| Nonreciprocal devices based on gyromagnetic ferrites are indispensable fundamental components in RF and microwave/millimeter-wave electronic equipments & systems. According to the requirements of reliable microwave/millimeter-wave systems and low-cost manufacturing technology, hybrid integrated circuits as well as monolithic integrated circuits haven been developed for the microwave/millimeter-wave components and subsystems. At present, it is difficult for the discrete nonreciprocal components with transversely-magnetized ferrites to achieve planar integration. Moreover, as frequency goes up, not only the“drop-in”technology used to fabricate the classsical Y-junctionn circulator in microstrip becomes very demanding and expensive due to the dependence of the circulator diameter on the wavelength, but the limitation in available saturation magnetization values and the strong bias field required to overcome the large demagnetization factor of the thin ferrite disk in the direction perpendicular to the plane of the disk present some difficulties. It is difficult for the permanent magnet to provide a resonance field more than 10,000 Oe.A possible solution is to use longitudinally-magnetized ferrite-coupled-line (FCL) in a distributed circulator. This device, which is more suitable for monolithic integration, has the advantage that it does not suffer the size-constraints of the junction circulator and requires only a weak biasing field due to its in-plane magnetization. In this thesis, FCLs have been analyzed. The main results are as follows:1. The conditions for the optimal nonreciprocal operation of longitudinally-magnetized ferrite-coupled-line are obtained for the first time from the scattering-matrix treatment.2. A new design procedure has been proposed with modifications to the coupled-mode method shown to be necessary for microstrip and other non-TEM lines.3. The characteristics of ferrite-single-microstrip (FSL) on a longitudianally-magnetized ferrite substrate is discussed for the feasibility of implementing FCL circulators on full ferrite substrates and bidirectional phase shifters using these structures. 4. The performance of a pair of uniform linear FCL is studied numerically. It is found that the operation frequency of a standard, uniform microstrip FCL increases with saturation magnetization of ferrite used but is otherwise insensitive to other parameters. For higher frequency applications, one has to switch to ferrite of higher saturation magnetization, but this process cannot go on forever, because there is only so much ferrite available in the market so an up limit exists for the highest saturation magnetization ferrite can provide. In the case when the required operation frequency is higher than any existing ferrite can sustain, while new ferrite of higher saturation magnetization is yet taking time to develop, a standard, uniform microstrip FCL with dielectric overlay (superstrate) is proposed in this paper to create vital extension of usable frequency band for FCL devices.5. However, the dielectric overlay may be required to have limited permittivity and thickness. A nonuniform zigzag structure is proposed on the ferrite substrate to provide a new way to increase the center frequency of operation. In order to verify this, nonuniform zigzag lines are proposed on a ceramic substrate with a ferrite as superstrate to decrease the center frequency of operation. It is found that the operation frequency band of a FCL can be extended with this zigzag technique.6. 3-port microstrip circulators with uniform FCLs work at 6.2GHz and 10.3GHz are built on ferrite substrates with saturation magnetization 4?Ms=1820Gauss and 4?Ms=3040Gauss, respectively. Another 3-port microstrip circulators with uniform and nonuniform FCLs work at 10.3GHz are also fabricated on the same ferrite substrate with saturation magnetization 4?Ms=1820Gauss. These devices are investigated both theoretically and experimentally. The measured results confirm the theoretical findings. |
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