The Design And Research Of Novel Ultra-Wideband Coupler And Filter Miniaturization

With the rapid development of microwave technology,the demands for microwave passive components,such as filters and directional coupler,used in microwave communications,microwave navigation,remote control,satellite communications and military electric countermeasures are increasing.Because of increasing radio communications users,the frequency resources become increasingly stringent.The frequency space assigned to the various types of communication systems becomes more and more dense.In order to cope with the increasing demand for capacity in restricted spectral bandwidths,filter structure tends to use the form of cross-coupling which is based on the general Chebyshev functionf.The interposition of cross-coupling between cavities can lead a transmission zero,so to increase the steepness of cut-off frequency and enhance the superiority of filters.The use of cross-coupling filter can reduce the filter order,the insertion loss and band distortion.Comparing with the direct coupling filter of the same suppression,the corss-coupling filter has a good implementation of filter miniaturization.Directional coupler as an important component in microwave systems have a wide range of applications,such as mixers,amplifiers,modulators and an antenna system to merge or separate the phase othogonal signals,or to extract monitor signal for monitoring circuit.However,there are many defects in the production by using the traditional parallel-coupled line to realize the strong coupling.In this paper,it is presented a new type of sublayer-type coupling structure parallel line to break through the limitations of manufacturing process.This new structure is realized by adding the underlay conductor under the edge-coupled stripline and paralleling with it for same length.The design and fabrication method of a 6-dB coupler worked in ultra-wide band from 0.35GHz to 3.8GHz have been stated in detail.The coupler has 5 sections comprising two sections of using underlay structure and three sections of using conventional stripline.The capacitive open-line is loaded to the coupler with discontinuity of striplines for compensating circuit.This method can improve the circuit's match performance and reduce the component's return loss.Filter design is based on Chebyshev filter synthesis,and focuses on the miniaturization of cross-coupling filter by synthesizing with network forms and step-impedance resonator.After systematicly discussing the fundamental characteristics of step-impedance resonator.An analysis of the generalized Chebyshev transfer function and synthesization of prototype network corresponding to both of symmetric and asymmetric distributions then follow.A filter with center frequency of 2GHz and bandwidth of 50MHz is designed in the cross-coupling case.The experiment result shows the feasibility of the design.The design reduces the filter volume by 30%.