A Novel Method to Design Stub-loaded Microstrip Filters with Arbitrary Passband Based on the Reflection Theory and Monte Carlo Method

Abstract

In this paper, a novel method for microstrip filters with arbitrary passband design is proposed. A kind of stub-loaded microstrip filter with asymmetric structure is proposed. The mathematic function of total reflection coefficient at the input port of the filter is derived based on the reflection theory, an ultra-wide-band (UWB) filter which can work from 11GHz to 39GHz is fabricated and measured to verify that our function can calculate the reflection coefficient precisely. The procedure to design stub-loaded microstrip filters with arbitrary passbands is given in this paper, this design procedure is based on the Monte Carlo method. A bandpass filter (BPF) which can work on 7--9.5GHz is designed and measured as an example. The comparison between calculated dimensions and practical dimensions of this filter shows a satisfactory fitting degree. A low-pass filter (LPF) which can work below 4GHz is designed and compared with some prior arts in order to show that our proposed filter is simple in structure and small in size. By using our proposed method, the stub-loaded microstrip filter can be designed quickly and easily. Based on the results mentioned above, we can count that the method proposed in this paper has a good application in microstrip filter design.