The range of your cell phone can be increased by equipping it with an external external directional antenna. How to independently produce such the antenna, and is told in the article. The antenna can be successfully use in the country, in a remote country house, and even given its small the dimensions in the field.
The advantages of cellular telephone experience and new new users of cell phones. The opportunity at any time and from virtually anywhere to call the right person makes this kind of communication, perhaps the most popular and attractive.
But in addition to the numerous and indisputable advantages of cellular telephony, as every technical tool, have certain inherent disadvantages. Remember having to pay for every second of the conversation. In addition, cellular characteristic phenomena such as the presence of "dead" zones and the deterioration of communication quality at a considerable distance from the antenna nearest base station.
Many cell phone users probably know the situation when have to search long for the place where the apparatus can realize sustainable the network connection. Moreover, such situations arise not only away from the antenna network base station (which is typical for remote locations, for example, on a garden a plot), but in the city, where the base station signal can be shielded buildings, structural members, etc.
To help in these cases, an external antenna connected to a mobile phone. It certainly limits the mobility of the subscriber, "binds" it to this the antenna, but this limitation can be quite an expensive price to pay for high-quality communications.
When designing stationary external antenna for cell phone was chosen the zigzag design of the antenna [1, 2], widely used in professional communication and popular radio and TV viewers.
Antennas of this type in the range of frequencies used in cellular telephony, allow to realize a good performance at compact dimensions, it is enough easy to manufacture and set up, have a good repeatability of the parameters in their manufacture.
Zigzag antenna consists of eight closed conductors of length L, forming two diamond-shaped cells (see figure). The antenna design is such that its conductors excited at the points a and b, form a kind of common-mode antenna of four vibrators. Antinodes (maxima) are current the feed points and corners marked P. the Antenna has a linear polarization, in the shown case - vertical.
The radiation pattern of the antenna is maintained in the range of frequencies with overlapping fmax/fmin = 2...2,5. The directional characteristic of the antenna is symmetrical relative to the plane of the conductors.
To increase the directivity of the zigzag antennas used reflector, reflecting the falling portion of the energy toward the leaf antenna. Phase field, reflected by the reflector in the plane of the blade antenna should be close to the phase the fields radiated by the blanket, then the in-phase addition of the fields radiated and the reflected signals increases the directional coefficient (KND) the antennas. The phase of the reflected field depends on the shape and size of the screen, but way, and the distance between it and the leaf antenna.
Standard GSM cellular communication provides communication ranges frequency 890...960 MHz for GSM 900 and 1710...1880 MHz for GSM-1800 [3, p. 102], moreover, at frequencies 935... 960 MHz and 1805...1880 MHz organized direct channel, and at frequencies 890...915 MHz and 1710...1785 MHz return channel. In the frequency range 890...960 MHz antenna is a traveling wave ratio (IPM) is not worse 0,77 and KND no worse than 7 dB compared to the half-wave dipole. In the frequency range 1710...1880 MHz IPM antenna of not less than 0.5, and KND - no worse than 6 dB.
The antenna design is clear from the figure.
The basic calculation parameter L determines the operating frequency of the antenna. For zig-zag antenna directional coefficient action depends on the ratio L/λ and KND is maximized when L/λ to 0.4. Maximum IPM to 0.8 is achieved at L/λ is 0.3, while the relationship L/λ = 0,25...0,5 IPM is an amount not less than 0.5. Therefore, for high frequency the operating range of the antenna was chosen value of L = 80 mm, L/λ is 0.37. In addition to L, the value of IPM is influenced by the width of the vibrators antenna d and the distance from paintings of the antenna and the reflector. Usually it is recommended to choose d = 0,033 λmax, where λmах - maximum wavelength operating range of the antenna. In our case, d = 10 mm From the point of view of increasing directivity of the antenna the distance to the reflector preferably to reduce, as from the point of view of harmonization is to increase. In this design it is 45 mm, which provides the above-mentioned characteristics of the antenna.
The canvas of the antenna 1 and the reflector 2 is made of one-sided foil-tion fiberglass brand of SF-1 with a thickness of 1...1.5 mm Blade antenna formed two symmetrical square cells that are cut from Folle-giovannoli fiberglass on the outside of the contour of the antenna. Inner contour zigzag antenna prozharivaetsya cutter from the side of the foil, after which foil from the inside of the loop antenna is removed. To facilitate removal of foil can be preheated powerful soldering iron. If you want you can delete and a large portion of the dielectric inside the antenna.
In the points close to the tops of the cells aerial fabric, drill hole screw MOH or M4. The same holes are drilled in the reflector 2 (screen). Canvas antenna 1, on the one hand, and the reflector 2, on the other, are screwed to the posts 3 screws. Racks are made of any dielectric material (PTFE, plated hardened paper, plexiglass, etc.), you can put and metal stand. Inside of them on each side, drill holes with a diameter of 2.4 or 3.2 mm to a depth of about 10 mm screw threaded MOH or M4. The antenna is fed coaxial cable with a characteristic impedance of 50 Ohms. B solder the center conductor of the cable is released from the braided shield, and to the point and - braid (shield).
The cable is routed along the vibrators forming one side of the cell antenna, and output through the point of zero potential antenna curtain For attachment P. cable can be soldered to the tinned wire to the vibrator antenna. Further, the cable fixed to the front and out through the hole in the screen of the antenna. By the end of the feeder solder connector FME 740, to which is screwed an adapter (antenna the adapter can be purchased in cellular) under external connector cell phone antennas.
It should be noted that the value of IPM depends strongly on the type coaxial cable. As a rule, the thinner the cable, the greater the attenuation, that degrades the performance of the antenna. At the same time thin cable with connect it to a telephone less constraining movement of the subscriber, this cable is easier to connect to the antenna adapter. In General, if the distance from the point at which the antenna provides an acceptable signal quality, to the location of the telephone apparatus is not more than 2...4 m (for example, the antenna is located indoors at the window ), we can use a thinner cable with polyethylene dielectric (for example, Kazakhstan 50-1,5-11).
If to ensure acceptable signal the antenna is required to make greater distance requirements for feeder tightened. Good performance for this case have the cables RK 50-2-21, RK 50-2-2. In the described design as the feeder length of 2.5 m was used high-frequency coaxial cable RK 50-2-21 with the attenuation coefficient at a frequency of 900 MHz is not more than 0.6 dB/m at a frequency of 2 GHz and 0.8 dB/m.
If you intend to install the antenna outside, to reduce sail the design of the reflector can be made in the form of a lattice of metal rods or the tubes located at a distance of 0.05 λmin from each other, here λmin - the minimum wavelength of the working frequency range of the reflector Elements Orient parallel to the line a-b, i.e. in the plane of polarization. For grounding antenna connecting points p-P antenna curtain screen with metal poles, and the screen is securely attached to the ground bus (mast, pole). Inside antenna cloth remove glass fiber exempt from foil, and the elements of vibrators antenna curtain to protect the corrosion-resistant coating with low dielectric the losses.
When the test antenna is possible to increase the signal with two gradations of the scale indicator cell phone Motorola M3788 to four, provided that quality telephone communication.
If the antenna gain is not enough, increase it by the construction of the antenna array, for example, two or four zigzag antennas, or using a reflector type "truncated" mouthpiece [2, p. 77]. But these significantly complicate the design and configuration of the antenna and therefore the author not tested.
The data on the frequencies and wavelengths of the various cellular standards listed in table. Using them and for the conversion of the linear dimensions, to construct such an antenna for other bands.
Literature
Author: V. Vasilevsky, Dzerzhinsky, Moscow region.