This paper presents a novel low complexity, constant envelope UWB communication system for personal network and sensor network applications: FM-UWB. FM-UWB uses double FM: digital FSK followed by high modulation index analog FM to create a constant envelope UWB signal. FDMA techniques at the sub-carrier level may be exploited to accommodate multiple users. A wideband delay line FM demodulator that is not preceded by any limiting amplifier constitutes the key component of the FM-UWB receiver. This allows multiple users to share the same RF bandwidth. The system is intended for low data rate, short-range (< 10 m) applications. Due to its simple architecture, FM-UWB radio will be low cost and have low power consumption.