Research And Design Of Novel Microwave Devices Based On Coupled Transmission Lines

The coupled structures are important components in RF/microwave circuits and systems. They are used to transmit signals, and to construct also various RF and microwave devices. However, in high-speed and high-density integrated electronic systems, the crosstalk due to the coupled effects within the signal lines must be eliminated. Therefore, in RF/microwave circuits and systems, it is essential to research on the coupled structures and their effects. However, the classic fields researched often focus on couplers and filters, whereas other studies and their applications are comparatively fewer.This paper puts special emphasis on the expanding application areas of coupled structures. It not only provides some novel filters, but also applies the coupled structures to the field of the power dividers. Moreover, the crosstalk within multi-signal lines is investigated, with effective methods of eliminating crosstalk. The main contents are as follows:1. The research on the novel ultra-wideband (UWB) bandpass filter (BPF) based on the fork-form structures. Through modifying on the traditional parallel-coupled two-line structure, the fork-form resonator with good electrical performances is obtained, and the novel filter from the fork-form structure can be designed. Therefore, the traditional coupled structure can be fabricated easily, but also the coupled degree within three lines can be increased so as to extend the operational bandwidth.2. The research on the novel lowpass filter (LPF) based on the broadside- coupled microstrip/coplanar waveguide (CPW) composite structures. Different from the LPF using the traditional microstrip open-circuited branch lines, the hybrid structure integrates the microstrip open-circuited resonators with CPW short-circuited resonators due to the broadside electromagnetic coupling principles, which not only effectively suppresses the high-order harmonics, but increases the width and depth of the stopband.3. The research on the novel dual-band BPF based on the broadside-coupled microstrip/CPW composite structures. The hybrid structures integrate the microstrip open-circuited resonators with CPW open-circuited resonators through the broadside electromagnetic coupling principles. As a result, the filter exhibits good dual-band characteristics, including the low insert loss within the dual passbands, good return loss, and high isolation between dual passbands.4. The research on the novel UWB BPF based on the broadside-coupled microstrip/CPW composite structures. The hybrid structures integrate the microstrip main transmission lines/parallel-coupled open-circuited resonators with CPW open-circuited/short-circuited resonators through the broadside electromagnetic coupling principles. As a result, the filter exhibits good UWB characteristics, including the good return loss, the sharp transition slops from the passband to stopband, and wide and deep stopband attenuation.5. The research on the novel planar six-way power divider based on the microstrip two-line/three-line coupled structures. Through a two-way Wilkinson power divider using the folded two-line coupled structure and two three-way power dividers using three-lines coupled structure hybrid expanded, the six-way power divider obtained exhibits good characteristics, including the wide operational bandwidth, low insertion loss, good return loss and high isolation near the center frequency.6. The research on the crosstalk within multiconductor transmission lines (MTLs) and the methods of eliminating it. Traditionally, there are three methods of eliminating crosstalk, including the terminal matched technology, adding the grounding defended lines between adjacent signal lines, and transforming the microstip layout to stripline one. The effects of these methods, however, were not ideal since they were used often individually. In this paper, a synthetic method of eliminating crosstalk based on the three conventional technologies is presented, and a very good result of eliminating crosstalk within MTLs is obtained.In a word, coupled structures and their coupled effects have wide appications. The novel devices discussed in this paper provide a good basis on the coupled structures and technologies which can apply to RF/microwave circuits and systems, and even practical engineering as well.