Antenna Systems & Technology - Fall 2016 - 14

NEW PRODUCTS & SERVICES COMPONENTS / SUBSYSTEMS It's important to keep in mind that while common, this is not the only deployment technique that can be used. One example of this is a technique commonly deployed by CommScope, called the Butler Matrix. As we already discussed, the array factor is dependent on its antenna elements' spacing, phase shifts, and amplitude variation. Considering that AE's can't be moved, the only method to change pattern shapes revolves around phase and amplitude variations. Ralph Lowe and Jesse Butler (for whom the matrix is named) first described this matrix in 1961. It is essentially constructed out of phase shifters and hybrid combiners, such that each antenna element sees different shift and amplitude combinations of the input ports. Please see figure 3 for a more detailed look at how feeding the input signal from a different input port results in a different beam direction. From here, there are two key uses: Switched Single Port Feed An application in which only one input signal is switched across all input ports - so Figure 4. Four-port Butler Matrix that only one port is connected at a time. This will result in the beam being steered towards traffic areas, but required some intelligence to be added to the switch position decision. Multi-Port Simultaneous Feed If instead, two ports are fed with different signals simultaneously, the antenna will radiate dual beams, superimposed on each other. This is the same technique that is used in commercial twin beam antennas. It's important to keep in mind, however, that electrically oversteering beams can result in undesired grating lobes, as shown in figure 3 - something to keep an eye on while comparing twin beam antennas. Myth 5: Beam Steering Requires Active Antennas Even though techniques highlighted in the Butler Matrix are labelled as "electrical", these types of techniques might still need some mechanical actions to operate. One example includes e-tilt that gets adjusted by mechanically pulling tilt control sticks. Many operators believe that the only solution lies in active antennas - antennas with integrated radios. However, these are still being debated in the industry - despite reducing the footprint of a site, they restrict future upgrades and harden maintenance. Yet, one of the main long-term benefits is fully electrical beam steering and massive MIMO. However, in reality, we are actually able to do full electrical beam steering over regular antennas with the support of the base station. Let's take the TTTT65AP-1XR as an example: * Planar array antenna, 2496-2690 MHz, 65 degree horizontal beamwidth, single internal RET * Four columns of x-polarized arrays * Tested for 0 and 30 degree beam steering The TTTT has four x-polarized arrays with two input ports each. The antenna is designed for TDD-LTE with 0 degree and 30 degree beam steering directions. The BTS radios are connected to the four column arrays. The radios apply specific amplitude and phase difference as per the antenna manufacturer-provided data. On page 15 there is a table that showcases the values provided to the BTS vendor for application at the antenna ports. There will mainly be two beams that can be formed: 1. Broadcast beam: Changing phase and amplitude across ports 2. Service (steered) beam: Changing phase only across ports 14 Antenna Systems & Technology Fall 2016 www.AntennasOnline.com http://www.AntennasOnline.com

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