Analysis of a broad band planar inter-digital slow-wave structures was carried out for millimeter-wave traveling-wave tubes. The analysis of the structure was carried out using CST-Microwave studio for the dispersion and interaction impedance characteristics. Further the analysis was extended for normalized gain parameter to study the effective bandwidth of the structure.

Design and analysis of ferrule-loaded folded waveguide slow wave structure is carried out for a high-power millimeter-wave traveling-wave tube (TWT). The design of the structure is carried out by numerical simulation. A typical structure has been designed and fabricated at the Ka-band, and cold test measurement is carried out for the cold circuit parameters and the results are compared against numerical analysis. To compare the efficacy of the ferrule-loaded folded waveguide structure, a conventional folded waveguide structure is also designed for the same operating bandwidth, and cold circuit parameters are compared. The comparison results shows that the interaction impedance of the ferrule-loaded folded waveguide structure is double compared with the conventional structure at the cost of reduction in cold bandwidth. Furthermore, particle-in-cell (PIC) simulation is also carried out to estimate the output power and gain for both the structures for the same operating band, and the results are compared. The comparison results show that the cross section is reduced by 22% and the overall interaction length is reduced by 50% for the ferrule-loaded FW-SWS compared with the conventional FW-SWS for the same output power of about 500 W.

An equivalent circuit approach for the analysis of cold circuit parameters such as dispersion and interaction impedance characteristics was used for the design of staggered double slot square-shaped coupled-cavity slow wave structure at millimeter waveband and the results were validated against numerical analysis at Ka-band and W-band. The derived lumped parameters of the square-shaped coupled-cavity slow wave structure (CC-SWS) is different from the reported cylindrical CC-SWS. A typical structure was fabricated at Ka-band and cold test measurement was carried and the results were compared against the proposed equivalent circuit approach. The comparison of results shows that the equivalent circuit is simple but accurate to predict within 3% and 10% accuracy against numerical simulation and cold test measurement for dispersion and interaction impedance characteristics, respectively.

Design, development and RF characterization of a staggered double slot coupled-cavity slow-wave structure at mm-wave band is presented in this paper. Design is carried out using commercially available microwave circuit simulation software CST-Microwave studio. A typical structure had fabricated at Ka-band and cold test measurement was carried out for the RF parameters such as dispersion and interaction impedance characteristics and the results were compared against numerical simulation which shows close agreement.

Studies on design and RF characterization were carried out for two different types of slow-wave structures (SWS) at W-band frequencies: 1) a meander-line SWS along with step impedance transformer, and 2) a folded-waveguide slow-wave structure along with tapered waveguide coupler. Quasi-TEM analysis was used for the design of these structures and the structures were fabricated using wire-cut and spark-erosion electric discharge machining. Dispersion characteristics and S-parameters of the structures were measured and compared against those obtained from analysis and 3-D electromagnetic simulation using CST-microwave studio.

Novel variants of meander-line slow-wave structures such as rectangular ring-bar configuration and ladder-configuration are proposed for broadband millimetre-wave travelling-wave tubes. The analysis of the structures are carried out for the dispersion and interaction impedance characteristics at W-band using CST-Microwave studio, and the results are compared against a conventional meander-line slow-wave structure for the same dimensions. It is observed that compared to a conventional meander-line structure, the novel variants rectangular ring-bar configuration and ladder-configuration show 40% and 70% increase in cold bandwidth, respectively.

Return-loss resonance method is used to estimate the loss per unit length of two different slow-wave structures namely a tapered ferruled coupled-cavity structure operating at centimeter-wave band and a ferrule-less folded-waveguide structure operating at millimeter-wave band. The loss estimated by this method was found to be within 2.5% and 5% compared against those obtained using conventional transmission loss method (S21 value) and numerical simulation carried out using CST-Studio. This approach was found to be very simple yet reasonable accurate to estimate the loss of the periodic structures operating in cm- and mm-wave bands.

A planar inter-digital type slow-wave structures is proposed for forward first-space-harmonic operation. The proposed structure supports hybrid (even and odd) modes. The analysis of the proposed structures is carried out using CST-Microwave studio for the mode analysis and slow-wave characteristics (dispersion and interaction impedance characteristics) at W-band. Fabrication and cold test measurement of the structure is in progress and the measured results will be presented at the time of conference.

The new concept of symmetric (double-folded) and asymmetric (single-folded) folded meander-line slow-wave structures is proposed for broader bandwidth and higher interaction impedance characteristics, respectively. The structures are analyzed using 3D numerical simulation in CST-Microwave Studio for the dispersion and interaction impedance characteristics at Ka-and W-bands. The results are compared against the conventional meander-line structure for the same dimensions. The proposed symmetric structure shows 35 % enhancement in cold bandwidth and the asymmetric structure shows more than 50 % enhancement in the interaction impedance.

Analysis of a W-band meander-line slow-wave structure has been carried out using quasi-TEM approach and validated against CST-Microwave studio for the dispersion and interaction impedance characteristics. A waveguide coupler is designed using HFSS and large signal analysis is carried out for output power and gain. A cold test model of the structure is fabricated at Ku-band frequency and cold test measurement is carried out for the dispersion characteristics and results are compared against analysis results.

An E-plane rectangular folded-waveguide slow-wave structure with metal grating on the broad wall of the waveguide along the direction of the electric field has been proposed and analyzed for the dispersion and interaction impedance characteristics through three dimensional electromagnetic modeling in CST Studio. The effects of the presence of grating on the bandwidth and interaction impedance are demonstrated.

A new geometry of a matched termination using lossy dielectric materials for an overmoded cylindrical waveguide is explored in this present work. The matched termination is designed based on attenuating the microwave using lossy dielectric materials or resistive materials by numerical simulation. The geometry is optimized such that it can be used for a cylindrical waveguide operating on fundamental and other higher order modes. The matched termination is fabricated and tested for its characteristics and the results are validated against simulated values.

A simple yet accurate equivalent circuit model was developed for the analysis of slow-wave properties (dispersion and interaction impedance characteristics) of a rectangular folded-waveguide slow-wave structure. Present formulation includes the effects of the presence of beam-hole in the circuit, which were ignored in existing approaches. The analysis was benchmarked against measurement as well as with 3D electromagnetic modeling using MAFIA for two typical slow-wave structures operating in Ka- and Q-bands, and close agreements were observed. The analysis was extended for demonstrating the effect of the variation of beam-hole radius on the RF interaction efficiency of the device.

A ridge-loaded E-plane rectangular folded-waveguide slow-wave structure has been proposed and analyzed using a simple quasi-TEM analysis for the dispersion and interaction impedance characteristics, including the effects of the beam-hole discontinuity. The analysis has been validated against the approximate parametric analysis and the 3D electromagnetic modeling using CST Microwave Studio. The analysis has been used for demonstrating the efficacy of the ridge-loading on broadbanding of the structure.

In a broadband coupled-cavity slow-wave structure, the problem of bandedge oscillation is overcome by resonant loss technique by introducing lossy dielectric resonators in the cavity. To reduce the dimensions of the dielectric resonators, high lossy and high dielectric constant, materials are used. In this paper, the effects of introducing 2, 4 and 8 lossy dielectric resonators (operating either on E010- or H111-mode), on the dispersion, interaction impedance and start oscillation current are studied.

An analysis of rectangular folded-waveguide slow-wave structure was developed using conformal mapping technique through Schwarz’s polygon transformation and closed form expressions for the lumped capacitance and inductance per period of the slow-wave structure were derived in terms of the physical dimensions of the structure, incorporating the effects of the beam hole in the lumped parameters. The lumped parameters were subsequently interpreted for obtaining the dispersion and interaction impedance characteristics of the structure. The analysis was benchmarked for two typical millimeter-wave structures, one operating in Ka-band and the other operating in Q-band, against measurement and 3D electromagnetic modeling using MAFIA.

An E-plane serpentine folded-waveguide slow-wave structure with ridge loading on one of its broad walls is proposed for broadband traveling-wave tubes (TWTs) and studied using a simple quasi-transverse-electromagnetic analysis for the dispersion and interaction impedance characteristics, including the effects of the beam-hole discontinuity. The results are validated against cold test measurements, an approximate transmission-line parametric analysis, an equivalent circuit analysis, and 3-D electromagnetic modeling using CST Microwave Studio. The effect of the structure parameters on widening the bandwidth of a TWT is also studied.