  We present a mixer-duplexer-antenna leaky-wave system based on periodic
space-time modulation. This system operates as a full transceiver, where the
upconversion and downconversion mixing operations are accomplished via
space-time transitions, the duplexing operation is induced by the nonreciprocal
nature of the structure, and the radiation operation is provided by the
leaky-wave nature of the wave. A rigorous electromagnetic solution is derived
for the dispersion relation and field distributions. The system is implemented
in the form of a spatio-temporally modulated microstrip leaky-wave structure
incorporating an array of sub-wavelengthly spaced varactors modulated by a
harmonic wave. In addition to the overall mixer-duplexer-antenna operation,
frequency beam scanning at fixed input frequency is demonstrated as one of the
interesting features of the system. A prototype is realized and demonstrated by
full-wave and experimental results.
