HIGH-FREQUENCY DESIGN AND PERFORMANCE OF TUBULAR CAPACITORS

The electrical design, analyses, and performance of tubular capacitors is presented. At very low frequencies the most important properties o f tubular capacitors are their capacitance and voltage rating. Simple formulas for capacitances are derived for spiral and concentric type t ubular capacitors. By numerical methods the regions of greatest electr ic stress in the dielectric are disclosed. The influence of bumps on t he capacitor plates is examined by the method of conformal transformat ion. It is shown that a small circular ridge running the length of the capacitor can reduce the voltage rating by 50%. At high frequencies t he inductance of the capacitor becomes important because it sets an up per bound on the highest frequency at which the capacitor behaves idea lly. In a previous paper it was shown that two plate capacitors can be connected in many ways and that their high frequency behavior is infl uenced by the particular connection used [1]. For a spiral wound tubul ar capacitor we consider only the type B connection [1], even though a type A connection is possible, and exhibit its equivalent circuit. In the case of concentric cylindrical tubular capacitors only a type B c onnection is possible. For that configuration we present a closed form electrostatic induction coefficient and inductance coefficient matric es. These are used to do high frequency analyses. Some examples are co nsidered. The role of the local ground plane of the tubular capacitor test fixture is investigated. It is shown that the closer the ground, local or test fixture to the tubular capacitor, the higher the first r esonant frequency. The analyses presented here are based upon two-dime nsional field calculations and coupled transmission line theory. Many of the earlier analyses of capacitors are strictly one dimensional. We check these results with some static three-dimensional models for the dc capacitance.