About the antenna with an active reflector. Encyclopedia of radio electronics and electrical engineering
Encyclopedia of radio electronics and electrical engineering / HF antennas
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When manufacturing an antenna with an active reflector (HB9CV), some of its features were revealed, which, in my opinion, were not taken into account in previous publications (see, for example, "Radio" 1968, No. 9).
First of all, it should be noted that the performance of the antenna is greatly influenced by the design of the phase-shifting line. The constructive calculation of the phase-shifting line (see figure) can be performed with sufficient accuracy as follows. The geometric length of the line is determined (with some margin for terminating the ends of the cable) from the expression
The electrical length of the line is
Electrical length of cut
Electrical length of cut
In this case, the geometric length of the segments is defined as
In all formulas: l - working wavelength in meters; Lg,lg - geometric length in centimeters; Le,le - electrical length, in degrees;
x - cable elongation factor, depending on the material of its internal insulation (for common domestic cables with polyethylene insulation x = 1,52),
In the antenna for the 14 MHz band, the line calculated in this way from the PK-75-9-13 cable had le = 35, lp = 260 and L = 295 cm. segments with an accuracy of no worse than ±5°.
The line can be made from the same type of cable used to feed the antenna. Despite the fact that at the point of connection to the power cable line, the input impedance is half the input impedance of each antenna element, a small (compared to the operating wavelength) cable length of the phase-shifting line with unmatched wave impedance practically does not increase the SWR value.
The antenna built and tested at the UA4LK radio station showed good results when making communications over various distances. Its gain was 5-6 dB in power, the width of the front radiation lobe at the level of 0,7 - about 60 °. Due to the more efficient action of the reflector, it was possible to significantly reduce interference from stations (including local ones) that are outside the front radiation lobe. The effect of this suppression is estimated by ear in the range of 20-30 dB.
Author: F. Kozlov (UA4LK), Ulyanovsk; Publication: N. Bolshakov, rf.atnn.ru
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