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XPD - Cross Polarization Discrimination
By:Bruce Bahlmann
Preethi Ramkumar
A measure of the strength of a co-polar transmitted signal that is received cross-polar by an antenna as a ratio to the strength of the co-polar signal that is received.

The ratio of the co-polarized average received power to the cross-polarized average received power. XPD quantifies the separation between two transmission channels that use different polarization orientations. The larger the XPD, the less energy is coupled between the cross-polarized channels. The XPD values were found to decrease with increasing distance.

Polarization can be used as a tool to reduce co-channel interference due to a property of polarized transmissions known as Cross Polarization Discrimination or XPD. Due to XPD, when a horizontally polarized antenna receives a co-channel signal sent from a vertically polarized antenna (and vice versa), the effective signal strength is reduced by several dB.

In a Cross-polar discrimination, the difference in dB between the peak of the co-polarized main beam and the maximum cross-polarized signal over an angle is measured within a defined region. The ratio of the radiation intensity, in a given direction, to the radiation intensity that would be obtained if the power accepted by the antenna was radiated isotropically. The four transmitters on the Horizontal polarity are separated from the four transmitters on the Vertical polarity by the XPD value of the antenna feedhorn. Typical XPD values range from 30 DB for standard antennas to 40 DB for Ultra High Performance antennas.

Other Related Definitions for XPD
"The cross-polarization discrimination (XPD) for a location is calculated as the ratio of the sum of the powers from the same slant Tx/Rx antenna pairs to sum of the powers from the opposite slant Tx/Rx antenna pairs. This can be done using the total power from each PDP or for a particular delay (path) common to all the PDPs. The main path is at the delay of the CPDP maximum power in the first cluster. The second path is at the delay of the CPDP maximum power in the second cluster. Not all locations have a second path." [Steven Howard QUALCOMM Inc.]

"Cross-polarization discrimination [ XPD ]: The difference between the co-polarized main beam gain and the cross-polarized signal measured within an angular area in azimuth of twice the maximum HPBW of the frequency band. Better is the cross polarized discrimination, lower is the level of disturbing signal (coming from the opposite slant), in order to insure a safer reception. Measured both in the main axis and at 60° opening angle." [RFS World]

"cross-polar discrimination (XPD): The XPD of an antenna for a given direction is the difference in dB between the peak co-polarized gain of the antenna and the cross-polarized gain of the antenna in the given direction." [BWA Systems IEEE802.]

"Cross-Polarization Discrimination is the ratio between the energy received in the wanted (transmitted) polarization to that received in the unwanted (orthogonal) polarization (commonly referred to as XPD)" [Advanced Satellite Communications by Dr. Jeremy Allnutt] 
Links Related to XPD
Basics of Cross-Polarization Discrimination (XPD)– The guide to Cross-Polarization Discrimination (XPD)
Documentation of XPD– Very informative website
Documents and other papers related to XPD– The best place for all Internet related Cross-Polarization Discrimination issues
Analysis of Cross-Polarization Discrimination– (XPD) Polarization Matching
XPI and XPD– RPC Telecommunications
Products and Solutions for XPD
High XPD Microwave Antennas- Andrew
Interference Reduction Techniques- Aperto Networks
- Performance of spatial multiplexing in the presence of polarization diversity– Communication Theory Group

Other XPD Related Products

More Information About XPD
Books about XPD
Smart Antennas for Wireless Communications: With MATLAB - by Frank Gross
Smart Antennas - MIMO, OFDM & Single Carrier FDMA for LTE: PAPR Comparison - by Arslan Ali Basit, Rahim Umar and Haris Majeed

Other XPD Related Books

Used and New XPD for Sale

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