Investigations On Absorptive Differential Microwave Devices And Antennas

With the rapid development of integration and clock frequency in modern electronic circuits and systems,the problems of electromagnetic interference and signal integrity have been becoming serious.Therefore,electromagnetic compatibility has been a key factor which restricts the performance improvement for integrated circuits or systems.Owing to the anti-phase characteristic,differential transmission scheme has been widely employed in high-speed digital circuits to improve its immunity to crosstalk,electromagnetic interference and external environmental noise.Moreover,differential feeding scheme also has promising applications in radio frequency system and antenna designs.The differentially fed radio frequency front-end shows the advantages of low parasitic radiation,harmonic suppression,high linearity and large dynamic range.Besides,the differential antenna exhibits low cross-polarization level and could be directly integrated with the differential circuits and systems without extra balun,thus reducing insertion loss and improving integration for systems.Due to the advantages of differential transmission or feeding technology,this dissertation proposes a series of differential microwave devices and antennas for different engineering applications.The main research contents are given as follows.(1)A resistor-free absorptive wideband common-mode(CM)filter is proposed.The proposed filter could well protect the signal integrity of differential signals within 8 GHz,and absorb the electromagnetic energy of CM signals in specific frequency bands.Therefore,the electromagnetic interference problem caused by CM signals in high-speed digital circuits could be solved thoroughly.In this design,the inherent conductor loss and dielectric loss of the complementary split ring resonator(CSRR)is utilized to absorb the destructive CM energy around resonance frequency,leading to CM absorption without loading lumped resistors.As a result,the proposed filter shows the advantages of simple design,easy fabrication and potential mass applications in high density circuits.In addition,a perturbation technique is proposed to broaden the CM absorption bandwidth by perturbing the physical dimensions of adjacent resonator elements in a CSRR array.In this dissertation,the CM absorption mechanism of CSRR is studied,and its lossy even-mode equivalent circuit model is established.The extraction formulas for key circuit parameters are derived by matching CM full-wave simulation results to Butterworth low-pass response.The measured mixed-mode S-parameters and the differential eye diagrams under different data rates demonstrate that the proposed CM filter could achieve good differential mode transmission and wideband CM absorption simultaneously.(2)A differential dual-mode patch antenna with wideband CM absorption and its array are proposed.This antenna exhibits differential dual-mode radiation,which could broaden the narrow impedance bandwidth of traditional patch antenna caused by high quality resonance of fundamental mode.Meanwhile,due to its wideband CM absorption performance,the proposed antenna could thoroughly solve the electromagnetic interference problem caused by CM signals in the front-stage differential circuits.In this dissertation,a novel differential feeding network is proposed by adding an absorptive stub in the symmetric plane of traditional balanced microstrip structure.In addition,the co-design of T-shaped coupling aperture and the patch with stepped widths makes the proposed antenna operate under TM01 and TM11 modes.However,the orthogonal polarization currents of TM11 mode contribute to the frequency-dependent pattern tilt in H-plane.Subsequently,a 2×4 planar array is proposed to reduce the H-plane pattern tilt.The measured results demonstrate that the proposed array exhibits differential dual-mode radiation performance,wideband CM absorption and stable broadside radiation patterns.(3)An ultrawideband differential tapered slot antenna with reflectionless band-notch response is proposed to thoroughly solve the interference problems between ultrawideband communication systems and narrow band wireless systems.Under the differential mode excitation,the split ring resonator array loaded on the back side of the tapered slot could be excited effectively,and then its inherent conductor loss and dielectric loss are utilized to absorb the electromagnetic energy of reflected signals in the notched band.In this scenario,the reflectionless band-notch gain response could be realized without increasing circuit size,and the destructive influence of the reflected signals on the front stage active module could be eliminated.This dissertation investigates the effect of different coupling schemes on the absorption performance of dual resistor-free split ring resonators,and the lossy equivalent circuit model is established to explain the absorption mechanism.To improve the absorption bandwidth and efficiency,one-dimensional and two-dimensional magnetoinductive waveguides made up of split ring resonators are proposed,and their dispersion relationships are analyzed by means of equivalent circuit model to predict the notched band.Furthermore,a wideband balanced transmission structure is proposed,which could support the transmission of wideband traveling wave slot mode under differential mode excitation and exhibit inherent CM suppression.On the basis of the proposed transmission structure,a differentially fed tapered slot antenna loaded with magnetoinductive waveguides is proposed with a reflectionless band-notch response.(4)A tri-band bandpass filter based on multi-mode spoof surface plasmon polaritons(SSPPs)is proposed to meet the demand of multi-band communication in modern wireless communication systems.The novel multi-mode SSPPs unit-cell is constructed by a pair of single-conductor coupled stubs,which breaks the limitation of single mode under the cut-off frequency of traditional SSPPs transmission structure.In this scenario,a notched band could be introduced under cut-off frequency without loading extra resonators,leading to the dual-band bandpass response.In addition,the multi-mode SSPPs unit-cell could be considered as a combination of multiple split ring resonators at self-resonance frequency,which could construct a one-dimensional magnetoinductive waveguide.Therefore,the resonant tunneling effect could be realized above the cut-off frequency of the traditional SSPPs transmission structure,contributing to the third passband.This dissertation investigates the dispersion relationships of the proposed multi-mode SSPPs,and the influence of key geometric parameters on the multi-band response and low cutoff frequency.Furthermore,an equivalent circuit model is established for the proposed filter to reveal its physical mechanism.The measured results demonstrate that the proposed SSPPs filter has achieved good tri-band bandpass performance.This dissertation provides novel ideas and methods for the design of differential microwave devices and antennas,which has promissing applications to solve electromagnetic interference problems in high speed digital electronic circuits and radio frequency systems.