Radio disturbances of digital microwave links are likely to increase as man-made structures screen the radio propagation paths, and unwanted waves reflected or scattered by the structures interfere with radio signals. This paper describes a practical method for evaluating the influence of propagation impairments due to man-made structures on digital microwave links and provides some model calculations of those impairments. Since multilevel and quadrature modulation techniques are employed to achieve high spectral efficiency for recent digital transmissions, not only average level attenuation but also in-band distortion and intersymbol interference have to be taken into account. Propagation distortion, diffraction loss and cross-polar interference due to reflected and scattered waves from man-made structures such as buildings and conductor structures are evaluated.

The superconducting magnet on a maglev vehicle vibrate and heats up inside under the influence of various disturbances in running. We have investigated the characteristics of heating in the superconducting magnet vibrating under the electro-magnetic disturbance from the ground coils. This magnetic disturbance has a frequency component ranging widely from 0 Hz to several hundred Hz which is proportional to the speed of the maglev vehicle. It was revealed that an extreme increase of heat load on the inner vessel of the energized magnet occurred at a particular frequency and it surpassed the capacity of the refrigerator installed in the tank of the superconducting magnet. As a result of the investigation, we could identify broadly three factors of heating, and now we have good prospects of largely suppressing the heating by reducing the disturbance through the folded arrangement of the ground coils and a structural improvement of the magnet.

An electric field is created around a telecommunications line by common-mode currents caused by clock signals, switching pulses and digitally transmitted signals. This field is a potential source of interference to radio reception. This paper describes measurement results for interference fields radiated from a telecommunications line. A method using optical fiber was used to measure the relation between common mode voltage and radiated electric field, and the results were compared with the calculated results discussed in IEC/CISPR. Our results show that the limits discussed in the CISPR are effective in restricting the electromagnetic interference due to conducted disturbances at telecommunication ports. The electric field strength from the telecommunications line caused by telecommunications signals is estimated on the basis of the relation between the common mode voltage and the radiated field strength. In this estimation, the dependence on the longitudinal conversion loss (LCL) of the telecommunications line is taken into account. The results show that the telecommunications signal on the ISDN basic access interface is not an interference source provided that the LCL of the telecommunications system meets the requirements for the ISDN interface.

It is an important problem whether or not we can reject the disturbances from distributed parameter circuit. In order to analyze this problem structurally, it is necessary to investigate the basic equation of distributed parameter circuit in the framework of state space. Since the basic equation has two parameters for time and space, the state value belongs to an infinite-dimensional space. In this paper, the disturbance-rejection problems with incomplete state feedback and/or incomplete state feedback and feedforward for infinite-dimensional systems are studied in the framework of geometric approach. And under certain assumptions, necessary and/or sufficient conditions for these problems to be solvable are proved.