| 摘要 |
A miniature antenna (10) for operation at frequencies in excess of 200 MHz has a ceramic core (12) in the form of a cylindrical rod having a relative dielectric constant greater than 5. Plated on the outer surfaces of the core is an antenna element structure comprising a single pair of appositely disposed helical elements (10A, 10B) having a common central axis coincident with the central axis of the core. At a distal end of the antenna, they are connected to a coaxial feeder structure passing axially through the core, and at their proximal ends they are connected to the rim of a cylindrical trap conductor (20) which, at the proximal end of the core is coupled to the screen of the feeder structure. At the operating frequency, the antenna behaves as a loop, the radiation response having nulls directed generally perpendicularly on each side of a plane containing the central axis of the core and the connections of the helical elements with the feeder structure and with the conductive sleeve. The antenna is intended primarily for a handheld communication unit such as a cellular or cordless telephone handset, the present of the nulls in the radiation pattern reducing radiation into the user's head.
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