By introducing cavity resonators to microstrip structures, subwavelength cavity resonator microstrip antennas with left- and right-handed metamaterial bilayered substrates are proposed and investigated. Due to the phase compensation, the total height of the antennas is reduced rather than increased. With certain sets of parameters, as a breakthrough to the restricted bandwidth of the conventional microstrip antennas, greatly broadened bandwidth can be achieved. Under other conditions, antennas with narrow bandwidth and resonant sensitivity can be realized. Corresponding applications for sensor use are proposed, and distinct advantages over the nonresonant electromagnetic wave sensors are demonstrated.