Technical Analysis: Beamforming vs. MIMO Antennas

1 I R E L E S S |M O B I L E R A D I O |M I C R O W A V E |I N - T U N N E L |I N - B U I L D I N G |T V & R A D I O |H F & D E F E N S EWHITE PAPERM arch 2014 Written by Chuck Powell, antenna Engineer, RFST echnical Analysis: Beamforming vs. MIMO AntennasThe Clear Choice I R E L E S S |M O B I L E R A D I O |M I C R O W A V E |I N - T U N N E L |I N - B U I L D I N G |T V & R A D I O |H F & D E F E N S EWHITE PAPERPage2 Beamforming vs.

2 MIMO AntennasMarch 2014 Written by Chuck Powell, antenna Engineer, RFSThe Clear Choice Mobile data traffic is expected to grow13-fold between 2012 and 2017, to astaggering 10+ exabytes per Summary MIMO (Multiple Input Multiple Output) Antennas operate bybreaking high data rate signals into multiple lower data rate signalsin Tx mode that are recombined at the receiver. In Rx mode thebenefit is due to the Rx diversity that improves the receiversensitivity. MIMO Antennas typically have narrow beamwidths, withtwo or more columns of dipoles spaced a wavelength apart tomaximize gain and minimize coupling between arrays are inherently different from MIMO in that themultiple columns of dipoles work together to create a single highgain signal.

3 The columns need to be closely spaced (half-wavelength)together and have wide beamwidths in order to scan the beam awayfrom boresite, while maintaining the gain of the both techniques work well, an antenna optimized for onemethod, does not work well for the other. Compromise geometriesexist, but the user is sacrificing the performance of the system inorder to save money on the relatively inexpensive a Beamforming solution is selected, the user will have the choiceof an active or passive (switched- beam ) solution. The active solutionis steered and shaped by changing the power level and phasesbeing output by the radios.

4 Each column is fed by a dedicated radio,with a calibration port being used to guarantee the overallamplitude and phase that the antenna is seeing at its inputs. Thebeam can be steered to any angle within the specified range of thesystem and its sidelobes suppressed as passive solution will have all phasing and amplitudes controlled by apower divider inside the antenna . The divider, also known as a ButlerMatrix, is a passive device, so the number of beams, their pointingangles, and sidelobe levels cannot be changed. It is similar to breakingthe sector into smaller sub-sectors.

5 The user will see the benefits ofhigher gain and reduced interference due to the smaller sectors. They will not receive the advantages of an active antenna that cansteer the beam directly at the user or a null in the direction of aninterferer. Because each switched beam , rather than each column, ispowered by one radio, the overall EIRP of the passive antenna willbe less than that of the active antenna that uses all the radios toform the I R E L E S S |M O B I L E R A D I O |M I C R O W A V E |I N - T U N N E L |I N - B U I L D I N G |T V & R A D I O |H F & D E F E N S EContentsExecutive Summary2 Definitions4 Introduction7 MIMO8 Beamforming Using Half-Wavelength Spacing10 Beamforming Using Full-Wavelength Spacing13 Beamforming Using.

6 65 Wavelength Spacing15 Beamforming vs. MIMO Antennas17 Active Antennas19 Calibration Board, RAE, & ACU21 Passive Switched beam Antennas22 Passive antenna Limitations29 Conclusion30 References32 Company profile33 WHITE PAPERPage3 The Clear Choice Beamforming vs. MIMO I R E L E S S |M O B I L E R A D I O |M I C R O W A V E |I N - T U N N E L |I N - B U I L D I N G |T V & R A D I O |H F & D E F E N S EDefinitionsWHITE PAPERPage4 The Clear Choice Dipoleis a type of radiating element.

7 A single dipole has a wide pattern in both theelevation/vertical orientation and the azimuth/horizontal orientation. Linear Arraysconsist of multiple dipoles in a single column to create a narrow elevation/verticalpattern, while maintaining a wide azimuth/horizontal Patternis a term used for the individual dipole s pattern in the array. It is a function ofthe antenna /dipole s architecture and is independent of the RF Array Factoris the mathematic solution derived from feeding multiple dipoles together inphase. It is dependent upon the spacing between dipoles and the RF phase and amplitude beingseen by each of the Array Patternis the combination of the element pattern and the array factor.

8 It is theactual pattern created by the array and what is used by customers. Rectangular Arraysconsist of multiple columns of dipoles phased together to create a narrowazimuth/horizontal patterns. Each column is already a phased linear Patternis a term used for the individual column s pattern in the array. It is also known asthe unit beam pattern. Typically the pattern of each column is as identical as possible to the othercolumns in the rectangular array. It is dependent upon the antenna /columns architecture, but it isindependent of the RF Array Factoris the mathematic solution derived from feeding multiple columnstogether in phase.

9 It is dependent upon the spacing between columns and the RF phase andamplitude being seen by each of the Array Patternis the combination of the column pattern and the rectangular arrayfactor. It is the actual pattern created by the array and what is used by customers. MIMO (Multiple Input Multiple Output) Antennas operate by breaking high data rate signals intomultiple lower data rate signals in Tx mode that are recombined at the receiver. In Rx mode thebenefit is due to the Rx diversity that improves the receiver sensitivity. They contain multipleindependent arrays, with each array transmitting part of the Antennas are rectangular arrays, whose columns work together to form a narrowbeam that is steered to angles off boresite and shaped for improved vs.

10 MIMO I R E L E S S |M O B I L E R A D I O |M I C R O W A V E |I N - T U N N E L |I N - B U I L D I N G |T V & R A D I O |H F & D E F E N S EDefinitionsWHITE PAPERPage5 The Clear Choice Active or Adaptiveantennas are beamformer Antennas whose beam is steered and shaped bychanging the power level and phases being output by the radios. The beam can be steered to anyangle within the specified range of the system, which is the 3 dB beamwidth of the columnpattern, and its sidelobes suppressed as needed.