HF antenna Square (principles of operation). Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / HF antennas

 Comments on the article

One of the reasons that determined the noticeable increase in the activity of Soviet shortwaves and their success in international competitions is the widespread use of directional antennas. The most popular in our country are "squares" with two, three or more beamforming elements. These antennas will be discussed in the article. The main goal pursued by the authors is to give recommendations to the shortwave operator in the selection and tuning of antennas, summarizing the experience of Soviet and foreign shortwave operators.

Comparison of "squares" and "wave channels"

The widespread use of "squares" led to the need to compare their characteristics with the parameters of another antenna popular with radio amateurs - the "wave channel".

The table shows the results of measurements of the characteristics of some antennas "square" and "wave channel", borrowed from the magazine "QST", 1968, No. 5. It follows from it. that the parameters of both antennas are approximately the same if we compare "wave channels" that have one element more than "squares". With the same number of elements, the "square" will have a gain of about 2 dB more. According to our data, this figure can be increased to at least 2,5 dB if the distances between the elements are chosen optimally.

Antenna parameters	Square			Wave channel
Amount of elements	2	4	6	3	5	7
Gain relative to an isotropic radiator, dB	8.2	11,5	13,4	8.8	12	13,3
Width of the directivity pattern according to the level of half power, deg.	60	50	39	61	47	40

To understand the physical reason for such a significant difference, let us consider the directions of currents (in Fig. 1) in the frame - the "square" element and in the half-wave dipole - the "wave channel" element.

From fig. 1 it follows that only the currents flowing in the horizontal parts of the frame take part in the formation of the "square" diagram, since the fields from the currents flowing in the vertical parts are mutually compensated. Therefore, the frame is equivalent to a system of two in-phase shortened vibrators, spaced apart in height by a distance L/4. It is known that the radiation pattern in the vertical plane of such a system has a smaller angle compared to the pattern of a single dipole and, consequently, its amplification is higher. Quantitative gain in gain, depending on the parameters and the height of the rise of both elements, can be from 2,2 to 3,1 dB. This gain can be determined by the formula, which is valid with sufficient accuracy for KB ranges:

A=40000/FgFv where A is the gain factor, Fg and Fv is the width of the radiation patterns in the horizontal and vertical planes, respectively.

Substituting in the formula the average values ​​Fg=180° and Fv=135° for the dipole, Fg=170° and Fv=80° for the frame, we get that the gain of the dipole is 1,64 times or 2,15 dB (in terms of power), gain frame - 2,94 times or 4,68 dB. Thus, the average gain gain is 2,53 dB. This figure is real and confirmed in practice.

A similar gain is achieved when the frame is located at an angle down, which is used in many designs. This option differs from the one discussed above only in that in it the radiation pattern is formed by the horizontal components of the currents flowing in all four sides of the frame, and the fields from the vertical components are compensated.

One more feature of the "square" can be noted. Since the frame of length L forms a symmetrical closed loop, the influence of the ground and surrounding objects, which degrades the characteristics of the antennas, is less.

Choice of the optimal design By optimal we mean such design data of the antenna, which provide the maximum forward/backward radiation ratio at a sufficiently high gain. It seems necessary to introduce this definition because of the existence of two methods for tuning directional antennas - for maximum gain and for the maximum forward / backward radiation ratio. These maxima do not coincide, and, as practice shows, the loss in terms of forward/backward radiation when tuning according to the first method turns out to be greater than the loss in amplification in the second case.

In the process of designing an antenna, a radio amateur must determine the number of elements, the distance between them, and their dimensions. To solve the first problem, let us turn to Fig. 2.

It shows the antenna gain A and the forward/backward radiation ratio B as a function of the number of elements n. The graphs are based on the results of measurements (coinciding with the calculated data) on "square" antennas with optimal characteristics for the 14 MHz band. As you can see, the growth of both parameters slows down as the number of elements increases, and this becomes especially noticeable for n>3. Given the difficulties associated with the manufacture and tuning of multi-element antennas, the authors believe that in most cases it is advisable to limit the number of elements to three. In the opinion of some foreign radio amateurs, a four-element antenna is structurally more convenient due to the symmetrical (with respect to the vertical axis passing through the center of mass) arrangement of elements. We leave the final decision to the reader.

To select the optimal distances between the elements, we consider the dependence of the amplification A on the distance S, expressed in fractions of the wavelength L (Fig. 3). The diagram shows in black the dependence of the amplification on the distance between the selector and the reflector of a two-element "square". In the shaded area corresponding to the gain maximum (S = 0,175-0,225L), it practically does not change, therefore, in this case, the choice of distance within the specified limits is not critical.

For antennas with more than two elements, the task becomes more complicated due to the introduction of additional independent variables (two for a three-element antenna, three for a four-element antenna, etc.). Therefore, it is advisable to set one of the distances (for example, between the vibrator and the reflector) and choose other distances as optimal. So, if we take the vibrator-reflector distance for a three-element antenna equal to 0,2L, we can determine the optimal vibrator-director distance using the curve shown in Fig. 3. Obviously, this "square" will have the greatest gain at a distance between the vibrator and the director equal to 0,175L, and in this case, when the distances change from 0,14 to 0,21L, the gain remains practically constant, although, as expected , due to the decrease in the wide bandwidth of the antenna, the dependence of the gain on S becomes steeper.

(click to enlarge)

To illustrate what has been said, we can cite a graph slightly transformed for "squares" at 14 MHz from the same "QST" magazine. Based on the study of a large number of antennas, the dependence of the gain on the length L of the traverse for fastening the elements was determined (Fig. 4). The shaded areas on the graph are the practically possible limits for changing the length of the traverse for an antenna with a given number of elements. It follows from the graph that antennas with a shortened traverse are inferior in gain (two- and three-element - by about 2 dB) to antennas with distances between elements of about 0,2 L.

The length of the vibrator frame lv can be calculated by the formula:

where Ky is the elongation factor, depending on the number of elements and the ratio of the length of the frame to the diameter of the wire; Lp is the wavelength for which the antenna is designed.

To determine the length of a two-element "square" vibrator, the elongation factor is taken equal to 1,01, with three or more elements it is 1,015-1,02.

The length of the reflector of the two-element "square" is chosen by 5-6% more than the length of the vibrator. For a three-element "square", the length of the reflector should be 3-4% longer, the director - 2,5-3% less than the length of the vibrator; for a four-element "square", the length of the reflector should be 2,5-3% more, the length of the directors - 2% less.

In practice, the reflector and director are made a little shorter than determined by calculation, so that they can be adjusted using short-circuited loops.

Multi-range systems

Everything said earlier referred to single-range "squares". In practice, it is often necessary to resort to the creation of a multi-range system. It should be noted, however, that any combination in the vertical plane of elements tuned to different frequencies, especially multiples of two (that is, 14 and 28, 7 and 14 MHz, etc.), leads to a deterioration in the main characteristics of the antenna. Let's give two examples. A two-element "square" at 14, 21 and 28 MHz with frames in different planes (the so-called "hedgehog" design) has a gain of up to 9 dB and a forward / backward emission ratio of up to 24 dB; the same characteristics of a similar "square" made on a traverse do not exceed 8 and 22 dB, respectively. Three-element "square" for two bands (14 and 21 MHz) with spaced reflectors provides amplification up to 13 dB and the ratio of emissions forward / backward - up to 30 dB; for a three-element three-band "square" (a 28 MHz range is added and the frames are located one inside the other), these characteristics deteriorate to 11,5 and 27 dB, respectively.

To reduce the influence of elements located in the same plane and operating at multiple frequencies, you can, by properly connecting the feeder, apply their polarization decoupling (horizontal polarization for one and vertical polarization for another range).

The decoupling of the elements of the 14-28 MHz ranges in a three-element "square" determined by calculation reaches 20 dB.

To obtain the best performance from a multi-range system, it is desirable to maintain optimal element spacings for each range. However, here, due to design difficulties, radio amateurs are often forced to compromise. One example of such a compromise for a three-element "square" at 14, 21 and 28 MHz can be achieving near-optimal performance on the first two bands and worse performance on the third. In our opinion, such a decision is quite justified due to the peculiarities of the passage and the different workload of these ranges. Depending on the specific requirements for the antenna, the radio amateur may choose another option.

Literature

1. Radio No. 6 1976

Publication: cxem.net

See other articles Section HF antennas.

Read and write useful comments on this article.

<< Back

Latest news of science and technology, new electronics:

Machine for thinning flowers in gardens 02.05.2024

In modern agriculture, technological progress is developing aimed at increasing the efficiency of plant care processes. The innovative Florix flower thinning machine was presented in Italy, designed to optimize the harvesting stage. This tool is equipped with mobile arms, allowing it to be easily adapted to the needs of the garden. The operator can adjust the speed of the thin wires by controlling them from the tractor cab using a joystick. This approach significantly increases the efficiency of the flower thinning process, providing the possibility of individual adjustment to the specific conditions of the garden, as well as the variety and type of fruit grown in it. After testing the Florix machine for two years on various types of fruit, the results were very encouraging. Farmers such as Filiberto Montanari, who has used a Florix machine for several years, have reported a significant reduction in the time and labor required to thin flowers. ... >>

Advanced Infrared Microscope 02.05.2024

Microscopes play an important role in scientific research, allowing scientists to delve into structures and processes invisible to the eye. However, various microscopy methods have their limitations, and among them was the limitation of resolution when using the infrared range. But the latest achievements of Japanese researchers from the University of Tokyo open up new prospects for studying the microworld. Scientists from the University of Tokyo have unveiled a new microscope that will revolutionize the capabilities of infrared microscopy. This advanced instrument allows you to see the internal structures of living bacteria with amazing clarity on the nanometer scale. Typically, mid-infrared microscopes are limited by low resolution, but the latest development from Japanese researchers overcomes these limitations. According to scientists, the developed microscope allows creating images with a resolution of up to 120 nanometers, which is 30 times higher than the resolution of traditional microscopes. ... >>

Air trap for insects 01.05.2024

Agriculture is one of the key sectors of the economy, and pest control is an integral part of this process. A team of scientists from the Indian Council of Agricultural Research-Central Potato Research Institute (ICAR-CPRI), Shimla, has come up with an innovative solution to this problem - a wind-powered insect air trap. This device addresses the shortcomings of traditional pest control methods by providing real-time insect population data. The trap is powered entirely by wind energy, making it an environmentally friendly solution that requires no power. Its unique design allows monitoring of both harmful and beneficial insects, providing a complete overview of the population in any agricultural area. “By assessing target pests at the right time, we can take necessary measures to control both pests and diseases,” says Kapil ... >>

Random news from the Archive Biological clock repair 22.02.2017 One of the main regulators of our biological clock is the hormone melatonin: two hours before sleep, the level of melatonin begins to rise, and we begin to feel sleepy, and upon awakening, on the contrary, its level drops. The time when hormone levels remain high is called biological night, and it obviously must coincide with astronomical night. But we have not gone to bed with evening twilight for a long time and do not get up at dawn: many of us go to bed well after midnight, and wake up not at all with the first rays of the sun, and then nod off all day. Daytime sleepiness is due to the fact that the level of melatonin remains elevated - the hormonal clock goes astray, remaining in biological night mode for most of the day. And the problem here is not only that we want to sleep: because of the knocked down internal clock, the body experiences a constant lack of sleep, and lack of sleep, as we now know, has a bad effect on metabolism and increases the likelihood of diseases such as diabetes, obesity and associated cardiovascular disorders. Is it possible to return the biological clock to its previous settings? Scientists from the University of Colorado at Boulder told how this can be done: it turned out that it was enough to spend a week in nature for the melatonin rhythm to return to normal. True, a week-long outdoor recreation has one strict condition: you can’t take any electronic devices with you and no sources of artificial lighting. It was the sunlight, which people saw four times more in nature than in ordinary life, that was able to put their daily rhythms in order. The point is not only in the amount of sunlight, but also in the fact that during the day there was light, and at night there was no light, except for the light from the fire flame. At the same time, individual differences in daily cycles between different people were smoothed out. Among us there are "larks" who like to wake up early, and "owls" who like to fall asleep late, but a week on the campaign turned the "owls" into "larks". Of course, shifts in the melatonin cycle occurred in everyone, but in the "owls" they were most noticeable. The changes were not only in the level of the hormone - after being in nature, daytime sleepiness disappeared in people. Subsequently, it turned out that a week is even too much, two days is enough. Kenneth Wright and his colleagues repeated the experiment with fourteen young people aged 20 to 30 - nine of them went out of town for the weekend, five stayed in the city. In just two days in nature, the daily fluctuations of melatonin approached their norm by one hour. Compared to a week-long (or rather, six-day) hike, two-day changes accounted for 69% of the hormonal changes that occur in six days. Simply put, in two days without artificial light and without gadgets, the biological clock returned to normal by more than half.

Other interesting news:

▪ Glasses clean themselves

▪ Razer Ornata - the first keyboards with Razer Mecha-Membrane switches

▪ Radar sports speedometer from TI

▪ Birds can see magnetic fields

▪ Teclast X2 Pro Hybrid Tablet

News feed of science and technology, new electronics

Interesting materials of the Free Technical Library:

▪ section of the site Microcontrollers. Article selection

▪ Article Law - I am dumb before the law. Popular expression

▪ article Why was Carthage at enmity with Rome? Detailed answer

▪ article Small-fruited horse fennel. Legends, cultivation, methods of application

▪ article The sun is a cook. Encyclopedia of radio electronics and electrical engineering

▪ article Intact banknote. Focus Secret

Leave your comment on this article:

All languages ​​of this page

Arabic	Hebrew	Polish
Bengali	Hindi	Portuguese
Chinese	Italian	Spanish
English	Japanese	Turkish
French	Korean	Ukrainian
German	Malay	Vietnamese

Home page | Library | Articles | Website map | Site Reviews

www.diagram.com.ua
2000-2024