Cisco Cisco Catalyst 6000 Multilayer Switch Feature Card MSFC2 White Paper
© 2013 Cisco and/or its affiliates. All rights reserved. This document is Cisco Public Information.
Page 26 of 41
Product ID
Description H/E plane
Product
Gain
AIR-ANT2410Y-R
2.4 GHz 55°/47° single element yagi (1 Piece,
3 Required)
3 Required)
10 dBi
AIR-ANT25137NP-R
Dual-Band 2.4 GHz 36°/36° 5 GHz 55°/48° MIMO
directional patch
directional patch
*
Requires AP 3502P
13/7 dBi
Use of Directional Antennas and Downtilt
One challenge often faced in a lecture hall or auditorium is the need to provide more bandwidth than a single use
of the channels available in 2.4 GHz will allow. Using a directional antenna can provide cell-to-cell isolation if
placed, mounted, and adjusted properly. One aspect of using directional antennas is the concept of mechanical
downtilt. Downtilt involves adjusting the antenna down to change the coverage pattern that is created.
The coverage pattern can be adjusted by changing the mounting height or the mechanical downtilt angle,
Figure 12.
Figure 12. Adjusting Directional Antenna Using Downtilt
The values for the formula above are:
●
H = height of the antenna
●
A = downtilt angle
●
BW = the 3 dB horizontal beamwidth of the antenna
By adjusting the downtilt of the antenna, it is possible to “dial in” - or add WLAN coverage - to specific areas within
the coverage zone. APs and RF energy operate much like light cast by lighting fixtures. It is possible to light an
entire warehouse with a bare bulb on the ceiling, but the result is low levels of light in some areas. But if there are
multiple fixtures, including some with higher patterns of luminosity to illuminate larger, the result is comprehensive
overall lighting. RF is invisible, so measuring the coverage and adjusting it appropriately requires tools to measure
the coverage. For each antenna placement, simply walking the area below it and adjusting the antenna to change
the pattern based on Received Strength Signal Indication (RSSI) levels to match coverage requirements is
generally all that is required at the initial installation. Antennas hear the same as they transmit. If measuring and
adjusting are done carefully, using consistent measurements and tools, good results can be achieved.