| In the vehicle and ship communication system,short-wave and ultra-short-wave are the main method. The transmission and reception of the communication signal depends on the ominidirectional antenna which radiates short and ultra-short wave. However, there are many kinds of antennas in the traditional communication system, among which the mutual coupling cannot be neglected. The forms and functions of these antennas cannot meet the developments of integration, broadband and miniaturization of the antenna system. Thus, it is necessary to research how to broaden the antenna bandwidth and realize the integration and miniaturization.This paper provides an integrated antenna structure, which is composed of a discone antenna and a monopole antenna. The monopole antenna resonates at the lower band 30MHz~650MHz and the discone antenna at the higher band 650MHz~3GHz.The whole integrated antenna has the bandwidth 100:1. The discone antenna is placed on the top of the monopole antenna, which increases the whole height little, meanwhile it also can be regarded as a method of top load of the monopole antenna, which is conducive to its miniaturization.Firstly, the influences of the main basic parameters on the radiation performance have been investigated to the design of the discone antenna. The profile has been optimized, and two kinds of discone antenna with a multi-elliptical profile and a broken-line profile is designed. Then, considering the design requirement of the integrated antenna, an optimized discone antenna with the band 650MHz~3GHz is designed, with the height 10 cm and the radius 6cm.Secondly, to the design of the monopole antenna, lumped elements is loaded to broaden its bandwidth and miniaturize its size, and the load positions as well as the values is optimized. In addition, extra improvement of the antenna performance is obtained by optimizing the radius of each pole at different heights. The height of the whole monopole antenna with the discone antenna on the top is 1.5m, only max?/ 6.67, and the operation band is 30MHz~650MHz.Finally, considering the material and the load of lumped elements, a prototype of the integrated antenna is fabricated and measured. Besides, a transmission line transformer is designed and fabricated to improve the impedance matching of the monopole antenna. From the measured results, the S11 of the discone antenna is lower than 2 within 650MHz~ 3GHz; the gain on the horizontal direction is about 1dB. The S11 of the monopole antenna is improved to be lower than 3 when the impedance is matched. |
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