Results 1 - 10 of 6317
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[en] The use of increased sensitivity and temporal resolution at mm-wavelengths has revealed a number of novel features associated with solar activity. Of particular interest are the ultra-fast time structures superimposed on impulsive bursts. They are distinguished by time scales and repetition rates much shorter than the impulsive time scales. (Auth.)
[en] A fast-hopping 3-band (mode 1) multi-band orthogonal frequency division multiplexing ultra-wideband frequency synthesizer is presented. This synthesizer uses two phase-locked loops for generating steady frequencies and one quadrature single-sideband mixer for frequency shifting and quadrature frequency generation. The generated carriers can hop among 3432 MHz, 3960 MHz, and 4488 MHz. Implemented in a 0.13 μm CMOS process, this fully integrated synthesizer consumes 27 mA current from a 1.2 V supply. Measurement shows that the out-of-band spurious tones are below -50 dBc, while the in-band spurious tones are below -34 dBc. The measured hopping time is below 2 ns. The core die area is 1.0 x 1.8 mm2.
[en] The development of a one gigawatt, high current relativistic klystron tube is underway for producing one microsecond long, 1.3 GHz microwave pulses at a 5 Hz pulse repetition frequency. This paper describes the theory, modeling, and experimental development of the microwave tube. The one microsecond pulse length is almost an order of magnitude beyond what has been achieved with a high current relativistic klystron. Achieving a peak power approaching 1 GW for 1 μs requires a stable electron beam on that time scale, and an optimized extraction efficiency in the output cavity. The microwave tube design was guided by theory and particle-in-cell code modeling that relate output cavity extraction efficiency to the amplitude of the beam harmonic current modulation and output cavity shunt impedance. Current experimental results are presented. The 1 MV, 10 kA, 1μs pulse length, 5 Hz pulse-repetition-rate pulsed power modulator used to power the relativistic klystron is also described. 4 figs., 6 refs
[en] The dielectric constant and the loss angle in the (111) direction of CdTe at room temperature between 65 and 75 GHz have been determined. The results are compared to those of other authors and discussed. Problems of sample preparation are dealt with. (G.Q.)
[en] In this paper we discuss the linearity response of the Planck-LFI receivers, with particular reference to signal compression measured on the 30 and 44 GHz channels. In the article we discuss the various sources of compression and present a model that accurately describes data measured during tests performed with individual radiomeric chains. After discussing test results we present the best parameter set representing the receiver response and discuss the impact of non linearity on in-flight calibration, which is shown to be negligible.
[en] The 64-m spacecraft communication antenna of the NASA-JPL Deep Space Network has been equipped for spectral line observations at K band (18--25 GHz). To demonstrate the potential of this system, preliminary observations of the (1, 1) transition of ammonia are reported for a selection of eight southern molecular clouds. Estimates of gas density and ammonia column density are reported for six sources
[en] The nonreciprocal effect is studied theoretically and experimentally by the example of collinear acousto-optic interaction in a birefringent crystal. It is shown that this effect at ultrasonic frequencies ∼1 GHz and above considerably influences the parameters of modern acousto-optic devices, in particular, tunable acousto-optic filters. The nonreciprocal effect is estimated for different acousto-optic materials. (acoustooptics)