A well known work from Fikier which is more focussed on building electrostatic loudspeakers. This dutch classic can be downloaded here. Dutch only.
J.H. Streng
Yet another work by a Dutchman, but this time in English. Theoretical study on charge movements on the diaphragm, radiation patterns and air loading of strip radiators. Download it here
Baxandall
The best work on electrostatic speakers, period. Download it here