Sunday, October 6, 2013

cruciform dipole antenna

It is known that the directivity pattern of a conventional dipole antenna has the shape of a horizontal eight . It is obvious that in order to be able to carry out qso with correspondents located in different areas of need for this dipole is placed on the rotator . But if you do not have a rotary device that can apply an antenna system of two perpendicular arrangement of the two dipoles. This dipole antenna system is connected via a single coaxial cable dipole excited with a phase shift of 90 degrees to form a cross-shaped antenna ( first figure) . Diagram of a cruciform dipole system in the horizontal plane has a substantially circular shape . From this figure it can be seen that both dipoles are connected through the quarter wave transformer . Strengthening of the cross- dipole system is not great and there are some difficulties in the negotiation. Increase efficiency of the antenna system and hence its gain and to avoid difficulties in coordination can be applied if the antenna system is based on loop dipoles such loop dipole itself has a higher gain and efficiency than conventional bit wideband linear dipole. In the second picture a) - wiring diagram of the dipoles and Figure b) - the radiation pattern . As can be seen from the figure the coaxial cable is connected directly without the agreement and the point where the cable impedance of 75 ohms . Input impedance of each dipole is 300 ohms. Dipole disposed at a distance equal to L / 2 (half wave ) . Currents flowing in the opposing antennas are shifted from each other by 180 degrees, and thereby forming a circular pattern . Placing a few of these antennas on top of each other giving you greater gain relative to a conventional dipole.

cruciform dipole antenna-1

cruciform dipole antenna-2

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