Abstract: Undesired signals from interfering satellites are separated from desired signals from a target satellite by using a sum beam and a difference beam as in a monopulse radar. Both desired and undesired signals are received by an antenna and separated by different mode couplers from a waveguide. The fundamental mode of the waveguide provides the desired signals along with components from the interfering signals. Both desired and undesired signals are picked up from the waveguide through a fundamental mode coupler. The higher order modes of the waveguide provide the interfering signals alone, representing the difference beam which will be aligned along the boresight. In a circular waveguide, the TM.sub.01.sup.o will yield a difference pattern for vertical polarization in any plane, and a TE.sub.21.sup.o or TE.sub.01.sup.o mode will result in a difference pattern for horizontal polarization. A square or a rectangular waveguide could be used instead of a circular waveguide to achieve the same result.