A method of stabilizing a variable filter for an analog electromagnetic signal against circuit oscillation includes the steps of: providing a signal loop comprising a signal input, a signal output, and a plurality of variable circuit elements connected in the signal loop, the plurality of variable circuit elements comprising an adjustable resonator and an adjustable gain block, the signal loop having a variable frequency response that is characterized by a central frequency, a frequency passband, a response Q, and an operating point and a resonator response curve that are plottable in a Cartesian s-plane having an origin, a real axis, and an imaginary axis; and maintaining stability of the variable filter within an operating range by controlling the adjustable resonator and the adjustable gain block such that, in the Cartesian s-plane, the resonator response curve satisfies an orthogonality stability condition.