Phased array antenna with independent signal calibration

An antenna array, comprising:

• a substrate;
• and
• an array of antenna devices formed on the substrate, wherein each of the antenna devise comprises:
• a first ground plate arranged in a first layer and disposed on a first surface of the substrate;
• a first signal port and a second signal port arranged in a second layer adjacent to the first layer, and configured to transmit a first radio-frequency (RF) signal and a second RF signal;
• a first feed line and a second feed line arranged in the second layer and connected to the first signal port and the second signal port, respectively;
• and
• a radiation element in a third layer disposed on a second surface of the substrate opposite to the first surface,
• wherein the first ground plate is arranged to form a first slit and a second slit in the first layer for transmitting the first and second RF signals, the first feed line and the second feed line have different line lengths, and the radiation element at least partially overlaps the first slit and the second slit from a top-view perspective.