432 MHz antenna with circular polarization. Encyclopedia of radio electronics and electrical engineering

Encyclopedia of radio electronics and electrical engineering / Antennas. Measurements, adjustment, coordination

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The article describes an antenna with circular polarization for operation in the amateur band 432 MHz. This antenna can be useful in its ability to compensate for signal fading caused by a change in the plane of polarization of the electromagnetic wave. Such changes, in particular, are observed when working through amateur radio IC3.

The advantages of this version of the antenna are simple design of available materials, wide antenna pattern, good SWR in a given frequency band. During its development, materials from the Internet were used [1, 2].

It consists of two crossed (rotated by 90 degrees relative to each other) three-element wave channels, which are displaced in space by a quarter of a wavelength. Schematically, the proposed antenna is shown in fig. 1.

Rice. 1. Schematically proposed antenna

The lengths of the elements of both antennas: 11 and 14 (reflectors) - 34,4 cm, 12 and 15 (vibrators) - 33,6 cm, 13 and 16 (directors) - 29,8 cm. Distances D to their centers relative to the starting point of reference (the center of the first reflector l1) are given in the table.

Table

The antenna is assembled on the basis of a non-reinforced PVC water pipe of a suitable diameter, approximately 0,5 m long. As antenna elements, you can use a rigid wire made of copper, brass or aluminum with a diameter of 1,5 ... 2 mm.

To fix the vibrators, it is necessary to provide special inserts made of plastic tubes, which must first be glued into the antenna carrier pipe. It is also possible to assemble the antenna on the basis of a square wooden block with a length of about 0,5 m, which will somewhat simplify the markings for the fasteners of the elements, but increase the mass of the structure.

To ensure matching of wave impedances, the vibrators of each of the three-element antennas are connected to a 50-ohm cable (of any length) through segments of a coaxial cable with a wave impedance of 75 Ohms, length k·λ/4 (k is the shortening factor). For a conventional cable with a solid polyethylene dielectric, this will be 12 cm.

The radiation pattern of this antenna is close to a hemisphere. The width of the RP at the level of -3 dB is about 90 degrees, the direction of maximum radiation is along the Z axis. The result of its simulation in the MANNA-GAL program is shown in Fig. 2.

Rice. 2. Antenna simulation result in the MANNA-GAL program

The theoretical SWR calculated on the MANNA-GAL program is less than 1,5 in the frequency band from 425 to 445 MHz. With the dimensions indicated in the article, it reaches a minimum value of 1,1 at a frequency of 435 MHz.

The assembled antenna is shown in fig. 3.

Rice. 3. Assembled antenna

Literature

1. Mac Matiatos. Antenna Circular Polarization. - URL: sv1bsx.50webs.com/antenna-pol/polarization.html.
2. Likhobabin V. Broadband antennas wave channel 435 MHz. - URL: ra6foo.qrz.ru/w435.html.

Author: Igor Lavrinenkov

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