3 Diversity - Xpol Design

8/9/2019 3 Diversity - Xpol Design

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Kathrein/Scholz 12/01

Diversity

Multipath propagation

Diversity principle

Space diversity

Polarization diversity


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Diversity / Multi Path Propagation

signals especially in cities consists of the direct wave and a lot of reflections

the reflections differ in amplitude, phase and polarization

summarized signal level varies a lot within short distances

Rx1

Rx2


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Diversity / Principle

unsymmetrical situation of downlink and uplink :

uplink (mobile) : limited power, small antenna

downlink (BTS) : high power, high antenna gain

Consequence : Diversity

the diversity concept bases on the idea to have two independent signalsavailable at the base station (two Rx antennas)

considering both signals results in avoiding nulls and improving the averagesignal level (diversity gain)


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Example for Combining

Diversity with two antennas

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0

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Time

SignalLevel[dB

]

Rx 2

Rx 1

Combined Signal

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-30

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Time

Signallevel[dB]


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Maximal Ratio CombiningMaximal Ratio Combining

Amplitude+ Phase

Both signals are permanently

added with equalized amplitudesand phase regardingmaximum signal/noise ratio

reachable diversity gain :6 - 7 dB

Selection CombiningSelection Combining

Logic

Switching between the two

signals and selecting thebetter one

reachable diversity gain :

3 - 4 dB


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Diversity / Space Diversity

space diversity uses two vertical polarized Rxantennas (Rxa and Rxb) with a horizontal

spacing of 12-15

Omni base station

- 3 omni antennas- Tx antenna on a higher level

> to achieve an ideal omni pattern

> to reach the required isolation

between Rx and Tx (>30 dB)

3m

3m


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Sector base station

- 3 directional antennas persector

- all antennas at the same

level due to better isolationcompared to omnis



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good diversity performance,but big spacing required

expensive support structures

duplexers reduces the numberof antennas but not theapplied spacing

raising problems to receivepermissions from the land

lords to install antennasystems


Without Duplexer

With Duplexer


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Diversity / H/V Polarization Diversity

polarization diversity uses two antennas

of orthogonal polarization

horizontal and vertical radiatingelements are combined in a commonradome

interlocked dipoles, same size of asingle antenna

Disadvantages :

good diversity performance only in cities

horizontal polarization cannot be used

for Tx

Without Duplexer

With Duplexer


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instead of horizontal and verticalpolarization the dipoles are slanted+/- 45

identical situation for bothterminations

equivalent diversity resultscompared to space diversity either in

cities or in rural areas both terminations are suitable for Rx

and Tx

Xpol is the technology for futuresystems !!

Diversity / X Polarization Diversity

Without Duplexer

With Duplexer


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instead of 9 resp. 6 antennas per basestation, only 3 Xpol antennas arerequired

extremely reduced size

due to exellent isolation (> 30 dB for any

possible port combination), mounting ona single pole mast with minimumspacing

specific 3-panel brackets available

Diversity / X Polarization Diversity


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Xpol Design

antenna construction

polarization orthogonality

cross polar ratio

diversity performance


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Xpol Design / Construction

100% symmetricalconstruction

90 beam width

rotating the single dipole +/-

45 X shape

65beam width

rotating the pair of dipole +/-

45 rhomb shape

65 half power beam width 90

739 622


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Xpol Design / Voltage Simulation

3D-simulation of an original65 dipole for 800/900 MHz

Voltage (e-plane)


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Xpol Design / Orthogonality

uncorrelation of the twosignals is achieved byorthogonal polarizations(90 angle in between)

slanted polarization canbe separated into avertical and a horizontalcomponent

equal amplitudes of V andH results in a polarizationangle of 45 andconsequently inorthogonal polarization

measurements in the farfield


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Orthogonality is indicated by identical vertical and horizontal components of theslanted polarization

Xpol Design / Orthogonality


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Xpol Design / Cross Polar Ratio

Ratio between the co-polar and the cross-polar signal (opposite compared toidentical polarization)

Measure for the uncorrelation between two signals

CPR


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CPR is important not only in main direction but within the whole sector

recommended values : main direction > 20 dB / sector +/-60 > 10 dB

Kathrein antennas provide much better values !

Xpol Design / Cross Polar Ratio


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Equal

vertical and

horizontal components

orthogonal polarizations

high cross polar ratio

excellent diversity performance

Xpol Design / Diversity Performance

3 Diversity - Xpol Design

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