A total-power radiometer at 48 GHz has been constructed and used for detecting pedestrian and bicycle traffic. The high operating frequency was selected in order to obtain a high angular resolution. The best way to distinguish a human being from the background is to direct the antenna to the road from above in an angle of 40-70 degrees. Hereby the road reflects the cold sky and thus the brightness temperature of the road is low. On the other hand, the brightness temperature of a human being at millimeter waves is almost the same as his physical temperature. Cars among human beings can be detected radiometrically because the brightness temperature versus the car position has a specific feature. First the front of the car reflects the high brightness temperature of the surroundings and then the top reflects the low brightness temperature of the sky.
The Radioastron space research satellite, expected to be launched in 1994, will have on board four sensitive, two-channel radiometers. In this paper, the design and testing of the 22 GHz receiver is described. The most important properties of the receiver are sensitivity, phase stability and gain stability. To reach maximum sensitivity, a modern space qualified low noise HEMT amplifier (LNA) has been designed. The measured LNA noise temperature is 101 K. For maximum phase and amplitude
Two Gunn oscillators, conventional intermediate frequency building blocks, and a modified GaAs diode detector are combined to form a portable monostatic 10 ns instrumentation radar for outdoor K(a)-band radar cross section measurements. At 37.8 GHz the radar gives +20 dBm output power and its tangential sensitivity is -76 dBm. Processing bandwidth is 125 MHz, which also allows for some frequency drift in the Gunn devices. Intra-pulse frequency chirp is less than 15 MHz. All functions are steered by a microcontroller. First measurements convince that the construction has a reasonable ability to reduce close-to-ground surface clutter and gives an effective way of resolving target detail. This is beneficial especially when amplitude fluctuations disturb measurements with longer pulses. The new unit operates on 12 V dc, draws a current of less than 3 A, and weighs 5 kg.
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