A Novel Hybrid-Channel Attenuation Measurement System at 50–110 GHz
A novel hybrid-channel attenuation measurement system has been built for the measurement of Vand W-band waveguide attenuators from 50 to 110 GHz. The measurement system combines two single channels of the V and W bands together into one system. The V-band channel is used as the measurement channel and the W-band channel is used as the synchronization channel when the V-band attenuator is measured and vice versa. The measurement system is free of cross talk between the two channels and removes the need for isolators between the local oscillator and the mixer since the RF signal frequencies in the two channels are different. In addition, a compensation module was designed to cancel the self-mixing produced by the W-band mixer at frequencies above 102 GHz. The expanded uncertainty of the system is evaluated to be 0.004-0.08 dB at frequencies ≤102 GHz and 0.005-0.11 dB at frequencies 102 GHz for an attenuation range from 0 to 80 dB.
Attenuation-Measurement System in the Frequency Range of 18–40 GHz
The attenuation-measurement system of the National Metrology Institute of Japan - the dual-channel intermediate-frequency (IF)-substitution method using an inductive-voltage divider (IVD) as a reference standard - is improved to cover the frequency measurement range of 18-40 GHz. Higher accuracy is obtained by raising the IF to 10 kHz and employing two seven-decade IVDs in cascade arrangement. The use of the frequency doublers at each local port of the mixers allows the low-pass filters to be installed to satisfy the essential isolation between the channels. A 10-kHz voltage-ratio standard has been constructed and used as a reliable technique for uncertainty evaluation and long-term accuracy control of the 10-kHz null-balance receiver. The expanded uncertainties are expected to be 0.002 dB for attenuation up to 40 dB, 0.005 dB for 60 dB, and 0.03 dB for 80 dB
Monte Carlo simulations of magnetovolume instabilities in anti-Invar systems
We perform constant pressure Monte Carlo simulations of a spin-analogous model which describes coupled spatial and magnetic degrees of freedom on an fcc lattice. Our calculations qualitatively reproduce magnetovolume effects observed in some rare earth manganese compounds, especially in the anti-Invar material YMn2. These are a sudden collapse of the magnetic moment which is connected with a huge volume change, and a largely enhanced thermal expansion coefficient.