Abstract: A novel center-fed cage antenna using the composite structure is proposed. The antenna has a composite structure of a cage and an asymmetric biconical structure. The impedance bandwidth and radiation pattern bandwidth are enhanced, and the tilting and ripping of radiation patterns are eliminated. A helical shorting wire is used to reduce the antenna height effectively. The antenna is analyzed and optimized by the method of moments (MOM). A prototype operating in VHF／UHF bands is constructed and tested. Measured results show that a VSWR (less than 3.0∶1) bandwidth of 650 MHz(100～750MHz), without additional matching or loading network, is obtained. The overall measured radiation gain of the proposed antenna in the horizontal plane is stable and larger than 1.5dBi in the operating frequency band(100～400MHz). Furthermore, a size reduction rate of 50％ compared with a general dipole antenna is realized.

Key words: center-fed cage antenna, shorting wire, broadband antenna