The present invention relates to a method and an apparatus for measuring the phase shift between a first and a second signal.
Measuring the phase shift between two phase shifted signals is required in many applications like feed-forward amplifiers or the estimation of the direction of arrival (DOA) in array antennas, conf. Bong-Gee Song, Ritcey, J. A., “Maximum Likelihood Estimation of the Angle of Arrival”, Antennas and Propagation Society International Symposium, 1994, AP-S. Digest, pp. 1568-1571, Vol. 3, June 1994; or Balogh L. and Kollar, I., “Angle of Arrival Estimation based on interferometer principle”, Intelligent Signal Processing, 2003 IEEE International Symposium on, pp. 219-223, September 2003. According to the prior art this is usually done by calculating the correlation between the two signals. However, using a digital approach to this end requires downconversion of both signals, analog-to-digital conversion with high-speed ADCs for wideband signals, and fast signal processing. On the other hand, using an analog approach by e.g. multiplying or mixing the two signals results in an unambiguous measurement range of only 180° and, furthermore, a biased measurement of the phase shift due to DC offsets of the mixer's output which is typically temperature dependent.