MIMR (Multifrequency Imaging Microwave Radiometer) is an instrument under development for the European Space Agency (ESA) by the European Industry, with Alenia Spazio as Prime Contractor. It is a conical scanning passive microwave radiometer, which shall measure the Earth surface brightness temperature by processing the received electro- magnetic Earth surface radiation in linear polarization. Its output products will be of prime importance for monitoring of the environment, and will provide useful data for climatology and meteorology with day and night operation capabilities and near global daily coverage. The experience gained through various programs since 1972 with NIMBUS satellite's series utilizing ESMR, NEMS, SCAMS, SMMR instruments and DMSP-Block 5D-2 satellite with on-board SSM/I instrument led to the MIMR concept with better performance than the instruments already flown. MIMR has successfully passed a design phase, which has established an instrument baseline suited for accommodation on either the NASA EOS or ESA METOP spacecrafts, and a breadboarding activity devoted to key items. A Demonstrator model of the Instrument is currently under development, which shall prove by test its challenging performance: it will be representative of the flight design, performing measurements at 6.8, 36.5 and 89.0 GHz. Within this paper emphasis will be put on the receivers key design topics, as driven by performance and technology trade-offs, with an overview of the achieved performance in the frame of development activity.