This paper presents a prototype analog 4-channel-I/Q polyphase-FFT filter bank (PFFB) using passive switched capacitor circuits to channelize wideband signals. Like FFTs, the proposed PFFB shares computations for low power. The PFFB allows for a longer 'effective window length' than is possible in a standard FFT. This characteristic of the PFFB maintains a narrow main-lobe bandwidth combined with low side-lobe amplitudes. The passive switched capacitor structure enables high linearity and low power implementation. The measured performance of the prototype fabricated in TSMC 65nm CMOS shows >40dB side-lobe suppression, +25dBm IIP3, and 208μVrms integrated output noise for all channels at 1GS/s operation. The total power consumption for the PFFB (8-channels total) is 34.6mW (34.6pJ/conv).