WERA HF Radar Beamforming

https:///weradocs/Wera_Beamforming.shtml

Last update:

WERA HF Radar Beamforming

New File for Antenna Locations

A new algorithm to perform beam forming based on antenna geographical location in Latitude and Longitude is now implemented. The phase shifts for the antennas required to steer the beam into a specific direction is calculated from the distance between an antenna and a "virtual target" at a given range. This approach no longer depends on the arrival of the electromagnetic wave to be a parallel wave front, but takes care of the real geometry; e.g. to form a beam to some "virtual target" perpendicular to the array at a narrow range, the way to the antennas at the ends of the array is longer than to the antennas in the center.

new beamforming

There are two windowing functions available to reduce the side lobes: A Hamming window and an Ultra Spherical window. In some cases, especially at long arrays (16 antennas and more), the Ultra Spherical window results in a better side lobe reduction. In other cases the Hamming window offers the better results. To apply the windowing function, the antenna spacing calculated from the projection of the array in direction to the "virtual target" is used for the Hamming window, e.g. the spacing which can be seen when looking from the "virtual target" to the array. The Ultra Spherical window is currently based on a constant antenna spacing, which has disadvantages is case of unequal antenna spacing and curved arrays.

Antenna sensitivity patterns have been calculated for typical situations. Note that this is the pattern of the receiving antenna array in case of a constant sensitivity of the single antennas, i.e. a circular pattern, and that no coupling between the antennas has been taken into account. Also, the effective antenna pattern of the total system is the product of the receive antenna pattern shown here and the transmit antenna pattern. The antenna patterns for some cases are cataloged here:

16 antenna linear array

12 antenna linear array

8 antenna linear array

16 antenna curved array

12 antenna curved array

The antenna location file name for the sites is defined in Params.cfg . The antenna locations are given in geographical degrees (look here for the data format).

The antenna window selection for the sites (Hamming / Ultra Spherical) is defined in Params.cfg . The default antenna window is Ultra Spherical.

Compatibility with old Measurements

The new antenna location file is the most advanced approach to pass the characteristics of the receive antenna array to the processing software. Old configurations are compatible with the new approach and are handled in the following way:

If the name of an antenna location file is passed in Params.cfg and this file does not exist, a linear array is assumed and the file is generated and written to the disk based on other information supplied:
ARR1_nnn, ARR2_nnn, ARRD_nnn, DIST_nnn, and True_North from the measurement header.
If the name of an antenna spacing file DIST_nnn is given, the values from this file are used together with the array direction (True_North) from the measurement header.
If the file DIST_nnn is not given, the antenna spacing defined in ARRD_nnn is used together with the array direction (True_North) from the measurement header.
If ARRD_nnn is not given, a linear array with 0.5 lambda spacing is assumed.

Comments to: gurgel@ifm.uni-hamburg.de (Klaus-Werner Gurgel)