All page numbers refer to 17th edition of the ARRL Antenna Book
Described by Christman (KB8I) in Ham Radio, this is two 1/4 wave verticals, spaced 1/4 wavelength apart, fed 90 degrees apart by carefully selected feedline lengths. The feedlines are 84 and 161 degrees long (for 50 ohm line)
ref: "Feeding Phased Arrays: An Alternate Method" Ham Radio, May 1985, pp 58-89,61-64
page 8-26 from 17th ed of Antenna Book
4 verticals, arranged in a square 1/4 wavelength on a side, fed with 1/4 wavelength feed lines (either 50 or 75 ohm) to do "current forcing". The elements are fed 0, -90, -180 in a diamond, with the 90 being created by a series L, shunt C network. 4 sets of L and C values are given depending on the self resistance of the element, ranging from 65 ohms (4 radials) to 36 ohms (infinite perfect ground).
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50 ohm feedline
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75 ohm feedline
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|---|---|---|---|---|
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Rself
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Xl
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Xc
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Xl
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Xc
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65
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17.1
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-13.7
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38.5
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-30.9
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54
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20.2
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-15.6
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45.5
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-35.2
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45
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23.6
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-17.6
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53.1
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-39.6
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36
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28.4
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-20.2
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63.9
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-45.5
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page 8-31
Technique 1, measure Z1 with element 2 open and shorted
Technique 2
Measure Z11 with element 2 open
Measure Z22 with element 1 open
Measure Z1X with element 2 connected with a 1/2 wavelength TL (or with both
elements connected to a common point with an odd number of half wavelengths
to one and and even number to the other)
Z12 = Z21 = -Z1X +/- sqrt((Z1x-Z11)(Z1x-Z12))
radio/antenna/phased/arrl.htm - 12 Mar 2003 - Jim Lux
(phased arrays) (antennas)
(radio) (Jim's
home page)