Design of coaxial-cable pulse transformers

Coaxial-cable pulse transformers with good high-frequency response (30-ns rise time) and excellent high-voltage interwinding insulation (≲300 kV primary to secondary) were designed, built, and tested. They have the advantage that the open-circuit transformation ratio is unaffected by the thickness of the interwinding insulation, and good coupling is maintained with step-up designs. An equivalent circuit was developed, involving two coupling coefficients, which predicted the measured results with reasonable accuracy. Values of primary, secondary, and leakage inductances were 1.4, 2.2, and 0.8 µH, respectively.