Antenna device and communication device

A communication device comprising:

• an antenna device;
• and
• a communication unit that transmits or receives a wireless signal via the antenna device,
• wherein the antenna device includes:
• a substantially-flat-plate-shaped dielectric substrate;
• a metal base plate arranged on a first surface of the dielectric substrate;
• substantially-flat-plate-shaped first and second antenna elements arranged on a second surface of the dielectric substrate that is opposite to the first surface and on an opposite side of the dielectric substrate from the metal base plate so that a slit is formed;
• a first feeding portion that feeds power to the first antenna element;
• and
• a second feeding portion that feeds power to the second antenna element, and
• a phase difference between feeding signals supplied to the first and second feeding portions, respectively, is approximately 180 degrees,
• wherein a distance between a feeding point of one of the first and second antenna elements and the slit is determined depending on an input impedance to be matched.