Fundamental microwave key devices used in achieving compact mobile/portable telephones (raidio units) are discussed. The historical development flow of the systems and radio units are introduced, with respect to the 800-/900-MHz and 1.5-GHz Japanese cellular radio systems. The design concept of the developed radio units is briefly described. Tehnical requirements for RF circuits are reviewed and the developed key devices are practically applied to the circuits. Key factors in the requirements are also shown. Finally. future trends fro the key devices are surveyed from the stand point of achieving a smaller and more light weight pocket radio unit.

An improved gate current model of GaAs FET's is presented. A conventional gate current and the reverse breakdown characteristics. Conseguentli, the model has been determined only by the forward current model fails to fit measured results in the reverse bias range, under which power amplifiers operate. The proposed model improves this problem and shows a great enhancement in accuracy throughout the whole operation range of FET's. The model consists of three diodes and a resistor, which are standerd elements implemented in commercially available circuit simulators, and thus it can easily be used for analyzing performances of various FET circits.

An effect of source harmonic tuning on linearity of power GaAs FET's under class AB operation is demonstrated. To improve efficiency of the power amplifiers, GaAs FET's are often poerated under class AB condition. Due to lower bias current, a class AB amplifier begins to show nonlinearity at lower input power comparing with class A operation, and as the power level of the input signal increases, however, an output power sometimes increases abruptly. From nonlinear circuit simulation, we have found this phenomenon is occurred by the distortion in gate RF voltage, and by suppressing even-order harmonics in the input circuit of GaAs FET, class AB amplifiers can be effectively linearized. In this paper, we show the condition for improving the linearity of power CaAs FET's under class AB operation by the source harmonic tuning technique.

AlGaAs/GaAs power HBTs for digital cellular phones have been developed. A three-dimensional thermal analysis taking the local-temperature dependence of the collector current into account was applied to the thermal design of the HBTs. The HBTs were fabricated using the hetero-guardring fully selfaligned transistor technique. The HBT with 220µm² 60 emitters produced a 31.7 dBm CW-output power and 46% poweradded efficiency with an adjacent channel leakage power of -49 dBc at the 50kHz offset bands for a 948 MHz π/4-shifted QPSK modulated signal at a low collector-emitter voltage of 3V. Through comparison with the conventional GaAs power FETs, it has been shown that AlGaAs/GaAs power HBTs have a great advantage in reducing the chip size.

A GaAs multilayer microwave integrated circuit(MuMIC) power amplifier with a harmonic rejection filter has been developed for 1.9-GHz digital European cordless telecommunication system. Adoption of the MuMIC structure has auccessfully ended up with Q-factor of 462 harmonic rejection filter. As a result, power-added efficiency of 62.2% and P_1dB of 27 dBm have been obtained at drain supply voltage of 3.6V.

A miniature transceiver, including highly integrated MMIC front-end, for 1.9 GHz band personal handy phone system(PHS) has been developed. The terminal, adopting direct conversion transmitter and receiver technology, consists of four high-density RF circuit modules and a digital signal processing LSI with 2.7 V power supply. The four functional modules are a power amplifier, a transmitter,a receiver, and a frequency synthesizer. Each functional module includes one IC chip and passive LCR components connected with solder bumps on module substrate. The experimental miniature PHS handset has been fabricated to verify the design concepts of the miniature transceiver. The total volume of the developed PHS terminal is 60cc, including the 12cc front-end which comprises the four RF functional circuit modules. The air interface connection with the PHS base station simulator has been confirmed.

A simplified equivalent circuit, which is useful in L-band, of switching MOSFET is presented. The MOSFET model accounts for the relatively low resistivity of Si substrate. By using this circuits, the relationship between the MOSFET equivalent circuit parameters and a series-shunt FET connected SPDT switch characteristics has been revealed. In order to evaluate the relationship mentioned above, enhancement type NMOSFETs and a SPDT switch with the FETs are fabricated. The MOSFET equivalent circuit parameters at L-band were extracted from measured small-signal S-parameters of the FETs. The measured switch characteristics are fairly good agreement with the simulated results which has been accomplished by using the MOSFET model. This good agreements shows the effectiveness of the MOSFET model which is presented here.

A 1.9GHz direct conversion receiver(DCR) chip which integrates an LNA, I/Q mixers(MIX), active lowpass filters(LDF) and variable gain amplifiers(VGA) was fabricated. Because the DCR for QPSK modulation systems is sensitive to the 2nd-order nonlinearity, linearization techniques are adopted in MIX and LPF. The DCR chip was fabricated using a BiCMOS process, and the die size is 5.1 mm by 5.1mm. The chip can operate from 2.7 V supply voltage and consumes 165mW when all the functions are activated. Suppression of local signal radiation and the 2nd-order distortion indicate the feasibility of Si-based DCR for QPSK modulation systems such as PHS.

A refection type and loaded-line type phase shifter switching multi phase-states has been described. This novel phase shifter circuit is constructed by adding switching FETs to a conventional 2-phase-state phase shifter. A conventional 3 bit phase shifter can be replaced by this type of phase shifter. The total chip size is reduced to 2/3. This paper reports on the design, fabrication, and performance of the novel reflection-type and loaded-line-type phase shifter MMICs.

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.

Taking a 1.5-GHz SAW antenna duplexer for PDC, we have developed a new configuration for the transmitter final stage filter and a new weighting technique for the receiver top filter. These transmitter and receiver filters provide insertion losses as low as 0.8 and 1.6 dB, respectively. Combining the filters, we have developed a miniature antenna duplexer of which size is 1.40.60.2 cm³ , several-time smaller than that of a conventional dielectric-filter duplexer. It also ensures sufficient power-handing capabilities.

An extended configuration of a stepped impedance comb-line filter is presented. The parallel stripline sections of stepped impedance resonators are coupled electromagnetically and a coupling capacitor is introduced. The creation of an attenuation pole near the passband was detailed. A design procedure for the two-pole extended filter is derived from an analysis using even-and odd-mode impedances. Experimental filters were constructed by ceramic lamination technique. They exhibited excellent performances suitable for portable telephones.

A TE₀₁₀ mode dielectric resonator is proposed to be used in a millimeter-wave filter. The resonator was fabricated using the photolithographic technique, and high unloaded Q of 1610 was obtained at 60 GHz. A planar circuit type millimeter-wave filter, using TE₀₁₀ mode dielectric resonators, was fabricated using NRD guides as input and output circuits. The measured filter characteristics agreed with calculated values well. The filter can be applicable to future millimeter-wave mobile communications systems.

A new beam tilt dipole array antenna in a simple structuer has been developed for indoor base stations in the 1.9 GHz band. The antenna comprises a radiator and skewed off-center parasitic elements placed around the radiator. With this stucture, the main beam of the array antenna can be tilted for mobile terminals reception by the effect of mutual coupling. Studies on tilt characteristics for antenna dimensions and tilt mechanism by precise current measurements have clarified the operating principle. The antennas with a fan beam and an omnidirectional pattern have been designed. The measured tilt angle was varied in the range of 0 to 26 with little alteration of the horizontal radiation patterns.

A flat stick-shaped whip antenna was developed for Japanese commercial portable telephones. It provides a high gain even though it is short and retractable. It is an open-sleeve type antenna. i.e., the inductance-loaded dipoleantenna element parallels a twin-lead type feeder. It suppresses the currents on the radio housing even at short antenna lengths. Moreover, it is easy to achieve two resonant characteristies and able to construct retractable type. A relatively high gain is gotten even when the antenna is in a retracted state. This antenna has a suitable configuration for commercial portable telephones. This paper first calculates, the current suppression of the housing on a principal model of this antenna, i.e., without a twin-lead feeder. The second analysis determines the effects of the twin-lead feeder and the dielectric coat on the antenna. Next,the two resonant technique and the configuration for the retractable-type antenna describes. In addition, the return loss and radiation pattern for the trial model were measured. The return loss shows that the two resonant characteristics and the bandwidths of the high and low resonant frequencies are 2.2% and 1.5%(VSWR2), respectively. For when the antenna is extended, radiation patterns are nearly the same as for the case of the 1/2 wavelength dipole antenna, and the antenna efficiencies are -1.6 dB at 820 MHz and -1.1 dB at 950 MHz. Other hand, for the retracted state, they are destroyed by the housing currents, but the efficiency is relatively high of -1.8 dB at 950 MHz. In these experiments, it is clear that the antenna achieves high performances.

In this paper, authors propose a linear array antenna using two bifilar helical antenna elements placed along the helix axis to reduce beam direction movement according to frequency change. The beam direction movement of this proposed array antenna is smaller than that of a conventional bifilar helical antenna. Also, the gain of this proposed array antenna is higher than that of the conventional helical antenna for a cross point angle of radiation patterns at the different transmit and receive(Tx and Rx) frequencies. The conventional helical antenna is suitable for vehicle antennas in mobile satellite communication systems such as the MSAT system because it owns circularly polarized omni-directional radiation pattern and its thin pole form. However, this antenna has a disadvantage that the beam direction in an elevation plane moves according to frequency change. In the proposed array antenna, the beam direction movement is about 9 smaller than that of the conventional bifilar helical antenna on condition that antenna total length is 4.83 λ₀, antenna diameter is 0.12 λ₀, and frequency change is from 0.957f₀ to 1.043f₀(f₀ is center frequency and λ₀ is free space wavelength at f₀). Also, the Tx and Rx gains of this proposed array antenna at the cross point angle between Tx and Rx beams are about 2 dB higher than that of the conventional bifilar helical antenna on the same condition.

This paper describes GaAs MMICs used in wireless LANs for spread spectrum communications on the ISM band. Both the transmitter and the receiver are incorporated inside the MMIC. In our experiment using prototypes at a center frequency of 2.45 GHz, the transmitter has a saturation output power of 21.4 dBm and the total current consumption is 131.2 mA. The receiver has a noise figure of3.2 dB and a gain of 12.2 dB.

The E-polarized plane wave diffraction by a perfectly conducting strip located at the plane interface between two different media is analyzed by the Wiener-Hopf technique. Applying the boundary conditions to the integral representations for the unknown scattered field, the problem is formulated in terms of the modified Wiener-Hopf equation(MWHE), which is reduced to a pair of simultaneous integral equations via the factorization and decomposition procedure. The integral equations are solved asymptotically for large strip width via the method of successive approximations leading to the first, second and third order solutions, which are valid at high frequencies. The scattered far field expression is derived by taking the inverse Fourier transform and applying the saddle point method. It is shown that the high-frequency scattered far field comprises the geometrical optics field, the singly, doubly and triply diffracted fields and the lateral waves. Numerical examples of the radar cross section(RCS) and the lateral waves are presented, and the far field scattering characteristics discussed in detail.