Application of fractal antennas. Fractal ultra-wideband antenna based on a circular monopole. As the dimension increases, the total length of the broken line increases nonlinearly, determined by the relation

Over the past few years, I have regularly been faced with the challenges of developing UWB (ultra-wideband) microwave modules and functional units. And as sad as it is for me to say this, I get almost all the information on the topic from foreign sources. However, some time ago, in search of the information I needed, I came across one that promised a solution to all my problems. I want to tell you how the problems were not resolved.

One of the constant “headaches” in the development of UWB microwave devices is the development of UWB antennas, which must have a set of certain properties. Among these properties are the following:

1. Agreement in the operating frequency band (for example, from 1 to 4 GHz). However, it happens when it is necessary to agree in the frequency range from 0.5 GHz to 5 GHz. And here the problem arises of going below 1 GHz in frequency. I generally got the impression that the 1 GHz frequency has some kind of mystical power - you can get close to it, but it’s very difficult to overcome it, because in this case, another requirement for the antenna is violated, namely

2. Compactness. After all, it’s no secret that now few people need a waveguide horn antenna of enormous size. Everyone wants an antenna that is small, light and compact so that it can be shoved into a housing. portable device. But when compacting the antenna, it becomes very difficult to comply with paragraph 1 of the requirements for the antenna, because The minimum frequency of the operating range is closely related to the maximum size of the antenna. Someone will say that you can make an antenna on a dielectric with a high relative dielectric constant... And they will be right, but this contradicts the next item on our list, which says that

3. The antenna should be as cheap as possible and made from the most accessible and inexpensive materials (for example, FR-4). Because no one wants to pay a lot, a lot of money for an antenna, even if it’s three times brilliant. Everyone wants the cost of the antenna at the stage of manufacturing the printed circuit board to tend to zero. Because this is our world...

4. There is one more requirement that arises when solving various problems associated, for example, with short-range location, as well as with the creation various sensors, using UWB technology (here it must be clarified that we are talking about low-power applications, where every dBm counts). And this requirement states that the radiation pattern (DP) of the designed antenna should be formed in only one hemisphere. What is it for? In order for the antenna to “shine” only in one direction, without dissipating precious power into the “return”. This also allows you to improve a number of indicators of the system in which such an antenna is used.

Why am I writing all this..? In order for the inquisitive reader to understand that the developer of such an antenna is faced with a lot of restrictions and prohibitions that he needs to heroically or wittily overcome.

And suddenly, like a revelation, an article appears that promises a solution to all the above problems (as well as those that were not mentioned). Reading this article evokes a slight feeling of euphoria. Although the first time you do not fully understand what is written, the magic word “fractal” sounds very promising, because Euclidean geometry has already exhausted its arguments.

We get down to business boldly and feed the structure proposed by the author of the article to the simulator. The simulator growls gutturally like a computer cooler, chewing gigabytes of numbers, and spits out the digested result... Looking at the simulation results, you feel like a little deceived boy. Tears well up in my eyes, because... again your childhood airy dreams collided with cast-iron...reality. There is no coordination in the frequency range 0.1 GHz - 24 GHz. Even in the range of 0.5 GHz - 5 GHz there is nothing similar.

There is still a timid hope that you didn’t understand something, did something wrong... The search for the switching point begins, various variations with the topology, but everything is in vain - it’s dead!

The saddest thing in this situation is that until the last moment you are looking for the reason for failure in yourself. Thanks to my fellow workers who explained that everything was correct - it shouldn’t work.

P.S. I hope my Friday post brought a smile to your face.
The moral of this presentation is this: be vigilant!
(And I really wanted to write an ANTI-article about this, because I was deceived).

As we discussed in previous articles, it was found that the efficiency of fractal antennas is approximately 20% greater than conventional antennas.This can be very useful to apply. Especially if you want your own TV antenna to accept digital signal or HD video, to increase the range of cell phones, Wi-Fiband, FM or AM radio, and so on.

Most cell phones already have built-in fractal antennas. If you've noticed in the last few years, Cell phones no longer have antennas on the outside. This is because they have internal fractal antennas etched into the circuit board, which allows them to get better reception and pick up more frequencies such as Bluetooth, cellular signal and Wi-Fi all from one antenna at the same time!

Information from Wikipedia: "A fractal antenna differs markedly from a traditionally designed antenna in that it can operate with good performance at a wide variety of frequencies simultaneously. Typically, standard antennas must be "cut" at the frequency for which they are to be used and thus Thus, a standard antenna only works well at this frequency, making fractal antennas an excellent solution for wideband and multiband applications.”

The trick is to create your own fractal antenna that will resonate at the frequency you want. This means it will look different and may be calculated differently depending on what you want to achieve. A little math and it will become clear how to do this. (You can limit yourself to an online calculator)

In our example, we will do the simplest antenna, but you can make more complex antennas. The more complex the better. We'll use a spool of 18 gauge solid wire needed to build the antenna as an example, but you can go further by using your own etch boards to make the antenna smaller, or more complex with high resolution and resonance.

(tab=TV antenna)

In this tutorial we will try to create a TV antenna for digital signal or signal high resolution transmitted over a radio channel. These frequencies are easier to work with, wavelengths at these frequencies range from half a foot to several meters in length for half the wavelength of the signal. For UHF (decitimeter wave) circuits, you can add a director (director) or reflector (reflector) which will make the antenna more direction dependent. VHF (ultra short wave) antennas also depend on direction, but rather than pointing directly at the TV station, the "ears" of VHF dipole antennas must be perpendicular to the wavelength of the TV station transmitting the signal.

First, find the frequencies you want to receive or broadcast. For TV, here is a link to the frequency chart: http://www.csgnetwork.com/tvfreqtable.html

And to calculate the antenna size we will use an online calculator: http://www.kwarc.org/ant-calc.html

Here good pdf on design and theory:download

How to find the wavelength of a signal: wavelength in feet = (speed of light ratio in feet) / (frequency in hertz)

1) Light speed coefficient in feet = +983571056.43045

2) Light speed coefficient in meters = 299792458

3) Light speed coefficient in inches = 11802852700

Where to start: (VHF/UHF dipole array with reflector that works well for the DB2's wide frequency range):

(350 MHz is a quarter of an 8-inch wave - a 16-inch half wave, which falls in the ultra-high frequency range - between channels 13 and 14, and which is the center frequency between the VHF-UHF range for better resonance). These requirements can be modified to work better in your area, as your distribution channel may be lower or higher in the group.

Based on materials from the links below ( http://uhfhdtvantenna.blogspot.com/ http://budgetiq.wordpress.com/2008/07/29/diy-hd-antenna/ http://members.shaw.ca/hdtvantenna/ and http://current .org/ptv/ptv0821make.pdf) , only fractal designs allow you to be more compact and flexible and we will use the DB2 model, which has a high gain and is already quite compact and popular for indoor and outdoor installation.

Basic costs (costed about $15):

1. Mounting surface such as plastic housing (8"x6"x3"). http://www.radioshack.com/product/index.jsp?productId=2062285
2. 6 screws. I used self-tapping screws for steel and sheet metal.
3. Matching transformer 300 Ohm to 75 Ohm. http://www.radioshack.com/product/index.jsp?productId=2062049
4. Some 18 gauge solid wire. http://www.radioshack.com/product/index.jsp?productId=2036274
5. Coaxial RG-6 with terminators - limiters (and a rubber sheath if installed outside).
6. Aluminum when using a reflector.
7. A sharpie marker or equivalent, preferably with a fine tip.
8. Two pairs of small pliers - needles.
9. The guide is at least 8 inches.
10. Protractor for measuring angles.
11. A drill and a drill bit that is smaller in diameter than your screws.
12. Small nippers.
13. Screwdriver or screwdriver.

NOTE: HDTV/DTV editing in PDF http://www.ruckman.net/downloads-1#FRACTALTEMPLATE

Step one:

Assemble the housing with the reflector under the plastic cover:

Step two:

Drill small threaded holes on the opposite side of the reflector in the following positions and place a conductive screw.

Step three:

Cut four 8" pieces of solid core wire and expose it.

Step four:

Using a marker, mark every inch on the wire. (These are the places where we are going to make bends)

Step five:

You must repeat this step for each wire. Each bend on the wire will be equal to 60 degrees, thus creating a fractal. Resembling an equilateral triangle. I used two pairs of pliers and a protractor. Each bend will be at 1" notch. Make sure you visualize the direction of each turn before you do this! Use the diagram below for help.

Step six:

Cut 2 more pieces of wire at least 6 cm in length and expose them. Bend these wires around the top and bottom screws, and tie them to the center of the screw. Thus, all three come into contact. Use wire cutters to cut off unwanted parts of the wire.

Step seven:

Place and screw all your fractals with corners

Step eight:

Attach the matching transformer through the two screws in the center and tighten them down.

Ready! Now you can test your design!

As you can see in the photo below, each time you divide each section and create a new triangle with the same length of wire, it can fit in a smaller space, taking up space in a different direction.

Translation: Dmitry Shakhov

Below you can watch a video on creating fractal antennas:

(tab=Wi-Fi antenna)

I had previously heard about fractal antennas and after a while I wanted to try making my own fractal antenna to try out this concept, so to speak. Some of the advantages of fractal antennas described in research papers on fractal antennas are their ability to efficiently receive multi-band RF signals while being relatively small. I decided to create a prototype of a fractal antenna based on the Sierpinski carpet.

I designed my fractal antenna to have a connector compatible with my router Linksys WRT54GS 802.11g. The antenna has a low profile gain design and has been pre-tested at a distance of 1/2 km from the vane point WiFi Link with several trees on the way it showed pretty good results and signal stability.

You can download PDF version antenna template based on the Sierpinski carpet that I used, as well as other documentation at these links:

Making a prototype

This is a photo with a ready-made prototype of a fractal antenna:

I attached the Linksys WRT54GS RP-TNC - connector to the fractal antenna for testing

When I was designing my first fractal antenna prototype, I was concerned that the etching process on the PCB might isolate the triangles from each other, so I expanded the connections between them a bit. Note: Since the final toner transition finished more accurately than I expected, the next version of the fractal antenna prototype will be rendered with fine contact points between each of the fractal iterations of the Sierpinski triangle. It is important to ensure that the elements of the Sierpinski carpet (triangles) are in contact with each other and the connection points should be as thin as possible:

The antenna design was printed on laser printer Pulsar Pro FX. This process allowed me to copy the antenna design onto copper clad PCB material:

The laser printed antenna structure is then transferred to the PCB copper sheet by a thermal process using a modified laminator:

This is the copper PCB material after the first step of the toner transfer process:

The next necessary step was to use the Pulsar Pro FX "Green TRF Foil" laminator on the PCB. Green foil is used to fill any toner gaps or unevenly thickened coatings in the toner transfer:

This is a cleaned board with antenna design. The board is ready for etching:

Here I masked off the back side of the PCB using electrical tape:

I used the direct ferric chloride etching method to etch the board in 10 minutes. The direct etching method is carried out using a sponge: it is necessary to slowly wipe the entire board with ferric chloride. Due to the health hazards of using ferric chloride, I wore safety glasses and gloves:

This is the board after etching:

I wiped the PCB with a swab dipped in acetone to remove the toner transfer coatings. I used gloves when cleaning because the acetone will be absorbed through typical latex disposable gloves:

I drilled the hole for the antenna connector using a drill and a drill bit:

For my first prototype I used the RP-TNC connector from the standard Linksys router antennas:

Close-up of Linksys - RP-TNC compatible antenna connector:

I applied a little water to the PCB at the soldering area just before soldering:

The next step is to solder the wire from the RP-TNC connector to the base of the Sierpinski antenna on the printed circuit board:

Solder the second wire of the antenna connector to the plane of the PCB board:

The antenna is ready to use!

In mathematics, fractals are sets consisting of elements similar to the set as a whole. Best example: If you look closely at the line of an ellipse, it will become straight. Fractal - no matter how close you zoom in - the picture will remain complex and similar to general form. The elements are arranged in a bizarre way. Consequently, we consider concentric circles to be the simplest example of a fractal. No matter how close you get, new circles appear. There are many examples of fractals. For example, Wikipedia gives a drawing of Romanesco cabbage, where the head of cabbage consists of cones that exactly resemble the drawn head of cabbage. Readers now understand that making fractal antennas is not easy. But it's interesting.

Why are fractal antennas needed?

The purpose of a fractal antenna is to catch more with less. In Western videos, it is possible to find a paraboloid, where the emitter will be a piece of fractal tape. They are already making elements of microwave devices from foil that are more efficient than ordinary ones. We’ll show you how to complete a fractal antenna, and deal with the matching alone with the SWR meter. Let us mention that there is a whole website, foreign of course, where the corresponding product is promoted for commercial purposes; there are no drawings. Our homemade fractal antenna is simpler, the main advantage is that you can make the design with your own hands.

The first fractal antennas - biconical - appeared, according to a video from the website fractenna.com, in 1897 by Oliver Lodge. Don't look on Wikipedia. Compared to a conventional dipole, a pair of triangles instead of a vibrator gives a band expansion of 20%. By creating periodic repeating structures, it was possible to assemble miniature antennas no worse than their larger counterparts. You will often find a biconical antenna in the form of two frames or oddly shaped plates.

Ultimately, this will allow more television channels to be received.

If you type a request on YouTube, a video on making fractal antennas appears. You will better understand how it works if you imagine the six-pointed star of the Israeli flag, the corner of which was cut off along with the shoulders. It turned out that three corners remained, two had one side in place, the other not. The sixth corner is completely absent. Now we will place two similar stars vertically, with central angles to each other, slits to the left and right, and above them - a similar pair. It turned out antenna array– the simplest fractal antenna.

The stars are connected at the corners by a feeder. In pairs by columns. The signal is taken from the line, exactly in the middle of each wire. The structure is assembled with bolts on a dielectric (plastic) substrate of the appropriate size. The side of the star is exactly an inch, the distance between the corners of the stars vertically (the length of the feeder) is four inches, and the horizontal distance (the distance between the two wires of the feeder) is an inch. The stars have angles of 60 degrees at their vertices; now the reader will draw something similar in the form of a template, so that later he can make a fractal antenna himself. We made a working sketch, but the scale was not met. We can’t guarantee that the stars came out exactly, Microsoft Paint without much ability to produce accurate drawings. Just look at the picture for the structure of the fractal antenna to become obvious:

1. The brown rectangle shows the dielectric substrate. The fractal antenna shown in the figure has a symmetrical radiation pattern. If the emitter is protected from interference, the screen is placed on four posts behind the substrate at a distance of an inch. At frequencies there is no need to place a solid sheet of metal, a mesh with a side of a quarter of an inch will suffice, do not forget to connect the screen to the cable braid.
2. A feeder with a characteristic impedance of 75 Ohms requires coordination. Find or make a transformer that converts 300 ohms to 75 ohms. Better stock up on an SWR meter and select required parameters not by touch, but by instrument.
3. Four stars, bend from copper wire. We will clean the varnish insulation at the junction with the feeder (if any). The antenna's internal feed consists of two parallel pieces of wire. It is a good idea to place the antenna in a box to protect it from bad weather.

Assembling a fractal antenna for digital television

After reading this review to the end, anyone can make fractal antennas. We got so deep into the design that we forgot to talk about polarization. We assume it is linear and horizontal. This stems from considerations:

• The video is obviously of American origin, the conversation is about HDTV. Therefore, we can adopt the fashion of the specified country.
• As you know, few countries on the planet broadcast from satellites using circular polarization, among them the Russian Federation and the United States. Therefore, we believe that other information transmission technologies are similar. Why? There was a Cold War, we believe that both countries strategically chose what and how to transfer, other countries proceeded from purely practical considerations. Circular polarization was introduced specifically for spy satellites (moving constantly relative to the observer). Hence there is reason to believe that there are similarities in television and radio broadcasting.
• The antenna structure says it is linear. There is simply nowhere to get circular or elliptical polarization. Therefore - unless among our readers there are professionals who own MMANA - if the antenna does not catch in the accepted position, rotate it 90 degrees in the plane of the emitter. The polarization will change to vertical. By the way, many will be able to catch FM if the dimensions are set 4 times larger. It is better to take a thicker wire (for example, 10 mm).

We hope we explained to readers how to use a fractal antenna. A couple of tips for easy assembly. So, try to find wire with varnished protection. Bend the shapes as shown in the picture. Then the designers diverge, we recommend doing this:

1. Strip the stars and feeder wires at the junction points. Secure the feeder wires by the ears with bolts to the backing in the middle parts. To perform the action correctly, measure an inch in advance and draw two parallel lines with a pencil. There should be wires along them.
2. Solder a single structure, carefully checking the distances. The authors of the video recommend making the emitter so that the stars lay flat on the feeders with their corners, and rest on the edge of the substrate with their opposite ends (each in two places). For an approximate star, the locations are marked in blue.
3. To fulfill the condition, tighten each star in one place with a bolt with a dielectric clamp (for example, PVA wires made of cambric and the like). In the figure, the mounting locations are shown in red for one star. The bolt is schematically drawn with a circle.

The power cable runs (optionally) from the reverse side. Drill holes in place. The SWR is adjusted by changing the distance between the feeder wires, but in this design this is a sadistic method. We recommend simply measuring the impedance of the antenna. Let us remind you how this is done. You will need a generator at the frequency of the program you are viewing, for example, 500 MHz, and additionally a high-frequency voltmeter that will not give up on the signal.

Then the voltage produced by the generator is measured, for which it is connected to a voltmeter (in parallel). We assemble a resistive divider from a variable resistance with an extremely low self-inductance and an antenna (we connect it in series after the generator, first the resistance, then the antenna). We measure the voltage of the variable resistor with a voltmeter, while simultaneously adjusting the rating until the generator readings without load (see point above) become twice the current ones. This means that the value of the variable resistor has become equal to the wave impedance of the antenna at a frequency of 500 MHz.

It is now possible to manufacture the transformer as required. It’s difficult to find what you need on the Internet; for those who like to catch radio broadcasts, we found a ready-made answer http://www.cqham.ru/tr.htm. It is written and drawn on the website how to match the load with a 50 Ohm cable. Please note that the frequencies correspond to the HF range, SW fits partially here. The characteristic impedance of the antenna is maintained in the range of 50 – 200 Ohms. It’s hard to say how much the star will give. If you have a device on your farm for measuring the wave impedance of a line, let us remind you: if the length of the feeder is a multiple of a quarter of the wavelength, the antenna impedance is transmitted to the output without changes. It is impossible to ensure such conditions for a small and large range (remember that the extended range is also included in the features of fractal antennas), but for measurement purposes the mentioned fact is used everywhere.

Now readers know everything about these amazing transceiver devices. Such an unusual shape suggests that the diversity of the Universe does not fit into typical boundaries.

Wire fractal antennas studied in this diploma work, were made by bending wire according to a paper template printed on a printer. Since the wire was bent manually using tweezers, the accuracy of making the antenna “bends” was about 0.5 mm. Therefore, the simplest geometric fractal forms were taken for research: the Koch curve and the Minkowski “bipolar jump”.

It is known that fractals make it possible to reduce the size of antennas, while the dimensions of a fractal antenna are compared with the dimensions of a symmetrical half-wave linear dipole. In further research in the thesis, wire fractal antennas will be compared with a linear dipole with /4-arms equal to 78 mm with a resonant frequency of 900 MHz.

Wire fractal antennas based on the Koch curve

The work provides formulas for calculating fractal antennas based on the Koch curve (Figure 24).

A) n= 0 b) n= 1 c) n = 2

Figure 24 - Koch curve of various iterations n

Dimension D the generalized Koch fractal is calculated by the formula:

If we substitute the standard bending angle of the Koch curve = 60 into formula (35), we obtain D = 1,262.

Dependence of the first resonant frequency of the Koch dipole f K from the fractal dimension D, iteration numbers n and resonant frequency of a straight dipole f D of the same height as the Koch broken line (at the extreme points) is determined by the formula:

For Figure 24, b at n= 1 and D= 1.262 from formula (36) we obtain:

f K= f D 0.816, f K = 900 MHz 0.816 = 734 MHz. (37)

For Figure 24, c with n = 2 and D = 1.262 from formula (36) we obtain:

f K= f D 0.696, f K = 900 MHz 0.696 = 626 MHz. (38)

Formulas (37) and (38) allow us to solve the inverse problem - if we want fractal antennas to operate at a frequency f K = 900 MHz, then straight dipoles must operate at the following frequencies:

for n = 1 f D = f K / 0.816 = 900 MHz / 0.816 = 1102 MHz, (39)

for n = 2 f D = f K / 0.696 = 900 MHz / 0.696 = 1293 MHz. (40)

Using the graph in Figure 22, we determine the lengths of the /4 arms of a rectilinear dipole. They will be equal to 63.5 mm (for 1102 MHz) and 55 mm (for 1293 MHz).

Thus, 4 fractal antennas were made based on the Koch curve: two with 4-arm dimensions of 78 mm, and two with smaller dimensions. Figures 25-28 show images of the RK2-47 screen, from which resonant frequencies can be experimentally determined.

Table 2 summarizes the calculated and experimental data, from which it is clear that the theoretical frequencies f T differ from experimental ones f No more than 4-9%, and this is a quite good result.

Figure 25 - Screen RK2-47 when measuring an antenna with a Koch curve of iteration n = 1 with /4-arms equal to 78 mm. Resonance frequency 767 MHz

Figure 26 - Screen RK2-47 when measuring an antenna with a Koch curve of iteration n = 1 with /4-arms equal to 63.5 mm. Resonant frequency 945 MHz

Figure 27 - Screen RK2-47 when measuring an antenna with a Koch curve of iteration n = 2 with /4-arms equal to 78 mm. Resonant frequency 658 MHz

Figure 28 - Screen RK2-47 when measuring an antenna with a Koch curve of iteration n = 2 with /4-arms equal to 55 mm. Resonant frequency 980 MHz

Table 2 - Comparison of calculated (theoretical fT) and experimental fE resonant frequencies of fractal antennas based on the Koch curve

Wire fractal antennas based on a “bipolar jump”. Directional pattern

Fractal lines of the “bipolar jump” type are described in the work, however, formulas for calculating the resonant frequency depending on the size of the antenna are not given in the work. Therefore, it was decided to determine the resonant frequencies experimentally. For simple fractal lines of the 1st iteration (Figure 29, b), 4 antennas were made - with a length of /4-arm equal to 78 mm, with half the length and two intermediate lengths. For the difficult-to-manufacture fractal lines of the 2nd iteration (Figure 29, c), 2 antennas with 4-arm lengths of 78 and 39 mm were manufactured.

Figure 30 shows all the manufactured fractal antennas. Figure 31 shows the appearance of the experimental setup with the 2nd iteration “bipolar jump” fractal antenna. Figures 32-37 show the experimental determination of resonant frequencies.

A) n= 0 b) n= 1 c) n = 2

Figure 29 - Minkowski curve “bipolar jump” of various iterations n

Figure 30 - Appearance all manufactured wire fractal antennas (wire diameters 1 and 0.7 mm)

Figure 31 - Experimental setup: panoramic VSWR and attenuation meter RK2-47 with a fractal antenna of the “bipolar jump” type, 2nd iteration

Figure 32 - Screen RK2-47 when measuring a “bipolar jump” antenna of iteration n = 1 with /4-arms equal to 78 mm.

Resonant frequency 553 MHz

Figure 33 - Screen RK2-47 when measuring a “bipolar jump” antenna of iteration n = 1 with /4-arms equal to 58.5 mm.

Resonant frequency 722 MHz

Figure 34 - Screen RK2-47 when measuring a “bipolar jump” antenna of iteration n = 1 with /4-arms equal to 48 mm. Resonant frequency 1012 MHz

Figure 35 - Screen RK2-47 when measuring a “bipolar jump” antenna of iteration n = 1 with /4-arms equal to 39 mm. Resonant frequency 1200 MHz

Figure 36 - Screen RK2-47 when measuring a “bipolar jump” antenna of iteration n = 2 with /4-arms equal to 78 mm.

The first resonant frequency is 445 MHz, the second is 1143 MHz

Figure 37 - Screen RK2-47 when measuring a “bipolar jump” antenna of iteration n = 2 with /4-arms equal to 39 mm.

Resonant frequency 954 MHz

As experimental studies have shown, if we take a symmetrical half-wave linear dipole and a fractal antenna of the same lengths (Figure 38), then fractal antennas of the “bipolar jump” type will operate at a lower frequency (by 50 and 61%), and fractal antennas in the form of a curve Koch operate at frequencies 73 and 85% lower than those of a linear dipole. Therefore, indeed, fractal antennas can be made in smaller sizes. Figure 39 shows the dimensions of fractal antennas for the same resonant frequencies (900-1000 MHz) in comparison with the arm of a conventional half-wave dipole.

Figure 38 - “Conventional” and fractal antennas of the same length

Figure 39 - Antenna sizes for the same resonant frequencies

5. Measuring radiation patterns of fractal antennas

Antenna radiation patterns are usually measured in “anechoic” chambers, the walls of which absorb the radiation incident on them. In this thesis, measurements were carried out in a regular laboratory of the Faculty of Physics and Technology, and the reflected signal from the metal cases of instruments and iron stands introduced some error into the measurements.

The own generator of the panoramic VSWR and attenuation meter RK2-47 was used as a source of the microwave signal. An ATT-2592 electromagnetic field level meter was used as a radiation receiver from the fractal antenna, allowing measurements to be made in the frequency range from 50 MHz to 3.5 GHz.

Preliminary measurements showed that radiation from the outside significantly distorts the radiation pattern of a symmetrical half-wave linear dipole coaxial cable, which was directly (without matching devices) is connected to a dipole. One of the ways to suppress transmission line radiation is to use a monopole instead of a dipole together with four mutually perpendicular /4 “counterweights” that play the role of “ground” (Figure 40).

Figure 40 - /4 monopole and fractal antenna with “counterweights”

Figures 41 - 45 show the experimentally measured radiation patterns of the antennas under study with “counterweights” (the resonant frequency of the radiation practically does not change when moving from a dipole to a monopole). Measurements of the microwave radiation power flux density in microwatts per square meter were carried out in the horizontal and vertical planes at intervals of 10. Measurements were carried out in the “far” zone of the antenna at a distance of 2.

The first antenna to be studied was a rectilinear /4-vibrator. From the radiation pattern of this antenna it is clear (Figure 41) that it differs from the theoretical one. This is due to measurement errors.

Measurement errors for all antennas under study can be as follows:

Reflection of radiation from metal objects inside the laboratory;

Lack of strict mutual perpendicularity between the antenna and counterweights;

Not complete suppression of radiation from the outer shell of the coaxial cable;

Inaccurate reading of angular values;

Inaccurate “targeting” of the ATT-2592 meter at the antenna;

Interference from cell phones.

Answers to questions from the forum, guest and mail.

The world is not without good people:-)
Valery UR3CAH: "Good afternoon, Egor. I think this article (namely the section "Fractal antennas: less is more") corresponds to the theme of your site and will be of interest to you :) Is it true? 73!"
Yes, of course it’s interesting. We have already touched on this topic to some extent when discussing the geometry of hexabims. There, too, there was a dilemma with “packing” the electrical length into geometric dimensions :-). So thank you, Valery, very much for sending the material.
"Fractal antennas: less is more
Over the past half century, life has rapidly begun to change. Most of us accept achievements modern technologies for granted. You get used to everything that makes life more comfortable very quickly. Rarely does anyone ask the questions “Where did this come from?” and “How does it work?” A microwave oven heats up breakfast - great, a smartphone gives you the opportunity to talk with another person - great. This seems like an obvious possibility to us.
But life could have been completely different if a person had not sought an explanation for the events taking place. Take, for example, Cell Phones. Remember the retractable antennas on the first models? They interfered, increased the size of the device, and in the end, often broke. We believe they have sunk into oblivion forever, and part of the reason for this is... fractals.

Fractal patterns fascinate with their patterns. They definitely resemble images of cosmic objects - nebulae, galaxy clusters, and so on. It is therefore quite natural that when Mandelbrot voiced his theory of fractals, his research aroused increased interest among those who studied astronomy. One of these amateurs named Nathan Cohen, after attending a lecture by Benoit Mandelbrot in Budapest, got the idea practical application acquired knowledge. True, he did this intuitively, and chance played an important role in his discovery. As a radio amateur, Nathan sought to create an antenna with the highest possible sensitivity.
The only way to improve the parameters of the antenna, which was known at that time, was to increase its geometric dimensions. However, the owner of the property in downtown Boston that Nathan rented was categorically against installing large devices on the roof. Then Nathan began experimenting with different antenna shapes, trying to get the maximum result with the minimum size. Inspired by the idea of ​​fractal forms, Cohen, as they say, randomly made one of the most famous fractals from wire - the “Koch snowflake”. Swedish mathematician Helge von Koch came up with this curve back in 1904. It is obtained by dividing a segment into three parts and replacing the middle segment with an equilateral triangle without a side coinciding with this segment. The definition is a little difficult to understand, but in the figure everything is clear and simple.
There are also other variations of the Koch curve, but the approximate shape of the curve remains similar.
When Nathan connected the antenna to the radio receiver, he was very surprised - the sensitivity increased dramatically. After a series of experiments, the future professor at Boston University realized that an antenna made according to a fractal pattern has high efficiency and covers a much wider area. frequency range compared to classical solutions. In addition, the shape of the antenna in the form of a fractal curve makes it possible to significantly reduce the geometric dimensions. Nathan Cohen even came up with a theorem proving that to create a broadband antenna, it is enough to give it the shape of a self-similar fractal curve.
The author patented his discovery and founded a company for the development and design of fractal antennas, Fractal Antenna Systems, rightly believing that in the future, thanks to his discovery, cell phones will be able to get rid of bulky antennas and become more compact. In principle, this is what happened. True, to this day Nathan is in a legal battle with large corporations that are illegally using his discovery for production. compact devices communications. Some famous manufacturers mobile devices, such as Motorola, have already reached a peaceful agreement with the inventor of the fractal antenna."

Despite the seemingly “unreal and fantastic” situation with growth useful signal absolutely realistic and pragmatic. You don’t have to be a rocket scientist to figure out where the extra microvolts come from. With a very large increase in the electrical length of the antenna, all its broken sections are located in space in phase with the previous ones. And we already know where the gain in multi-element antennas comes from: due to the addition of energy in one element re-emitted by other elements. It is clear that they cannot be used as directional antennas for the same reason :-), but the fact remains: a fractal antenna is really more effective than a straight wire.

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• Duchifat: Is it really 9 milliwatts?

  With the new antenna, the reception of the Israeli Duchifat-1 has become noticeably better. It is always audible faintly, but it seems to be better with a stack of two 7-element antennas. Received a couple of telemetry frames. It's a bit sparse, I'm afraid my decoder is not correct. Or an inaccurate “translation” of packet numbers into parameters from DK3WN. In the package, the power from the sensor (forward) is only 7.2 milliwatts. But if he is telling the truth, then 10 milliwatts of his power on Earth can be heard perfectly :-)

• How beautiful this world is, look

  I just sat at the same table with the whole world. The passage indulges in the equality of microvolts from all directions. The same thing I wrote yesterday and the day before yesterday. Anyone who has been visiting me for a long time has already read it. And he listened. Below is a soundtrack of three interesting QSOs conducted at intervals of 5-7 minutes. There were still connections between them, but not so expressive, Japanese, Americans.... They can no longer be called DXs due to their large number :-)

  So, for the non-believers, three audios one after another: 9M2MSO, Malaysia, Puerto Rico NP4JS and finally the charming Cecile from Venezuela YY1YLY. I am grateful to the Almighty for the fact that we are so different, colorful, cool and interesting. All connections are like SSB selection. as if specially for everyone so that everyone can listen.... :-)

• Successful centenarian

  The successful DelfiC3 flew with its 125 milliwatts, it is perfectly audible, it is decoded with the Java gadget RASCAL perfectly and also sends the received lines to the support team website. AUDIO - Picture of the decoder below.

  

• Lost WEB receiver?

  We just had time to talk about the Java machine when SUN slipped us another pig :-) Of course, everything is for the benefit of the user. Only they forgot that they need to notify millions of people about the tightening of security requirements WEB users receivers, which in 90 percent of cases work through a Java machine. And, by the way, not only them. The creators of WED receivers (And, by the way, Windows itself too :-) try to do without JAVA using HTML5 and other twists, but it doesn’t always work. Too long a story connects them: everything is tied to the characteristics of the hardware. My laptop, for example, using HTML5 can provide control of the receiver, but cannot receive sound :-) Just think, the receiver shows everything, but is silent :-) In short, today only Vadim, UT3RZ, will help you.

  "UT3RZ Vadim. Priluki. http://cqpriluki.at.ua In connection with the update of Jawa on January 14, 2014 to version 7 Update 51 (build 1.7.0_51-b13) problems arose with listening to WEB SDR receivers. The creators of Jawa, pursuing the security goals of computer users, in their new version 7 Update 51 introduced the need for user confirmation of security manually.

• Check your TNC's ears

  Out of boredom, I listened (poked;-) to the ISS digipeater channel. It rustles quite well and quite actively. Audio control, of course, recorded everything. The toad crushed the recording. Here I put it, check the settings of your modems or TNCs. It's beautiful there, in Space. It’s really really boring: the same faces all year round :-(

  

• Telegram UR8RF

  Radio Promin
  

  I love everyone. Today, November 17, on Radio Promin on protyazhi 40 Khvylin Volodymyr UY2UQ learned about amateur radio. You can listen on the Radio Promin website in the audio archive on November 17.
  Hour 15:14:14 - 15:54:38 http://promin.fm/page/9.html?name=Audioarhiv1http://promin.fm/page/9.html?name=Audioarhiv1
  73! With the car Oleksandr UR8RF

• The Internet goes to Morse

  In December 2011 Google company announced the release of a Gmail app for iOS that lets you quickly take short notes. The company's press release noted that such records were used by cavemen when making drawings on rocks. And now the software for quick notes has received its logical continuation - Google announced a fundamentally new way of typing on the keyboard of mobile devices.
  Gmail Tap is the name of the application with which the transition from the usual 26-key smartphone keyboard to a two-button one will become a reality. You heard right. From now on, users of both iOS and Android devices will be able to use Gmail Tap to type text messages using only two buttons - a dot and a dash. Google specialists led by Reed Morse (the great-great-grandson of the famous inventor of Morse code) are offering users a simplified version of Morse code, with which SMS messages can be typed no slower than with a standard keyboard. The ability to type two messages at the same time is admirable. The mode for advanced users “multi email mode” involves the use of two keyboards - a standard one at the bottom and an additional one at the top of the screen. And even a novice Gmail Tap user can quickly learn how to type without actually looking at the keyboard. Look how easy it is: