My colleague recently posted a good blog article previewing some of the course content from the CommScope Infrastructure Academy class titled “Microwave Radio Antenna Link Fundamentals.” Jim Syme
presented the concepts of antenna directivity and gain in microwave systems,
explaining how these characteristics compensate for the inherent losses within
a microwave link. I’d like to expand these topics a bit to talk about how
they influence microwave antenna size.
In general, antenna directivity and gain
refer to the values associated with the boresight of an antenna. The boresight
is the axis of symmetry of the antenna, which defines its maximum performance values.
Gain is a measured value but directivity is computed. As such, gain is always
less than directivity, reflecting the real-world measurement instead of atheoretical value.
The challenge in antenna design is tomaintain the gain of the antenna in the boresight direction but reduce its
directivity/gain in other directions. The ability to do this is called side
lobe discrimination. Side lobe discrimination can be improved by tapering the
energy distribution on the radiating aperture so that edges of the aperture are
illuminated less. This results in a reduction in effective aperture size, hence
reducing the gain of the antenna. This technological challenge can be overcome
by utilizing Class 4 ETSI (European Telecommunications Standards Institute)
microwave antennas, whose side lobes are reduced without compromising the gain.
CommScope’s line of Class 4 antennas is called Sentinel.
How does the move to Class 4 antennas impact
the antenna size? The size of the antenna is decided based on the required receive signal level (RSL). In dense
environments where high capacity is in demand to satisfy user needs, the carrier to interference (C/I) ratio (the
amount of power in an RF carrier to the power of the interference that exists
within the channel) is another parameter that dictates the size of the antenna.
In some cases, larger sized antennas are used not because of RSL but to improve
C/I. The larger antennas solve the problem in this regard but also increase
CapEx and OpEx costs. Using low side lobe Class 4 antennas allows operators to
use relatively smaller size antennas even in dense and high capacity demand
areas. There is a huge potential for low side lobe antennas to mitigate today’s
and tomorrow’s microwave link challenges.
In summary, Class 4
antennas with better side lobe discrimination offer opportunities to use
physically smaller antenna in dense environments where interference is a
concern, increasing the available link capacity and potential revenue
generation. Another colleague of mine will be announcing a white paper soon
that goes into even more detail. In the meantime, leave a comment with any