21Mhz Deltaloop Antenna

<Introduction>

It is obvious that the small but low elevation angle antenna is preferable for the small DXpedition, because the antenna is one of the biggest headaches for us due to the trade-off. We know the bigger antenna has more gain, more F/B ratio, and narrower FWHM. But the bigger antenna is heavy and big. As the result we would dwell on convey it. A wire-loop antenna is an option to relieve the headache. The antenna has lower elevation angle, more gain than a dipole antenna. A cubical quad and a delta loop antenna have been used widely used as the one of a wire-loop.

For the 15M band, the loop length should be approx 15M, it requires approx 5M wire on each side. On the other hands, several web sites said that “landscape deltaloop” which has shorter top element and longer side element is radius of rotation effective and another effect on its impedance. A landscape delta loop indicates 50 ohm resistance on the real part of its impedance. Generally speaking triangle delta loop antenna would indicate nearly 100 ohm when the antenna were at resonance. As the result, we can make a delta loop antenna from a dipole of a lower band which employs 1:1 balun.

In this website, I would like to conduct some simulation to see how much impedance depends on the inner angle of the bottom corner. Also the ideal inner angle of the bottom corner was obtained for portrait delta loop for 50ohm source. Finally the SWR and the resistance were evaluated to proto type.

<Conclusion>

1) Narrower inner angle of the bottom corner gave lower impedance.

2) 3.9m for top element, 5.58m for slant element is preferable for 50ohm

3) No significant impact was observed on the radiation pattern when the inner angle of the bottom corner became narrower.

4) The proto type reproduced the simulation data.

<Result>

Please see the data in below. As you can see, the resistance data, radiation pattern data, and outlines are shown on each of inner angle of the bottom corner, 60, 50, 40degree.

The resistance is approx 100ohm at 60 degree, approx 50ohm at 40 degree. I verified the narrower inner angle of the bottom corner gives smaller resistance for the delta loop antenna.

In order to check the side-effect to radiation pattern, I calculated the gain and elevation angle. All simulations were calculated by MMANA assuming the perfect ground. Both gain and elevation angle were not so big difference. The gain increased 0.19dBi=4.4%, the elevation angle became lower 3degree.

I made a proto type of 40degree model. In very below, you can see the SWR data on 15Meter band. The resonance frequency 21.035 MHz. The approx 45 ohm resistance was measured almost same as the simulation data foresaw.

<Data>

Inner angle of the bottom corner	Resistance	Radiation pattern	Outline
60	104 ohm	Gain/ 9.08 dBi Elevation angle/ 25degree
50	75 ohm	Gain/ 9.20dBi Elevation angle/ 23degree
40	56 ohm	Gain/ 9.27dBi Elevation angle/ 22degree

<SWR data>