.700 Mhz Spiral Duplexer Developed

Diplexer is an important component for channel election and signal synthesis and separation in modern communication systems. Its electrical performances are crucial for communication systems. With the rapid development of modern microwave communication techniques, the spectrum is becoming more and more precious and crowded. The requirements for diplexer with high selectivity, low loss, small size and low cost are increasing, which promotes the deeper research for the microwave filters.In the frequency range of 100MHz-1500MHz, If using lumped element (LC) filters, the Q value is low, the insertion loss is high, although the size of the filter is small; If using the waveguide or the coaxial structure filters, then the size is big; But the helix filter are precisely situated between these two kinds of filters, the Q value can achieve above 1000, insertion loss is lower than the LC filters'; moreover the size of the helix filters are small and can realize narrow bandwidth, the manufacture is easy and so on.Based on these characteristics of the helix filters, this paper has mainly designed a narrow band helix diplexer. Its simulation will be needed very high performance and large memory of computer due to the complexity and specificity of helix structure, but time consuming will be longer. We obtain the size of the diplexer by simulation the coupling coefficient and group delay. Moreover, the development cycle is greatly shortened.The main works are described as follows:1. The paper systematically describes basic concepts and theories microwave filters, explicit design formulas are given for relatively narrowband helix filters, analyze the theories of helix filter emphasizely, discuss the realization of structure and some of questions when design helix filters2. Generalized the initial value of the filter from the theory and formula of filter design3. Using 3D EM simulation software HFSS, slot size and tapping location can be accessed from detailedly analysis size of coupling slot in a resonant cavity helix filter and group delay of each of filters. So we can obtain the size of diplexer. 4. According to the dimension through simulation, processing and tuning the filter which meet the specifications5. Analyze the experimental data...