金属ロッド共振器を用いた60GHz帯自己注入同期NRDガイドガン発振器

摘要

To stabilize oscillation frequencies, a ceramic resonator with an unloaded Q factor of about 4000 was usually used in the self-injection locked NRD guide Gunn oscillator. Recently, it has been found out that a new type of resonator, which consists of a circular metal rod inserted in the horizontal mid-plane of the parallel metal plate housing, has the unloaded Q factor of about 1500. With this fact in mind, we investigated the self-injection locked NRD guide Gunn oscillator using the circular metal rod resonator in the viewpoint of easy-fabrication and cost-effectiveness in this paper. At first, the cutoff frequency of the first higher order mode in the tri-plate type of guiding structure having the circular metal rod as the center conductor was calculated because the dominant mode was the TEM wave, and the setting range of the diameter of the circular metal rod to suppress the higher order modes was cleared up. Next, the transmission loss was calculated as a function of the diameter, and it was obvious that the small transmission loss calculated to be around 3 dB/m could be obtained at 60 GHz. Finally, the oscillation characteristics of the band-stop type of self-injection locked NRD guide Gunn oscillator were calculated constructing the circular metal rod resonator and it was found out that the oscillation performance was the same as that of the self-injection locked NRD guide Gunn oscillator using the ceramic resonator at 60 GHz..%従来の自己注入同期NRDガイドガン発振器では、周波数安定化のために無負荷Qが4000程度のセラミック共振器を用いていたが、平行平板ハウジングの水平対称面に金属ロッドを配置した構造の共振器では、1500程度の無負荷Qが得られることが明らかになつてきた。そこで共振器の加工精度や低廉性の点から、本論文では金属ロッド共振器を用いた自己注入同期NRDガイドガン発振器を検討した。まずこの共振器では共振モードとしてTEM波を利用することから、金属ロッドを中心導体としたトリプレート導波路において、金属ロッドの直径に対する第1高次モードの遮断周波数を計算し、高次モードが抑制される中心導体直径の設定範囲を明らかにした。次に金属ロッドの直径をパラメータとして導波路の伝送損失を計算し、60GHz帯において3dB/mと低損失な特性が得られることを示した。これらの結果を踏まえ、金属ロッド共振器を用いて帯域阻止型の自己注入同期NRDガン発振器の発振特性を計算し、数値的検討ではあるが、60GHz帯においてセラミック共振器を用いた場合と同程度の安定な発振器実現の可能性を明らかにした。