A low-noise 2-GHz-band VCO for frequency synthesizers used in mobile/portable radio sets is designed and implemented. This frequency band has become increasingly important for mobile/portable radio to alleviate the present frequency congestion problem below 1 GHz. So far, however, low noise VCOs which satisfy the severe requirements of mobile radio systems operating above 1 GHz have not been investigated. The design specifications are summarized, and it is shown that the VCO phase noise reduction requires a rigorous designed oscillator. Oscillator noise characteristics are reviewed, and design principles are clarified. In order to suppress the 1/f noise, a Clapp oscillator circuit and a microstrip resonator are adopted. A Si BJT and GaAs MES FET are compared under optimum bias conditions. The noise level of the Si BJT oscillator is 13 dB less than to that of the GaAs MES FET at a 25-kHz offset frequency from the oscillation frequency, and was thus adopted in our VCO implementation. The following performance levels were obtained: 28 MHz variable frequency range with control voltage from 1 to 5 volts, 112 dB single sideband noise to carrier ratio in 1-Hz bandwidth at 25 kHz offset, and 37.5 dB noise ratio from 5 Hz to 20 kHz with respect to signal.

A circuit configuration suitable for MMIC's (Monolithic Microwave Integrated Circuit) has been proposed. It is Planar MMIC possessing slotlines, coplanar waveguides etc. on the upper side of the substrate. Novel Planar MMIC hybrid circuits have been fabricated and tested at 26 GHz band.

Correction factors are presented for estimating the RF electromagnetic field strength in the compliance assessment of human exposure from an indoor RF radio source in the frequency range from 800 MHz to 3.5 GHz. The correction factors are derived from the increase in the spatial average electric field strength distribution, which is dependent on the building materials. The spatial average electric field strength is calculated using relative complex dielectric constants of building materials. The relative complex dielectric constant is obtained through measurement of the transmission and reflection losses for eleven kinds of building materials used in business office buildings and single family dwellings.

A multi-terminal serial optical link(MSOL) achieves very simple and cost effective radio cell configurations because only one pair of fibers is needed. In addition, low cost Fabry-Perot laser diodes(FP-LDs) can be employed. MSOL has a substantial problem in that the beat noise degrades the C/N in the up-link. To reduce this noise, we propose using an automatic wavelength-offset control(AWOC) circuit. The AWOC circuit offsets the LD wavelength by controlling the laser bias current to minimise the RF band beat noise which is inherent in MSOL systems, and enables high C/N optical-microwave transmission. An experimental MSOL consisting of 5 radio access stations, each equipped with AWOC, is constructed to estimate the noise free dynamic range for 800-MHz 20-carrier signal transmission. The up-link comprises a single mode fiber connecting five 1.3-µm FP-LDs operating at 0.2 mW. The down-link consists of a single mode fiber and one 1.3-µm Distributed Feedback type Laser Diode(DFB-LD) emitting at 4.0 mW. The experimental device achieves over 15 dB noise reduction compared to MSOL without AWOC in the temperature range of 0 to 40. By using the proposed AWOC, MSOL can achive low cost optical fiber RF microcell systems that are easy to install. Additionally, when we install MSOL in the radio base station, the links become more cost effective than coaxial cable links; they offer a wide dynamic range and higher transmission quality.

This paper proposes the test phantom for the cochlear implant to estimate electromagnetic interference (EMI) from a cellular phone. This test phantom is constructed from a square tank filled with saline solution. The use of a flat phantom provides a level of consistency in duplicating the exposure conditions in the EMI tests. The measurement and calculation results show that there is no difference in the E-field strength near the surface of the phantom when comparing flat and head-shaped phantoms and that the flat phantom is sufficiently thick to disregard the influence of reflective waves near the surface of the phantom. The calculation results also indicate the appropriateness of using physiological saline (0.18 g/l) up to 3 GHz when comparing the E-field strength inside a phantom comprising physiological saline and in a 2/3 muscle model. The results of actual EMI testing of a cochlear implant show that there is no difference in the maximum interference distance when using either the flat or head-shaped phantom. Based on these results, this paper presents the validity of using the flat phantom in EMI tests from cellular phone for the cochlear implant.