Antennas are designed to radiate or receive electromagnetic waves in the part of transmitting or receiving system. They are transducers which transform electric energy into waves so as to radiate radio waves, that¡¦s the primary purpose of antennae. Utilizing the characteristics of helical antennae operating in the axial mode including high directivity, broad bandwidth and circular polarization in satellite communication (ex. GPS) is detailed described in this thesis. The microwave dielectric ceramic material becomes very popular in satellite and wireless communication in recent years because of its high-K, high-Q,and stable-temperature-coefficient characteristics.Our study also utilizes its feature of high dielectric coefficient to shrink the size of the antenna significantly. In this study, we fabricate and analyze the antenna combining the advantages of the helical antenna and the microwave dielectric ceramic material.

Helices are broadband antennas that provide moderate gain, largely real input impedance and circular polarization when operating in the axial mode regime. A modified form of the helix, the spherical helix, has been shown to yield similar polarization and gain characteristics over a narrow bandwidth but a much larger beamwidth. This investigation examines multifilar hemispherical helices and produces two specific designs with some desirable radiation characteristics. The side-fed quadrifilar helix and the top-fed bifilar helix are the new hemispherical designs which are studied in detail both numerically and experimentally. The Numerical Electromagnetics Code 4 is used to analyze the radiation characteristics of the proposed multifilar hemispherical helices. Directivity, E- and H-plane radiation patterns, axial ratio and input impedance of a few example designs are calculated. Measurements, taken in the anechoic chamber at the Virginia Tech antenna range, generally confirmed the simulation results. It is shown that the bifilar hemispherical helix provides a flat gain curve over the measured bandwidth (~14%) and generally elliptical polarization with near circular polarization in limited case. / Master of Science

No / A miniaturized conical helix antenna is presented, which displays vertical polarization with electrically small dimensions of 10mm×10mm×45mm. The resonance of the antenna is made tunable by adding a variable digital MEMS capacitor load at the bottom of the helix, giving a tuning range of 316 MHz to 400 MHz. The antenna demonstrates considerable impedance matching bandwidth and gain over the entire tuning frequency band. Most importantly, the antenna is capable of compact, flexible and easy integration into a wireless device package or for platform installation. / Datong of Seven Technology Group, for their support under the KTP project grant No. 008734.