According to the teachings presented herein, a reconfigurable filter apparatus includes at least first and second passive filter sections connected in parallel to yield a composite filter response. Each passive filter section has a respective passband response and at least one of the passive filter sections is a ‘de-tunable’ passive filter section. Each de-tunable passive filter circuit includes a detuning circuit operable to exclude the respective passband response of the de-tunable passive filter section from the composite filter response by detuning a resonator within the de-tunable passive filter section. ‘Detuning’ the resonator can be understood as short-circuiting, opening the resonator, or otherwise disabling it, such that the filter path is blocked. Advantageously, the resonator(s) that are selectively detuned in this manner is isolated from input and output ports of the de-tunable passive filter section with respect to frequencies outside of the respective passband response of the de-tunable passive filter section.