Multi-Polarization and Antenna Polarization Explained
Wireless radio communication equipment operates most reliably when the path between transmitting and receiving antennas are within an observer’s line of sight (LOS) or where no obstructions exist between antennas to impede the signal. However, such a path rarely exists in areas where most communications take place today. Natural and man-made obstructions between antennas, such as widely varying elevations, trees, mountains, buildings, vehicles, and pollution frequently diminish the strength of a radio signal. These obstructions absorb, reflect, refract, diffract, and scatter the radio waves and alter the radio signal’s polarization (vertically or horizontally polarized E and H-wave fronts) among multiple paths (figure 1). Altered polarization changes the relative phase relationship between the transmitting antenna and the receiving antenna, which can make the signal too weak to be processed at the receiving antenna (figure 2). Therefore, the challenge for radio engineers is to design wireless radio communication equipment to operate reliably under less than ideal conditions.
Unfortunately, many antenna design firms test their products under ideal conditions. Most antenna researchers do not typically consider the negative influence of various obstructions in new antenna design programs. Historically, antenna design has concentrated on making antennas that transmit strong signals exclusively along line-of-sight paths. Moreover, most testing is done in an anechoic chamber, where two antennas (one at each end of the wireless link) can “see” each other: Thus, the radio wave is created and remains unaltered between the antennas. Furthermore, each generation of improved antennas continue to be designed without considering the effect of various obstructions in the real world.
Multi-Polarization and Antennas
Recently, however, one antenna company designed and developed a new antenna that overcomes the deficiencies of most classical and less-than-optimum performing antennas that are widely produced today. This new design is called the Multi-Polarized antenna, and it propagates signals with considerably less loss than most other types – regardless of natural or man-made environmental obstructions.
The theory behind the antenna’s development is described and supported with experimental data. This antenna concept applies to all wireless communications, which includes WiFi installations (home, office, hotel, airport, hospital, retail, marina, municipal, and mining), cell phones, government and commercial equipment, as well as Bluetooth, satellite, and space applications.
Waves undergo phase cancellation
Many factors contribute to an antenna’s less-than-optimal performance. For instance, because of different signal-path lengths between antennas (which produce variations in phase), a resultant signal from combinations of wave fronts may partially or completely cancel at the receiving antenna. Therefore, peak or hot and null spots appear (figure 3).
For example, a vertically polarized whip-style antenna can lose communications because it receives signals of various strengths and polarizations (not all vertically polarized) over paths of different lengths.
In addition, temperature and humidity inversions in the atmosphere and Faraday ionosphere effects can alter the radio waves. In an effort to improve space communications on or among other planets or heavenly bodies, special radiation patterns, antenna polarization, and spatially diverse changing needs must be considered.
High gain antennas
High-gain antennas do not help: They are no different from other antennas when it comes to antenna polarization: They do not work as well when the signals and the antennas are not of the same polarization. That is, singularly (vertically) polarized antennas work best with vertically polarized waves (and the same with the horizontal orientation). In addition, high-gain antennas are designed to have a radiation pattern that is deep but narrowly focused in the forward direction. The back and side lobes are smaller than the forward lobe and are less sensitive to signal pick-up. So, when the antenna’s high-gain forward directional lobe does not capture the primary signal and all lobes capture reflected signals from different directions with altered polarizations, the received signals can be too weak to be useful.
A number of techniques have been developed to overcome some of these deficiencies. Among them are switching diversity, electronically steerable antenna arrays, and Multiple Input Multiple Output (MIMO) arrangements. Unfortunately, these approaches are expensive because they require multiple radios and antennas (figure 4).
Receiver switching diversity (or spatial diversity) is a system where a single radio switches between two antennas. The reasoning behind this is that the chances are more likely that one of the two antennas will be in a peak or hot spot than if only one antenna is used.
Desirable characteristics
Single-feed antennas that have built-in spatial diversity (detects signals from different directions), built-in antenna polarization diversity (handles multi-polarized waves), and broad azimuth and elevation (radiation) patterns are most desirable.
The antenna with Multi-Polarization also considers spatial diversity, broad signal patterning, enhanced magnetic field energy transfer, and UWB (Ultra Wide Band) performance. In addition, the Multi-Polarized antenna performance exceeds the singularly polarized (including advanced types), circularly polarized, EH, and fractal antennas (figure 5).
Supporting data
Moreover, recent studies support these findings. For example, Bell Laboratories (1) discussed the “reflected-z” wave and six total electric (E-field) and magnetic (H-field) wave axes (figure 6). Others have demonstrated multiple (typically 3-4) resultant waves of various polarizations coming from different directions in urban and suburban wireless environments .
With the Multi-Polarized antenna, these various (partially out-of-phase and effectively additive) E and H field waves are used to improve real-world wireless connectivity. In fact, obstructed environmental testing of polarization and spatially diverse antennas at a number of poor signal (dead or null-spot) locations shows more connections in average throughputs.
In a relatively static, obstructed environment, fewer reduced signal strength readings are observed with standard signal strength utility software. In a dynamic obstructed environment, special Real Signal Strength Indication (RSSI) signal software reveals near-instantaneous dropouts caused by fluctuating obstructions such as of moving leaves, people, cars, and so forth. When the signal is weak (as is often the case when using conventional antennas), the Ethernet Protocol signal-processing circuitry in the wireless equipment has to request multiple message packets to try to maintain contact. This delay reduces the data throughput.
Test Procedure for Multi-Polarization
Use the following test procedure to compare the performance of Multi-Polarized antennas to conventional antennas. In an obstructed environment, find the range where a conventional antenna begins to drop out, and repeat the test at various locations around that range. Determine how often the dropouts occur, then test the Multi-Polarized antenna at the same locations. The result is an increase in the frequency of sustained connections with faster throughput (figures 7-11).
Conventional or standard-style antennas:
• Lack the ability to use the obstructed environment’s polarization-diverse signals,
• Lack the three-dimensional geometry or spatial diversity to capture signals in proximity that do not suffer from multi-path phase cancellation, and
• Lack the broad signal patterning of the Multi-Polarized antenna needed to capture reflected signals.
Radiation pattern
Theory logically concludes, and testing verifies, that a smaller Multi-Polarization antenna outperforms a similarly sized standard antenna in most typical locations, but especially so in those areas that would require higher signal saturation for conventional antennas to perform adequately. For example, most often, it is more important to improve a coverage area from 90% saturation (loss of connectivity 10% of the places/time) to 99% saturation (see blue area, figure 12), than it is to increase the “rarely connected system” in remote areas (see yellow area below) to “occasionally connected systems”.
Summary
Radio frequency signals can be viewed as a fog or a smoke bomb that penetrates different shaped nooks and crannies with a variety of polarizations. At the receiving end, Multi-Polarization antennas connect more clients at higher data throughput rates both at a distance as well as at closer proximity in a non-LOS or near-LOS location than standard antennas of similar size or gain. For multiple-element, complex interactions, element length must be adjusted to optimize the (theoretical) electromagnetic-field performance. This applies to both parasitic elements and multiple-component fed elements (figure 13).
Multi-Polarization Bibliography
1. Andrews, M. R., Mitra, P.P., & DeCarvalho, R., Nature 409, Tripling the Capacity of Wireless Communications Using Electromagnetic Polarization, Bell Labs, Lucent Technologies, Harvard University.
2. Argenti, F., et al, Antenna Polarization Diversity for Multiband UWB System, Department of Electronics & Telecommunications, University of Florence, Italy, 2004.
3. Black, Jerry and Taylor, Cedric, Comparison of Space and Polarization Diversity 800MHz Cellular Antenna Systems Through Empirical Measurements, Nortel Networks.
4. Channel Models for Fixed Wireless Applications, IEEE 802.16.3C-01/29r2, 2001.
5. Suvickunnas, Pasi, Methods and Criteria for Performance Analysis of Multiantenna Systems in Mobile Communications (esp. page 35: 5.4 ‘Single versus dual-polarized MIMO antenna systems’). PhD. Thesis, Helsinki University of Technology, Finland, 2006.