The European Union Funded BuNGee Project comprises a consortium of eight academic and industrial organisations whose aim is to dramatically improve the infrastructure capacity density of the mobile network by an order of magnitude (10x) to 1Gbps/km2 anywhere in the cell, far exceeding present rates available of 100Mbps/km2.
The Hub Base Station (HBS) antenna is a new development and construction which has been necessary in order to exploit digital techniques being developed by the consortium. This antenna, HBSA-3.5DS/1955 has dual polar, slant linear polarisation (for MIMO - multiple input multiple output) and can project six separate beams of each polarity covering a 90˚ arc. By positioning four antennas in a square formation 360˚ coverage is achieved.
The internal construction of antenna array comprises multiple high gain sector antenna elements which are spaced a half wavelength apart. The close spacing allows reduced azimuth sidelobe levels when the sectors are phased together to provide a set of slewed high gain beams. In order for the six narrow (15˚) high gain beams to cover the 90˚ arc, two Butler Matrix beam-forming devices are used to feed the two polarisation of each element of each antenna. By a using fixed phase shifters and couplers, the Butler Matrices provide defined sets of phases into each of the antenna elements resulting in two sets of 6 “skewed” beams. Further system benefit can be achieved by amplitude weighting to each of the elements within the array which reduces the azimuth sidelobes significantly. Depending on the sidelobe levels required the peak gains for each (of the 12 beams) is 16-18dBi with 15˚ beamwidth in azimuth and 10˚ in elevation.
Antenna deployment
The Hub Base Station antenna is intended to be deployed within an urban “Manhattan Grid” formation, providing coverage through 360˚ by positioning four antennas just above roof-top height. These communicate with line-of-sight (or virtually line-of-sight) dual-slant linear Hub Subscriber Station antennas which have also been developed. These are sited below rooftop within the grid and share their location with different frequency Access Base Station nodes whose antennas point up and down streets to communicate with personal mobile terminals.
The antenna installations are intended to be cost effective; multi-beam technology will be more efficient to install where considerations such as weight, wind speed, and mast/roof-top rental are paramount. Below-rooftop deployment and co-location of the Hub Subscriber Antenna/Radio and Access Radio/Antennas reduces the cost of installation and may allow quicker deployment. Carefully controlled antenna beamwidth and intelligent MIMO techniques as well as judicious positioning of other Hub Base Station multi-beam antennas will reduce interference within the system, increasing Signal to Noise ratios. A nominal peak gain per antenna of 19dBi, while providing useful penetration also produces a well-defined beam set with the extra advantages of dual polar technology at both ends of the link (2x2 MIMO). Re-use of the spectrum for this dense data-rate means lower license fees for operators per bit of data transmitted.
Summary
The Multi-Beam Antenna developed by Cobham Antenna Systems, Microwave Antennas to be deployed in the BuNGee communications project is a novel approach to dual polar, beam forming technology. The use of a Butler matrix to produce a set of beams spanning a wide sector allows for significant increase in the data throughput when compared with a wide beam antenna of high gain, and is more compact than having the equivalent of six separate narrow beam antennas. This rewards the user with reduced installation and deployment costs while being able to control individual beams where needed.
References: www.ict-bungee.eu which gives an overall summary of the BuNGee project and stakeholders
Article: Published in Microwave Journal, January 2012 issue
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