Research And Design Of Microstrip Filtering Antennas Based On SIR

With the development of RF devices in modern communication systems towards miniaturization,integration and portability,filters and antennas as the most important two parts of the RF front-end circuit,respectively play the role of frequency screening,receiving and transmitting electromagnetic waves,the integration of the two parts of the circuit be raised higher requirements.The traditional design method is to design the filter and the antenna separately and then cascade these two components by employing additional impedance matching network,which would not only enlarge the entire volume but also increase the insertion loss.Based on the research of the filters,the integration of the filters and antennas as a single module has gained an increasing attention in the antenna research.The filtering antenna with both filtering and radiating function has many advantages such as miniaturization,improved performances and so on.In this thesis,two bandpass filters are analyzed and designed based on the stepped impedance resonator(SIR)theory.Furthermore,a single-band and dual-band filtering antennas are designed according to above analysis.The main research contents are as follows:Firstly,based on the traditional SIR,transmission zeros are successfully introduced to achieve the performance improvement of the bandpass filter by adding two short-circuited vias,which is much simpler and more compact in structure than those of the traditional SIR.Based on the above proposed bandpass filter,the filtering antenna is realized by cascading the proposed filter and the designed single-frequency inverted L-type antenna.A single-band bandpass filter with a center frequency of 5.2GHz,an insertion loss of 1.32 d B,and a 3d B fractional bandwidth of 19.2%,and a filtering antenna with a center frequency of 5.2GHz,a minimum reflection coefficient of-25.2d B,and a maximum gain of 4.2d Bi are achieved.The filter and the filtering antenna can be applied in a 5.2 GHz frequency band of the WLAN(Wireless Local Area Network).Secondly,based on the traditional SIR,an open-circuit stub-loaded SIR resonator is studied and proposed by analyzing the resonant characteristics through utilizing the even-odd mode theory.A dual-band bandpass filter with transmission zeros is designed and realized through the way of proximity coupling-slot feed.Furthermore,a dual-band filtering antenna is successfully realized by replacing one port of the dual-band filter with an elaborately designed dual-band antenna that can be viewed as the third order of the filtering network.Consequently,a dual-band filter with a center frequencies of 2.45GHz/5.2GHz,maximum return losses of 14.7d B/18.7d B,and radiating gains of 3.5d Bi/2.7d Bi are successfully realized.The filter and the filtering antenna can be both applied in a 2.4GHz/5.2GHz frequency band of the WLAN(Wireless Local Area Network).Finally,the proposed two kinds of filters and filtering antennas are fabricated and measured.The transmitting performances of the filters and the radiating characteristics of the filtering antennas are tested by utilizing vector network analyzer and microwave anechoic chamber,respectively.The measurement results are in good agreement with the simulation ones.The two proposed filtering antennas with good selectivity and out-of-band suppression can be a promising candidate in practical applications,and which also provides a solution for the subsequent research and development of microstrip filtering antennas.