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 of tubular capacitors are their capacitance and voltage rating. Simple formulas for capacitances are derived for spiral and concentric type tubular capacitors. By numerical methods the regions of greatest electric stress in the dielectric are disclosed. The influence of bumps on the capacitor plates is examined by the method of conformal transformation. It is shown that a small circular ridge running the length of the capacitor can reduce the voltage rating by 50%. At high frequencies the inductance of the capacitor becomes important because it sets an upper bound on the highest frequency at which the capacitor behaves ideally. In a previous paper it was shown that two plate capacitors can be connected in many ways and that their high frequency behavior is influenced by the particular connection used [1]. For a spiral wound tubular 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 connection is possible. For that configuration we present a closed form electrostatic induction coefficient and inductance coefficient matrices. These are used to do high frequency analyses. Some examples are considered. 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 resonant frequency. The analyses presented here are based upon two-dimensional 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.