A composite antenna and array antenna using the same. The antenna has a three-layer structure including a patch antenna, a slot antenna and a transmission line. A first layer includes a patch antenna resonating at half a wavelength, a second layer includes a slot antenna resonating at half the wavelength, and a third layer includes a transmission line and a feed point. The three layers are coupled and the entire composite antenna unit satisfies a resonance condition. A signal is fed through the transmission line and coupled to the slot antenna, and the signal from the slot antenna is further coupled to the patch antenna. This composition antenna has a desirable antenna gain, and an increased antenna bandwidth compared to a single patch antenna or slot antenna.