Design Of Wideband Differential-fed Microstrip Patch Antennas Based On Multimode Resonance

With the rapid development of modern wireless communication technology,the integration of communication systems is getting higher and higher.This also puts forward the new request to the modern antenna.Microstrip patch antennas,as a resonant-type antenna with low profile,light weight,and easy to conformal to the structure,have been widely used in various wireless systems.However,in the communication system,the RF front-end usually uses differential signal processing technology,which has the advantages of easy identification of small signals and strong anti-interference ability.Therefore,when using a traditional single-port antenna as a system load,an additional conversion balun is needed.The differential microstrip patch antenna proposed in recent years solves the contradiction between the differential RF front-end and the single-port antenna.It removes the conversion balun and eliminates the loss and extra costs.The antenna is driven directly by the differential signal.However,as a resonant-type antenna with a high Q,the operation bandwidth of the microstrip patch antenna is usually narrow,and the typical value is 5%.Based on this background,this thesis mainly studies the differential-fed patch antenna based on multimode resonance technology,focusing on the bandwidth expansion of the antenna.The researches of this paper are as follows:1.A broadband differential microstrip patch antenna with multiple parasitic mode resonance:The antenna is consisted of a quarter-wave microstrip-line resonator,rectangular parasitic patches and a pair of complementary split-ring resonators.First,a quarter-wave microstrip-line resonator is introduced as a capacitive coupling feeding structure which can generate a non-radiative resonant mode.Second,a set of rectangular parasitic patches is loaded co-planarly along the non-radiative edges of the DMPA.Thus,a parasitic radiative mode at the high side of the operation band is added.Then,a pair of CSRRs is etched on the ground beneath the feeding lines,which has compensated the mismatched impedance of the DMAP at the low side of the operation band.Since the resonant modes mentioned above do not belong to the inherent modes of the microstrip patch antenna,these modes are classified as parasitic modes in this thesis.In the end,the simulated and measured results show that the antenna achieved a wide bandwidth of 26.7%(5.35GHz to 7GHz)at the profile of 0.051center frequency wavelengths,and achieved a stable gain(7.7dBi to 10.7dbi)without any air gaps introduced.2.A broadband differential-fed microstrip patch antenna with 5.8 GHz WLAN band-notched under quad-mode resonance:The antenna consists of two hybrid shape radiation patches and a pair of capacitances loaded loop(CLL)resonators.The broadband performance is achieved by integrating TM₁₀ and TM₀₁ radiation modes of rectangular patches and TM_1,0,-1 radiation mode of triangular patches.Then these three radiation modes are adjusted close to each other to form a wide operation band.After that,with the loading of CLL resonators,a nonradiative resonant mode is introduced.Thus,the low-frequency band of the proposed antenna can be further expanded,and a frequency notch point is introduced in 5.8 GHz WLAN band.Finally,the proposed antenna is fabricated and measured.The measured impedance bandwidth is about 43.5%(5.93 GHz-9.23 GHz)while keeping a compact structure without any air gaps.Additionally,the broadside gain is varied from 4 dBi to 6 dBi with a notch point at 5.8 GHz.3.A quad-mode wideband differential-fed microstrip patch antenna with radiation patterns reshaped:Based on the traditional rectangular microstrip patch antenna,the radiation patch is etched with multiple slots and loaded with shorting pins.With this arrangement,the TM₁₀?TM₃₀?TM₁₂?TM₃₂ modes of the antenna are excited.The bandwidth of the proposed antenna is 4 times wider than that of the traditional single-mode resonant patch antenna.In this thesis,an antenna array is used to explain the radiation nulls of the high-mode in broadside,and the principle for the correction of radiation null is given according to this array model.The measured results are in good agreement with the simulation ones.The antenna achieved a wide bandwidth of 29.4%(3.22GHz to 4.33GHz)at the profile of 0.058 center frequency wavelengths.The in-band broadside gain of the antenna is stable,and there is no radiation null in broadside.The cross-polarization of the antenna is below-20dB.