MIMO and Smart Antennas for Mobile Broadband ... - 4G Americas

5 inputs forming the five beams shown and the right figure is from an array of 20x6 elements used to form9 cross polarized beams.Figure 30 – Multi-beam transmit patterns. The left figure corresponding to an antenna array with a center beam gain of 20.5 dBi; theright figure has a center beam gain of 23 dBi.The technology seems to have application for capacity enhancement in many situations. Anotherexample tilts the two polarizations separately tilted to produce two rows of 9 beams as shown in Figure31. This product is touted for covering tiers of bleachers in sports stadiums.Figure 31 – Mutli-Beam Antenna array pattern for 2 rows of 9 beams. 21Two-beam antennas have been implemented as RET antennas with the networks implemented in eachrow of the array. This is also possible with multi-beam antennas; however the complexity rapidly growswith the number of beams.The basic antenna consists of an array of dual-polarization columns fed from two butler matrices so as toobtain a number of beams pointing at different azimuth angles.A butler matrix is a microwave network with n input ports and n output ports allowing the forming of up ton beams when connected to the n port antenna. The input ports are all matched and isolated from eachother as are the output ports. The network has the special characteristic that if a signal is applied to input4G Americas MIMO and Smart Antennas for Mobile Systems – October 2012 – All Rights Reserved43