Double square antennas. Scheme, description

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ENCYCLOPEDIA OF RADIO ELECTRONICS AND ELECTRICAL ENGINEERING
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Double square antennas. Encyclopedia of radio electronics and electrical engineering

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Encyclopedia of radio electronics and electrical engineering / VHF antennas

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One of the reasons for the popularity of the double square antenna is the ability to create a multi-band system. On each band, such an antenna has a good diagram, high gain and an SWR close to one. Most often, radio amateurs use an antenna assembled on eight spacers made of insulating material (radio amateurs call this design a "spider").

The operation of such antennas in areas of the USSR with strong winds showed their unreliability. "Double squares" behave much more reliably, having a bearing boom-traverse, on which elements in the form of wire frames are attached. Passive frames are configured using short-circuited loops. But this antenna has a significant drawback: the distance between the active frames and reflectors is the same on all bands, and the maximum gain is achievable only on one of the bands.

Double square antennas

The antenna described below does not have this drawback. The "double square" antenna for the 14 MHz band is taken as the basis, and for the 21 and 28 MHz bands it is a three-element antenna. The antenna (Fig. 1) is made on a boom, the frames are located. downward angle. "Double square" for the 14 MHz band has an optimal distance between the elements - 0,2 lambda, which guarantees the maximum gain. All three reflectors are located in the same plane (B), the director frames for 21 and 28 MHz are in the same plane with the active frame for the 14 MHz band (A), and the active frames for the 21 and 28 MHz bands are on independent struts in the middle part of the boom ( B). The distance AB is 165, BV - 260 cm. The remaining dimensions of the antenna are given in Table. one.

Table 1
Range, MHz Frame side length A,cm Frame train length A,cm Frame side length B,cm Frame side length B,cm Frame train length B,cm
14 535 - - 540 150
21 345 80 355 360 100
28 245 60 265 270 70

Vertical spacers can be made of any material (including metal pipes), horizontal spacers can be made of insulating material (wood, bamboo, synthetics), or metal pipes broken by insulating inserts. To feed the antennas at 14 and 28 MHz, feeders made of coaxial cable with a wave impedance of 75 ohms are used, and at 21 MHz - 52 ohms. Feeders are included in the breaks in the lower corners of the active frames. Balancing is not applied in this case.

Literature

Radio, No. 2 1970 p. 37

Publication: N. Bolshakov, rf.atnn.ru

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