This paper presents the design and simulation of a compact axial and radial corrugated horn antenna for Ku-Band defense and aerospace applications. The antenna employs a combination of axial and radial corrugations to achieve efficient mode conversion into the hybrid HE11 mode, resulting in improved beam quality with low cross-polarization and reduced sidelobe levels. An axially corrugated profile shortens the horn length while maintaining high gain and radiation efficiency, making it suitable for defense and aerospace systems where size and performance are critical. The antenna was designed and analyzed using CST Microwave Studio. Simulation results show that the antenna achieves gain above 20 dBi with low sidelobe levels across the Ku-Band, demonstrating its potential for next-generation defense and aerospace platforms.

High-voltage insulation structures are critical in interfacing high-power radio frequency (RF) devices with pulsed power sources (PPSs). These structures are intended to carry hundreds of kilovolts and tens of kiloamperes of pulsed power. They commonly suffer from breakdown during the operations due to the high electric stress encountered. In this study, we present an electrostatic analysis of a high-voltage structure in three different dielectric regions—transformer oil, solid insulator (nylon), and vacuum. Two types of structures, namely, nylon-based structure (structure-1) and alumina-based structure (structure-2), are analyzed. The geometries are modeled, simulated, and analyzed using ANSYS Maxwell 3-D in DC conditions. The objective of the study is to investigate the electric field distribution and identify the peak electric field value in each region of the structures. The structures which are studied in this article are generally used in integrating the high-power RF device with a pulsed power system. The peak electric field value and its location are critical in assessing breakdown risk. Fixed voltages of 400 and 600 kV are applied between the electrodes separated by dielectric material. Appropriate dielectric properties are selected for the regions to closely represent the practical conditions. Peak electric field value and its location are thoroughly checked with different mesh counts to minimize the numerical errors. The simulated results of the high-voltage structures are validated through experiments, and the structure successfully withstood the high-voltage pulse without dielectric breakdown. The simulation study is extended to a compact and modular alumina-based structure (structure-2) that serves as an ultrahigh vacuum (UHV) envelope as well as high-power devices.

The Magnetically Insulated Line Oscillator (MILO) functions as a high-power microwave (HPM) radiator, known for its unique ability to generate a self-insulating magnetic field. An internal insulation barrier is formed by this self generated magnetic field, preventing electrical breakdown, which is crucial for achieving gigawatt-level operation. In this study, a MILO operating in the S-band frequency is designed, analysed, and optimized using simulations. The design includes a choke cavity, slow-wave structure, and extraction region. The disk is supported by four stubs, which are strategically placed to ensure impedance matching and enhance output power. The results, obtained using CST Studio's 3D Particle-In-Cell (PIC) simulation method, show that the MILO generates an average output power of similar to 800MW at S-band frequency 350 kV as applied voltage and current of 29.5 kA. The variation of the slowwave structure vanes is analysed. This analysis helps to understand how changes in the vane design impact the overall performance of the MILO, including factors such as energy conversion efficiency, impedance matching, and power output. By adjusting the geometry of the vanes, it is possible to optimize the device's operation to achieve better microwave generation and performance characteristics.

A broadband folded waveguide slow-wave structure was designed by MWS CST solver at sub-THz frequency spectrum. Therefore, high aspect ratio fully metallic copper structure was fabricated by high precision CNC micro-milling machine. The micron feature size structure dimensions were obtained within 5 micron tolerances. The insertion-loss measurement results were fairly matched with simulated results in the desired frequency band.

Horn antennas are fundamental components in high-power microwave (HPM) and millimeter-wave systems due to their high gain and robust power handling capabilities. This paper presents an in-depth comparative analysis between a standard conical horn antenna and a conical corrugated horn antenna designed for operation in the X-band. The primary motivation is to develop an antenna capable of efficiently radiating HPM fields in the order of more than 100MW. Both antenna models were designed and simulated using CST software. The simulation results demonstrate that while the conventional conical horn provides a simpler design and respectable performance, the corrugated horn antenna achieves vastly superior radiation characteristics. The corrugated design exhibits a high gain of 21dBi with a side lobe level (SSL) of -35.6dB and cross polarization suppression better than -30dBi. These characteristics, stemming from the generation of the pure hybrid HE11 mode, make the corrugated horn the preferred choice for demanding HPM applications.

A scheme of symmetric ridge loading of the top and bottom shorting cavities of an extended interaction cavity is proposed in this article for the broadbanding of an extended interaction klystron (EIK). While implementing this scheme, the periodicity of the ladder circuit has not been changed. In order to demonstrate the efficacy of the ridge loading in broadbanding, 3-D electromagnetic analysis was carried out on a W-band extended interaction cavity structure. The ridge loading is found to reduce the ohmic quality factor of the extended interaction cavity by 25% against that of no loading for the cavity operating at 95 GHz. At the same time, the ridge loading has shown marginal changes on the characteristic impedance and the peak axial electric field of the structure. A particle-in-cell (PIC) analysis has shown an enhancement in the 3-dB hot bandwidth of the ridge-loaded EIK (464 MHz) by around 250% in comparison to an unloaded device (185 MHz).

A cylindrical-pillar-based new meta-surface-assisted ultra-wideband window is proposed, designed and simulated, in the present paper, for a wideband gyro-traveling-wave tube. The return-loss characteristics were analyzed by simulation in a high-frequency structure simulator to calculate the bandwidth at an allowable return loss of -17 dB and the center frequency of 44.42 GHz of the operating bandwidth of 32.10 GHz (28.31-60.47 GHz) which is 72.26% relative bandwidth for the operating circular TE0,1 mode. The results with respect to which parameters/characteristics were validated within 5% against those obtained using CST Microwave Studio. The sensitivity analysis was also carried out to obtain the manufacturing tolerances. Interestingly, an improvement of 8.03% (from 64.23% to 72.26%) at an allowable return-loss of -17 dB was obtained in the proposed window over the bandwidth achieved in previously reported square-pillar with cylindrical-tip-based meta-surface-assisted window.

The feasibility of a photonic band-gap (PBG)-based interaction structure was analytically explored for a multiple-beam extended interaction klystron amplifier. This configuration accrues the advantages of the multiple-defect PBG-based extended interaction structure and multiple-beam operation. The mode configurations were analysed through 3D electromagnetic simulation and the applicability of the photonic band-gap cavity was studied for the multiple-beam operation of an extended interaction klystron amplifier. A typical six-defect cavity operating at around 83 GHz was designed for electron–wave interaction at 2π mode with 6 electron beams each carrying 300 mA current at the accelerating potential of 16.5 kV. A particle-in-cell simulation shows that an output power of ∼2 kW is possible with electronic efficiency of around 6.7%. A frequency-scaled-down interaction structure at Ku-band was fabricated and cold measurements were carried out to ascertain the feasibility. The measured values of the frequency for various modes, loaded quality factor and 3 dB bandwidth were found to be within 0.36%, 5.3% and 4.07%, respectively, against those from the simulation.

A novel technique was developed for broadbanding of the interaction structure of an extended interaction klystron (EIK) through symmetric loading of the top and bottom shorting cavities while maintaining the periodicity of the ladder circuit the same. A 3-D electromagnetic analysis was carried out on a $W$ -band structure in order to demonstrate the efficacy of the loading in broadbanding. The loading is found to marginally reduce the ohmic quality factor and the characteristic impedance of the structure. Measurements were also carried out on frequency scaled-down structures at $X$ -band for validating the simulation. Symmetric stagger tuning of the circuit is facilitated through this loading and particle-in-cell analysis shows an enhancement in the 3-dB hot-bandwidth of the EIK by around 400% in comparison to an unloaded device.

The paper has reviewed the worldwide attempts to improve the performance of microwave tube (MWT) interaction structures and MWTs employing them, accruing the exotic properties of metamaterials (MTMs). The review has encompassed the investigations based on theoretical study, using electromagnetic analysis and/or simulation, as well as experimental study. The success of and challenges to face in developing MTM assisted MWTs have also been highlighted.

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.

Analytical formulations for the resonant frequency of a reentrant cavity for klystron are available in the literature only for such cavities having a single beam-tunnel. An improved analytical formulation has been proposed in this paper for the calculation of cavity gap-capacitance of reentrant cavities having single and multiple beam-tunnels and its effects on the resonant frequency are studied. The results obtained through analysis have been validated against those obtained from the 3D electromagnetic field simulations and measurements. The proposed analytical formulation provides good estimation of resonant frequency of cavity with single and multiple beam-tunnels.

Study of multipaction breakdown margins in the output connector of a travelling-wave tube (TWT) is essential for application in satellite-borne systems. A TWT uses a coaxial ceramic window, a coaxial output coupler and / or a waveguide output coupler that are prone to multipaction breakdown boosted by high RF power due to the ion accumulation in critical regions during the transition of the satellite through plasma pockets in space. A detailed procedure for estimating the multipaction susceptibility margins in a TWT using CST studio and analytical equations is presented in this paper, and output couplers of two typical TWTs are analysed and the results are presented.

A compact X-band power booster TWT was designed and developed for space applications that provides minimum of 350W of peak RF output power with 25% duty over a bandwidth of 800MHz with RF efficiency of 22% and minimum gain of 27 dB. This TWT uses an electron gun operating at a cathode voltage of 6 kV and current of 275 mA with beam filling factor of 0.5. The electron beam is focused using PPM structure with peak field of 2600G generated using Sm2Co17 magnets. The SWS comprises tungsten tape helix supported by three azimuthally, symmetrically placed T-shaped APBN support-rods inside a metallic envelope. The dimensions of SWS were derived using the in-house parametric codes and optimized using Eigen-mode solver of CST Studio to achieve the required dispersion characteristics. The beam-wave interaction analysis was carried out using the in-house 1D-codes and was optimized using 3D PIC simulations. The SWS employs positive velocity taper near the output coupler in order to enhance RF interaction efficiency and to reduce the second harmonic content. The length of the SWS is around 93 mm. A 3-stage depressed collector is used to enhance the overall efficiency of the TWT. A prototype TWT is developed and tested for performance and has achieved overall efficiency of 45% with TWT length of 250 mm and weight of 980 grams. This TWT is subjected for operational temperature cycling at +70°C and -20°C and also random vibration to verify the structural integrity and has met the requirements.

This paper discusses the design and development of compact high-efficiency pulsed X-Band helix Travelling Wave Tube (TWT) delivering a minimum of 250W of peak output power over a bandwidth of 800 MHz with RF efficiency of 20% and minimum gain of 27 dB. Initial Electron-wave analysis was carried out using 1D-codes and was optimized using 3D PIC Solver in CST Studio. This TWT employs positive velocity taper near the output coupler in order to enhance RF interaction efficiency and reduce the second harmonic content at the output power from the device. The length of the SWS is around 95 mm with overall packaged TWT length of around 220 mm. Single stage depressed collector is used in the TWT and overall efficiency of 35% is achieved. Two prototype TWTs were developed and tested for performance.