Capacitors

Dielectrics (1)

  • Air – used for variable capacitors with a set of fixed and moving plates allowing the effective plate area to vary.  Used for tuning circuits.  As plate spacing determines working voltage, capacitors used for antenna matching require large spacing, up to 1cm
  • Paper – layers of metal foil (aluminium) separated by paper: physically large, high working voltages
  • Plastics – High working voltage.  Polythene, polypropylene, mylar can be lossy at HF; polystyrene, PTFE less lossy, more stable