 8 0.000 -3.854 0.000 0.000 0.000 6.675 0.002
GW 1 20 0.000 0.000 6.675 0.000 3.854 0.000 0.002
GW 2 8 0.000 3.854 0.000 0.000 -3.854 0.000 0.002
S 1 23 100 0
The SWR plot
The Zenith plot
The Azimuth plot.