Design of an integrated Ka band receiver module for passive microwave imaging systems

Presently different imaging principles for MW radiometry are in use. Most of them still perform pure mechanical scanning as well as a combination with electronic scanning by using parts of a focal plane array, for instance, as known from modern optical cameras. In principle, there are two main problems with mechanical scanning systems, on one hand the antenna aperture dimension has to be large for a given wavelength in order to get a sufficient spatial resolution. On the other hand it is important to record an image in a reasonable period of time. Most of the mechanical scanning systems are working with a rotating antenna structure. The velocity of this rotation cannot be increased arbitrarily due to inertia problems caused by the antenna size and mass. Hence, the trend is going towards fully electronic and quick beam steering or two-dimensional focal plane arrays. These systems are able to achieve high frame rates, but they still are very expensive, because they require a significantly higher number of receiver modules compared to a mechanical scanning system. Furthermore one has to handle a rising complexity by the integration of such a high number of receiver modules, all consisting of many discrete components following the antenna frontend. Also the weight is an important factor with respect to airborne/spaceborne platforms. Consequently, in order to minimize the weight and the costs, the whole receiver components have to be realized in a considerably integrated design by using MMIC (Monolithic Microwave Integrated Circuit) technology as far as possible