Overview
This paper presents a high-power microwave generator using virtual cathode technology (vircator) in axial release configuration for electronic warfare applications. The research was conducted by Libor Dražan and Roman Vrána at the Department of Radar, University of Defence, Brno, Czech Republic.
Technical Specifications
Device Configuration
- Cathode diameter: 17.5 mm (rk)
- Working chamber radius: 40 mm (R)
- Critical vacuum current: Icr = 4.63 kA
- Anode type: Grid anode made from pyrolitic carbon (enables repeated operation vs. foil anode single-shot design)
- Cathode construction: Cylindrical carbon block with adjustable distance dka to cathode-anode gap for impedance matching
- Operating frequency band: 0.5 - 1.5 GHz dominant frequencies; target shift to 3 GHz band required for DEWM applications
Power Supply Systems
The vircator is powered by different generators depending on application:- Electromagnetic ammunition (DEWM): Magneto-cumulative generator (MCG)
- Weapons for Defense of Objects (WDO): Marx generator
Test Setup Components
- Aluminous cylindrical stator with 16 screw helical coil (2 mm copper wire)
- Copper armature tube (38 mm outer diameter, 4 mm wall thickness) filled with octogen explosive
- Load coil: copper strip loop connecting stator to armature
- Crowbar switch: brass plate for primary current source disconnection
- Insulator circle separating stator and armature
Performance Results
Measured Outputs (from Fig. 15-17)
- Peak current: ~4 × 10⁴ A (Fig. 15)
- Voltage pulse: ~3 V peak (Fig. 16)
- Frequency spectrum: Dominant frequencies in 0.5 - 1.5 GHz band (Fig. 17)
Design Requirements for DEWM Application
To meet directed energy weapons microwave specifications: 1. Shift dominant frequencies from 0.5-1.5 GHz to 3 GHz band via optimized cathode sizing and anode-cathode distance tuning 2. Increase specific dielectric strength of output window 3. Maintain vircator impedance matching to pulse forming line (PFN)Theoretical Framework
Current Density Calculation
The electron beam current density i [A/m²] is calculated as: ``
i = eV ce ne / c (Eq. 18)
`
where:
- e = electron charge
- nV = electron volume density
- ce = electron velocity
Plasma Frequency
The electron beam plasma frequency ifp is approximately:
`
ifp ≈ 7109 pe (Eq. 19)
``
Applications
According to the authors, vircators are "the device of choice" for electromagnetic weapon designers due to:
- Very powerful single pulse capability
- Mechanical simplicity and robustness
- Small form factor
- Broad operational frequency band coverage
- Decimeter and centimeter wave capabilities (170 kW - 40 GW power range)
Funding
Research supported by Czech Ministry of Defense through ŽELETON, APPM, and GENVLN projects.