Research Of Microwave Passive Devices Based On Spoof Surface Plasmon Polaritons

In recent years,massive applications based on Spoof Surface Plasmon Polaritons(SSPPs)have been proposed.By loading the periodic holes or slots in the metal strip,the electromagnetic energy can be tightly confined to the metal-medium interface,and exponentially attenuates in the normal direction.The characteristics of strong field confinement,adjustable high-frequency cut-off frequency,dispersion characteristics,compact structure and easy conformal make SSPPs have broad application prospects in the field of microwave and millimeter waves.By studying the principle of Spoof Surface Plasmon Polaritons,a delay lines for real-time analog signal processing,filter and filtering antenna are designed respectively in this paper.All of these designs have been fabricated and measured.And the measured result shows good agreement with the simulated one.The main contents are summarized as follows:(1)Designed and fabricated a reflective delay line for real-time analog signal processing system.The delay line is composed of a section of SSPPs transmission line and a reflection frame.The dispersion characteristics of the SSPPs transmission line enable it to achieve high resolution in a compact size: the slope of the group delay time relative to the frequency can reach 8.5ns/GHz.By modulating the SSPPs transmission line and controlling the geometric size of the reflection frame,the working frequency band and the maximum group delay time can be controlled.(2)A band-pass filter has been designed and fabricated.The band-pass filter is composed of a pair of SSPPs transmission lines and a pair of L-shaped coupling branches.The whole structure is symmetrical.The passband can be controlled by modulating the length of the SSPPs transmission line,the dispersion of SSPPs unit and the geometric parameters of L-shaped coupling branches.It overcomes the problem of excessive bandwidth of the previous filter,the relative bandwidth is only11.2%.Meanwhile,the in-band rejection is below-12 d B and the out-of-band rejection is below-15 d B and the insertion loss is less than-1.5d B.Furthermore,it has a quite compact structure.(3)Designed and fabricated a filtering antenna.The end-fire antenna based on SSPPs naturally has a long feeder line,which is very suitable for adding some filtering structures.The antenna part adopts three pairs of bow-tie radiating elements with different sizes of sector-shaped patch distributed according to logarithmic period.The "?" shaped directors are introduced to make it has a better end-fire characteristics and gain.Metal through holes and patches are loaded at the end of the SSPPs transmission line to achieve low-frequency rejection,while combining ?-shaped patches symmetrically distributed along the SSPPs TL with the high-frequency cut-off characteristics of SSPPs transmission lines to achieve high-frequency rejection.Thus,the upper and lower cutoff frequencies of the passband can be individually modulated.The gain of the filtering antenna in passband is 8.5d B.Meanwhile,within 500 MHz close to the edge of the passband,the rejection at low frequency is-2d B while the rejection at high frequency is-7d B,which shows a good roll-off coefficient.