NEW SCIENCE AND ANTENNA TECHNOLOGYMULTI-POLARIZATION: REAL-WORLD WIRELESS

rethink the antennaTM

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Wireless radio communication equipment operates most reliably when the path between transmitting and receiving antennas are within an observer’s line of sight (LOS), 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 path lengths change 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.

The Multi-Polarized AntennaRecently, 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.

Horizontal

Horizontal

Vert

ical

Vert

ical

TransmittingAntenna

ReceivingAntenna

Signal or

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+

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++ Poor

Signal

PoorSignal

Orthoganal Polarization Antennas

TransmittingAntenna

ReceivingAntenna

Signal

HorizontalHorizontal

Vert

ical

Vert

ical

or

+

+ +

+ + +

++

GoodSignal

GoodSignal

Same Polarization Antennas

Figure 1

Transmitting/Receiving Antenna Polarization Relationships

Radio waves reflect, diffract, refract, and scatter on their way from the transmitting antenna to the receiving antenna, and these anomalies can alter the signals’ polarization. For example, a vertically polarized transmitted wave is well received at a vertically polarized antenna, and likewise for horizontal polarization. But a vertically polarized wave induces a minimum amount of signal in a horizontally polarized antenna.

+

++

+

Path 2

The Signals of the Two Paths Cancel Each Other

Path 1

Reflection Point 2

Reflection Point 1

TransmittingAntenna

ReceivingAntenna

Figure 2

Multi-Path Signals

Because of the different lengths of various signal paths available between antennas and the variations in phase among these signals (because of refraction and reflection), multipath signals can add and subtract at the receiving antenna and partially or even completely cancel the resultant wave. The outcome is a substantially decreased or totally unusable signal at the receiving antenna.

Waves undergo phase cancellationMany 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, polarization, and spatially diverse changing needs must be considered.

High gain antennasHigh-gain antennas do not help: They are no different from other antennas when it comes to 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.

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Peak PeakNull Null RelativeSignalStrength

Antenna

Antenna Location

Figure 3

Relative Signal Strength – One Antenna

When randomly polarized waves undergo whole or partial cancellation, the receiving antenna will see peaks or hot spots and nulls in signal strength and produce dropouts in communications. A singularly (vertically) polarized whip-style antenna, for example, will experience a degrading signal and lose communication for one or both of these reasons. In addition, antennas with narrow radiation patterns can ignore signals arriving from a variety of directions.

Peak PeakNull Null Peak PeakNull RelativeSignalStrength

Antenna 1 Antenna 2

Multiple Antenna Location

Figure 4

Relative Signal Strength – Multiple Antennas

When a system employs a technique called receive diversity, that is, when the radio switches between two antennas, the chances that one of the two antennas will be in a hot spot are more likely than if only one antenna is used.

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Desirable characteristicsSingle-feed antennas that have built-in spatial diversity (detects signals from different positions in space), built-in polarization diversity (handles multi-polarized waves), and broad azimuth and elevation (radiation) patterns are most desirable.

The Multi-Polarized antenna 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).

H

H H

H

Multi-Polarized Antennas

Standard StyleSingularly Polarized Antenna

H-fields Polarization Diverse

VS.

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TransmittingAntenna

Reflected-z Wave

Various Length Elements

E-fields (x, y, z)

Shown with resultant broad pattern (approaching hemispheric) andelliptical polarization (x & y-axes components) signals.

Built-in Spatial Diversity

“HOT” Spot(Multi-path Signals In-phase)

“Null” Spot(Multi-path Signals In-phase)

Elliptical-x,y Wave

Elliptical-x,y Wave

Elliptical-x,y Wave

Advantageous induction of magnetic field (and resultant signal increase)in distant antenna by another antenna is greater due to higher magnetic field strength differentials in 3-dimensional design.

Figure 5

Advantage Of Multi-Polarized Antennas

The MP antenna has a lot more to offer than traditional antenna designs: polarization diversity, spatial diversity, broad signal patterning, improved magnetic-field energy transfer capability, and ultra-wide band (UWB) performance.

Supporting dataMoreover, 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 (slow fade). In a dynamic obstructed environment, special Real Signal Strength Indication (RSSI) signal software reveals near-instantaneous dropouts (fast fade) 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 signal-processing circuitry in the wireless equipment and Ethernet Protocol has to request multiple message packets to try to maintain contact. This delay reduces the data throughput.

Test ProcedureUse 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.

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Resultant Multi-Polarized Waves

Multi-Polarized Antenna

Reflected Z-Wave

Time

a

a

b

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+

Figure 6

Reflected-Z Wave

It can be demonstrated that the “reflected-z” wave (as discussed by Bell Labs and others) along with six total electric (E-field) and magnetic (H-field) waves, produce multiple (typically 3-4) waves of various polarizations that can come from different directions in an urban/suburban wireless deployment. But with the MP approach, these various (only partially out-of-phase and therefore effectively additive) E and H-field waves are uniquely used for improved real-world wireless connectivity.

In a relatively static-obstructed environment, the fewer number of reduced signal strength readings can be seen with standard signal strength utility software.

Multi-PolarizedAntenna

Fringe Area /Radius Begins... Number of Locations with Loss of Connectivity Begins to Grow

Far /Deep Fringe Area /Radius... Only Few Sites Remain With Connectivity

Statically Obstructed Environment – Many Locations Tested

Statically Obstructed Environment – Many Locations Tested

Statically Obstructed Environment – Many Locations Tested

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Not Connected Connected

Rubber Duck Antenna

Multi-PolarizedAntenna

Rubber DuckAntenna

Multi-PolarizedAntenna

Rubber DuckAntenna

-95 dBm -95 dBm

RSSI / S/N RSSI / S/N

RSSI / S/N

For Example, Where a Signal Above -95 dBm Denotes Connectivity:

Figure 7

Real Signal Strength Indiction - Signal-to-Noise Ratio

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RSSI readings at one location over time in a dynamically obstructed environment show the difference in response and improved performance of the MP antenna design over a singularly polarized antenna.

In a dynamic-obstructed environment, special Real Signal Strength Indication (RSSI) software can show near-instantaneous dropouts caused by fluctuating obstructions such as moving leaves, people, and cars. This, in turn, causes equipment that uses standard-style antennas with Ethernet Protocol data handling capability to retry receiving dropped packets, which just results in a further overall drop in throughput.

Dynamically Obstructed Environment – One Location Tested; RSSI / S/N Readings Taken Over Time

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RSSI / S/N (dBm)

Figure 8

Real Signal Strength Indiction

Elapsed Time

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RSSI (Multi-Polarized Antenna)

RSSI (Singularly Polarized Antenna)

Elapsed Time

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Figure 9

RSSI in Dynamic Environment

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Multi-PolarizedAntenna

Mean Signal

Dynamically Obstructed Environment – Many Locations Tested

Signal Over Time At these Locations

Resultant Less ThanExpected Throughput

Transient Drop in Signal Strength/Connection:Changes With Obstructed Pathways.

Rubber DuckAntenna

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Figure 10

Dynamically Obstructed Environment -Multi-Polarized Antenna

Even when a higher signal strength from the standard antenna can be easily observed, the MP antenna often maintains a higher throughput than a standard antenna.

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Momentary Drop in RSSI withSingularly Polarized Antennain a Dynamically Obstructed

Environment Results in Retries and with Such a Drop

in Throughput

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Figure 11

Dynamically Obstructed Environment -Singularly Polarized Antenna

In a dynamically obstructed environment, equipment using a singularly polarized antenna can suffer a momentary drop in RSSI, which triggers multiple retries and an associated drop in communications throughput.

Radiation patternTheory logically concludes, and testing verifies, that a smaller Multi-Polarized 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 red area, figure 12), than it is to increase the “rarely connected system” in remote areas (see blue area below) to “occasionally connected systems”.

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The typical coverage area for an antenna can be divided into two ranges: a required moderate range and a remote or sparsely connected range. The inner circle defines the largest concentration of clients in residential or industrial-park WiFi WWAN settings. The area required for good coverage comprises sites for cell phones, WiFi VOIP phones, broadcast radio, government and commercial two-way radio, as well as Bluetooth within an automobile. The outer circle defines the sparsely connected area.

= Client (Potential)

Moderate Range

Remote Areas

Figure 12

Antenna’s Typical Coverage Area

SummaryRadio frequency signals from a Multi-Polarized antenna can be viewed as a fog that penetrates different shaped nooks and crannies with a variety of polarizations. At the receiving end, Multi-Polarized 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 (See electromagnetic interaction formula).

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Although predictably fewer peaks appear for the smaller MP antenna compared to the standard, full-size antenna, the MP antenna remains connected to a larger percentage of clients – with higher data rates – over time.

Although There Are Predictably Fewer Peak Signals With a Smaller Multi-Polarized Antenna Compared With The Standard Technology 'Full Size' Antenna, a Greater Percentage of Clients Are Still Connected.

RSSI (Standard Antenna)

RSSI (Multi-Polarized Antenna)

Elapsed Time

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No Connection

Greater Percentage of Clients Still Connected, Even With the Comparatively Smaller Multi-polarized Antenna

Multi-Polarized Antenna

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Figure 13

Multi-Polarized Antenna Advantage

Electromagnetic interaction formula:

For example:

Where (for (1-P)):

Similar calculations apply to such as:

0.25λ

Reflector

D1(adjusted) = 0.95∗[984/f(MHz)]∗(1/4)∗(12)∗(k-factor) ∗ [1-[(1-P)of 0.45λ ∗ (1.1/0.95)]] ∗ [1-[(1-P)of 0.20λ ∗ (1.0/0.95)]] ∗ [1-[(1-P)of 0.22λ ∗ (0.9/0.95)]]

0.20λ 0.22λ

1.1 Dr

Dr D1 D2

0.95 Dr

0.90 Dr

Re-Adjustment of Antenna Elements

10

0.050

0.0010.002

0.000

0.0030.0040.0050.0060.0070.0080.0090.0100.0110.0120.013

0.10 0.15 0.20 0.25 0.30 0.35 0.40 0.45 0.50 0.55 0.60 0.65 0.70 0.75 0.80 0.85 0.90

λ - Spacing

(1-P)

(1-P) Curve

Dr6 Dr5

Dr4

Dr3

Dr2

Dr1

© 2011 MP Antenna, LTD. All rights reserved. MP Antenna products and technology are protected under United States Patent No. 6,496,152. Other patents pending. REV. 052611AD11

rethink the antennaTM

www.mpantenna.com

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, 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.