A low-profile printed cavity antenna (PCA) under triple-mode resonance is proposed towards a simultaneous impedance bandwidth and a radiation pattern improvement. Based on the cavity model, the far-zone radiated fields of the PCA are theoretically investigated. The results demonstrate that its E-plane half-power beamwidth (HPBW) could be significantly improved by using two half-mode cavities instead of a single-patch resonator. After that, the width of the radiating patch is progressively enlarged and separated in order to excite three resonant modes for bandwidth-enhancement. Moreover, two additional conductive vias are loaded below the radiating patch in order to reduce its increased E-plane cross polarization. In final, the proposed antenna is fabricated and tested. Experimental results show that its impedance bandwidth is obviously extended to about 14.3% with appearance of three in-band attenuation poles. Meanwhile, a low-profile property with the height of 0.027 free-space wavelength is achieved. In particular, the PCA has acquired a wide E-plane HPBW of around 135°, while keeping a low cross polarization of below -20 dB in both E- and H-planes.