(A) study on antenna miniaturization and cylindrical ferrite rsonator antennas using low loss Li-ferrite

Abstract

As the demands on the compact and multi-functional electronic devices increase, there are two trends in the wireless communication systems. One is the downsizing of the devices. Another is the development of the adaptive systems. However, the space allowed for the antennas is limited. Many techniques for antenna miniaturization while retaining the antenna performance and developing antennas that have functions of multiband, wideband, tunable operation have been investigated and these issues are still technical challenges. This thesis presents techniques of the antenna miniaturization and multi-functional ferrite antennas utilizing a static magnetic bias. First of all, A quasi-Yagi antenna with the miniaturized transition for 2.4 GHz applications has introduced and experimentally investigated. A composite right/left-handed transmission line and planar artificial transmission line were used to design the microstrip-to-coplanar strip transition and to balance the output of the transition over a wider frequency range. A key feature of the proposed transition is the smallest occupied area, which is 0.087 $lambda_{g}^{2}$. The 3 dB back-to-back insertion loss bandwidth is around 84 %. Based on the proposed transition, a quasi-Yagi antenna was designed. The bandwidth for VSWR < 2 is 30.3 %. The antenna offers excellent end fire radiation performance. The maximum gain and front-to-back ratio are 5.1 dBi and 21 dB, respectively. The antenna occupies less space, which enables the integration of more circuit components. Secondly, a magneto-dielectric material based compact multi-band internal antenna covering nine bands (LTE/GSM/GPS/DCS/PCS/UMTS) has introduced and experimentally investigated for mobile handsets. In order to design wide- and multi-band antenna, a coupled-fed feeding scheme and a commercially available magneto-dielectric material (MF-112) were employed. The magneto-dielectric material has low loss properties up to 3 GHz. A T-shaped monopole feeding line generating parasitic capacitance is applied. It plays an important role to shift the resonances, especially in the low band. The overall size of the antenna is only 0.0875 $lambda_0$ x 0.0375 $lambda_0$ x 0.01 $lambda_0$. The antenna offers an acceptable radiation performance and is suitable for applications to modern mobile phones. Third of all, theoretical models of a cylindrical ferrite resonator antenna with a static magnetic bias along the z-axis have introduced. The simple models provide first and second order solutions, which lead to reasonably accurate predictions for the $HE_{11δ}$ mode splitting behavior. The characterization of a ferrite material was performed. Based on the measured material parameters, the cylindrical ferrite resonator antenna operating at 9.25 GHz was designed. Two split and orthogonal modes of the antenna are successfully achieved and verified. The presented theory is shown to correlate well with the measured results. The mode splitting behavior involves three tunabilities: frequency. bandwidth, and polarization. The operating frequency of the prototype antenna can be chosen in the range from 8.46 to 10.155 GHz. The polarization can be switched from linear to circular. The bandwidth can be extended from 6 to 12.3 %. The antenna offers an acceptable radiation performance while retaining a good impedance matching. Fourth of all, theoretical models of a cylindrical hybrid resonator antenna with a static magnetic bias along the z-axis have introduced. The hybrid resonator consists of an annular ring ferrite and a cylindrical dielectric. The simple models provide first and second order solutions, which lead to reasonably accurate predictions for the $HE_{11δ}$ mode splitting behavior. The cylindrical hybrid resonator antenna operating at 9.5 GHz was designed. Two split and orthogonal modes of the antenna are successfully achieved and verified. The presented theory is shown to correlate well with the measured results. The mode splitting behavior involves three tunabilities: frequency. bandwidth, and polarization. The operating frequency of the prototype antenna can be chosen in the range from 9.16 to 9.84 GHz. The polarization can be switched from linear to circular. The bandwidth can be extended from 7.3 to 12.7 %. The antenna offers an acceptable radiation performance while retaining an acceptable impedance matching. Finally, a novel cylindrical resonator antenna configuration has proposed. In the proposed configuration two resonances including the full- and half-cylindrical $HE_{11δ}$ -like modes can coexist simultaneously at different frequencies by placing a metallic post array in the resonator. Moreover, compared with the conventional $HE_{11δ}$ mode cylindrical dielectric resonator antenna having the same size, the proposed antenna operates in lower frequency band (miniaturization) and showed improved bandwidth.