Directional antenna with vertical polarization. Encyclopedia of radio electronics and electrical engineering

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New solutions do not often appear in antenna technology. These, undoubtedly, include a curious version of a two-element directional antenna with vertical polarization proposed last year by Vladimir Polyakov. In this article, he talks about a possible modification of it.

The description of the antenna, which is formed by two closely spaced vertical vibrators about half a wave long, fed from the lower ends through a quarter-wave two-wire line, was published in the "KB journal" (V. Polyakov. Vertical directional antenna. - "KB journal", 1998, No. 5, pp. 27-31). It is schematically shown in Fig. 1, a (XX - feeder connection points). Already in those experiments it was noticed that the shape of the "shoulders" of the antenna, as well as their location, are not critical. The total length of each vibrator, which should be slightly less than ZL/4 for one of them "director", and slightly more than this size for the other "reflector", has a noticeably greater effect. Such a difference in the lengths of the vibrators is necessary for the correct phasing of the currents in them and the creation of unidirectional radiation.

And why not make the vibrators straight and diverging from the base at a slight angle to the vertical, as shown in fig. 1b? Indeed, between their "centers of gravity", where the antinodes of the current are located, there will still be a distance of about L / 8, which is required for the normal operation of the antenna. As for the quarter-wave line, it will have a wave resistance variable along the length, which, again, is not scary. The radiation of the diverging quarter-wave conductors of the line should not be significant, since they are located close, and the currents in them, in accordance with the principle of operation of the antenna, are almost antiphase (Fig. 1, c).

Experimental studies of the antenna fully confirmed the expected results - the antenna showed good directivity and turned out to be easy to tune. Some problems arose with her nutrition. At first, the antenna, like the previous one, was fed "according to science" - at points XX, not far from the short-circuited end of the quarter-wave line. The central conductor of the cable was attached to the director, and the braid to the reflector. Further, the cable was laid along the reflector and went vertically down from the short-circuited end of the quarter-wave line (a point with zero potential). It turned out to be inconvenient to move the feed points when tuning the antenna along non-parallel vibrators. In addition, it seemed difficult to change the length of the vibrators and the position of the feed points at the same time.

Nevertheless, the antenna worked, giving radiation directed towards the short vibrator with a gain of 4 dB compared to the half-wave vibrator. Then the antenna was fixed on a "grounded" base (a metal plane imitating the roof of a car) and it became quite inconvenient to move the power points. Then it was decided to connect the central conductor of the cable from below to the active vibrator "director", and connect the cable braid and the reflector to the base. The considerations were as follows: the input impedance of an active vibrator with a length of 3L / 4 is about 50 ohms, instead of 37 ohms for a quarter-wave, and should provide good matching. Is the reflector now passive? I think not, since it is resonant and is connected directly to the cable sheath, so it should effectively "suck" the current from it.

All these arguments were confirmed in practice and the antenna efficiency increased by about 0,5 dB. In the experiments, the factory television antenna turned out to be very convenient - a "whisker" with two telescopic elements, the ribbon cable of which was replaced with a coaxial one.

The design of the resulting antenna, the dimensions of which were selected for a frequency of 430 MHz (Fig. 2), exactly corresponded to the letter V. It would be called a V-antenna, but this name has long been firmly attached to a horizontal wire antenna. Also known - "Inverted V" antenna. By analogy, I propose to call the design "Vertical V" antenna or VV.

It's easy to set up. Fig. 2 It is only necessary, by changing the length of the dipoles and tilting them, to achieve a maximum of radiation in the main direction. The signal was recorded by a simple field indicator placed a few meters from the antenna.

Antenna gain is estimated at 4,5 dB relative to a half-wave vibrator (about 6,5 dB relative to an isotropic radiator). The radiation pattern in the horizontal plane (in azimuth), taken at points through 45 °, is shown in Fig. 3.

Some non-uniformity of radiation to the side is explained by the influence of surrounding objects (the author did not have a "clean" antenna range for these measurements). The forward/backward radiation ratio was not too high, about 12 dB. It can be improved by extending the reflector further, but at the cost of some reduction in gain gain.

Author: Vladimir Polyakov (RA3AAE)

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