Design On Vehicle-borne Wide Beam Quadrifilar Helix Antenna

In order to meet the requirement of real-time communication while moving, it requires that the antenna of satellite telecommunication system must have the characteristics of wide beam radiation. The quadrifilar helix antenna is such a kind of wide beam antenna with the good characteristics of cardioid-shaped and circularly polarized radiation pattern. Thus it becomes the first selection of the satellite antenna system. My thesis concludes several parts, which is mainly about three designs of vehicle-borne quadrifilar helix antenna and a type of power divider network. In addition, this paper also presents a new type of quadrifilar helix antenna with a novel structure. The specific details of this thesis are listed as follows:First, it presents a study on designing two antennas. The first antenna has a normal structure with single screw spiral arm. The spiral arms of the angle are made in 44°. The antenna operates at the center frequency of 2.2GHz and left hand circular polarization. The measured data show that the bandwidth of the antenna for VSWR≤2:1 achieve in 2.15~2.25 GHz, covering the band what we need. The gain during-70°~70° is higher than-0.5dBi, and the AR during-65°~65° is lower than 3dB. We divide the each spiral arm of second antenna into two branches, a longer arm and a shorter one. The antenna operates at two center frequencies of 2.2GHz and 2.73 GHz. The spiral arms of the angle are still keeping in 44°. The measured data show that the bandwidth of the antenna for VSWR≤2:1 achieve in both two band which is covering 2.15~2.25 GHz and 2.7~2.76 GHz. In low frequency, the half power beam width is 122°, and the AR during-61°~61° is lower than 3dB. In high frequency, the half power beam width is 130 °, and the AR during-65°~65° is lower than 3dB.Second, we design a type of quadrifilar helix antenna with the method of folding spiral arms. It realizes the antenna height reduced by 10%. Besides, we present a power divider to match the antenna. The network consists of one Wilkinson power splitters and two 90° hybrids. The test results show that the bandwidth of port of assembled antenna for VSWR≤2:1 achieve in 1.8~2.4GHz, which has bandwidth increased by 22%. The gain during-70°~70° is higher than-1dBi. Its half power beam width is 125° and the AR during-61°~62° is lower than 3dB. Those antennas can meet the application requirements of vehicle satellite communication system.Third, we simulate a kind of quadrifilar helix antenna with the structure of a hemispherical surface. Due to its half spherical shape, it realizes the antenna height reduced by 62%. The simulation results show that the gain during-68°~68° is higher than 0dBi, and the AR during-75°~75° is lower than 3dB.