Akihiko Akasegawa

C-band 340-W and X-band 100-W GaN power amplifiers with over 50-% PAE

In this paper, we report a C-band power amplifier with over 340-W output power using 0.8-µm GaN-HEMTs and an X-band power amplifier with over 100-W output power using 0.25-µm GaN-HEMTs. We used two-chip configurations and the three-stage impedance transformers to extend the bandwidth for both circuits. The input and output lines adjacent to each chip are divided by four to suppress the non-uniform heat distribution in a chip at high frequencies. As a result, we obtained 343-W output power and 53-% power added efficiency (PAE) at 4.8 GHz. This is the highest output power ever reported C-band power amplifiers. We also obtained 101-W output power and 53-% PAE at 9.8 GHz. This is also the highest PAE ever reported X-band power amplifiers with over 50-W output power.

Over 10W C-Ku band GaN MMIC non-uniform distributed power amplifier with broadband couplers

A 6–18 GHz monolithic microwave integrated circuit (MMIC) power amplifier (PA) was successfully developed using a quarter wavelength short stub and a monolithic broadband coupler for a non-uniform distributed power amplifier (NDPA) topology. This topology improved the output power at 18 GHz and attained a flat output power profile over 6–18 GHz. It also achieved filtering characteristics for both lower and higher cut-off frequencies. A fabricated MMIC PA with 0.25µm GaN HEMTs delivered an output power of more than 10 W with average power added efficiency (PAE) of 18% over 6 to 18 GHz. To the best of our knowledge, this is the best combination of output power and bandwidth for any solid-state MMIC amplifier operating up to the full Ku-band.

RF power dependence of microstrip disk resonators with YBCO films for 4 GHz band

High-Tc superconducting (HTS) power filters have an attractive possibility of being applied to the base stations of the- future mobile-communication systems. In the microstrip structure, disk-shape-patterned HTS resonators are considered potential candidates for the HTS power filters. In order to research the application feasibility of disk resonators, the resonator samples were fabricated with different quality YBCO thin-films, and the power handling and third intermodulation-distortion (IMD3) of the samples were then examined for the incident continuous wave power of up to about 10 W around 4 GHz at cryogenic temperatures. We discuss the results on the relationship between the RF power dependence and the YBCO film qualities.

RF Power Properties of YBCO-Film/LAO Microstrip Disk Resonators for 4 GHz Band

This paper presents RF power properties of YBCO films on LaAlO 3 substrate examined using microstrip disk shape-patterned resonators for around 4 GHz. Characterization of the YBCO films for the resonators was carried out. For input-output power measurement, the resonators with the condition of strong I/O couplings were designed and fabricated. The RF power properties of the resonators at cryogenic temperatures were measured. The resonator condition to obtain the handling power over 10 W at 30 and 70 K was confirmed. The temperature dependence of the break-down powers at 4GHz for the resonators showed two broad peaks. We discuss the unique phenomenon with magnetic flux model, as referred to the YBCO films characteristics results.

Precise Measurement of IMD Behavior in 5-GHz HTS Resonators and Evaluation of Nonlinear Microwave Characteristics

The intermodulation distortion (IMD) of a 5-GHz HTS resonator is precisely measured and a nonlinear analysis is conducted. When designing a radio communication system that uses an HTS microwave device, the devices IMD characteristic is one of the most important problems that must be quantitatively evaluated. The amplitudes of third-order IMD (IMD3) and higher-order IMD, which are generated in an HTS resonator given a two-tone fundamental signal, are measured in detail using a fundamental signal cancellation circuit. Moreover, the relative phase of IMD3 is obtained by using a novel measurement system constructed around a reference IMD3 generator. The measured IMD3 phase shows a drastic change in a relatively low IMD3 amplitude region. In addition, the measured resonator exhibits strong higher-order IMD. A nonlinear evaluation using complex power series representation confirms that the drastic phase change may be due to the higher-order distortions present in IMD3.

HTS microstrip disk resonator with an upper dielectric layer for 4GHz

We propose HTS microstrip disk resonator with an upper dielectric layer as a candidate resonator structure of HTS compact power filter for 4GHz band. The electromagnetic simulations on the upper dielectric layer examined the current distributions of the HTS resonators that had TM11 mode resonance of about 4 GHz. By the simulations, it is evaluated that of the maximum current density near the end portion of the disk-shape pattern of the resonator with the thick upper-layered structure decreases by roughly 30-50 percent, as compared with that of the resonator without it. Then, we designed and fabricated the resonator samples with and without the upper dielectrics. The RF power measurement results indicated that the upper dielectric layer leads to an increase in handling power.

Novel dual mode disk-shaped resonator filter with HTS thin film

We propose a novel dual mode disk-shaped resonator filter with high temperature superconductor (HTS) thin films. The 5 GHz-band YBa2Cu3O7-x (YBCO) microstrip dual mode disk resonator filter on an MgO (100) substrate keeps a perfect circle shape and a waveguide line of about a half-wavelength that is capacitively-coupled with the disk resonator to generate a dual mode. The fabricated filter had an equivalent frequency response of a two-pole filter with two attenuation poles. The coupled coefficient of two orthogonal modes can be controlled by the length of coupled waveguide line and the gap space between feeder and disk resonator. The fabricated filter showed very low third-order intermodulation distortion (IMD3) of -73 dBc with an output power of 10 W at a temperature of 65 K. In addition, the proposed structure can be fabricated using a side lithography and etching processes. This is an advantage for multi-stage filter applications. We believe this filter is a promising candidate structure for RF transmit system applications.

High-Tc Superconducting Dual-mode Disk Resonators with Attenuation Poles using Ground-slot

In order to meet stringent requirements on transmit filters, high-Tc superconducting dual-mode disk resonators with attenuation poles have been designed, fabricated, and measured. Using a ground-slot perturbation along the asymmetric plane from the feeder lines, the resonator fabricated with YBCO superconducting double-sided films showed high performance with attenuation poles at the both sides of the passband resulting in higher selectivity. From the experimental results, a design concept focusing on phase responses was found to be applicable to the appearance method of the attenuation poles.

Film-thickness dependence of the microwave properties of YBCO films

Abstract We examined the film-thickness dependence on the microwave properties and microstructure of c-axis oriented YBCO films with thickness up to approaximately 1 μm on MgO(100) substrates by pulsed laser deposition, using different growth conditions. The surface roughness that was caused by Cu compound outgrowths allowed misoriented grains to form in the thicker films resulting in higher resistance Rs. By lowering growth rate, the thick films with higher orientation were obtained, and exhibited lower Rs and unloaded Q of 8E+4 at 70 K in a 2 GHz microstrip line resonator.

AFI Suppressing Effect of an HTS RF Receive Filter with High Selectivity for Base Stations of Digital Wireless Communications

We report on suppressing adjacent-frequency interference (AFI) by using a RF receive bandpass-filter (BPF) with high-selectivity. By considering a high temperature superconducting (HTS) multi-pole BPF as a high selective BPF, the effect was estimated by numerical simulations. The simulations of the RF signals with an OFDM modulation transmitted to the demodulator via the BPF were carried out using the HTS BPF for 5GHz band. The results confirmed the improvement of the bit error rate (BER) characteristic with the assumed HTS BPF with the high multi-poles under a strong AFI.