Broadband Continuous Frequency Tuning in a Terahertz Gyrotron With Tapered Cavity

• Published in: IEEE transactions on electron devices Vol. 62; no. 12; pp. 4278 - 4284
• Main Authors: Qi, Xiang-Bo, Du, Chao-Hai, Liu, Pu-Kun
• Format: Journal Article
• Language: English
• Published: New York IEEE 01.12.2015; The Institute of Electrical and Electronics Engineers, Inc. (IEEE)
• Subjects: Axial modes; Bandwidth; Bandwidths; Broadband; Broadband communication; Competition; continuous frequency tuning (CFT); Frequency-domain analysis; gyrotron; Gyrotrons; Holes; Oscillators; Q-factor; tapered cavity; terahertz; Tuning; tapered cavity; gyrotron; Broadband; terahertz; continuous frequency tuning (CFT)
• ISSN: 0018-9383; 1557-9646
• DOI: 10.1109/TED.2015.2493563

Broadband continuous frequency tuning (CFT) in a terahertz gyrotron is promising for advanced terahertz applications. However, it is challenging to realize broadband CFT in a conventional open cavity, because a long cavity is helpful to expand the bandwidth but is generally difficult to suppress the high Q -factor gyromonotron competition. In this paper, a tapered cavity with a long effective interaction length is proposed to expand the CFT bandwidth. The tapered circuit can reduce the Q-factor of the first-order axial mode and accordingly suppress the gyromonotron competition. By selecting a reasonable Q-factor cavity, a gyrotron could generate effective radiation sequentially under gyromonotron and gyrobackward-wave oscillator (BWO) states during the magnetic field tuning. In gyromonotron range, the bandwidth is expanded because of the cutoff frequency shifting. On the other hand, in gyro-BWO range, the bandwidth is expanded because of the axial mode transition. The CFT bandwidth of 4 GHz is realized in a tapered 330-GHz TE12,4 mode low-voltage gyrotron. The principle is important for developing broadband CFT terahertz gyrotrons.