The poor low-frequency performance of geometrically designed beam-waveguide (BWG) antennas is shown to be caused by the diffraction phase centers being far from the geometrical optics mirror focus, resulting in substantial spillover and defocusing loss. Two novel solutions are proposed: (1) reposition the mirrors to focus low frequencies and redesign the high frequencies to utilize the new mirror positions and (2) redesign the input feed system to provide an optimum solution for the low frequency. A novel use of the conjugate phase-matching technique is utilized to design the optimum low-frequency feed system, and the new feed system has been implemented in the JPL research and development BWG as part of a dual S-/X-band (2.3-GHz/8.45-GHz) feed system. The new S-band feed system is shown to perform significantly better than the original geometrically designed system.

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In this paper, the Focal-Plane (Complex-Conjugate Phase-Matching) Method is used to select the appropriate gain and location of a feed for S-Band (2.295 GHz) operation of DSS-13, the new NASNJPL Deep Space Network (DSN) 34-m Beam WaveGuide (BWG) antenna. It is found empirically that the Focal-Plane Method gives a better design in terms of the GIT figure than previous S-Band designs.