The cellular industry is constantly re-inventing itself to survive, evolve, and flourish in a market that changes every day. In this competitive environment, wireless operators rely on their networks to gain a competitive advantage, with a particular focus on creating additional bandwidth. Yet even as cellular operators, vendors, operations, spectrum, and the wireless ecosystem evolve, wireless architecture in the form of the base station antenna has evolved more slowly.

From analog FM voice 1G system deployments of the 1980s to data-centric digital evolved 3G networks of the late 2000s, the evolution of mobile technology as well as the Internet and broadband is occurring at all levels and layers in the ecosystem. For example, handsets have evolved to support the changing times, battery technologies have evolved to support handsets, and applications have evolved from voice to the iPhone App Store phenomenon.

Even the natural evolution of the handset for optimal interfacing and input has changed dramatically. Apple’s iPhone, which offers a large touchscreen, two-finger control, and one-button operation, is a great example of evolution and natural selection (people buy it) compared to the shoulder strap for the battery, a dial, and handset and cord for the early 1G phones.

The ways networks are operated have changed as well. Outsourcing was one of the big operator changes in the 2000s. Who would have thought an Ericsson services company would be looking after an operator’s network running Nokia- Siemens base station equipment?

We have observed decile increases in mobile wireless bandwidth every 10 years. This has been supported by a number of factors, including more spectrally efficient air-interface standards and higher-density network topologies, such as microcells, picocells, and now femtocells. These bandwidth increases also are fuelled by the progression of the even wider ecosystem: silicon fabrication, software capabilities, signal- processing capabilities driven by Moore’s Law, to name a few.

But unlike other telecommunications and information and communications technology (ICT) industries, the cellular industry relies on RF propagation to deliver information. This delivery of RF energy has evolved at a much slower pace than its baseband counterparts.

RF power-amplifier output powers, linearity, and efficiencies have crept up slowly over the years. Supplementary techniques such as frequency hopping, time diversity (interleaving and error correction coding), Rx diversity, and multiple-input multiple-output (MIMO) have emerged to make the RF propagation link more robust, but these methods essentially involve baseband processing.

Maxwell’s Law

The humble basestation antenna, responsible for the actual delivery and reception of the RF, has evolved the slowest. Unfortunately, RF physics including antennas are bound by Maxwell’s Law, which doesn’t promise a doubling in performance anytime soon.

Shaping the antenna “beam” to direct energy toward the ground using a beam that has between 6° and 12° of beamwidth in the vertical plane and over a sector of between 60° and 90° of beamwidth in the horizontal plane from a network of cellular three-sector sites is considered the optimum means of delivering RF energy .

This provides for a tessellation of sectors that maximize coverage footprint and minimize overlaps from a minimum number of site locations of practical heights, which might be from 15 m to 50 m above the ground. Figures 1 and 2 show ideal uniform cell sizes as well as optimized cell sizes.

This optimal antenna beam-pattern dictates the antenna size and form factor (because of Maxwell’s Law), which is typically a panel-type radiator between 1.5 and 2.5 m long and a few hundred millimeters wide, depending upon the RF frequency band(s). For example, an antenna cannot be made smaller without a change in beam-pattern.

In turn, this cellular tiling of sector footprints has dictated the tower and site ecosystems that have been deployed to support these antennas, which need to meet certain wind-load criteria. This has led to expected or anticipated norms for zoning and planning permission of cellular antennas and sites. Finally, the whole property ecosystem demands rentals from operators that want to place antennas on third-party properties such as rooftops and towers.

Antennas Are The Answer

Approximately 10 million cellular base station antennas are deployed in the world, with about 95% falling into the form factor described above. The addition of more antennas or more antenna real estate can increase network capacity. This approach might be simply for a new spectrum band, or for new technologies, or to support MIMO, or to create additional sectors for increased spectral reuse across a network of sectors and sites. It is also possible to add multiple antenna arrays together in one much larger radome and create very narrow beams that are directed onto actual mobile users and traffic hotspots.

Such “smart antenna” techniques are designed to collapse the spectral reuse in time and space, but require complex and often expensive phased array electronics and amplifiers behind each and every antenna array element. Such techniques were available 10 years ago, but they were never adopted because the current ecosystem of a couple of million sites was designed for panel-type antennas and wind loading, zoning, and other factors.

While these fundamental laws have been followed with antennas, there have also been some progressive developments in cellular antennas. Companies such as Kathrein and Andrew introduced X-Polar antennas in the 1990s. This removed the need for the spatial diversity technique that was used then at sites that required at least a pair of antennas.

This meant antenna deployments could be halved, easing rentals, zoning, and tower loads. Spatial diversity configurations are still used and are advantageous in some environments, but X-Polar antennas now generally dominate sites around the world. GSM networks relied upon minimi zing interference between different base station cells by means of re using spectrum spatially.

However, when CDMA-based technologies such as 1X and UMTS were deployed, they were designed to reuse spectrum at every sector and site across a network of sites. This meant that co-channel inter-site RF interference had to be managed carefully and was done so through antenna beam tilt optimization. Too much co-channel interference meant loss of capacity.

Attempting to eliminate co-channel interference by aggressive downtilting could create service gaps between sites. This coverage/capacity tradeoff led to the introduction of variable electrical tilt (VET) antennas, which then led to remote electrical tilt (RET) antennas. RET systems control the beam tilt remotely from the antenna itself, either in the basestation cabinet or at a network operations center. Also, RET systems could continuously tweak and optimize antenna tilts without sending a rigger up the mast.

New spectrum bands are being released, including 700 MHz and AWS (1700/2100 MHz) in the U.S., as well as 800-MHz digital dividend and 2.6 GHz in Europe and other parts of the world. Furthermore, existing spectrum bands across the world are being deregulated to allow 2G, 3G, and 4G technologies to co-exist in the same bands. The U.S. already ha s technology- neutral spectrum.

Operators are starting to share networks to save costs, and this may become even more prevalent over the next decade. Some observers may wonder why competing operators would share assets. A similar question was asked when the likes of Ericsson introduced the concept of outsourcing network operations. Capital efficiency is a primary concern of CEOs, and reducing the assets deployed and the recurring operating expenses is a double benefit to the bottom line.

Finally, we are promised the truly broadband mobile data rates enabling services such as video streaming and responsive Web surfing when this new spectrum is used and Long-Term Evolution (LTE) and MIMO techniques are exploited. All these developments, fuelled by the hockey-stick growth in data services, lead to one thing: more antennas on more sites using the currently evolved basestation antenna.

Inherent in the evolutionary process are constant challenges that are addressed by creative thinking, innovative methodologies, and new technologies. Antennas are no exception. Quintel QTilt technology, for example, allows for multiple independently tilting (RET) beams to be supported for different information/signals sources carried on the same antenna array (Fig. 3).

Similar to when X-Polar antennas were launched more than a decade ago, as well as when multi-band antennas emerged and promised a halving of physical panel antennas, Quintel promises another halving. T wo different operators or two different access technologies can be combined onto a single antenna array. These could be GSM850 and LTE700 signals independently tilted for optimization purposes or two operators in the same band that are network-sharing and using the same technology but want to maintain some network design independence.

Therefore for triple-band antenna assemblies (the current state of the art for base station antennas) , up to six independent tilts can be achieved with Quintel to meet the network design needs of two different yet sharing operators or for different access technologies in each of the bands.

Antenna technology is evolving, and it’s helping operators leverage their networks as a competitive tool. More importantly, it’s laying the groundwork for exciting capabilities that will benefit wireless customers in coming decades.