Directional Pattern, Reception Characteristic; How To Perform Measurements - Gigahertz Solutions UBB27 Mode D'emploi

Ultrabreitbandantenne UBB27 / Ultrabroadband Antenna UBB27
Directional pattern / reception
characteristic of the UBB27
The directional pattern of reception of the
antenna held upright resembles a lying
doughnut, like indicated in the following
drawing:
Its best reception is:
Isotropic (uniform over the whole circum-
ference) in the perpendicular plane around
the resonator axis,
For vertically polarized radiation sources.
Its sensitivity decreases with an increased
angle of incidence to the ground plane. The
radiation from below is shielded by the
ground plane. This considerably reduces the
distortions of the radiation field to be meas-
ured. It also isolates the antenna from the
instrument,,casing, connectors
measuring technician below the antenna.
Power densities of horizontally polarized
sources in the horizontal plane will be dis-
played as lower values by up to – 10 dB. To
better analyze a horizontally polarized TV
transmitter, turn the UBB27 horizontally with
the ground plane in the direction of the
transmitter (like a wheel rolling towards the
source to be measured).
© Gigahertz Solutions GmbH, D-90579 Langenzenn
Directional pattern and reception characteris-
tics are similar to those of the so-called bi-
conical antennas, with the UBB held vertical-
ly corresponding to the bi-conicals, and their
"cages" upwards and downwards. An ad-
vantage of the UBB over the bi-conical an-
tenna is the measurements are more repro-
ducible. This is because of the downward
shielding of the ground plane
Note of caution concerning far field condi-
tions
Please remember, that this antenna (and the
LogPer as well) has been designed for far
field conditions and provides reliable data
only when those prevail.
Where does the far field begins? From 1.5 to
10 times the wave length. A simple rule of
thumb for this complex subject. (2.5 wave
lengths) gives
27 meters at 27 MHz
2.7 meters at 270 MHz
27 centimeters at 2.7 GHz.
Note: Inside the Near field the electrical and
the magnetic field should be measured sepa-
rately (one cannot calculate e.g. the magnetic
field strength from the electric field strength
and the
and vice versa). Under far field conditions a
single measurement gives the power density
(in W/m², mW/m² or µW/m²).

How to perform measurements

Under most measuring conditions the anten-
na is to be held vertically.
The instrument should be held relatively high
with an outstretched arm to reduce the field
Revision 2.0 (09/15)
distortions from the measuring technicians
body. If one holds it directly in front of one-
self, then the body partly shields the radiation
from the backside.
The measurement itself is executed the same
way as with a logarithmic-periodic antenna,
except that there is no need to point it in all
directions, as the UBB is omni-directional in
the plane perpendicular to the resonator. For
further detail refer to the instruction manual
for the specific instrument in use.
The UBB27 in most typically shows higher
readings than a LogPer antenna, for two
reasons:
With its smaller dimensions it can show so-
called "hot spots", highly localized areas of
intense radiation due to multiple reflections
etc, more clearly.
Sources in the expanded frequency band
below that specified for the LogPer anten-
nas may contribute to the total immission.
It is calibrated to a slightly higher average
readings so that the lower edge of its spec-
ified tolerance band still never goes below
the reading of a comparative measurement
with a logper-antenna even in frequency
bands where it is in its specified plus toler-
ance.
Measurements obtained with the UBB27 are
as accurate as those obtained from the
LogPer antenna. Please Note: The latter has
a narrower tolerance band, because of a
lower volatility of their frequency band curve,
which on the other hand is much narrower. In
addition they are much bigger and provide
average power densities over a wider area.
Both can be and should be used when eval-
uating the immission in a given situation. It is
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