Loop antenna with aspect ratio 1:3. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / HF antennas
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Emil Tafro proposed the design and tested several types of antennas based on a rectangular wire frame with an aspect ratio of 1:3. The advantage of such loop antennas is a low suspension height, provided that the short side is vertical. For example, it is enough to raise the frame for the 40-meter band (Fig. 42) to a height of about 10 meters so that its lower side is 5 meters from the ground.
The frame is powered by a 50-ohm coaxial cable. To adjust the frame to SWR 1:1 in a given part of the range, it is useful to include a short-circuited loop in the gap on the lower side of the frame (Fig. 43).
It is possible to make a dual-band antenna, for example for 80 and 40 meters, by placing an antenna at 80 m inside the 40 m frame (Fig. 44).
For those who want to get a more efficient antenna, you can suggest adding an active frame, for example, a reflector (a similar design for the 40-meter range is shown in Fig. 45) or adding one or more frame directors.
A 4-element loop antenna with an aspect ratio of 1:3 for 40 meters was built and tested in comparison with a 3-element full-size Yagi placed at a height of 45 meters. Both antennas had a fixed direction to the USA. Of the 100 contacts with American radio amateurs, 90 preferred the loop antenna in terms of signal strength and all 100 correspondents were better heard on the "frames" than on the Yagi. At the same time, the range of 40 meters in the direction of the USA "opened" 30 ... 45 minutes earlier and "closed" the same time later when using a 4-element loop antenna. Figure 46 shows a diagram of a dual-band (40 and 80 meters) double loop antenna.
Since the distance between the frames was chosen optimal for 80 meters and is equal to 10,6 m, this is a lot for 40 meters, and additional measures had to be taken to match the active 40-meter band with a 50-ohm cable by connecting between the power points of the frame and the 50-ohm feeder of a quarter-wave segment of a 75-ohm cable (its physical length, taking into account the shortening factor, is 7 meters). Table 1 gives the dimensions of two-element antennas for five bands.
Table 1
| Range, MHz |
active frame |
Reflector |
Distance between frames, m |
| Short side, m |
Long side, m |
Short side, m |
Long side, m |
| 3,5 |
10,60 |
31,80 |
11,13 |
33,39 |
10,20 |
| 7 |
5,30 |
15,90 |
5,56 |
16,68 |
5,00 |
| 14 |
2,67 |
8,01 |
2,80 |
8,40 |
2,50 |
| 21 |
1,78 |
5,34 |
1,87 |
5,61 |
1,70 |
| 28 |
1,33 |
3,99 |
1,39 |
4,17 |
1,27 |
Author: Emil Tafro, T99W; Publication: N. Bolshakov, rf.atnn.ru
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Comments on the article:
RA4FEV
I want to install an antenna based on a rectangular frame with a ratio of 1/3 with an active frame, I listened to good reviews on the air and your publication was very useful to me, thank you very much for your article.
UA3EEL
On a rectangle with sides 1: 2, the gain will be more.
Vaha
Apparently a slope of 20-30% will give a good beam angle?
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