A 15-50 GHz-band GaAs MMIC variable attenuator has been developed for microwave and millimeter-wave wireless communications systems. The attenuator employs a balanced distributed configuration using shunt connected HEMT's in order to realize a broadband operation, a low insertion loss and a good impedance matching with simple control bias scheme. The MMIC was fabricated with a pseudomorphic HEMT device technology. It has exhibited an insertion loss as low as 1.6 dB with an attenuation control range as wide as 21 dB at 26 GHz. It has also shown a good linearity of an input power of more than 12 dBm at 1-dB compression point and that of 26.3 dBm at a 3rd-order intercept point.

A K-band MMIC subharmonically pumped mixer integrating local oscillator (LO) amplifier has been developed. For up-converter application, it is necessary to reduce the leakage of second harmonic component of LO frequency to RF port, which is generated by nonlinear operation of LO amplifier. A quasi-lumped short-circuited stub using microstrip structure has been successfully applied to the MMIC mixer to enhance 2fLO-suppression. We propose a new configuration of a quasi-lumped short-circuited stub, which reduces the influence of parasitic elements of via-holes. The developed MMIC has a one-stage LO amplifier and it has shown about 10 dB-improvement of 2fLO-suppression compared to conventional configuration using a quarter-wavelength short-circuited stub.

A compact MMIC power amplifier which delivers P1dB of 25.8 dBm (380 mW) at 40 GHz has been developed. To make the chip width narrower, only one unit block using two parallel HEMTs is applied for a power stage. For achieving broadband interstage matching when using wide gate-width unit devices in the power stage, a new configuration of a unit block which contains a shunt capacitance is proposed.

A GaAs HEMT with flip-chip interconnections using a suitable transmission line has been developed. The underfill resin, which was not used for the conventional flip-chip interconnection structure, was adopted between GaAs chip and assembly substrate to obtain high reliability. The underfill resin is effective in relaxing the thermal stress between the chip and the substrate and in encapsulating the chip. There are various possible ground current paths for the GaAs chip in the structure with flip-chip interconnections. An actual ground current path is determined depending on the transmission line type for the chip. For an active device, it is important to utilize an assembly structure capable of realizing excellent high-frequency characteristics. In addition, each transmission line for the chip has its own transmission characterizations such as characteristic impedance. Therefore, it is necessary to choose a suitable transmission line for the chip. We evaluated the high-frequency characteristics of the HEMT test element groups (TEGs) with flip-chip interconnection for three types of transmission lines: with a microstrip line (MSL), with a coplanar waveguide (CPW), and with an inverted microstrip line (IMSL). All three types of TEGs had similar values of a maximum available power gain (MAG) at 30 GHz. However, it was found that the IMSL-type TEG, which had superior characteristics in high-frequency ranges of more than 30 GHz, is the most suitable type. The IMSL-type TEG had an MAG of 10.02 dB and a Rollett stability factor K of 1.20 at 30 GHz.

A novel K-band MMIC frequency doubler has been developed using resistive series feedback circuit. The doubler exhibits much better D/U ratio, smaller output power variation against ambient temperature and lower power consumption than those of the conventional single-ended doubler. This paper presents the simulation results on the effect of the resistive series feedback by harmonic balance methods. To obtain practical and accurate simulation results, newly developed gate charge model for Cgs and Cgd is introduced. The fabricated result of the proposed MMIC is also demonstrated.

A K-band monolithic driver amplifier with equalizer circuits has been developed. It is necessary for the equalizer circuit to be low losses in the high-frequency range and for its S21 values to increase as the operation frequency increases. In order to realize these features, it is desirable for the equalizer to have element location considering high-frequency current flows. In this paper, we present a novel low-loss, high-pass equalizer circuit layout that has superior characteristics in the high-frequency range. We used a high-pass filter as the equalizer circuit and performed a detailed evaluation of the high-frequency characteristics of the filter circuit test element groups (TEGs) for three layout types. It was found that the best filter circuit layout for the three types consisted of two capacitors and one resistor, placed with parallel connections. The resistor is located at the center and the capacitors are located at both sides of the resistor. This filter is called the CRC-type in this paper. An MMIC test sample, a K-band monolithic amplifier with CRC-type filter circuits, was fabricated. The amplifier had a gain of 21.6 dB, a Rollett stability factor K of 28.9, an input VSWR of 1.63, an output VSWR of 1.92, and a 1 dB compressed output power of 22.6 dBm at 26 GHz.