A.H. Systems Model SAS-551 Passive Monopole Antenna
©
A.H. Systems inc.
– REV E
10
CALIBRATION
Equivalent Capacitance
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. Our telescoping rod with a BNC connector
that is supplied with the SAS-551 has an average radius of 2.223mm. 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 effective height of the monopole. The
effective height 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.
