Research On Several Novel Microwave Passive Devices And A Teraherz Filter

Filters and power dividers/combiners are key devices widely used in communication systems. Their dimensions and property affect the size and performance of the entire communication system directly. Modern communication systems are developed rapidly with smaller sizes, continuously improved performances and broadened operating frequencies. Passive components are important parts that affect the performance of communication systems significantly. It is very important to develop passive components with small profile and high performances. Recently THz technology attracts more and more attentions because of its ability to carry large amounts of information and its huge application value in medical imaging, aerospace and other fields. It is very important to develop passive component in teraherz frequencies.Using novel structrures and process technologies, this thesis focus the studies in several novel passive components including filters and power dividers operating at microwave frequencies and a filter operating at terahertz frequencies. Main contents are summarized as follows:Firstly, a novel defected ground structure(DGS) with two transmission zeros was proposed for the first time. This new structure could improve the selectivity of filters and reduce the circuit size at the same time. A low pass filter was designed with the proposed defected ground structure. Compared with filters constructed with conventional dumbbell defected ground structures, the selectivity of the filter employing the novel defected ground structure improved for eight times. At the same time the stopband performance got better. This proves the effectiveness of the proposed structure.Secondly, a BPF was designed by cascading a microstrip highpass ?lter(HPF)consists of a ladder-shaped transmission line with zigzag slot on the top plane and the open loop DGS on the bottom one and a lowpass ?lter(LPF) constructed by a ladder-shaped transmission line on the top plane and a combined open loop DGS on the bottom one. The ?lter has the great advantage of adjustable passband including both center frequency and bandwidth. The BPF shows good selectivity and stopband performance.Thirdly, power dividers based on novel multilayer SIW coupling structures were developed. The two-way out-phase power divider was based on two-layer substrate integrated waveguides. In the proposed structure, an input SIW in a upper layer is divided into two output SIWs in a lower layer by coupling the energy from a narrow slot etched on the broad side of the SIW. The proposed power divider shows good performance in a wide range of frequency. The out-of-phase power divider exhibits low passband insertion loss in a broad bandwidth. The outputs imbalance is also very good.The proposed structure has advantages of cheap to fabricate, compact in size and easy to integrate with planar circuits.Fourthly, a four-way two-layer SIW power divider based on a novel coupling structure was designed. The SIW divider constituted by two layers, the input energy in upper SIW was coupled through the gap between the two layers of the substrate to four outputs in the lower substrate. The power divider has high efficiency and low insertion loss. Because it was fabricated by PCB processing technology, the power divider has advantages of low cost, simple processing and easy to integrate with planar circuit.Fifithly, A SU-8 based WR-3 band(220–325 GHz) waveguide bandpass ?lter is constructed by three offset waveguide resonators operating at TE101 mode. It is fabricated by thick SU-8 photoresist micromachining technology. This ?lter with Chebyshev response is designed to have a centre frequency of 300 GHz, a fractional bandwidth of 3.3% and a passband return loss of 20 dB. This filter has a structure suitable for teraherz micromaching. The measured insertion loss in passband of the filter is relatively low. Good agreement between the measurement and simulation results of the proposed WR-3 waveguide filter was achieved by taking account of fabrication inaccuracies. Because of its simple structure, this filter has the advantage of being easy to fabricate. This novel filter topology is an alternative choice for terahertz waveguide filters with narrow bandwidths fabricated using layered micromachining techniques.Finally, the research work is summarized, and look forward to the next step of the research work.