Research On Flexible Coplanar Waveguide Microwave Filters Based On Inverted Converter

Coplanar waveguide(CPW) has been taken more and more attention for its advantages such as easy connections in shunt, insensitivity to substrate thickness, and low dispersion effect in the design of microwave and millimeter wave circuits. The CPW filter could get the good performance and make systematic integration easy. The capacitances and inductances in the lumped circuit can be inverted and transformed by inverted converter, and the inverted converter makes it easier to realize the microwave structures for capacitances and inductances, so the inverted converter plays an important role in microwave filter design. With the rapid development of flexible electronic technology, flexible material is gradually used in microwave devices such as filters and antennas to achieve the performance of softness, lightness and film property. It is necessary to study the bending effect on the performance of filters and inverted converters.In this thesis, the normalized admittance/impedance(J/K) values of inverted converters are calculated by using the method of transmission matrix cascading in the microwave network. Then, the relationships between J/K value, negative length and the frequency are obtained. And then six kinds of inverted converter structures are designed based on flexible material, which including gap capacitance J converter, cross inductance K converter, 1/4 wavelength high-low impedance inversion converter, a capacitance J converter, high and low impedance cross K converter. The influence on performance of inverted converter of the curvature is analyzed.Three kinds of coplanar waveguide filters are designed based on flexible material by using several inverted converter structures. The influences of the curvature on the performance including center frequency, relative bandwidth and return loss of microwave filter are investigated.Finally, one of designed filters is fabricated and measured in straight and bending state by Vector Network Analyzer. The measurement results illustrate that there is little change of return loss and insertion loss of filter on the straight and bending state. But there is a shift about 6% on center frequency of filter under bending state compared to the straight state.