Polarization Types | Polarization Parameters | Radar Signal Polarization

Polarization

Polarization is a property of an electromagnetic wave that describes the orientation of the electric field vector with reference to the antenna's orientation. The three basic types of polarization are illustrated in the following figure:

Some antenna polarization types

In the illustration of linear polarization, the electrical field is polarized in the y direction in the coordinate system. In special cases of linear polarization, the electrical field is aligned vertically or horizontally with reference to the antenna. In the other two types of orientation shown, the tip of the E vector describes an ellipse and a circle, respectively, as it rotates over time. Circular polarization can be right-handed (as in the illustration) or left-handed.

STK computes the polarization match, which is a quantity between a transmitter and a receiver based on their polarization types, positions, and attitudes.

Reference: See Kraus, John D., Antennas, 2nd ed., New York: McGraw-Hill (1988), pp. 70-73.

For a simple receiver or transmitter model, you select the polarization type on the Model Specs tab. For all other receivers and transmitter models, you select the polarization type on the Antenna's Model Specs tab.

See the Technical Notes for a discussion of signal loss due to polarization mismatch.

Polarization Types

STK Communications makes the following polarization types available:

Polarization Parameters

Depending on the polarization type chosen, the following parameters are available for specification:

Polarization parameters

Parameter Description
Reference Axis Applicable to the linear, vertical, horizontal, and elliptical polarization types. Specify the antenna body axis (X, Y, or Z) with respect to which the electrical field is oriented.
Tilt Angle The angle between the reference axis and the electric field vector.

If x axis is selected as the reference, positive tilt is measured from x to y in the xy plane.

If y axis is selected as the reference, positive tilt is measured from y to -x in the xy plane.

If z axis is selected as the reference, positive tilt is measured from z to x in the xz plane.

Axial Ratio Applicable to the elliptical polarization type, this is the ratio of the major to the minor axis of the polarization ellipse. The range is -1e+15 through -1.0 and 1.0 through 1e+15.
Cross-Pol Leakage
(Receiver only)

Whenever STK detects a complete polarization mismatch between the transmitted signal and the received signal under ideal conditions, the Cross Polarization Leakage value is applied to model the less-than-ideal real-world performance. The value, ranging from -9999.9 dB to -0.001 dB, reflects the performance of the user's system, where -9999.9 dB represents ideal conditions (no leakage).

Note: Earlier versions of STK assume that there is no Cross Polarization Leakage.

 

The following figure illustrates tilt angle and axial ratio for the elliptical polarization type:

Polarization parameters for elliptical polarization type

The polarization match between the transmitting and receiving object is calculated dynamically on a scale of 0 to 1, where 0 is no match and results in no received signal, and 1 is perfect (no loss).

Note: Currently, de-polarization due to rain is not supported.

Radar Signal Polarization

You can set a polarization type for a Radar’s transmit side signal and one for its receiver side signal. Transmit signal polarization interacts with the target Radar Cross Signal (RCS) and is modified based on the polarized RCS type. The updated polarized signal is received by the Radar receiver and interacts with the receive side polarization. For more information on Polarized RCS types, see Radar Target RCS Complex Polarization Scattering Matrix. You also have an option to enable a parallel radar channel with an orthogonal polarized signal and identical system characteristics. For more information, see Orthogonal Polarization.

For information on computing polarization data, see Analyzing Polarization on Radar Performance.

Transmit Side Polarization

Radar transmit side polarization enables the transmitted signal to be polarized with respect to the radar antenna’s body-axis. The default antenna orientation aligns the antenna boresight (direction of signal propagation) to the Z-axis of the body. The electric E-field may be aligned to reference X-axis or Y-axis. The terms vertical and horizontal refer to the E-field being perpendicular or along the reference axis. For example, X-axis is being used as the reference axis; the horizontal polarization will align the E-field vector along the X-axis, while vertical polarization will place the E-field vector perpendicular to the X-axis. The tilt angle with linear polarization will place the E-field at the tilt angle from the reference axis.

The final orientation of the polarization vector is actually computed using the attitude of the object, parent/grandparent objects and also depends on the direction vector to the target.

Receive Side Polarization

Radar receive side polarization sets the receive antenna polarization with respect to the receive antenna body axis. The Z-axis is the default antenna orientation along the boresight

The polarization reference axis settings on the receive side are similar to the settings on the transmit side.

Whenever transmit polarization is set, the receiver side must also be set to compute the polarization mismatch loss.

Transmit and Receive Orthogonal Polarization

Radar target reflections respond differently to diverse signal polarizations. Radars use orthogonal signal polarizations to elicit a different response from the target. Select Enable Transmit/Receive Orthogonal polarization to create a secondary signal channel with exactly the same system characteristics, but with a polarization setting orthogonal to the original channel; that is, the orthogonal channel is modeled with the same frequency, power and signal attributes, etc.

The orthogonal channel can be enabled, independently, on the transmit side or the receiver side of the radar system. The orthogonal polarizations are created by STK based on the polarization of the original channel; for example, vertical & horizontal, RHC & LHC, Linear with tilt angle & Linear with tilt angle plus 90 degrees are examples of the orthogonal polarization pairs. In case of the elliptical polarization settings, the orthogonal channel contains the settings which are diagonally opposite on the Poincare polarization sphere.

The targets with a complex valued scattering RCS may respond differently to the two incoming signals and may create up to four reflections. The following diagram implies a bistatic operational mode, but the radar configuration may be monostatic. The same analytical capability applies regardless of the radar receiver's position and whether it shares an antenna for transmitting or receiving.

The four reflections may be received by the two orthogonally polarized receiver channels. These signals are combined in the signal post processing system to compute the individual channel and aggregate system performance data.

Radar Target RCS Complex Polarization Scattering Matrix

STK supports fixed as well as aspect dependent symmetric, mono-static and bi-static Radar Cross Sections (RCS) for all types of radar target objects. For more information, see Radar Cross Section (RCS).

The aspect dependent user RCS data is provided in a simple text file. See External RCS Files for an example and format of an RCS file.

Radar Jammer Polarization

Other mono-static radars and RF transmitters may act as jammers to a radar receiver. Starting with STK 9, polarization has been extended to the jamming signals. Each (orthogonal) polarized receiver is matched to the incoming jamming signal polarizations to compute the impact of the interference on its performance, as shown below.

Jammer polarized signals also under go the same attitude and orientation computations as other radar signals to process the polarization mismatch to the radar receiver.

When the jammers are not polarized then the polarization mismatch computation to the radar receiver's main and orthogonal channels is skipped. In this case, the jammer will the same impact on each channel.

Analyzing Polarization on Radar Performance

You can generate reports that provide the following data:

For more information on Radar Polarization data providers, see Radar Polarization Data Providers.