Design And Research On Flexible LCP Coplanar Waveguide Microwave Filters Based On Inverter

Coplanar waveguide(CPW) has numerous advantages over other planar transmission line such as low dispersion, small parasitics, compact structure, great flexibility, especially in microwave and millimeter wave band, so it has been widely used in the design of modern microwave filter.The capacitances and inductances in the lumped circuit can be transformed by inverter, and inverter make it easier to use microwave structure for designing filter. With the development of flexible electronic technology and popular wearable devices, flexible material is gradually applied to various microwave devices. Inverter and filter designed in this paper are composed of liquid crystal polymer(LCP) as a substrate. Therefore, this article will focus on the performance of curve filter and performance difference between flat and bend filter.Firstly, the design theory of coplanar waveguide microwave filter based on the inverter is introduced and a method for computing the performance of an inverter under flat and bending condition is proposed. This method based on microwave network parameters, combined with simulation of HFSS and data processing of MATLAB. With the technology, we can get the performance of the concrete structure of inverter and study the effect of bending substrate on the performance of the inverter.Secondly, we propose two novel coplanar waveguide inverters, namely enhanced cross inductor K inverter and stub capacitance J inverter. The design rules and performance of these two kinds of inverters are analyzed and summarized by using the method of solving the performance of the flat inverter. By using the method which computes the performance of the inverter under bend state, the effects of bending on the performance of the inverter is analyzed and summarized and prepare for analyzing of curve filter.Finally, according to the design theory of microwave filter, we designs three CPW bandpass filter which is based on liquid crystal polymer by using inverters. In order to verify the correctness of the design, these filters were processed, and measured in a flat, curved condition respectively. The effect of curve on the performance of coplanar waveguide microwave filter,such as the center frequency, insertion loss, return loss, and 3dB bandwidth, is analyzed from the perspective of attenuation constant, port impedance and bend inverter. The difference between simulation and measurement is analyzed from dielectric loss tangent and measuring process.