A 16 × 16 fully metallic ridge gap waveguide (RGW) monopulse radar antenna with wide bandwidth (BW), low sidelobe levels (SLL) and high efficiency has been designed, fabricated and measured at V band. The structure is composed of a symmetrical four quadrant radiation array, feed-network with Taylor distribution and an innovative RGW monopulse comparator. Firstly, a wide BW RGW slot antenna unit has been designed, the radiating layer exists four radiation slots which are excited by a cavity-backed. A series of feed network with Taylor distribution has been designed to realize various equal-phase but unequal-power symmetric RGW dividers. The RGW dividers is designed for constructing an amplitude-tapering feed-network for the array, phase differences are balanced by adjusting the waveguide phase velocities. Furthermore, a low-loss RGW planar Magic-Tee is designed to be used in a monopulse comparator network consisting of two vertically stacked layers. The fabricated monopulse array antenna indicate that the array can achieve a 10% relative impedance bandwidth. The gain of more than 30 dBi and the first SLLs which are below −23 dB in the E-plane and H-plane in the sum radiation pattern are realized. The null depth in the difference radiation pattern is measured to be 25 dB below the peak of the sum radiation pattern at whole bandwidth.