Theory And Realization Of Controllable Mixed Electric And Magnetic Coupling Filters

Modern communication systems require extraordinarily stringent specifications on microwave filters. In mobile and integrated communication systems, miniature, multi-band, ultra-wideband, and high performance filters are required for microwave integrated circuits (MICs) and monolithic microwave integrated circuits (MMICs). In satellite communications and wireless base stations, compact volume, low loss, high power handling capacity and low cost filters and multiplexers are required. In order to meet these requirements, innovations on filter theory and realizations are pursued. This dissertation is, therefore, devoted to constructing a new theory of filter synthesis, proposing new methods of analysis and design, and creating novel filter structures.The innovations of this dissertation are listed below.1. The concept of the electromagnetic multiple-coupling path is proposed, which overcomes the limitation of the traditional physical multiple-coupling route. In order to reduce the number of resonators, increase the flexibility of designs, and enhance the performance of filters, the controllable mixed electric and magnetic (EM) coupling filter is proposed. Without the assistance of cross-coupling, the proposed mixed electrically and magnetically coupled filter can realize a quasi-elliptic filtering response which is better than that of traditional cross-coupled filters. The proposed mixed EM coupled filter has an inline configuration that resolves the isolation problem between the input and output, thus making the filter very suitable for multiplexers applied in wireless base station and satellite communications. Each of the transmission zeros of the proposed mixed EM coupled filter can be indepently tunable without affecting other transmission zeros, and therefore, asymmetrical filtering responses that are often required for preventing interferences between channels can be easily achieved. A new definition and extraction method are proposed for mixed electric and magnetic coupling. By using this extraction method the electic and magnetic coupling coefficients can be extracted seperately from the mixed EM coupling. Based on the new definition, a simple and effective gradient optimization synthesis technique in the low-pass prototype frequency domain is proposed.2. Several compact planar filters with adjustable mixed EM coupling structures are proposed to implement quasi-ellitptic filtering responses. These filters, including the open-loop filters and hairpin-comb filters, can be constructed with smaller spacings between the resonators due to the canceling effect of the electric coupling and magnetic coupling, and therefore, they are suitable for integrated communication systems and high temperature superconducting filter applications.3. An inline coaxial quasi-ellptic filter with controllable mixed electric and magnetic coupling is proposed. A complete procedure from the matrix synthesis to the practical tuning for designing this filter is presented, which can be an instruction for engineers. The performance of the EM coupled filters are superior over the conventional cross-coupled filters that have the same resonator numbers, and therefore, the EM coupled filters are desirable for wireless base stations and satellite communication systems.4. A mixed EM coupled TE01δmode dielectric resonator (DR) filter is proposed. Besides, the mechanism of the generation of transmission zeros caused by the probe fed DR is fully studied. A new coupling mechanism is discovered: the single TE01δmode DR itself contains two coupling paths. Based on this new meahnaism, the method of controlling the feeding probe to create and tune transmission zeros is proposed and an iris-only coupled quasi-elliptic DR filter with an inline configuration is designed and fabricated. This innovation significantly reduces the difficulty for the design of quasi-elliptic DR filters, and it must be significantly meaningful to practical engineering applications.Amoung the above mentioned innovation areas, the first one belongs to the the area of filter synthesis theory while the second, third, and fourth belong to the area of filter realizations. Additional important issues of microwave filter designs addressed in this dissertation are: dual-band filters, ultra-wideband filters, and ultra-wide rejection-band bandpass filters.