Measurements on a single channel hybrid element have shown 3 dB video bandwidths greater than 20 % with a maximum video response of ~500 V/W. The video response as a function of RF frequency is shown below. A lowest single sideband (SSB) conversion loss of approximately 10 dB was measured at 94 GHz.
Variation of the estimated conversion loss with changing LO power has been measured. A substantial amount of LO power (~1.0 mW) is required per element in order to achieve the optimum conversion loss of ~10 dB. This in turn requires both a high power LO source and an array inter-element spacing as tight as possible for the most efficient utilization of LO power. A novel, staggered element array design has been employed so that antenna elements are as close as possible, while maintaining sufficient separation between IF sections for reduced inter-channel crosstalk. The mask overview for a 20 channel monolithic array is shown below.
Monolithic arrays were fabricated using a self-aligned process employing GaAs MBE wafers. Typical values of the measured diode series resistances were in the 9 to 12 Ohm range. From these values, the estimated diode cutoff frequencies range from 660 to 890 GHz. Testing on single channels of the array have shown 25%, 3 dB video bandwidths and a best SSB conversion loss of ~14 dB. From these results, a DSB conversion loss of 11 dB is anticipated, indicating that noise temperatures in the 3500 K range should be readily achieved.
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