Publisher：Energies  

This study proposes a patch antenna with an H-shaped slot with direct matching and harmonic tuning (rejection) functions for microwave power transfer. This antenna enables an integrated active antenna in which the power amplifier and antenna are directly connected without using a matching circuit for the fundamental frequency and harmonic rejection filter to improve the efficiency of the amplifier. The integrated design also reduces the total size of the amplifier and antenna, allowing for a higher-density array antenna. Characteristic mode analysis was performed to explain the working principle of the harmonic rejection function. The designed antenna at 5.8 GHz was fabricated to study its harmonic tuning function. The magnitude of the reflection coefficient of the proposed antenna was at a fundamental frequency of −40.4 dB for an amplification device with an optimum load impedance of 100 Ohm. At the second harmonic frequency, the magnitude and phase of the reflection coefficient at the second harmonic frequency were −0.79 dB and −177.6°, respectively; at the third harmonic frequency, they were −0.92 dB and −179.5°, respectively. Finally, the designed antenna was integrated into an amplifier circuit to verify that it achieved similar drain efficiency as when using the impedance tuner. It was confirmed that the harmonic rejection function of the proposed antenna increases the drain efficiency of the integrated power amplifier by 5.5%. The measurements revealed that this antenna is suitable for use in microwave power transfer because of its fundamental matching and harmonic-processing capabilities.

DOI： 10.3390/en16052128

Web of Science

Scopus

Publisher：Asia-Pacific Microwave Conference Proceedings, APMC  

This study demonstrates an single stage amplifier with a gain between 37 GHz and 44 GHz, 6.9 dB at 40.1 GHz, using a GaN HEMT, which has an fmax of only 41 GHz. A transistor amplifier is usually designed at a frequency reasonably less the fmax because it is the frequency limit where unilateral gain becomes unity; theoretically, no amplification can be realized over this frequency. To overcome this theoretical limit, the novel method was developed to control the standing wave distribution in the gate finger. Through this method, the potential gain of the transistor increased around fmax, and moreover, the fmax value itself increased significantly. The GaN HEMT in this study is demonstrated to increase the fmax from 41 GHz to 70 GHz. Furthermore, by using this method, an amplifier which has gain over the fmax frequency is realized.

DOI： 10.1109/APMC57107.2023.10439935

Web of Science

Scopus

Publisher：Asia-Pacific Microwave Conference Proceedings, APMC  

A microwave-discharge ion thruster utilizing water-vapor for satellites is being developed due to the advantages in safety, cost-effectiveness, and size improvements compared to other thrusters. The thruster system consists of an oscillator-stage, driver-amplifier-stage, final-amplifier-stage, and a microwave-discharge ion thruster. To realize the advantages of a water-vapor based system, we developed a dielectric resonator oscillator (DRO) with a 10-W-class GaN power transistor. The oscillator has to induce 1 W output as the driver-amplifier-stage requires 1 W (30 dBm) input to operate at the most optimal power efficiency. In this report, we explain the development of the DRO which is a 32.6 dBm output at 4.2501 GHz, and detail the environmental evaluations complied with space standard from the SMC-S-016.

DOI： 10.1109/APMC57107.2023.10439705

Web of Science

Scopus

Publisher：Asia-Pacific Microwave Conference Proceedings, APMC  

Microwave-discharge ion thrusters utilizing water vapor offer several advantages, including safety, low cost, and miniaturization, making them suitable for satellite applications. The thruster system comprises an oscillator stage, driver-amplifier (DA) stage, final-amplifier stage, and a microwave-discharged ion thruster. For the driver-amplifier stage, a DA with an output power of 10 W and a drain efficiency of 60% was developed. The amplifier is a class-F power amplifier using a 10-W-class GaN power transistor. In this report, we explain the development of the DA and detail the environmental evaluations conducted in accordance with the space standards outlined in the SMC-S-016.

DOI： 10.1109/APMC57107.2023.10439805

Web of Science

Scopus

Language：Japanese   Publisher：IEICE Electronics Express  

In this paper, we compare the distortion and power characteristics between AlGaN/GaN high-electron-mobility transistors (HEMTs) with different epi-structures. Third-order intermodulation distortion (IM3) measurement evaluates distortion characteristics, and on-wafer load and source-pull measurements evaluate the power performance. The results show that the AlGaN/GaN HEMTs directly fabricated on GaN substrates without nucleation layer perform better than those fabricated on SiC substrates. Furthermore, the distortion performance is compared with and without field plate.

DOI： 10.1587/ELEX.18.20210486

Scopus

Language：Japanese   Publisher：2020 4th Australian Microwave Symposium, AMS 2020  

Efficiency is critical element for microwave power amplifier, especially for energy applications. In this paper, the new design approach to enhance the efficiency which eliminates the output matching circuit is proposed. A 2.4GHz GaN power amplifier is demonstrated using the proposed design method. By eliminating the matching circuit and applying inverse class-F operation, the drain efficiency of 82.3% and power added efficiency of 78.8% are obtained for 30W power amplifier.

DOI： 10.1109/AMS48904.2020.9059420

Scopus

Language：Japanese   Publisher：Asia-Pacific Microwave Conference Proceedings, APMC  

Thermal S-parameters and its calculation method are proposed to design power amplifiers considering dynamic thermal response, and the method is applied to. 11ac WiFi PA design. The proposed method is much faster than commercially available method and useful for the practical power amplifier design.

DOI： 10.1109/APMC46564.2019.9038799

Scopus

Event date： 2022.3

Event date： 2020.11

Language：Japanese   Presentation type：Symposium, workshop panel (nominated)  

Venue：オンライン   Country：Japan  

Event date： 2020.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：WEB  

Event date： 2020.9

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：WEB  

Event date： 2018.7

Language：English   Presentation type：Oral presentation (invited, special)  

Venue：Kitakyushu   Country：Japan  

Language：Japanese  

Venue：名古屋   Country：Japan  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：WEB  

Language：Japanese   Presentation type：Oral presentation (general)  

Venue：WEB  

Presentation type：Oral presentation (general)  

Venue：広島   Country：Japan