Microstrip leaky-wave antenna fed by an aperture-coupled microstrip operating at K-band is presented. Using the aperture-coupled microstrip as a feeding structure can fully exploit the wideband characteristic of the microstrip leaky-wave antenna. The dimensions of the antenna are obtained from the calculation of the propagation characteristics. Measurement shows a bandwidth of 22% for VSWR < 2:1 and a peak power gain of 12 dBi at 22 GHz for one element. Four-element array is developed with a gain of 18.7 dBi and the frequency-scanning feature is exhibited. The waveguide model is verified by measuring the 3-D radiation pattern of the microstrip leaky-wave array.