Broadband Design Of Ultra-Short Wave Antenna

This paper mainly researches the broadband design of ultra-short wave antenna. Miniature ultra-short wave antenna has a much smaller size than its wave length. It belongs to electrically small antenna, whose input impedance has a very small real part with a considerable large imaginary part. It is very difficult to achieve matching with feed. So it becomes the emphasis of the research to design reasonable matching networks. It is difficult to realize matching within the wide band for traditional passive matching networks due to the limitation of Gain-Bandwidth constraints. However non-Foster matching is not limited by the constraints. So it can achieve matching within wider frequency band. By this method, this paper design a dipole antenna with height of 1.2m and radius of 6cm. Its frequency band is 30MHZ-88 MHZ. This paper designs a reasonable negative impedance converter(NIC). The negative impedance element produced by NIC can offset the imaginary part of the antenna. So its imaginary part decreases from the original 400 W down to 12 W. Finally its VSWR is less than 3.1and Gain is larger than-0.2d B. The Gain can be up to 2.2d B.In addition, in view of the miniaturization and broadband development trend of the ultra-short wave antenna, this paper also designs an reconfigurable ultra-short wave antenna. The reconfigurable antenna is that kind of antenna who can achieve the features and functions by itself which should be achieved by several antennas working together.The reconfigurable antenna this paper presented puts the radiator and antenna matching network into segment. To implement the segmentation, we design an control circuit based on monolithic integrated circuit. Thus to control the radiator and matching networks' on-off. The control circuit can realize that different radiators and matching networks can work within its corresponding frequencies. The antenna selected is in the form of asymmetrical middle feed element antenna. The network is realized by Simplified Real Frequency method(SRFT). The antenna has a total height of 1 m. It's feed point is located at the location 0.325 m from the bottom. Its lower arm remains the same however the upper arm is divided into two segmentations. When the second segmentation is not connected to the antenna radiation body, the antenna works from 215 MHZ to 512 MHZ. On the contrary, when it is connected to the antenna, the workig frequency is within the range from 108 MHZ to 215 MHZ. Different radiators correspond to different matching networks. Finally its VSWR is less than 1.8, and its Gain is larger than 0.9d B within 108MHZ-512 MHZ.. The Gain can be up to 2.2d B.