Differential Signal Propagation in Spoof Plasmonic Structure and its Application in Microwave Filtering Balun

Abstract

In this paper, a filtering balun is proposed based on spoof surface plasmon polariton (SSPP) structure which composes of symmetric H-shaped periodic metallic strip, two types of microstrip-slotline cross-coupling structures and the transition structure between them. The SSPP structure is applied to support odd mode propagation with 180º phase difference and equal magnitude along both sides of the symmetric line, which could transmit the differential signal required for a microwave balun. And then, a new approach for effectively stimulating the odd mode of symmetric H-shaped SSPP structure based on waveguided slotline with a gradient transition structure is proposed and analyzed in detail. In addition, the dispersion characteristic of SSPP can intrinsically bring filtering feature with wide stopband in the balun design. Meanwhile, the two forms of microstrip-slotline cross-coupling structures can not only feed guided wave and realize a pair of balanced ports, but also improve the out-of-band rejection below the objective filtering band. For demonstration, a prototype filtering balun with operating frequency around at 2 GHz is designed, fabricated, and measured. The measured results agree well with the simulated ones which validate the proposed design method and reveal certain advantages of low insertion loss, good amplitude balance and out-of-phase performance as well as the wide stopband. INDEX TERMS Filtering balun, microstrip to slotline transition, odd mode, spoof surface plasmon polariton (SSPP)

Design of compact and broadband filtering balun based on N-shaped spoof surface plasmon polaritons

“…Due to the features of slow-wave effects, controllable dispersion properties, and lowpass transmission, a great variety of microwave passive devices are developed based on SSPP, including power dividers [13,14], BPFs [15,16,17,18,19,20], and filtering power dividers [21]. To date, multiple SSPP filtering baluns have been reported [22,23]. In [22], researchers proposed two filtering baluns based on the double-layer SSPP and the loading via holes.…”

“…Nevertheless, these filtering baluns suffer from bulky sizes. In [23], a novel wide stopband filtering balun is proposed by using the odd mode of symmetric SSPP strip, but its bandwidth needs to be improved. In [24], a broadband filtering balun based on odd-mode SSPP is reported.…”

“…Although it achieves an ultra-broad fractional bandwidth (FBW) of 99.24%, it occupies a large physical space and cannot reach an effective bandpass filtering response. In addition, the SSPP waveguides in [22,23,24] consist of conventional rectangle-shaped unit cells, so there is limited freedom to regulate the dispersion characteristics. Moreover, it is necessary to miniaturize the sizes of rectangle-shaped SSPP unit cells [25,26].…”

Plasmonic dual-band waveguide with independently controllable band-notched characteristics

“…1) Spoof SPPs also have excellent characteristics of SPPs, and their dispersion characteristics can be freely controlled by changing the geometric parameters of the waveguide, which provides a new method for manipulating surface electromagnetic waves. Due to the strong surface field localization, no diffraction limit as well as wide working bandwidth, a large number of plasma waveguides have been designed, [2][3][4][5][6][7][8][9][10][11][12][13] namely, the designed surface plasmon polaritons (DSPPs), to be applied in ultra wide-band microwave communication.…”

A Novel Low-Profile Phased Antenna With Dual-Port and Its Application in 1-D Linear Array to 2-D Scanning

“…In general, the electromagnetic energy of the leaky-wave antenna propagates in one direction, by adjusting the phase constant and the periodic structure to realize the energy is being leaked and radiated from the slot structure [28]- [32]. The spoof surface plasmon polaritons (SSPPs) structures are widely used in microwave equipment, such as antennas [35], [36], filters [37], [38], and metasurface [39]. To improve the performance of the wide-angle beam scanning, This work is licensed under a Creative Commons Attribution 4.0 License.…”