By use of small aperture antennas for receiving the broadcasting satellite (BS), its CN ratio have been measured in the period of three years. The charactristics of CN ratio in offset-parabola antenna and plane type antenna make difference in rain and night dew. The CN ratio values in these two antennas of nearly same antenna gain, sometimes occur the difference of above 2dB. In no rainy days, this difference of CN ratio is illustrated in regard to seasonal and diurnal characteristics. As the result, night dew have large influence to CN ratio of plane type antenna in Oct. and Nov ., 1993 morning.

View full abstract

CP-PASS(Circularly Polarized printed Antenna composed of Strip dipoles and Slots) can transmit and receive the circularly polarized wave using strip dipoles and slots. CP-PASS is expected to be combinedly used with active devices to realize the beam steering,etc. Generally, in the estimation of the antenna gain, radiation power is calculated by the integration of poynting power over the spherical surface.This method is, however, not practical because of consuming much time in this power estimation. This paper proposes a new method that estimates radiation power using mutual immittances in order to obtain antenna gain, and presented mathematical expressions.

View full abstract

There are many unknown points in the characteristics of low elevation propagation in equatorial district,and it has been desired to elucidate them. This time,by obtaining the cooperation of the observed data on the characteristics of low elevation condition at the antenna elevation angle 8 ' were able to be obtained. As the result,it was know that scintillation phenomena have always occurred. As to the time of scintillation occurrence,the frequency of occurrence increased around 1 5:00 in the daytime and around 20:00 in the nighttime. The scintillation in the nighttime monthly originated in the ionosphere,but also the ionospheric scintillation which overlapped on atmospheric scintillation has been often observed.

View full abstract

An offset fed reflector-lens antenna consisting of an artificial dielectric is proposed. This paper discribes the design method, the simulation results of focusing characteristics and experimental results of the radiation characteristics of this antenna. From the results, it is noted that the antenna shows a higher gain and lower sidelobe levels compared with the center fed reflector-lens antenna.

View full abstract

We fomerly proposed an antenna system for Wireless In-Building Local Area Network(WIB-LAN) consisting of a pair of circularly polarized antennas and hemispherical reflector installed on the ceiling. In this paper, the computational results using the Physical Optics(PO) method and experimental results of the scattering characteristics of a conducting hemispherical reflector are discussed. From the computational and the experimental results, it is noted that the hemispherical reflector is suitable to WIB-LAN.

View full abstract

Recently, many conducting plastic shielding materials have been retailed in connection with environmental electromagnetic problems. We formerly proposed a method of measuring the shielding effectiveness using a spherical cell as a means of evaluating shielding effectiveness. In this paper, the deviation effect of the input impedance of the probe antenna is investigated in connection with the shield effectiveness. The input impedance of the probe antenna is changed from the inherent value when the antenna covered by a lossy material cap.

View full abstract

Radiated emission from a printed circuit board (PCB) is a serious topic in a field of EMC/EMI. Magnetic fields generated by a PCB of finite area backed with copper foil are considered experimentally. Ground noises may cause the common-mode radiated emission, so that the magnetic fields near the back side of the ground plane are focused to consider the currents on it. Model lines of a trace located at the center of the PCB (centered model) and one near the edge (off-centered model) are used for measurment . Experimental results show that for the field levels near the back-side of the ground plane, the levels for the centered model are lower than those for the off-centered model. The fact suggest the increase of emission when the traces are located near edges of PCB.

View full abstract

The propagating field for the TM wave in a bent slab optical waveguide is calculated by the finite-difference vector beam-propagation-method. The attenuation constant α for the TM wave is compared with that for the TE wave. It is found that a for the TM wave is larger than that for the TE wave. The polarization dependence of bend loss is negligible, provided the refractive index difference is less than 2%.

View full abstract

The dielectric properties of water absorbed light-weight concrete were measured at frequencies between 100 and 900 MHz, as a function of water absorption rate between 0% and 100%. Experimental method is briefly discribed which the results of the dielectric constant and loss factor, which are presented as a function of frequency is some selected water absorbed light-weight concrete, show good agreement with theoretical expectation.

View full abstract

Multicarrier modulation technique using Discrete Fourier Transform (DFT), which is often called "Orthogonal Frequency Division Multiplexing (OFDM)" , is robust to frequency-time selective fading, and has a high frequency utilization efficiency with its own simple structure. This paper reviews our recent results on the system performance analysis of the multicarrier modulation ; the BER performance in a frequency-time selective fading channel, the frequency offset estimation method, the carrier recovery method for QAM using two-dimensional interpolation with pilot signal insertion, effects of nonlinearities of high power amplifier and D/A converter on the transmission performance.

View full abstract

Described is the performance of the Medium-wave radio transmitter using Hybrid Modulation which produces AM wave directly from the digitalized audio signal. In the prototype transmitter, the efficiency of the analogue type pwer amplifier was too low to construct much higher output transmitters because the analogue signal from D/A converter was amplified by the linear amplification. Employing of a carrier PWM modulator realized a module efficiency of 80% which is 40 points higher than the conventional one. Since this transmitter has no modulator module seen in conventional transmitter. Over-all efficiency of 84%~93% (=RF output/DC input) No transient over voltages,also, has occurred with the output of the transmitter shorted, which can was obtained at the MF band. protect power devices from breakdowns. In addition, use of the serial type combiner could suppress impulse surges from the output greatly. When a impulse surge of 10kV(peak) was impressed at the output transmitter, just few volts(peak) appeared at the output of the RF power modules which means that it has 30~40 times ruggedness compared to conventional ones for lightning surges.

View full abstract