| 摘要 |
An antenna 10 or an antenna assembly comprises at least one pair of elongate elements 10A-10D centred on a common axis and loaded with a dielectric material core 12, where each of the elongate elements 10A-10D has a feed end and an end linked to an end of the other element or elements. At least one pair of the said elements 10A-10D forms part of a conductive loop having an electrical length of substantially (2n-1)/2 times an operational wavelength of the antenna, where n is an integer. The elongate elements 10A-10D may include bifilar or quadrifilar, quarter turn helical formations. The linked ends of the elements may be connected together by a conductive element 10L encircling the dielectric core 12 at different positions along the axial length of the core. The elongate elements 10A-10D may be of different lengths but the loops formed provide a substantially balanced formation with a high input impedance of at least 500 ohms which can be connected to the balanced side of a differential amplifier 16 which can be arranged to provide a single output signal. Various connection arrangements between the antenna and its associated circuitry, such as an amplifier 16 or surface acoustic wave SAW filter, and a circuit board 14 are disclosed. Backfire and endfire antenna arrangements are described. |
