The effect of dipole coupled impedances on open field range calibration

Abstract

5473A Clouds Rest RoadMariposa, CA. 95338 ABSTRACTThe half wave dipole is the fundamental antenna used in the calibration of open field test sites. Coupling among the antennas and their images causes a change in antenna center impedance, resulting in a correction of several decibels in the site attenuation model. A derivation of the method of calculating the effect of the coupled impedances is given here along with a discussion of the correlations between the mathematical model and measurements on 3 meter ranges.

Decoupling of Two Closely Located Dipole Antennas by a Split‐Loop Resonator

“…Therefore, it is reasonable to assume that the input impedance Z of an individual SLR at frequencies near its resonance is practically equal to that of the resonant dipole and can be approximated as Z ≈ R 0 (1 + β γ ), where β ≈59 and γ = ( ω − ω 0 )/ ω 0 is relative detuning (Kazempour & Begaud, ). Substituting this approximation for Z , for Z 13 and for two resonant half‐lambda dipoles (McConnell, ) into , we obtain the decoupling condition as In the case h ≪ d δ ≈ d /2 and complex exponentials cancel out that reduces to the simplest equation from which we find the detuning γ corresponding to the decoupling For d = 30 mm (in this case h = d /3) and L l =290 mm, yields γ ≈0.0423 that implies the decoupling at the upper edge of the resonance band—at 312.8 MHz. Meanwhile, using a passive resonant dipole we have obtained γ ≈0.007, that is, the decoupling holds at 302.8 MHz.…”

“…Therefore, it is reasonable to assume that the input impedance Z of an individual SLR at frequencies near its resonance is practically equal to that of the resonant dipole and can be approximated as Z ≈ R 0 (1 + ), where ≈ 59 and = ( − 0 )∕ 0 is relative detuning (Kazempour & Begaud, 2001). Substituting this approximation for Z, (8) for Z 13 and Z M ≈ ( ∕24 kd) exp (−jkd) for two resonant half-lambda dipoles (McConnell, 1989) into (1), we obtain the decoupling condition as…”

Passive Decoupling of Two Closely Located Dipole Antennas

“…A very simple relation for the mutual impedance of two parallel antennas performed of wires with radius r 0 < 10 −3 λ separated by a gap d < L was heuristically obtained in [21]. In our notations this relation can be written for both Z 12 = Z M and Z 13 = Z 23 as follows:…”