| Microstrip co-directional (COD) coupler is mostly based on branch-line structure, which has big volume and narrow bandwidth. Due to the limitation of processing technology, the gap between the coupled lines of the parallel coupled line structure contra-directional (CTD) coupler can’t be too narrow, strong coupling can’t be realized. Compare with COD coupler and CTD coupler, the trans-directional (TRD) coupler has the advantages of strong coupling, small size, DC blocking and so on. Thus, the research of TRD coupler and its applications has important significance.In order to accommodate the needs of the development of communication system, TRD coupler has a lot of problems to be solved. Therefore, this dissertation is devoted to researches on the novel TRD coupler and its applications. Propose the design method for novel TRD couplers according to different application field, and apply TRD couplers to other microwave circuits for improving the performance of the circuit system. The dissertation is supported by National Natural Science Foundation of China, the Traffic Applied Basic Research Project of the Ministry of Transport of China, and the Fundamental Research Funds for the Central Universities. The main innovations of this dissertation are listed below:(1) A method for designing high directivity and weak coupling TRD coupler is proposed, and the strict parameters design mathematical expressions are given. Based on the method, two TRD couplers with 10 dB and 20 dB coupling are developed with capacitor shunted ground defected coupled coplanar waveguide (CPW) and inductor loaded asymmetrical coplanar waveguide (ACPW). Compare to the traditional parallel coupled line directional coupler with the same coupling, the directivity of the proposed weak coupling TRD coupler is better.(2) A miniaturization design method for the TRD coupler is proposed. The design equations for the transmission line which including LC elements are derived. Based on the method, a miniaturized TRD coupler with high directivity is designed. Compared with the traditional TRD coupler, the volume of the proposed TRD coupler is reduced by 47.6%, while the directivity is improved by 15 dB.(3) A method for designing the frequency tunable TRD coupler is proposed. The frequency tunable relative bandwidth reaches 66.7%. Moreover, a method for designing the coupling reconfigurable TRD coupler is introduced. The parameters design mathematical expressions are derived and the detailed design procedures are given. Based on the design procedure, a TRD coupler with coupling reconfigurable range of 3 ～40 dB is developed. When the coupling is 40 dB, the TRD coupler can be regarded as a crossover, and function reconfigurability is realized.(4) A method for designing the non-interspersed input/output ports 180° hybrid utilizing the TRD coupler is proposed. The hybrid is composed of CTD coupler, TRD coupler and two phase shifting lines. The phase difference of the two phase shifting lines is 180°. The coupling of the CTD coupler and TRD coupler in the 180° hybrid can be chosen freely according to the manufacturing accuracy, which shows high design flexibility. Moreover, it has no bond wires, via holes or multilayer structures, which can be easy for fabricating. Small volume and DC blocking feature are also the characteristics of the 180° hybrid. In order to broaden the application range of the hybrid, the TRD coupler is modified, and a non-interspersed input/output ports 180° hybrid with arbitrary couplings is proposed. The closed form design equations of the modified TRD coupler and the design method of the arbitrary coupling non-interspersed input/output ports 180° hybrid are given.(5) A high performance multimode satellite navigation terminal active antenna is proposed. The radiation part of this active antenna is integrated of shorted-annular-ring reduced-surface-wave (SAR-RSW) patch and inverted shorted-annular-ring reduced-surface-wave (ISAR-RSW) patch. The capacitor coupled feed method and air layer loaded method are utilized to enhance the impedance bandwidth of the antenna for covering the position and navigation signals of GPS, GLONASS, GALILEO and BD. The feed network of the active antenna is integrated of quadrature TRD coupler. With the use of TRD coupler to feed the SAR-RSW and ISAR-RSW patch, the circularly polarized bandwidth of the antenna is improved. In order to reduce the mutual coupling between the SAR-RSW patch and the ISAR-RSW patch, and improve the anti-multipath performance of the antenna, the mutual coupling reduction technology which is based on the defected ground structure (DGS) is proposed. In addition, the high gain wideband low noise amplifier (LNA) which is based on the RF/DC collinear technology is integrated on the feed network to improve the gain of the active antenna. |
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