Hiromitsu Uchida

Bandpass Directional Couplers with Electromagnetically-Coupled Resonators

Compact 90- and 180-degree directional couplers incorporating bandpass characteristics are presented. They can integrate a bandpass filter and a power-divider/combiner in an RF transceiver, resulting in its miniaturization. The bandpass directional coupler can be represented as a coupled-resonator network, and its coupling coefficients and external-Q can be determined from a desired coupling ratio and operational bandwidth of the bandpass coupler. Measured results are also presented on a Ku-band bandpass 180-degree directional coupler with TE 01delta-mode dielectric resonators

An X-band internally-matched GaN HEMT amplifier with compact quasi-lumped-element harmonic-terminating network

A compact quasi-lumped-element resonator is proposed as a harmonic-terminating network for internally-matched amplifiers. It is a parallel connection of an inter-digital capacitor and a transmission line, and its compactness is suitable for packaged internally-matched FET amplifiers. An X-band internally-matched GaN HEMT amplifier has been fabricated, in which the proposed harmonic-terminating network is used at the input of the HEMT for realizing an optimum 2nd-harmonic input impedance seen from the HEMT to maximize power-added efficiency (PAE). In measurements, PAE of 50 % with output power of more than 18 W has been obtained in a moderate bandwidth of 10 %.

A widely-tunable balanced bandstop filter with low reflections and separate stop-bands

A frequency-tunable bandstop filter (BSF) with low reflections, separate stop-bands, and more than one-octave tunable frequency range is proposed. The BSF consists of a pair of frequency-tunable shunt resonant circuits in a balanced configuration, which enables the low-reflection characteristics and a great deal of degree of freedom in its design, such as the separate stop-bands. An X- to Ku-band tunable BSF has been fabricated with a ceramic substrate and commercially-available varactor diodes, and its measured characteristics are presented in this paper.

Internally matched GaN FET at C-band with 220W output power and 56% power added efficiency

In this paper, a high power and high efficiency fully internally-matched GaN FET operating at C-band is presented. In this work, a C-band GaN amplifier is designed so that 2nd harmonic impedance is tuned to high efficiency and combining loss is maintained minimum. As a result, 224W output power and 56% power added efficiency was successfully obtained, which is the highest efficiency as for over 200W GaN amplifier operating in C-band.

A resistor-loaded microstrip line resonator with a punched hole structure for ultra-wide-stopband bandpass filters

A novel microstrip line resonator is proposed for ultra-wide-stopband microwave bandpass filters. It consists of a stepped-impedance resonator (SIR) with a high-impedance transmission line on punched hole structure (PHS), and thin-film resistors implemented in the SIR for absorbing higher-order resonance power. A fabricated 2-stage microstrip bandpass filter at ƒ0 = 2.0 GHz has realized a spurious response level < −29 dB up to 25 ƒ0, which seems to be the superior wide-stopband performance among ever-reported ones in the category of microwave microstrip line filters.

A Q-band low-profile waveguide BRF with built-in open-ended λ/2 microstrip resonators

A new and low profile waveguide band-rejection filter (BRF) is proposed. In the waveguide BRF, two dielectric substrates with open-ended λ/2 mictostrip resonators are employed without via holes, and they are inserted in a hollow waveguide. For this simple configuration, this waveguide BRF is low-profile and easy to be fabricated compared with a conventional waveguide BRF, which employs resonant waveguide cavities outside the waveguide and needs costly machining processes. Q-band prototype waveguide BRFs were fabricated using alumina substrates, and the measured results showed high attenuation more than 50 dB at 47 GHz in 2 % fractional bandwidth with less variability.