Reseach On Low Lead-Angle LTCC Quadrifilar Helical Antenna

The developing direction of antenna is combining traditional antennas with advanced manufacturing techniques. LTCC QHA with low lead angle has several advantages such as short axial length, simple to process, and easy to install, and these are very important to thin handsets. However, existing QHAs are basically have a comparatively long axial length, which cannot meet the requirements of the LTCC technique. In this paper, how to lower the lead angle of the QHA in order to shorten its axial length is discussed, main contents are as follows.1. The relationship between the bandwidth and dimensions of the electrically small antennas is given in the theory of electrically small antennas. The loop-dipole equivalent model of the QHA is mainly studied. It is proved that this loop-dipole model has the same radiation characteristics with the QHA, including circular polarization and radiation pattern.2. According to the theory of dielectric resonant antenna, a cylinder dielectric resonant QHA model is built in the HFSS, and the validity of this model is verified by the simulated radiation characteristics. Then, in order to make this model fit the LTCC technique, the dielectric column and the feeding cells are reshaped.3. A method to reduce the size of the dielectric resonant antenna is proposed, which is adding short-circuit cylinders into the antenna. The effects of short circuit cylinders on the resonant frequency of the antenna is analyzed. Then according to this method, a dielectric resonant QHA with a high permittivity, =100, is designed, the size of this antenna is reduced to one-eighths compare to the traditional dielectric resonant QHA.4. A new way to lower the lead angle of the QHA is proposed, which is adding a short-circuit point to the feeding point, and two kinds of QHAs with low lead angle are proposed, including a multi-layer QHA and a combined QHA.5. The performance of the antennas is verified by using the HFSS, the value of Q is calculated by extracting the input impedance, then the theoretical bandwidth is calculated according to the theory of the electrically small antenna, and by comparing theoretical bandwidth to actual bandwidth, the method of calculating the value of Q is proved to be valid.6. A miniature phase-shifting power division feeding network is designed at the bottom of QHAs, which integrates the antenna and the feeding network. Then this kind of QHAs are compared to the QHAs that are fed by a 90° bridge phase-shifting power division network, the advantages and disadvantages of both feeding networks are analyzed.