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Correlation techniques improve the accuracy of antenna pattern
measurements whether the antenna is measured inside an anechoic
chamber, a compact range or an outdoor range. The method can be used
for near field and far field measurements alike.
This technology briefing describes how
an established signal processing technique, well-known and of
proven value in the communications field, can be applied very easily
to improve the quality of antenna pattern measurements by
effectively removing the effects of multipath, a phenomenon that
plagues all antenna measurements.
Together with our colleagues at TSC-UPC, Barcelona,
an Antenna Centre of Excellence, we are happy to share the exciting
results of the first phase of an experimental programme.
The radiation pattern of an array antenna was measured inside the
centre's anechoic chamber
and is shown in Fig. 1.
The performance of the anechoic chamber was then significantly
degraded by simulating the effect of a single
dominant multipath component, just one tenth the strength of the
wanted signal (10dBc) and arriving
at an angle of 30 degrees. As can be seen in Fig.2, the
measured pattern is severely distorted.
To overcome the distortion, a special signal is transmitted on
top of the wanted signal radiated by the range antenna. The signal
received at the antenna under test is then processed, or correlated,
with the special signal. Correlation processing effectively finds
the component that arrived via the
direct path -- the wanted component -- and removes everything
else, including the multipath that causes the distortion. The result
is striking as shown in Fig. 3 where the distortion has been almost
completely removed.
The correlation technique works in real time and does not require
measurement data to be processed off-line. This offers significant
time-savings over other compensation methods such as lengthy
computational algorithms. Signal processing techniques can be
deployed in both new and existing measurement ranges whether they be
indoor or outdoor, far field or near field. The technique presented
here is just one from Fizzle Technologies' portfolio of advanced
antenna
measurement solutions. |
