The invention concerns a microwave antenna module for use in an antenna system installed on board a space platform. The disclosed microwave antenna module includes a transmit/receive module, which comprises: a first package and a second package, that are hermetically sealed to one another and that are multilayer ceramic substrate packages; and an interposer connector, that is interposed between the first and second packages and comprises a body and connection means provided in the body. First and second electronic circuitries are connected to the connection means of the interposer connector for routing microwave, control and power signals through the connection means. The first electronic circuitry includes a directional coupler in stripline-coplanar configuration. Each microwave connection assembly includes: a respective first metal element, that extends through the body perpendicularly to a top surface and a bottom surface of the body, protruding from the top and bottom surfaces; a respective first dielectric element, that is coaxial with, and extends around, the respective first metal element surrounding completely the respective first metal element, and extends through the body between the top surface and the bottom surface thereof; and respective second metal elements, that are spaced apart from, and surround at least partially, the respective first dielectric element, extend through the body perpendicularly to the top and bottom surfaces thereof, protruding from the top and bottom surfaces, and are in electrical contact with the body, thereby being at the same electrical potential as the body.