An improved interferometer design for use with meteor radars

The measurement of the directions of radio meteors with an interferometric system is beset by two problems: (1) The ambiguity in the measured directions for antennas spaced by more than lambda/2 and (2) the effects of mutual impedance when the antennas are spaced at lambda/2 and less to avoid these ambiguities. In this paper we discuss the effects of mutual impedance between spaced antennas and describe an interferometer which both minimizes these effects and avoids the ambiguities associated with spacings larger than lambda/2. We have modeled a version of this design numerically and show that under ideal conditions an interferometer of total span 4.5 lambda can yield directions accurate to about 0.3 degrees with a signal-to-noise ratio of 20 dB. Finally, we have tested the design with observations from the 1996 Geminid and 1997 Quadrantid meteor showers and find that even without a ground plane, the interferometer provides unambiguous directions to an accuracy of the order of 1.5 degrees.