A novel leaky-wave antenna array with switchable radiation patterns is designed and manufactured at X-band based on a half-mode substrate integrated waveguide. It generates endfire and broadside radiation patterns in two orthogonal planes. The endfire radiation is bidirectional in the xz plane, and the broadside radiation is unidirectional in the yz plane. These two radiations can be controlled by triggering in-phase or out-of-phase port excitations. The excitations also enable the scanning beams to switch between xz and yz planes. A feeding network is designed with a 3 dB coupler and a phase tuner to generate the in-phase and out-of-phase excitations. In the feeding network, the phase difference is realized without using any phase shifter. The feeding network has two input ports, one for the in-phase excitation and one for the out-of-phase excitation. A prototype antenna was manufactured and tested to validate the concept.