Abstract: A rodless guide microwave radiation device, system, and method is disclosed for measuring at least one characteristic of a liquid in a vessel. A hollow metal waveguide conveys microwave radiation and is adapted to be disposed in a vessel for containing a liquid, the waveguide having a first end and a second end. A single chip radar sensor mounted on a PCB is disposed proximal to the first end of the hollow waveguide. The radar sensor is configured to transmit millimeter wavelength signals into the first end of the hollow waveguide for propagating down the waveguide toward the second end, and receive a return echo from the signal based upon a change in impedance upon encountering the liquid and propagating in the reverse direction of the waveguide, the single chip radar sensor including electronic circuitry for determining at least one characteristic of the liquid located in the waveguide based on detection of an impedance change according to time domain reflectometry.