Antenna with reverse radiation. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / HF antennas
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An antenna with reverse radiation is not much different from a wave channel type antenna, which has one or more directors, an active vibrator and a reflector. When converting a conventional antenna, a wave channel into an antenna with backward radiation, a flat reflector-wall is installed ahead of the first director at a distance of approximately 1/4 l (Fig. 1).
Rice. 1, a - antenna pattern of the wave channel;
b - antenna pattern with reverse radiation
(D - directors, V - vibrator, P - reflector).
The energy supplied to the active antenna vibrator is radiated towards the directors, reaching the reflector-wall is reflected from it (since the reflector wall is longer than K and has a pronounced inductive character), reaches the antenna vibrators again, inducing additional e .d.s.
Due to this, there is a significant narrowing of the radiation lobe and its rotation by 180 ° (that is, the energy is concentrated in a narrow direction).
In the above literature, it is reported that by attaching a reflector-wall to a conventional wave channel, it is possible to achieve a gain in return radiation of the order of 5,2 dB at a level of 0,5 compared to the wave channel antenna, the radiation angle narrows from 41 ° to 24,5 ° , side and back radiation become much smaller.
For a horizontally polarized antenna 1,5 l long with a reflector-wall (dimensions 2lx2l) and consisting of one active vibrator, three directors and three reflectors located one above the other (Fig. 2), the gain is 14,5 dB at level 0,5, 25,5; the radiation angle in the horizontal plane is 28°, in the vertical - XNUMX°.
The reflector-wall can be made of a metal sheet or a densely interwoven mesh (the latter is better due to less windage).
Rice. 2. General view of the antenna with a wall reflector.
Approximately the same result can be obtained when using a simpler wave channel antenna from one active vibrator, one director and one reflector. It is proposed to build antennas with backward radiation with a gain of 10 to 25 dB in cases where the wave channel antenna turns out to be too cumbersome, and it is not profitable to use parabolic antennas.
On fig. Figure 3 shows a relatively simple antenna for the 420 MHz band, on which measurements were made that fully confirmed the above properties of the antenna with back radiation. This antenna, without special adjustment, gives a gain of 4-4,5 dB more than the usual wave channel.
Rice. 3. Antenna with back radiation for 425 MHz
reflector-wall P is made of metal mesh,
distance between wires - 10 mm; all tube diameters
vibrators - 8 mm).
I would like our radio amateurs to start experimenting widely with such antennas, since only with good antennas can long-range reliable communications and good reception of television centers located outside the reliable reception zone be achieved.
Author: K. Fechtel (UB5WN), Kyiv; Publication: N. Bolshakov, rf.atnn.ru
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