Source of a Capacitor’s mysterious “self resonant frequency”.


In the Wikipedia case below the legs were left the same, so L was constant. So-called “self resonant frequency” duly increased by a factor of 3 each time C was reduced by a factor 10. Resonance is when ὡ=1/√LC. Obviously all the capacitors’ legs are of the same length. So with L constant, ὡ increases by a factor 3 when C falls by a factor 9. The capacitor itself has nothing to do with this “self resonant frequency”, which depends on its external legs. The capacitor itself has no internal series inductance, and no self resonant feqwuency.

Sample self-resonant frequencies for one set of C0G and one set of X7R ceramic capacitors are:

10 pF

100 pF

1 nF

10 nF

100 nF

1 µF

C0G (Class 1)

1550 MHz

460 MHz

160 MHz

55 MHz

X7R (Class 2)

190 MHz

56 MHz

22 MHz

10 MHz





In around 1965 I came across a book which had a list of various types of capacitor, including their manufacturers, their capacitance, and the length of their legs. It gave their “self resonant frequency”. I mentally formed their legs into a square of the same total length and treated each pair of opposite sides as a short transmission line. I then calculated the inductance of the square. Taking the stated capacitance, I could then calculate the capacitor’s so-called “self resonant frequency” while ignoring capacitor type.  That is, I calculated each capacitor’s “self resonant frequency” from its stated capacitance and the length of its legs.


This proved that the so-called “self resonant frequency  Ѡ=1/(LC) related the the capacitor’s legs, and it had no internal series inductance.


I have been making this point for more than fifty years, and yet today a Google search for “self resonant frequency” + capacitor gives us 500,000 hits, with mine coming at 3, 4 and 7. A Google search for “capacitor self resonant frequency” gives me hits no. 1, 2, 3 and 8. At hit no. 4, Wikipedia continues to talk nonchalantly about the non-existent “self resonant frequency” of a capacitor. It lets the cat out of the bag with; “The smaller the capacitance C and the inductance L the higher is the resonance frequency.” This confirms my work in 1965, that so-called “self resonant frequency” is reduced by reducing C, and is based on an inductance outside the capacitor,.


The squalid record on capacitor self resonant frequency, where we can see that an intellectual infrastructure does not exist anywhere in the world (“ Where are they? ”) can be extrapolated to electromagnetic theory, where I have found the same worldwide intellectual void in a much more important subject. Nobody is thinking about or discussing electromagnetic theory. They are only copying what others have written, and teaching what is in the books, replete with time-honoured oversights and errors.

Ivor Catt   29 March 2014