Phased array calibration and beamforming using signal processing

• Array antennas have a wide range of applications which includesground and airborne radar, weather radar and anti-collision radar.In addition, equally important applications exist forcommunications, both on earth and to satellites in space, as wellas for medical applications such as the detection and treatment oftumors.The modern trend in array design is to use digital beamforming andto integrate the antennas with the rest of the system moreclosely. This adds new possibilities, but also contributes to makethe system expensive. To make full use of the new technology, thisthesis presents a direction dependent signal processing arraycalibration method. The new method, called local calibration, alsoallows for larger array imperfections and, possibly, a loweroverall array cost. In contrast to other non-parametriccalibration methods, the proposed method can handle positionerrors and shows good performance also for sparse calibrationgrids, which is demonstrated by high resolution direction ofarrival estimation. The local calibration has also been includedin a convex beampattern optimization, which makes it possible toachieve a uniform sidelobe level also with unknown sensor positionerrors in the array. The embedded element pattern is included inthe optimization by extracting the direction dependence of thereceived power from the calibration. Another application for thelocal calibration method is to reduce the number of necessarycalibration measurements by calculating pseudo calibration datafrom a sparse grid of measured calibration data.Array signal processing is often performed assuming Uniform LinearArrays (ULAs), although this model is far too simple to reveal thetrue behavior of array antennas. Throughout this thesis, morerealistic models including mutual coupling and array imperfectionsare used. Specifically, the impact of mutual coupling and positionerrors on the adaptive beamforming performance in linear andcircular arrays is studied. In the studied cases, the circulararray is found to be more sensitive to neglecting the mutualcoupling. Robust adaptive methods are commonly used to handlemodel uncertainties, such as unknown mutual coupling, but evenbetter performance can be achieved if these methods are combinedwith a calibration.

Ämnesord

TEKNIK OCH TEKNOLOGIER  -- Elektroteknik och elektronik (hsv//swe)

ENGINEERING AND TECHNOLOGY  -- Electrical Engineering, Electronic Engineering, Information Engineering (hsv//eng)

Nyckelord

mutual coupling

calibration

array imperfections

beampattern synthesis

adaptive beamforming

convex optimization.

array signal processing

Array antennas

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