An antenna for dual-wavelength radiometry at 21 and 32 GHz

Accurate multiwavelength remote sensing of the atmosphere requires antennas with the same beamwidth at the various frequencies of operation. A single offset antenna with a corrugated feed which meets this criterion at 20.6 and 31.65 GHz is described. The planar near-field (PNF) scanning facility at the National Bureau of Standards (NBS) was utilized to measure the near-field patterns of the overall antenna for various feed positions, and with an apodizer placed on the reflector. Comparison of the far-field patterns, calculated using PNF methods, yielded the optimum configuration. In addition, the facility was used as a far-field range to measure the radiation pattern of the feed. The antenna is presently installed at Stapleton International Airport, Denver, CO, in a dual-channel radiometric system which continuously remotely senses water vapor and liquid, and it is performing satisfactorily.