| 摘要 |
An antenna 100 comprises first and second helical portions 103, 105 which are electrically coupled such that the second portion 105 acts as a top load to the first portion 103. The said helical portions are arranged such that, in use, the magnetic flux of the said coil portions 103, 105 cancel with one another. The helical coil portions 103, 105 are wound in opposite directions to provide the said flux cancellation and to reduce the inductive coupling such that a mainly capacitive top load to the first helical portion 103 is provided. The coupling between the said portions 103, 105 may be of a galvanic or non-galvanic (ie inductive or capacitive) nature. The second helical coil portion 105 may be arranged at least partly inside or outside the first coil portion 103. The pitch of the windings, the diameter of the wound portions and the position at which the coupling occurs between the coil portions may be varied to obtain the desired operational characteristics. The antenna may include a sleeve 107 as a spacer between the coil portions and the antenna may be enclosed in moulded plastic material with an outer envelope 109. The antenna may provide a compact arrangement which may be modified to provide broadband or multiple frequency band operation for a mobile station radio communication device. |
