What to make a gsm antenna from. Homemade passive mobile phone and Internet repeater. Here is the antenna design

I hate fishing, because I feel sorry for the wasted time. But, nevertheless, I spent the whole week preparing for fishing. The task was set to catch the mobile Internet and additional risks of the level of the received signal on the screen of a cell phone or smartphone, and it was necessary to catch it in the field without active amplifiers and batteries. This can be done using a passive repeater.

It’s probably already happened that in order to look at something on the Internet or make a call on a cell phone, you almost had to climb onto the roof or hang half out of the window, catching the risk on the screen of your cell phone or typing an SMS card to throw phone up, or raise it along with the flag on the flagpole.

First, try making a simple passive repeater for a 3G signal or cell phone. Two simple directional antennas made of wires, a coaxial cable connecting them, that's the whole structure. With the help of such a simple mobile device that does not require power, you can provide communication in a basement, in a metal hangar or garage, in a de-energized bomb shelter or in another place where a cellular signal does not reach.

The size of the antennas themselves will correspond to the selected communication frequency: for a cell phone frequencies are 900 MHz and 1.8 GHz, for mobile Internet about 2 GHz. For the experiment, I made an antenna at 900 MHz, but in practice it also turned out to be operational from 1.8 to 2 GHz. Subsequent measurements of the homemade antenna showed that the range of its excellent matching almost reached 2.080 GHz, otherwise I would not have received the 3G Internet signal.

If anyone has already assembled a “simple antenna for receiving terrestrial digital television” from two wire rings, they can easily cope with the task. Everything is done in the same way.

The diameter of the mandrel (glass) is 4.3 cm. Frequency is 1.9 - 2.2 GHz.

Determine the wavelength in meters L m = 300 / 900 MHz = 0.33 m

Diameter of the wire turn (ring) D = L / 3.14 = 0.33 / 3.14 = 0.106 (m)

Distance between rings S = L / 4 = 0.33 / 4 = 0.08 (m)

Accordingly, with increasing frequency, the frames will decrease in size, and losses in the coaxial cable will increase. Antennas at other frequencies will also be calculated.

How does this work. One directional antenna, removed from an absorbing reinforced concrete wall or raised above the metal roof of a country house, or simply raised above the ground, is oriented towards the base station. The second antenna, be it a basement or a room in a country house, should be aimed at a mobile phone or smartphone or located next to them.

Since the antenna is directional, it has a gain, in this particular case equal to 5 dB. Some of this gain will be lost in the cable. In the cable RK 75 - 3. 7-35, 6 meters long at a frequency of 900 MHz, I lost, as it turned out later, 3 dB, which, taking into account the error, coincides with the technical characteristics of the feeder used. The efficiency of the antenna in free space is better with increasing height. It induces more field strength and improves direct visibility with the base station, providing stable communication, since houses and trees are no longer an obstacle to radio waves.

If it is necessary to use several frequencies, several repeaters with different ring diameters will be required. Here, as when fishing, you need all sorts of bait, so I prepared the gear like an avid fisherman, bending wires like hooks of different diameters. Everything will depend on the conditions. Let's see what we can catch.

Test site.

All that's left is to try. Here is the fishing spot, an old gazebo. The rod is made from a miraculously preserved shortened antenna mast, which saved me when I was flying from the roof, and therefore I definitely won’t climb a tree, at my age bones don’t heal well. The pole was extended with plastic tubes, in which low-current wires are usually laid. Even a wooden glazing bead was used, because the antenna itself weighs little. Turning the fishing rod, I point the rings towards the nearest town, temporarily turning into a fox hunter. Next to the rings of the antenna below, I place my mobile phone.

Using a repeater, the mobile phone added three marks on the display, providing 100% communication with the nearest civilization (base station), located 6 kilometers behind the forest. For those who like to chat on a cell phone for a long time outside the city, such a device is simply necessary. As a rule, far from base stations, the phone produces full power, which is harmful to health. The correct phone (meaning a small SAR value - the sanitary norm), having a good connection with the base station, will deliver less power to the antenna, which means that the body will be less exposed to the microwave field. But I already talked about this in the article.
“protect yourself from cell phone radiation.”

By evening, more and more people want to check their mobile phones and smartphones. The tablet came to life, slowly loading, showing individual pictures of television programs. The smartphone began to flip through the pages of the GRANDFATHER CLUB…. They moved a few meters away from the repeater, but the Internet pages continued to turn over.

Everything works.

Or maybe this is a joke, maybe 3G is already working everywhere?

Offended, I throw my fishing rod on the ground. You can see from the dissatisfied faces that everything is frozen, lines and symbols have flown off the displays.

I hate fishing, so much free time is wasted!

True, I have not yet seen a fisherman who would not return to the old place to try another bait. Only the diameter of the mug was tested (900 MHz), the diameter of the glasses is still ahead (2-2.2 GHz). Well, the bait on the spiral antenna will complete the catch , I foresee in advance that the construction will be heavy, but for a hospital it’s what we need.

Yes, by the way about polarization. In a hurry, or maybe out of absent-mindedness, I completely forgot about it and already when I was looking at the photographs I remembered. Base mobile cellular stations have antennas with vertical polarization, and therefore the tackle on the fishing rod had to be rotated 90 degrees, so that the section of the rings was not at the bottom, but at the side, which corresponded to a similar polarization. However, it was possible to catch the radio signal even with horizontal polarization of the rings on the mast, despite the minimal loss of 6 dB due to mismatches, the experiment was a success. On the other hand, the forest has its own laws and the passage of a signal with horizontal polarization is better in it.

P.S.

Two years have passed. This summer, in 2016, I was preparing for the arrival of my grandchildren on vacation from their parents or vice versa, and I decided to install digital television in the gazebo, watch cartoons, and just to catch my breath. So that the antenna would not be conspicuous, I wove it from wires and called it an invisible antenna. The result was four rings, which performed better when receiving digital television than the two-ring design. I wrote in detail about this design in the article “Invisible antenna - phased eight for terrestrial digital television.”

I wove similar two antennas for a passive mobile communications repeater on the 900 MHz band, just in case someone needs the Internet. Today there is no Internet in our lowland yet. The "H" icon appears, but it takes years to load. The double eight, laid flat, was raised to the level of the roof of the gazebo, and it became invisible in the crown of the wild apple tree. Thanks to this design, the mobile phone added two risks to the two levels. This seemed to be the end of the experiment, but there was still a moment of triumph when young parents urgently needed the Internet. The repeater did not fail, caught the Megafon operator, and quickly downloaded the necessary information. At that moment I felt like a magician who, with the help of a wire frame, opens a new spring.

We live on the edge of a small village. Faced with the need for the Internet at home, we began to study what modern infrastructure offers in this sense.

It turned out that the most affordable and easiest way to connect to the World Wide Web is a GSM modem, inexpensive versions of which are often called a USB whistle. Such a modem is inexpensive, widespread and works well, but only in the area of ​​reliable signal reception of a cellular network base station. In the city, please be kind, but outside of it, it greatly depends on how developed the mobile network is. Often a modem requires a good external antenna raised to a certain height. Models of devices with connectors for connecting an external antenna are considered a kind of professional communication device and cost ten times more.

To work, you will need a minimum set of radio installation and plumbing tools, and a little patience. For working with small items, a special visor with magnifying glasses or a lamp with them is very useful. Make sure you have good lighting.

However, even in a simple “USB whistle” there is a technological connector for an antenna inside the case and you can use it. Some modems have access to the antenna connector, some do not; in the latter case, you will have to modify the plastic case, which will void the device's warranty. The antenna connector of a budget modem is very flimsy in design and is installed directly on the printed circuit board using the surface mount method. That is, it only holds on to the rations.

My connection option - I picked up a fairly flexible television cable in the store - without a foil screen, the central core is copper (soldered well) and multi-core (flexible). The connection looked like this.

That's it, the modem is connected.

Let's move on to the calculation and manufacture of the antenna.

Antenna type, “log-periodic” was selected, the accepted foreign abbreviation is LPA antenna. Its features are high gain and a very narrow (sharp) radiation pattern. In addition, with sufficiently careful manufacturing, the antenna will not require adjustment, which cannot be done without specialized RF measuring instruments.

We prepare the necessary materials and tools. At the first stage, we need to cut two strips of one-sided foil fiberglass 10mm wide, 1.5-2mm thick, and long - according to calculations. We will also need trimmings of “bare” copper wire with a diameter of 1.5-2.5 mm, which can be removed, say, from a cable for internal electrical wiring. Well, accordingly, a soldering iron, rosin, a ruler and wire cutters.

Due to the inconvenience of orientation, it was necessary to make a rotating unit. Some metalwork, cutting stainless steel, welding work.

Increasing the cross-section of the supply wires has already been tested during test activations of the antenna “on the stairs”. There was a connection and access to the network, but it did not work stably - it was interrupted periodically.

To place the antenna with the rotation unit, another place was chosen - the pediment of the roof of the house. The distance to it is somewhat greater and it was decided to place the power supply “at the top” - near the modem, eliminating the possible cause of failures. The “long” USB connection was made of two thin coaxial cables (central cores - two data lines, screens to a common wire).

What happened was the placement on the roof gable (access from the flat roof of the woodshed via a short ladder) and the general configuration of the equipment, which subsequently made it possible to conveniently experiment with different types of antennas. At that time, it was possible to connect relatively stably to the GSM (2G), sometimes WCDMA (3G) network. The antenna itself performed well. Some painstaking manufacturing (many precise dimensions) pays off in the absence of adjustments and high gain. The antenna also has a low windage and is not very attractive to birds.

Looking ahead. The reason for the unstable operation of the modem turned out to be the long USB cable, despite the well-being of the device’s power supply. Perhaps it was a matter of the type or even the type of modem, because there are descriptions of similar “extension cords” and larger footage on the Internet.

The manufacture and testing of two more types of antennas will be described separately.

The GSM standard was invented by Europe in 1982, along with several related to communication via radiotelephones. The direction of the antennas was problematic; the transmitters were located near the person’s head. The harm was noticed quickly, it is widely known: employees of enterprises involved in communications receive wage increases. Without thinking twice, the standard committee introduced a new type of modulation that allows for lower power. The antennas were first made retractable, but later they took on the appearance of stumps protruding from the body of the device. The filling rapidly decreased in size along with power supplies; the direction of small-sized antennas in the gigahertz range is relatively young. The first developments concern the 50s of the last century. DIY GSM antenna: how to make it, where to install it. Let's talk in more detail.

Development of the GSM standard, GSM antennas

Those who bother to look inside a mobile phone or other gadget are powerless to see structures that resemble an antenna familiar to the eye. A thoughtful manufacturer designs, guided more by experimental considerations, devoid of a coherent theory. There is no point in thinking that a review will reveal the company's corporate secrets. Since 3G, digital standards, there has been a constant struggle to accommodate more information using fewer resources. They mentioned the harm, inside the cell phone the emitter is located in the rear wall area, separated from the user by a ground screen. Microstrip technology has been known for a long time. Veselov’s book from the 80s describes the concept in the third part.

The efficiency of a GSM cell phone antenna is low, reaching 40%. Ordinary television ones sometimes go over 90. However, people don’t care; the harm to health is minimal. Every marsh sandpiper praises a cell phone, hears the interlocutor perfectly, and when the opponent’s connection is lost, the sound disappears... This means the cell phone is bad. The radiation pattern of the GSM antenna of a cell phone is one-sided - it does not shine in the direction of the speaker - it is greatly distorted. The user changes the balance of power with his hand, let alone obstacles! A GSM antenna is made by hand to improve reception by stationary objects. Mobility is limited to use by auto repair shops.

GSM antennas of transmitting stations are well equipped and emit excellent radiation. We hear the interlocutor (if he does not make sudden movements), the opponent will lose packets while jogging or in transport. The phone receives 5 stars and transmits much worse. Incoming packets with the opponent's voice arrive regularly, outgoing packets fail.

Now readers know: it is not possible to make a GSM antenna using microstrips yourself at home. Famous companies are fighting to solve the problem. Assembly and functional design takes minimal time, production is cheap. The layout of the internals (the antenna is not easy to fit into a modest space) is much more complicated.

The following standards are in use in the Russian Federation:

1. GSM 900: transmission frequency 890 – 915 MHz, reception frequency 935 – 960 MHz.
2. GSM 1800: transmission frequency 1710 – 1785 MHz, reception frequency 1805 – 1880 MHz.

A microstrip antenna consists of an emitter, a dielectric substrate, and a conductive screen. As the thickness of the emitter increases, the operating range, a tenth of the wavelength, increases. The dielectric thickness is less than the specified value. We are telling this for a reason. In the Wi-Fi range, microstrips are combined into grids, sealed with a plastic case, equipped with a single screen, and act as a single command, allowing for good amplification and, therefore, to catch a more distant signal. The towers are stationary and in direct visibility. If what is said is true for a specific situation, the solution is suitable.

Here is a picture (from the website http://www.carookee.net/) of a 2.4 GHz antenna. To start working at a frequency of 1800 MHz, you need to increase the dimensions proportionally in the ratio of 4 to 3. Please note, this applies to all lines, including connecting lines. First try the functioning of one square before reducing the getinax board to the sacrifice of the needs of mobile communications. The scale of the portal is incorrect - see the picture with dimensions, arrows are shown. Image taken from http://www.zero13wireless.net/. The numbers are in millimeters. Proportionally remove drawing number one, determine the dimensions. The areas are square; if they are distorted, correct them with a graphic editor; even Paint, included by default in Windows, will do.

For other frequencies, feel free to extrapolate the drawing to all cases in proportion to the wavelength ratio. Divide 2400 MHz into the standard GSM band. The ratio 2400/1800 was taken above. By doing this, readers will select the desired GSM antenna device. Containing 4x4 squares gives less gain (amplification of the GSM antenna signal), and is easier to point. The reception is blurry, it is unclear where the signal is coming from, the design is in place. In the case of a distant tower, clearly visible on the horizon, 9 squares would be appropriate. Please note that the feeder to the telephone (another receiving device) should not be long; the signal will fade on the way here, in the cable. I would like to place the device on the roof... assemble an amplifier using microstrips, buy a ready-made one in a store for the desired frequency. Find out the required number from your mobile operator. A state frequency service has been created, ask officials to talk to private owners.

Manufacturing of GSM antenna

Most readers have understood how a homemade GSM antenna can be made. The craft will require a getinax board of a suitable size with double-sided foil. Copper is applied on one side - it will be necessary to add a reflector structure from a sheet of steel or another metal with an area larger than the emitter. Then the copper is lined with the future contour of the antenna. Do it more carefully using a ruler and a corner. Then:

• The area under the antenna is covered with varnish, suitable for women's nails. The composition should not get on the surface in other places, on the joints; you can paint over large islands, then peel them off with a knife (to increase the processing speed).
• The boards are etched with copper sulfate. The foiling is double-sided - the back is completely painted over with varnish. Otherwise the screen will not dissolve! It’s just that the etching will not end in a conceivable time. Copper sulfate is not enough. The second side is not needed - tear it off with a knife. To preserve the screen you need to paint it with varnish.
• Etching is carried out until unnecessary areas of copper are washed off, the finished GSM antenna is washed with water, dried, and problem areas are cleaned with a knife.
• The product is placed inside a sealed plastic case of suitable dimensions on stands that do not affect the metal part. The screen needs to be grounded. Try placing it on the braid of a coaxial cable. We remind you: for WiFi, a wire with a characteristic impedance of 50 Ohms is used. How much to take for cellular communications: 50 seems appropriate because 900 MHz television is running out.

Types of GSM antennas

They wrote a lot about antennas for WiFi, readers guessed: the ranges are very similar... just take the drawings, transfer them to other frequencies, the dimensions are indicated everywhere in relation to the wavelength. Transpose sketches proportionally. The procedure is indicated above. It is easy to find on the Internet the so-called Kharchenko antenna (biquadrat), which is a pair of frames with one common point. More advanced solutions were presented, characterized by greater gain.

Readers will have a choice of which remote GSM antenna will be manufactured. Kharchenko's biquad design is made by radio amateurs from strips 10 mm wide, with a square side in the center of 80 mm. The dimensions were not checked, the dimensions are determined by the wavelength used by the GSM standard. For 900, 1800 MHz the difference will be two times. Check the dimensions of the drawings carefully. The frame must be proportional to a quarter of the wavelength. The formula is known from a physics course; there is no point in presenting four drawings that differ in small details. You need to understand: an external GSM antenna is similar in structure to WiFi, we believe that any of the sections can be moved here. The difference is limited by frequency, modulation. The first does not affect reception, the second determines the size of the GSM antenna.

When using an extension cord, try to place the amplifier close to the mounting point. Wire noise greatly reduces the sensitivity of the device.

Often in rural areas the signal strength from cell towers is low and we only see one or two bars on the phone. But there is an easy way to boost your signal without buying expensive 3G boosters. In this guide, we will create a 2G/3G/4G signal amplifier for a summer residence using improvised means. This amplifier will be able to increase the signal level in the house from one division to full scale. To do this, you need to build two modules - one outside the house and one inside. Both of them are the same and easy to create, assembly will take about 1-2 hours. Before starting work, put on safety glasses and gloves. The LTE antenna was primarily designed to enhance the E GSM 900, 2G signal. To get meaningful results, you need to at least catch at least some signal on the street.

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Use a homemade antenna for a 4G modem at your own risk.

To begin, find the necessary components:

1. Iron hanger 2-4 mm thick (be sure to check with a magnet that it is made of iron). Any iron wire will do; the absence of paint will increase the efficiency of the system.
2. Two blocks for connecting the cable (20A, if you have one).
3. Regular cable: - TV cable, coaxial, from satellite TV (you need 30 m of good quality cable, not cut, not from connected parts).
4. Wire scissors.
5. Pliers.
6. Screwdriver.

Step 1: Let's start assembling the remote antenna

Look at the picture. The first section that we will assemble from an old iron hanger will be the 3G antenna. It is indicated in black. It does not require cleaning off the exterior paint.

1. Align the wire using pliers (or your hands) and bend it 4 cm from one end at a 45 degree angle.
2. Then measure 8 cm from the bend and bend the wire inward 90 degrees.
3. Next, measure 9 cm again and make another bend 90 degrees inward.
4. The last bend will be the same as the first - 45 degrees, here we will install a block for connecting the cables. Place the block on both ends of the cable and secure it.

The wires are connected inside the connector block. Areas 4 cm long must be cleared of braid/paint. As a result, you need to assemble two identical modules.

The next step in assembling a GSM cellular and Internet signal booster is the wireless antenna, highlighted in orange and yellow in the picture. For this section we will need a regular TV cable. First, cut off about 15-20 cm of the top covering of the cable. You will see a shielding covering, it is metallic and looks like a net. Cut it off too, but don't throw it away - it will be used as material for the red area in the picture. Just twist it and trim it if it's too long. Then install it into the connector block and secure it (the U-shape is not necessary - the connection itself is important). Then go back to the cable core, carefully cut off the insulating layer - to create a 4G directional antenna we need the bare cable.

Let's look at the drawing again. At a distance of about 5 cm from the beginning of the core, we need to make 5 turns clockwise. You can wind the cable on a screwdriver bit with a diameter of 3-6 mm. The rest of the cable core should be level. Now we need to connect our wireless antenna with the 3G antenna. To understand how to do this, look at the pictures. Remember that we need to connect the antenna core with the iron wire and secure them in the connector.

After some research, I came to the conclusion that 7 turns of cable on the outdoor antenna and 5 turns on the indoor antenna are best for 4G amplification. Use your smartphone to locate the location with the best 4G signal - place the external antenna in that location. A good signal level is determined by approximately 3 bars on the phone; an unstable signal very often jumps up and down.

If after assembling the antenna the signal remains weak, try using trial and error to find the best number of turns on the antenna for you. Usually the best signal is found on the roof of a house or close to the roof. Place the internal antenna where it is most convenient for you - in a vertical position, preferably under the ceiling, in the room in which you do business, and also at a distance from the wireless router. For ease of antenna setup, I advise you to switch your phone to 2G mode. If your home has been struck by lightning, place the antenna in a safe location. Also, to strengthen the signal, you can try removing the case from the phone - it often jams part of the signal.

Non-insulated parts of the antenna should not touch walls or conductive surfaces.

Step 2: Addition

To boost the signal, you can try cutting a piece of kitchen foil about the length and thickness of your phone and sticking it to the left or right side of the phone (or try hiding it inside a phone case). Telephone headphones can also act as an antenna - many people have noticed that the signal is better with them.

Step 3: Extra Wire

Look at the photo above. I added an extra wire to try to increase the coverage area of ​​the indoor antenna. I got this result by trial and error: you need to take an additional wire 30 cm long, leave about 5 cm on one side and make 4 turns around the pencil, and then connect this wire to the connector. But this improvement will not increase the signal strength.

Step 4: Version 2.0

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Version 2.0 is more like science fiction. It has more promising performance, but still needs to be installed in a place with a stable signal. If something becomes unclear, look at the photographs.

Assembly, part 1.

1. Align the wire from the iron hanger.
2. Make a bend at an angle of 45 degrees at a distance of 4 cm from the end of the wire, clear these 4 cm of paint/coating.
3. Measure 8 cm from the bend and bend the wire inward 90 degrees.
4. Measure 9 cm after this bend and make another fold 90 degrees inward.
5. Next, measure 9 cm again and make another bend 90 degrees inward.
6. At a distance of 8 cm, make another fold 90 degrees inward.
7. Rotate the wire 90 degrees.
8. Measure 9 cm from the bend and bend the wire inward 90 degrees.
9. Measure 10 cm after this bend and make another bend 90 degrees inward.
10. Next, measure 10 cm again and make another bend 90 degrees inward.
11. Measure 11 cm from the bend.
12. The last bend is the same as the first - 45 degrees inward. You also need to remove the paint/coating from it.
13. Insert the ends of the wire into the connector and clamp them.
14. This will be an internal and external 3G antenna combined in one.

Assembly part 2.

1. Take the 3G antenna we made at the beginning of the tutorial (yellow)
2. Bend the antenna wires 90 degrees.
3. Attach the antenna to the connector as shown in the figure.

Assembly part 3.

1. The wireless antenna has almost the same design.
2. It will have 7 turns for the external module and 5 turns for the internal module.
3. It should reach the antenna described in “Assembly Part 1”, so it will have to be pushed a little through the connector.
4. After successful assembly, secure everything.

Step 5: Modifying the Antenna for the Wireless Router

Here's what I did with my Dlink 2750E ADSL N-300 wireless router. With a small modification to the antenna I was able to achieve a more stable connection through a solid concrete wall. You can also try this trick.

The situation was hopeless. The monotonous pine forest swirled around me like a colonnade. Two hours later I again found myself in the same place where I was before. I got lost and panicked. Cell phone service didn't work. I decided to find a higher place in the hope of getting a cellular signal. He rushed into the clearing and ran out into a clearing with a lone pine tree. On the tree there is a bird feeder and a piece of paper sealed in plastic with the text: “To make a call, place the phone in the house with the buttons facing up. Turn on speakerphone or connect a headset." Next, the telephone numbers of the forestry department, police, and administration were listed...

When I was already bringing the mobile phone into the feeding house, I noticed that on the phone, next to the symbol indicating the antenna, the cellular signal strength diamonds flashed. The revived telephone refreshed my mind, and the house turned out to be an antenna, protected by the roof from rain and snow, and a coaxial cable running upward from it at a height of 5 meters was connected to another directional antenna. A homemade GSM signal repeater, as I didn’t immediately guess. It does not need any power supply or amplifier, which is why it is called passive. In the mobile phone itself there is no need to look for a high-frequency connector for connecting an external antenna, since its built-in antenna complements the design of the repeater antenna.

The maximum communication range at this frequency in line-of-sight conditions, when hills, houses and trees do not block the path between the antennas, reaches 35 kilometers. It’s unlikely that I could have gone that far, the thought flashed in my head, because the phone is not directly connected to the antenna, there are probably losses in the passive repeater, and I was glad to see that I was separated from civilization, no matter how 10 km.

- Found! Everyone has already been put on their feet. “The devil’s tract”, you can’t get out of there without help, there are swamps all around, a quagmire. Stay where you are, don’t go anywhere, in 1.5 hours Musya will lead me there. Musya is my horse, she knows how to get there.

I had a lot of time to study the passive repeater design.

StandardGSM 900.

The antenna must work for both reception and transmission, so its range is from 890 (880) to 960 MHz, where in the range of 890 - 915 MHz transmission from a cell phone to the base station is provided, and within 935 - 960 MHz there is signal transmission from the base station to the phone.

Here is the antenna design.

photo 1.

DirectedGSM 900 patch antenna.

A suspended plate patch antenna is similar to a microstrip antenna. Its advantage is its small dimensions and ease of manufacture.

These are two plates and an L - vibrator. Antenna elements can be made of copper, brass, aluminum.

The larger plate is a reflector; it reflects radio waves. The braid of the coaxial cable is connected to the reflector. For the convenience of connecting the coaxial cable, desoldering and attaching the L-shaped vibrator, I used a high-frequency SMA type connector. If the cable is attached without a connector, then there is no need to drill a hole, but it is necessary to provide a dielectric fastening of the L-vibrator.

The thin plate is an active L-shaped vibrator, it is connected to the central core of the coaxial cable. I soldered it to the connector and used an additional fastening in the center using an insulator.

Rice. 2. Sketch of an L-vibrator.

A smaller flat plate, by analogy with a “wave channel” antenna, is called a director, and is not electrically connected to anything, but is mounted on dielectric supports - racks.

Rice. 3. Director.

Support posts can be made of plastic, foam, wood.

Purchased (factory) antennas for this frequency have a characteristic impedance of 50 Ohms, and are accordingly equipped with a cable with a characteristic impedance of 50 Ohms. So, for a homemade passive repeater, it is also advisable to adhere to a wave impedance of 50 Ohms, which is associated with lower losses compared to the 75 Ohm standard.

Options.

Compared to the gain of a quarter-wave rod, the antenna we made provided 5 dB more gain.

At the center frequency SWR = 1.2. At the edges of the range SWR = 1.5

Antenna as a passive repeater.

It is convenient to use such an antenna as a stand for a mobile phone when constructing a passive repeater, in which the cell phone with its built-in antenna will be the director.

Let me remind you that the repeater consists of two antennas connected by a coaxial cable. One antenna is raised above the ground and aimed at the base station, and the second antenna is located in close proximity to the mobile phone. At the lower table antenna, I made the director out of plastic, without changing the height of its mounting, and placed the phone on the pedestal.

When I did this experiment outside the city, the mobile phone added four levels to one risk. In addition, I received an SMS that I had left my home region. Typically, such messages come after 15 km from the test site, which is located on the border of two regions. In this case, the phone reliably received signals from a base station from a neighboring region.

The factory Radant 911 antenna was used as a directional antenna.

Frequency range 890 - 960 MHz, input impedance 50 Ohm, beamwidth 45 degrees, vertical polarization, gain 11 dBi. It was suspended under the roof of the gazebo, at a height of three meters from the ground. A two-meter 50 Ohm cable was connected to a patch antenna on the table. In the patch antenna, instead of the director, there was a mobile phone on a plastic pedestal.

In my experience with the repeater, I deliberately provide for additional losses by installing the antenna under the roof of the gazebo (1 cm of wood, plus soft roofing) to ensure that the passive repeater is working.