A.H. Systems Model Active Monopole Antennas
©
A.H. Systems inc
REV E
8
CALIBRATION
Equivalent Capacitance
With changes to our Active monopole antenna (converting the input connection from a BNC to a
more rugged ¼-20 input) our element diameter changed to 6.17mm (Average). It is our
recommendation to use a 12 pF for the ECSM fixture for an element height of 41” (1.04 meter) as
per ANSI C63.5:2017 and CISPR 16-1-6:2017.
The formula for calculating the capacitance is (per ANSI C63.5:2017 and CISPR 16-1-6:2017):
C
a
= (55.6
h
) / (ln(
h
/ a) – 1) * (tan(2 π
h
/
λ
)) / (2 π
h
/
λ
)
Eq 1
where:
h
= actual length of the monopole element (adjusted to 1.04m), m
a
= average radius of the antenna element (6.17mm), m
λ
= wavelength in meters
C
a
= capacitance of the dummy load
NOTE - Other fixtures with different capacitance are available as an option.
Effective Height Calculation
The correction factor for the calibration is dependent on the height of the monopole. The effective
height is calculation is:
h
e =
(
λ
/ 2π)
* tan(2
π
h
/
λ
)
Eq. 2
where:
λ
= wavelength in meters
h
= Telescoping element height in meters
Examples:
•
For a 41” (1.04 Meter) length, the effective height would be 0.52 meters (up to approximately
2 MHz) and the correction factor should be 20*Log(
0.52
) = -5.68 dB.
•
For a 1 Meter length, the effective height would be 0.5 meters (up to approximately 2 MHz)
and the correction factor should be 20*Log(
0.5
) = -6.02 dB.
