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Modification Program for the 837K-1 Antenna.

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The object of the 837K-1 Antenna modification program was to increase the antenna frequency band from the 240- to 315-MHz range to 235 to 400 MHz and allow the system to be compatible with the FLEETSATCOM frequency band. Delivered at the conclusion of the program was one modified antenna system comprising a modified 90 deg hybrid, modified standard height antenna element, extended height antenna element, 50-ohm termination, and interconnecting coaxial cables. Full-scale patterns were measured using a ground plane curved to approximately the same curvature of a C-135 aircraft. Scaled antenna patterns were made on a 115th scale model of a C-135 aircraft at selected frequencies from 235 to 400 MHz. Computer optimization techniques were used to select optimum network component values for matching the standard and extended height antenna elements. Trade-off studies determined the optimum height of the extended antenna element. The modified standard height antenna element meets specification requirements of 1.51 vswr over a 235- to 400-MHz frequency range and 2-kW CW power rating, but the average gain at 30 deg above horizon is -1.6 dB from 250 to 400 MHz and a minimum -2.7 dB at 235 MHz, instead of the 0 dB specified. The extended height element also meets specification requirements except that average gain at 30 deg above horizon is 0 dB from 250 to 400 MHz, decreasing to -1.24 dB at 235 MHz. Author

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Final rept. Jun 71-Mar 72,



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