| Microwave filter as an important element in the wireless communication system, it has the property of frequency selective transmission, which enables it to transmit energy in one or more passbands and to attenuate energy in one or more stopbands. With the continuous development of wireless communication, there are less and less spectrum resource can be used, and the frequency interval between assigned to all kinds of communication systems become more and more close, so the filter must have a higher performance to satisfy the demand. Dielectric resonator(DR) cavity filters have the advantage of high external unloaded Q, low insertion loss, high power capacity and compact size, therefor it is very necessary to research it, and possess important significance.Firstly, the background of DR filters and other microwave filters are briefly introduced, and the domestic and international status of the DR filters are simply analyzed and summarized; And then briefly introduce the basic theory of filter and the designing of bandpass filter based on coupling resonator.Secondly, according to the working mechanism of dielectric resonator, whose features and advantages are analyzed, including high-Q value, compact size, small temperature coefficient, and so on. Circular TEO1δ mode DR is analyzed intensively, including the distribution of electromagnetic field, and spurious suppression by the proportion of the DR. According to the mode chart, we get the optimal proportion of the DR to suppress spurious. Then analyzed the single DR cavity, coupling between two cavities and port coupling, wherein electric coupling is made of S-shape metal arc to enhance the coupling coefficient. A cross-coupling dielectric resonator cavity bandpass filter is designed and simulated, which is used in the wireless base station. The filter’s center frequency is2.6GHz, and its bandwidth is50MHz. The results of simulation show that the return loss in the transmission band is under18dB, and the insertion loss is less than0.4dB. At the same time there are four transmission zero in the stopband, and the size of single cavity is only30.3mm X30.3mm X26mm, meet the application requirements of the base stationFinally, the characteristics of the coaxial cavity resonator is briefly analyzed. The electromagnetic wave in the coaxial cavity resonator only work in the TEM mode, so when using a quarter wavelength coaxial cavity resonator, the first high-order mode is appear at the frequency corresponding to3/4/λ wavelength, that is to say the first high-order mode frequency is three times of the fundamental resonator frequency. This shows the coaxial cavity resonator has low spurious response, which is not possessed by dielectric resonator. At present, a spurious-free region up to the second or third harmonics is usually required for communication systems, thus if we can combine the advantage of dielectric resonator with coaxial resonator, and design a hybrid coupling filter, that will both maintaining a relatively high-Q and low spurious response. Therefore, it is necessary to study DR-coaxial hybrid filter. After analyzing the electromagnetic field distribution of the coaxial cavity resonator, it is found that there is a coupling between DR and coaxial cavity resonator, and the coupling coefficient can be controlled by changing the size of the window. At last, a hybrid filter is Successfully designed, which not only has a high-Q, but also low spurious response. |
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