A W-band extended interaction oscillator (EIO) driven by a pseudospark-sourced sheet electron beam (PS-SEB) is demonstrated in this letter. The idea of combining the advantages of a pseudospark-sourced electron beam (high beam current density), a sheet electron beam geometry (large beam cross-sectional area) and a ladder-like slow wave structure (high gain per unit length) to generate powerful millimeter-wave radiation was experimentally verified. The PS-SEB based EIO produced ~1.2 kW peak output power, an increase of six times in the measured power from an EIO based on a pseudospark-sourced pencil electron beam. Such a methodology offers a promising solution for portable, low-cost and powerful millimeter-wave and terahertz-wave radiation sources.

To meet the need to transmit increasingly massive volumes of data, a more than 3 kW continuous wave (CW) Ka-band sheet beam traveling-wave tube (SB-TWT) is reported for the first time. Working under unsaturated drive, the maximum gain obtained is 29 dB with a sheet beam of 30.9 kV, 0.82 A, and the efficiency exceeds 24% with a single-stage collector depressed to −15 kV. The 1-dB bandwidth reaches 6 GHz from 26 GHz to 32 GHz and the bandwidth with output power greater than 2 kW can even reach 7GHz from 26 GHz to 33 GHz. The realization of 99.8% static transmission as well as over 97% actual CW transmission of sheet beam is verified successfully, which benefits from adopting periodic cusp magnet (PCM) focusing, and thereby total weight is less than 15 kg. The relevant experimental details are introduced in this letter.

Recent hot test details and inspiring results of the W-band lossy-dielectric-loaded gyrotron traveling-wave tube (gyro-TWT) developed at the University Electronic Science and Technology of China (UESTC) are reported in this letter. Measurement of the gyro-TWT had achieved a pulse output power over 100 kW with a broad bandwidth of 8.5 GHz (92.0~100.5 GHz). For the first time as we know, the W-band gyro-TWT can stably operate with a 10% duty cycle and the average output power is over 10.3 kW in the frequency range. Excellent stability, pure spectrum and mode patterns are all verified in the hot test experiment.

A novel method to generate a TE $_{0n}^{{{(\mathrm {C})}}}$ ( $n = 1$ , 2, 3) ( $C$ is circular for short) or TE $_{1n'}^{{{(\mathrm {C})}}}$ ( $n' = 2$ , 3, 4) mode via a TE $_{m0}^{{{(\mathrm {R})}}}$ ( $m = 2n$ or $m = 2n' - 1$ ) ( $R$ is rectangular for short) mode generator is proposed in this paper. Two main components, including a TE $_{10}^{{{(\mathrm {R})}}}$ –TE $_{m0}^{{{(\mathrm {R})}}}$ mode converter with multiple coupling apertures and matching steps and a TE $_{m0}^{{{(\mathrm {R})}}}$ –TE $_{0n}^{{{(\mathrm {C})}}}$ or TE $_{1n'}^{{{(\mathrm {C})}}}$ mode converter, were, respectively, demonstrated. Two novel compact mode converters, respectively, exciting the TE $_{01}^{{{(\mathrm {C})}}}$ and TE $_{13}^{{{(\mathrm {C})}}}$ modes at $Q$ - and $W$ -band based on the aforementioned methodology were designed and analyzed. In the TE $_{01}^{{{(\mathrm {C})}}}$ mode converter design, symmetric cylindrical ridges were introduced to improve the mode purity and suppress the unwanted TE $_{21}^{{{(\mathrm {C})}}}$ mode by cutting off its surface current on the metal wall. Such a mode converter operating at $Q$ -band was manufactured and vector network analyzer measurements showed excellent S-parameter performance (port reflection <−12 dB) and mode purity (>90%), which agreed very well with our simulation. Besides, as an expansion of the TE $_{01}^{{{(\mathrm {C})}}}$ mode converter, the designed results of a high-order TE $_{13}^{{{(\mathrm {C})}}}$ mode converter excited by a similar methodology were also presented.