Antenna apparatus for transponder

An antenna apparatus comprising:

• a circuit board having an electronic circuit portion provided on one surface thereof and a grounding conductor layer provided on the other surface thereof;
• an antenna element mounted at the other surface of the circuit board;
• a shield case formed by sheet-metal processing and conducting to the grounding conductor layer to cover the electronic circuit portion at the one surface of the circuit board;
• and
• a resin case for accommodating the circuit board, the antenna element, and the shield case, the resin case being attached to an end portion of an air valve provided at a wheel rim of a tire of a vehicle,
• wherein the antenna element includes a radiating conductor disposed substantially parallel to the grounding conductor layer, a feeding conductor extending from the radiating conductor toward the circuit board and connected to the electronic circuit portion, and a grounding conductor extending from the radiating conductor toward the circuit board and connected to the grounding conductor layer, and a posture of the antenna element in the resin case is determined such that one side surface extending in a longitudinal direction of a space defined between the circuit board and the radiating conductor faces one of sidewalls of the tire.