A Q-enhanced radio-frequency filter featuring loss-compensating circuits with values that can be controlled to optimize loss compensation. Instabilities are avoided by temporarily introducing a reflection at a port (such as via short-circuiting the port) and testing for the beginning of oscillations. Certain embodiments provide negative-resistance circuits for loss compensation, including cross-coupled transistor pairs and adjustable capacitance. Further embodiments provide loss-compensating RF filters with planar inductors, including overlapping planar inductors.