This paper puts forward a novel dual-beam overmoded folded waveguide (FW) slow-wave structure (SWS), which is loaded with photonic crystals. In this novel structure, the two electron beams pass through the small gaps between the photonic crystal structures and the FW; the dimension of the FW is twice larger than that of the fundamental mode structure. The novel dual-beam photonic crystal overmoded FW traveling-wave tube (TWT) is proposed on the basis of the SWS. And, a mode converter is introduced to achieve the connection between the SWS and the input/output structure, and the mode transformation. At the operating voltage of 21.2 kV and the operating current of 320 mA, the proposed TWT can generate 128 W of output power at 220 GHz, and its 3-dB bandwidth is 7 GHz, ranging from 216 to 223 GHz.

A dual-beam planar dielectric-rod-support uniform metallic meander line slow-wave structure (SWS) for high-efficiency Ka-band traveling wave tube (TWT) is proposed in this paper. Two dielectric rods are placed on both sides of metallic meander line to support it, instead of the dielectric substrate in the conventional microstrip meander line. Furthermore, it can not only solve the problem of the electron charge accumulation on microstrip but also leads to a bigger interaction impedance. According to particle-in-cell simulation results, a dual-sheet-beam planar dielectric-rod-support uniform metallic meander line TWT can get an output power of 330.2 W at 38 GHz under the case of 10.6 kV beam voltage and 0.2 A beam current. The corresponding maximum gain and electron efficiency are 23.4 dB and 15.5%, respectively, where the length of whole SWS is only 20 mm.

A novel modified angular log-periodic folded waveguide slow wave structure (MALPFW-SWS) is proposed for high-gain traveling wave tubes (TWTs). Each unit of the MALPFW-SWS has different dispersion characteristics and thus it has the ability to suppress oscillations in TWTs. The dispersion equation of the MALPFW-SWS is derived and a Ka-band MALPFW-SWS is designed according to the dispersion equation for verification. The particle-in-cell (PIC) simulation indicated that the output signal is steady even the gain of the designed MALPFW-TWT reaches 40 dB. The frequency spectrum of the output signal also proved that the MALPFW-SWS can suppress oscillations. The cold test experiment results show that the transmission characteristics of the fabricated MALPFW-SWS are good and are in good agreement with the simulation results.

In this article, a novel dielectric-supported staggered dual-meander-line (DS-SDML) planar slow-wave structure (SWS) is proposed for a traveling wave tube (TWT) working at E-band. The proposed staggered arrangement of meander-lines (MLs) leads to a stronger beam-wave interaction and achieves higher output power as compared to the symmetric arrangement. The input-output couplers have been designed by using staggered stepped double ridge waveguide, to connect the standard E-band rectangular waveguide and the DS-SDML SWS. An attenuator and pitch tapering have been applied to the proposed SWS to suppress the unwanted frequencies and to improve the output power. Particle-in-cell (PIC) simulation results show that for an 11.8-kV, 200-mA sheet-beam, the output power can reach 283 W at 75 GHz, with a maximum gain and electronic efficiency of 34.5 dB and 11.9%, respectively.

An attenuator supporting meander-line (ASML) slow wave structure (SWS) is proposed for a Ka-band traveling wave tube (TWT) and studied by simulations and experiments. The ASML SWS simplifies the fabrication and assembly process of traditional planar metal meander-lines (MLs) structures, by employing an attenuator to support the ML on the bottom of the enclosure rather than welding them together on the sides. To reduce the surface roughness of the molybdenum ML caused by laser cutting, the ML is coated by a thin copper film by magnetron sputtering. The measured S₁₁ of the ML is below −20 dB and S₂₁ varies around −8 dB to −12 dB without the attenuator, while below −40 dB with the attenuator. Particle-in-cell (PIC) simulation results show that with a 4.4-kV, 200-mA sheet electron beam, a maximum output power of 126 W is obtained at 38 GHz, corresponding to a gain of 24.1 dB and an electronic efficiency of 14.3%, respectively.

In this paper, a novel angular log-periodic folded groove waveguide (ALFGW) slow-wave structure (SWS) has been investigated theoretically and experimentally for application in Ka-band traveling-wave tubes (TWTs). The dispersion relation for the ALFGW is derived analytically, and the dispersion characteristics are calculated for a Ka-band design. The designed SWS is fabricated using oxygen-free-copper that is silver electroplated. The measured cold-test parameters show good agreement with the simulation results, with S₂₁ varying from −2.7 dB to −4.8 dB and S₁₁ better than −13.6 dB over the frequency range of 30–38 GHz. Simulations of beam–wave interactions using a 4850 V and 0.4 A sheet beam with a high aspect ratio of 28:1 indicate an output power of 128 W, corresponding to a maximum gain and electronic efficiency of 18.1 dB and 6.6%, respectively. Due to the log-periodic form, a higher output power, higher efficiency, wider bandwidth, and lower operating voltage are achieved as compared to a TWT based on the conventional folded groove waveguide (FGW) SWS. These results show that the proposed ALFGW SWS has good potential for application in relatively high-power wideband TWTs.