This article designed a Ka -band traveling wave tube (TWT) with the single wall carbon nanotubes (SWCNTs) field emission cathode electron gun. The designed cold-cathode TWT was miniaturized and could instantly startup at room temperature because of the field emission cathode. First, SWCNT cathode was made by imprinting. The field emission measurement results showed that its turn-on field was as low as 0.57 MV/m, and the maximum emission current was about 10 mA. Then, a grid-controlled electron gun with planar field emission cathode was simulated based on the experiment results, which had low operation voltage of the electron gun and would prevent their grid mesh from burning. The optimized electron beam waist radius of the electron gun was 0.15 mm with the structure of the focusing magnetic field. According to experiment and simulation results, we preliminarily designed a Ka -band helix TWT with an average output power of 8.6 W and a gain of 24.6 dB at 28 GHz. The designed miniaturized TWT with a low-operation-voltage field emission cathode electron gun is expected to be used in low-power applications including 5G communication.

This paper presents a novel compact balanced-to-balanced (BTB) power divider featuring an exceptional reflectionless bandpass filtering response. A pair of three-line coupled structures (TLCSs) are utilized to provide wideband filtering response and equal power division. To enhance the frequency selectivity, an open-circuited stepped impedance stub is added to TLCSs, generating a pair of transmission zeros (TZs) on both sides of the passband. Additionally, simple absorption-isolation networks (AINs) consisting of two resistors and a half-wavelength transmission line (TL) are embedded to provide a full-band non-reflective response at the input port and achieve excellent isolation. The traditional half-wavelength TL between balanced ports is replaced by a stepped-impedance TL, improving in-band matching performance. Furthermore, a detailed theoretical analysis of the proposed design is derived, and parametric studies are presented. To verify the proposed concept, the new multifunctional BTB reflectionless filtering power divider (RFPD) operating at 1.9 GHz is fabricated and measured. The compact fabricated prototype exhibits a 10.8-dB input absorption, 21-dB common-mode (CM) suppression, and 22-dB isolation, all exceeding the bandwidth level of 263.2%. The results show good agreement between simulations and measurements.

A miniaturized radio frequency (RF) excited grid-free field emission cathode made by single-wall carbon nanotubes (SWCNTs) is suggested and studied. The λ/4 coaxial resonant cavity is used as field-emitted electron source with length of 26.5 mm and diameter of 12.8 mm. Electrons can be pulled out by a small electrostatic field and an RF electric field without interception. The RF electric field of inner conductor surface at the open end, which pasted SWCNTs, can reach 3 MV/m when the input power is 30 W, and the field is larger than the turn-on field of SWCNTs. The results of simulation and experiment both show that the maximum emission current under input RF power of 30 W is 30 times larger than without RF excitation, which can reach 24 mA at the anode voltage of 950 V. This miniaturized RF excited grid-free field emission cathode electron source can be used as electron source, in a high repetition frequency vacuum electronic devices, e.g., terahertz (THz) devices, and X-ray tubes.

A wideband dual-beam dielectric resonator antenna (DRA) with substrate integration capability was proposed for millimeter-wave (mm-wave) applications. The four rows of air vias along the x-direction and two extended rectangular patches could shift the undesirable radiation mode upward and move the conical-beam radiation mode downward, respectively. Thus, the TE₂₁₁ mode and the TE₄₁₁ mode of the patch-loaded perforated rectangular substrate integrated dielectric resonator (SIDR) supporting the dual-beam radiation can be retained in the operating band, and their radiation can be improved by the air vias along the y-direction. The T-shaped line coupled dual-slot structure could excite the above two modes, and a dual-slot mode supporting dual-beam radiation could also work. Then, a wideband DRA with a stable dual-beam radiation angle can be achieved, and its impedance matching can be improved by two air slots on two sides. Compared with the state-of-the-art dual-beam antennas, the proposed antenna shows a wider bandwidth, a higher radiation efficiency, and the substrate integration capability of DRA, making it more suitable for mm-wave applications. For demonstration, a 1 × 4 array was designed with the 10 dB impedance matching bandwidth of 41.2% and the directions of the dual beams between ±30° and ±35°.

A dual-beam end-fire dielectric resonator antenna (EFDRA) with wideband performance for millimeter-wave application is proposed. An equivalent electrical wall composed of three metal strips and a row of metal vias is introduced to the middle position of the dielectric resonator (DR) and connected with the T-shaped feeding structure to achieve wideband dual beam by generating the modified TE12δ mode and the anti-phase TE13δ mode. The two modes can be equivalent to two and four anti-phase magnetic currents respectively, which can both support dual-beam end-fire radiation and form wideband design. Meanwhile, the vertical E-field components contributing to unwanted broadside radiation in the two modes will cancel each other out because they are distributed symmetrically in even numbers with similar amplitude and anti-phase, thus can restrain broadside radiation. The T-shaped feeding structure is used to generate anti-phase currents, which can simultaneously excite the two modes. Compared with the state-of-the-art dual-beam end-fire antennas, the proposed antenna shows a wider bandwidth and higher radiation efficiency. For demonstration, a wideband dual-beam EFDRA prototype is designed and measured. The proposed antenna achieves a 10-dB impedance matching bandwidth of 27.6% (21.2-28 GHz) with a stable direction of the dual beams.

In this study, a functional segmentation method for the design of adiabatic devices is presented. This method can be applied to calculate the compact adiabatic waveguide shapes for adiabatic taper waveguides and adiabatic mode converters. We introduce two algorithms, namely the quadratic function segmentation design for the adiabatic taper waveguide and the cubic function segmentation design for the adiabatic mode coupler. The design shows that for each segment, there is no need for separate simulations to obtain the length of each segment, and only the length of each segment can be determined by equations. This approach is much less cumbersome than other numerical design methods for adiabatic devices. The proposed functional segmentation design requires only a device length of 36 μm to achieve 95% power transfer efficiency, while a traditional linear-shape connection requires a device length of 54 μm to achieve the same power transfer efficiency. Therefore, the device designed by the function segmentation method has better compactness compared to the conventional linear-shape connection design of adiabatic devices.