The problem of qualitative estimation of the parameters of various antennas. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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The problem of qualitative estimation of the parameters of various antennas. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / Antennas. Theory

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The problem of qualitative assessment of the parameters of various antennas remains relevant, especially today, when with the disappearance of technical literature available to radio amateurs, various kinds of "firms" appear, consisting of "businessmen" with a wide range of "intellectual" requests: from speculation in imported grubs to the production of antennas. In the brochures of these "jacks of all trades" I have personally seen statements of a very wide range from "only our antennas provide the best quality of work" (almost a modest statement at the present time), to a militaristic-chased phrase like "... an antenna with gain 19 dB was developed at the Higher Military Academy of Radio Communications (? - K.S.) and is produced by the defense industry for conversion ... ".

In addition to deliberate, to put it mildly, distortion of information, in various descriptions of antenna designs there are also parameters that are erroneously overestimated for both metrological and methodological reasons, since full antenna testing is not always possible and not accessible to everyone. In addition, the natural desire of the designer to present his work in the best possible light is quite understandable. The question is, what can really be expected from a certain antenna design? It is well known that in the simplest case, the receiving antenna is a single conductor located in space and "extracting" energy from the existing electromagnetic field around it to transmit it through the feeder to the receiving device. There are the following ways to optimize this process: - tune the antenna in resonance with the frequency of the received signal; - the location of the antenna in space in such a way that the electromagnetic waves crossing it give off the maximum amount of energy; - the antenna must "process" as much of the existing electromagnetic field as possible at the receiving point; - the connecting feeder must ensure minimal loss of the signal received by the antenna.

Despite the simplified representation, the above conditions allow some preliminary conclusions to be drawn: - narrowband antennas give better results; - it is required to select the optimal antenna suspension point - in the general case, high above the ground and accurately point it at the transmitter; - there are no "miracle antennas": small-sized and having the ability to "extract" electromagnetic energy from a large surrounding space, so large antennas (or antenna systems) have a higher efficiency. I will dwell on the very common VHF antennas of the "wave channel" type. It is their popularity that is the reason for various hoaxes and incorrect data, most often regarding these Kus antennas, which, in my opinion, is either the result of inaccurate measurements, or just advertising noise. Laboratory measurements of well-known high-quality samples of amateur and factory "wave channels" (given by [1,2, 10]) showed that the antenna Cos increases with an increase in the number of directors (with a mandatory lengthening of the traverse!) and with 11,5 directors it is about 6 dB (relative to Cos half-wave dipole). Extending the antenna to 15 wavelengths makes it possible to achieve a gain of up to 15 dB. A further increase in the size of the antenna increases Kus practically does not. All attempts to optimize the parameters of the "wave channel", such as: precision calculations on a computer, "jewelry" manufacturing, fine tuning, etc., brought the Kus of a single antenna to a value slightly exceeding 2 dB [15]. Therefore, any information about the Kus "wave channel" exceeding XNUMX dB, given in the literature or in company brochures, should be treated at least critically.

In conclusion, I want to say that, in my opinion, the most suitable for practical use in amateur conditions is the method for assessing the effectiveness of antennas, proposed in [3,4]. The essence of the method is to compare different antenna designs not according to Kus, but according to the width of the main lobe of the AP at half power. This parameter is available for measurement by relatively simple means, and knowing it, it is possible to evaluate the quality of various antennas by analogy with the known designs of "wave channels" with normalized gain (for orientation, such data are given in Table 1).

Table 1 Dependence of the "Wave channel" parameters on the number of antenna elements
Number of antenna elements 2 3 4 5 8 16 24 27
DN width in the horizontal plane, degrees ±2 70 60 55 48 45 33 25 23
Kus (relative to half-wave dipole), dB ±0.5 dB 5 7 8 9 10 13 15 15,5

Literature:

1. VHP Communication. NN 3-4/77.
2. P. Lolov. High quality Yagi antennas. Radio, television, electronics, N 5/89, p.24.
3. E. Gutkin. Multiband directional KB antenna. Radio, N 3/85, p. 17.
4. K. Kharchenko. Tuning KB antenna "wave channel". Radio, NN 7-8/81, p.19.
5. Radio amateur 2/94, p.57

Publication: N. Bolshakov, rf.atnn.ru

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