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Multi antenna Array Measurements Using Digitizers

There are numerous applications that employ antenna arrays for beamforming. From commercial and satellite communications to radio astronomy and RADAR, multiple antennas are employed for spatial selectivity and interference avoidance through beamforming techniques. When designing a phased array for beamforming, it is important to be able to measure the relative phase and amplitude between antennas in the array while minimizing errors caused by phase offsets created in the test system. For example in a dynamic phased array, the adjustable phase shifters in each element 'steer' the antenna and therefore need to have known phase relationship by the control system that is used to point the beam in the desired direction. The better the cross-channel phase coherence is of the measurement system used to align the antennas, the more precisely the beam can be positioned.

This presentation will discuss using a multi-channel phase coherent digitizer, along with the necessary signal conditioning and down-conversion ahead of the digitizer, to characterize the relative phase and amplitude relationships between antennas in a phased array. The discussion will cover: calibrating a digitizer-based system for matched cross-channel magnitude and phase, using digital down-conversion for optimizing the system sensitivity at the required bandwidth, and algorithms used on the resulting complex signals necessary to achieve measurement results of cross-channel (between antennas) phase and gain. At the conclusion of the presentation, a representative system configuration will be described with measurement results derived from the techniques presented.
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