A new loop antenna system is proposed to detect the magnetic field of the natural electromagnetic wave in space in a very wide frequency band from 0.1 to 100 kHz. A single small loop antenna is followed by a network consisting of two transformers in series, one of which is optimized to pick up the signals at lower frequencies and the other, the signals at higher frequencies. Detailed analyses of the network are performed and the optimized parameters both on the loop and network are deduced for a small loop with an area of 0.50.5 m2. The theoretically obtained pick-up factor and the threshold levels for minimum detection in each frequency band are confirmed through the laboratory experiments and the field observations of the natural VLF waves such as the whistler as well as the transmitted carrier signals from the VLF and MF stations. The system proposed has a potential merit when applied to the space experiment where the payload is limited. The work in this paper gives the fundamental for the design of the loop antenna system onboard the Japanese satellite (EXOS-D) to be launched in 1989.

A new antenna for a wristwatch phone is proposed. The proposed antenna is a one-wavelength rectangular loop along the cap of the wristwatch phone. The loop is fitted at the periphery of the openable cap connected to the wristwatch case by a hinge. In order to discuss the antenna gain, we define the two different conditions as follows. When the user opens the cap and talks over the wristwatch phone, his wrist is held in front of his face, which is called the "talk position" in this paper. When the user closes the cap and waits for a call, his wrist rests down at the side, which is called the "stand-by position. " We measured the radiation patterns and calculated the pattern averaging gain (PAG) of the proposed antenna for the two positions. In addition, we compared the proposed antenna with the other antennas: a planar inverted F antenna (PIFA) fixed on the strap and a normal mode helical antenna (NMHA) installed on the case. As a result, the PAG of the proposed antenna was about -5.5 dBd, which was the same as the PAG of the other antennas for the talk position. In the case of the stand-by position, the PAG of the proposed antenna was about -3 dBd, which was 7 dB higher than that of the other antennas. The gains of the proposed antenna reached the goal, which was the PAG of a whip antenna of a handy phone held near the head. The results demonstrate that the proposed antenna is suited to a wristwatch phone.

A wideband loop antenna system has been tested using the sounding rocket S-310-18 to confirm its performance in detecting electromagnetic waves for frequencies from ELF to MF band in the lower ionosphere. The loop antenna system detected the one-hop whistlers with a high Signal-to-Noise ratio in 0.1-12 kHz, the spectra of which are used to study the propagation characteristics in the ionosphere. The VLF signal transmitted from the NDT station (Yosami, 17.40.05 kHz) was continuously received during the flight of rocket. The altitude dependence of the wave intensity and polarization are obtained. The polarization change of NDT signal from linear (free space mode) to circular (whistler mode) was clearly observed at a certain altitude in the ionosphere. The three Omega waves from Tsushima were detected and their height patterns of wave intensity are derived. A middle frequency radio wave (873 kHz) from Kumamoto Broadcasting Station was for the first time detected by the wideband loop antenna. It was found that the wave intensity decreases abruptly in the lower ionosphere due to absorption and reflection. This phenomenon was found to occur during both ascent and descent. Thus, it has been shown that the wideband loop antenna system tested in this rocket experiment has potential merit when applied in a space vehicle.

The electron density profile in the lower ionosphere was determined from the right and left handed circular polarized wave fields of the 40 KHz ground based signal observed by means of a rocket borne receiver. The determination of the electron density from 70 Km up to 100 Km was made under the condition for the values calculated by the full wave analysis to agree with the observed values.

A feasibility study has been made of the detection possibility of radio wave noises, i.e., Martian atmospherics, emitted from discharges in the Martian atmosphere during large dust storms. The spacecraft NOZOMI, which was launched in 1998, is to be placed on an elliptic orbit around Mars with perigee of 150-200 km. An onboard-equipment LFA (Low Frequency Plasma wave Analyzer) has capability to measure the low frequency plasma waves in the frequency range from 10 Hz to 32 kHz. In order to know if the LFA can detect the atmospheric radio noises, the propagation characteristics of electromagnetic waves through the Martian ionosphere are studied theoretically by using a full-wave method. The ionosphere is modeled as a magneto-ionic medium based on the recent observations of magnetic anomaly by Mars Global Surveyor spacecraft, and the atmospheric constituent and electron density by Viking observations. Our calculation shows that the waves at frequencies less than a hundred hertz can propagate with low attenuation and reach to altitudes above 200 km in the whistler-mode in the regions of magnetic anomalies in the dayside ionosphere. It is shown that the radio noises emitted from electric discharge in an intense dust storm, with the intensity over -30 dBV/m/Hz at the ionospheric entry point, can be sensed by the LFA. The observational identification of Martian atmospherics will contribute to the physical study of charge/discharge process in the Martian atmosphere.

We have developed an estimation system of the electric parameters for liquid materials without a sensor connecting to the testing materials. A PC can be used for the calculation, and the calculation time is about 2 minutes. The accuracy is such that the estimated values are different from the nominal values by less than 2%.

Radiation properties of magnetic noise from the harness wires of a spacecraft (GEOTAIL) have been studied experimentally and theoretically. A simulation experiment on the noise radiation using a minimum set of subsystems of the spacecraft has shown that the intensity and the directional patterns of the noise radiation from the wires were largely changed by the existence of a conductive plate near the harness wires. The change in the noise characteristics is explained by eddy currents induced in the conductive plate by the signal current flowing in the wires. The eddy currents distributed in the conductive plate were calculated by the Finite Element analysis Method (FEM). The magnetic flux densities calculated from both the source signal current and its induced eddy currents for the wiring configuration of the simulation experiment have shown to be consistent with the values obtained in the experiment. The results in the present study have provided us an important information on a wiring method to diminish noise radiation from harness wires.

Using a single-site lightning location technique, a new portable lightning location system is developed. We incorporate an attitude detection technique using inertial sensors to detect an accurate electromagnetic field vector of sferics by palm-sized electromagnetic sensors which can have arbitrary attitude. The present paper describes the concept and the performance of the developed prototype of the portable system.

This paper presents the switched-beam slot antenna over the electromagnetic band-gap (EBG) reflector. This antenna is composed of two slot elements fed with a phase difference and the EBG reflector, which is used in order to realize a low profile structure. The radiation characteristics of this antenna are calculated using the FDTD method. Calculations show that the height of the antenna using the EBG reflector is 60 % lower than that of the antenna using a perfect electric conductor (PEC) reflector. The radiation characteristics at the center of the operating frequency band in the EBG reflector are equivalent to that in the PEC reflector. It is shown that the tilt angle of the main beam in the elevation plane varies with the operating frequency, and the variation in the case of the EBG reflector is caused by its frequency-dependent reflection phase. Moreover, the radiation pattern of the fabricated antenna is measured. The results demonstrate that the low profile design can be achieved by using the EBG reflector, and reveal the influence of the EBG reflector on the antenna efficiency.

The Akebono satellite observed the Australian Omega signals when it passed about 1000km over the Omega station. In this paper, we compare the observed Omega signal intensities with the values obtained using a full wave calculation and we discuss a mechanism of modulation of the signals. The relative spatial variations of the calculated Omega intensities are quite consistent with those observed, but the absolute calculated intensities themselves are several dB larger than the observed intensities. This difference in intensity may be due to the horizontal inhomogeneity of the D region, which is not modeled in the full wave calculation, or to an incorrect assumption about radiation characteristics of the Omega antenna. It is found that modulation of the observed signals is caused by the interference between the waves with different k vectors.