Efficiency and performance in coherent detection algorithms for synthetic aperture radiometry

Synthetic aperture interferometric radiometers require phase coherent detection to allow the visibility function to be measured and subsequently converted to brightness temperature images. Products of signals between channels produce the complex “visibility” terms of the spatial spectrum of the brightness temperature scene. Today´s technology offers the choice of either analog or digital detection methods for relatively low microwave frequencies. Digital detection may offer advantages, particularly in certain instrument configurations. This paper reviews the results of an evaluation of a particular digital method and a variety of FIR filter designs. A programmable, real time processor was developed to study various Hilbert Transform algorithms for digitally forming the in-phase (I) and quadrature (Q) components of the received signals. An overview of the test set-up and test results using several FIR filters is presented, allowing a trade between numerical simplicity and the gain and phase balance between I and Q