This paper describes the design and construction of a bistatic SAR receiver suitable for airborne applications, using orbital SAR systems (ENVISAT, ERS-2, RADARSAT, TerraSAR-X among others) as opportunity transmitters. The challenge of this design is to reduce the required data throughput of the recorded data. This is achieved storing data only in the time intervals when scattered signal from the target area appears. The task of detecting this time intervals is performed in real time using a matched filter of the signal received directly from the SAR transmitter. ; Peer Reviewed ; Postprint (published version)