Broadband Helix Traveling-wave Tubes Research Articles

Theory and Hot Test of High-Power Broadband Helix Traveling-Wave Tube Based on a Double-Graded Radius and Pitch Circuit

The classical Pierce’s 1-D small-signal theory of backward-wave gain, generalized to allow axially varying the double-graded radius and pitch circuit characteristics, is applied. Numerical calculations demonstrate that the double gradient circuit can effectively suppress the backward-wave oscillation (BWO). Furthermore, the hot test experiment is carried out to predict the performance of the tube. The hot test results show that this helix traveling-wave tube (TWT) based on the double-graded pitch and radius circuit has achieved over 5.06 kW of output power, and the corresponding device gain achieves more than 34.1 dB in the frequency range of 8–18 GHz.

Thermal Analysis of High-Average Power Helix Traveling-Wave Tube

The thermal simulation using ANSYS was carried out for estimating the maximum temperature and the temperature distribution in a high-average power broadband helix traveling-wave tube (TWT). The simulation was first carried out independently for the subassemblies such as the slow-wave structure, the output coupler, and the depressed collector; and the combined effect on the overall temperature inside the TWT was estimated subsequently. The simulation was carried out using several options of thermal interface resistances such as 100% contact and 50% contact, apart from considering various structural configurations, and an optimal thermal management solution was evolved for the device under consideration.

Second Harmonic Suppression for Broadband Helix Traveling‐Wave Tubes Using the Phase Velocity Variation of Output Circuit

Based on the principle of phase velocity ta- pering or stepping output circuit, using the phase velocity variation of the output circuit, four kinds of nonuniform output circuit models have been presented in broadband helix Traveling-wave tubes (TWTs). Taking an example of 6-18GHz, 100W broadband helix TWT and using the im- proved one-dimensional large signal program, second har- monic suppression performances have been studied by cal- culating the quantitative relationship between fundamental efficiency, second harmonic output power, and the stepping (tapering) position and strength of phase velocity variation for the four kinds of nonuniform output circuits. From the research results of backward wave and second harmonic suppression feature in two kinds of nonuniform output cir- cuits, we obtained the design principle of phase velocity stepping or tapering, which could suppress the Backward wave oscillation (BWO) and reduce the output power of second harmonic for broadband high-power helix TWTs.

Backward-Wave Suppression for Broadband Helix Traveling-Wave Tubes Using the Phase Velocity Variation of Output Circuit

Based upon the principle of suppression of backward-wave oscillation (BWO) using the phase velocity variation of output circuit in broadband helix traveling-wave tubes (TWTs), four kinds of nonuniform output circuit models have been presented. Two-wave theory has been used to calculate the backward-wave gain of two-section and three-section output circuits. This method breaks through the limits of equal-length section and weak tapering change in the two-wave theory. By calculating the backward-wave gain, the authors obtained the relationship between the oscillation-start current of backward wave and the tapering position and strength for these four kinds of output circuits, which develops the two-wave theory. These results provide the theoretical support for the suppression of BWO in broadband helix TWTs.

Backward-Wave Oscillation Suppression in High-Power Broadband Helix Traveling-Wave Tubes

The effects of the attenuator and the pitch step and taper on suppressing the backward-wave oscillation (BWO) in high-power broadband helix traveling-wave tubes (TWTs) are analyzed by a nonlinear 1-D beam-wave interaction theory in which the effects of the variation of the angular velocity of the macroparticles along the length of circuit are considered. It is found that the incorporation of an attenuator is an effective way to improve the stability of the TWT input section, while a pitch step or taper can be used to reduce the backward-wave gain in the TWT output section without compromising the inband saturated output power. An optimized design of a high-power broadband TWT with improved BWO suppression and forward-wave saturated output power is presented. The optimized design utilizes an optimally positioned attenuator, along with positive pitch tapers in the input and output TWT sections.

Improvements in Performance of Broadband Helix Traveling-Wave Tubes

The effectiveness of positive phase velocity tapering to improve the performance of a broadband helix traveling-wave tube (TWT) has been investigated. A large-signal model of an existing 4.5-18 GHz two-section mini-TWT with uniform pitch has been validated against the experimental results, and used as a starting point to design and develop a number of TWTs with different taper lengths. Comparisons between the experimental results of uniform pitch TWT and positively tapered TWTs show significant improvements in output power, electronic efficiency, and second harmonic content throughout the operating frequency band for the positively tapered TWTs. Increases in electronic efficiency and output power up to 5.2% points and 50 W (1.7 dB), respectively, have been achieved.

Positive phase-velocity tapering of broadband helix traveling-wave tubes for efficiency enhancement

A positive phase-velocity tapering of 1.5 octave broadband helix traveling-wave tubes for efficiency enhancement, where the phase velocity is linearly increased in the output section, was studied by using the one-dimensional nonlinear theory. At high frequencies, the electromagnetic wave in the positively tapered section traps the fastest electrons in the decelerating electric field, extracting more energy from the electron beam. At low frequencies, a decreased velocity difference between the electron beam and the electromagnetic wave destroys the phase condition for second-harmonic generation, retaining fundamental wave efficiency as well as reducing its second-harmonic power.

60-GHz space TWT to address future market

The market situation of space traveling wave tubes (TWTs) over the last four years is reviewed. It is exemplified that space TWTs are not only the key components for the traditional frequency ranges in C- and Ku-band, but also for new satellite communication systems as digital audio broadcasting in the lower L- and S-band frequency range and the planned, new global multimedia systems. There, Thomson Tubes Electroniques GmbH (TTEG) has developed the new family of Ka band TWTs, which provide the large bandwidth and power requirements for high data rate transmission. TTEG is also developing 60-GHz TWTs as RF intersatellite-links for global satellite systems. The promising results of the 560 g lightweight, 25 W, broadband helix TWT are mainly reported and the requirements compared with those for a parallel 60 W 60-GHz interdigital line TWT development.