| In recent years,with the development of science and technology,terahertz bioimaging technology is an emerging advancing front technology.Terahertz imaging technology can be used to carry out detection research at three different levels:tissue,cell and biological macromolecules.The terahertz system is also developing towards miniaturization and integration.It is usually divided into several different frequency bands for ultra-wideband(UWB)detection system.The key to the integration of the system is the ultra-wideband terahertz multiplexer with continuous frequency bands.A new design method of complementary high-pass/band-pass filter is proposed in this paper,which can be applied to ultra-wideband terahertz multiplexer system with Continuous Frequency Band.The main research contents are as follows:A novel design method of terahertz high-pass filter with broadband,simple structure and complementary characteristics is proposed.The filter is realized by interdigital capacitors and parallel short-circuit stub.First of all,the complementary mechanism of high-low pass filter is analyzed by circuit complementary theory.Second,the component values can be calculated according to the design principle of Chebyshev complementary high-low pass filter.Through the equivalent circuit principle,the microstrip model is established.The calculation formula of microwave frequency band is no longer applicable in terahertz frequency band due to the limitation of processing technology.By analyzing the equivalent circuit,the influence of parasitic parameters caused by oversize items is optimized.The optimized high-pass filter has low loss and a bandwidth of more than 42%.Finally,the high-pass filter is combined with the known low-pass to verify the complementary characteristic.The reflection coefficient of the output port is less than11dB in the whole frequency band after combining,and the loss of the high-pass input end to the output end is 5.2dB at the crossing frequency point,which proves that it has complementary characteristics and can be applied to ultra-wideband terahertz multiplexer systems.A non-stub terahertz bandpass filter with simple structure,broadband and complementary characteristics is proposed.Since the short-circuit branch punching structure technology will make the process complicated in terahertz frequency band,a band-pass filter structure with simpler structure and without vias is proposed,which only requires two interdigital microstrip lines.Its admittance curve also shows complementary characteristics similar to high-pass filters and has a bandwidth of 38%.It is verified by combining it with low-pass filter that the reflection coefficient of the output port is less than-12dB,and the loss of the high-pass input end to the output end is 4.35dB at the crossing frequency point.Compared with the branched high-pass filter,the overall transmission performance is improved,and the structure is more compact.Finally,the terahertz band-pass filter fabricated by Micro-ElectroMechanical System(MEMS)technology in the combiner is tested.The error analysis shows that the test results are close to the simulation results,which has certain reference significance in improving the integration ability of terahertz system. |
