Study On The Design Of Elliptic Function Bandpass Filters Constructed On Multilayer Substrates

Microwave filters can be designed using distributed-elements or lumped-elements. Thedistributed-element filters are featured with good performance and large size while thelumped-element filters are featured with tiny size and average performance. Moreover, theincreasing working frequency makes the design of lumped-element filers harder and harder. As aresult, it is the constant theme to design filters with high performance and tiny size. The multilayersubstrate structure is a promising way to realize this goal because the designer can design tinylumped-capacitors and lumped-inductors in multilayer way. Therefore, the size is not a problemanymore and the performance is focused on. Elliptic function bandpass filter, which has a highperformance in selectivity, is suitable for designing in multilayer way because it is only composedof serial LC resonators or parallel LC resonators. In this thesis, elliptic function bandpass filterconstructed on multilayer substrates is fully discussed and the contents are listed as follows:(1) Starting from the third-order elliptic lowpass prototype, the final bandpass filter circuitmodel is obtained and each parameter is analyzed to determine their influences on overallperformance. The way of tuning bandwidth is discussed. Meanwhile, it is found that when fixingthe resonate frequency of all resonators and changing the capacitances in the scale of±20%(inductances are also changed to keep the resonate frequency), the overall performances still meetthe requirements.(2)Based on the circuit model, a new compact multilayer substrate structure layout is proposed.Meanwhile, the sizes of each component are analyzed to determine their influence on overallperformance. It is also found that when fixing the resonate frequency of all resonators and changingthe sizes of capacitances in the scale of±20%(inductances are also changed to keep the resonatefrequency), the overall performances still meet the requirements, which is agreed with circuitsimulation results.(3) For experimental verification, two filters with different bandwidth are designed, fabricatedand measured. All the measured results are in accordance with simulated results, showing goodoverall performance.