Research On A Novel Sequential Rotating Quadruple Feed Microstrip Antenna And Its Phased Array

The reader terminal antenna is a conversion device for collecting and transmitting signals in the ultra-high frequency（UHF）Radio Frequency Identification（RFID）system,and its performance is critical to the communication quality of the system.The reader terminal antenna needs to have the performance of polarization-insensitive,high gain and strong directivity.And it needs to realize the functions of accurate positioning,long recognition distance and wide area.Therefore,this thesis studies the reader antenna in the UHF RFID system,and improves the performance of the reader through phased array technology.The thesis’s main work are as follows:（1）A novel circularly polarized antenna with integrated design of sequential rotating quad-feed network and microstrip patch was proposed.This antenna was used as the UHF RFID reader terminal antenna.Following consideration of the complexity of the process and the performance of the antenna,the excited patch and the feed network were designed in a coplanar manner.The stacked microstrip structure was used to produce dual resonance to expand the impedance bandwidth and improve the antenna gain.A circular hole was subtracted in the center of the excited patch to improve the impedance matching characteristics of the antenna.The ground bending structure was used to reduce the horizontal size of the antenna,while reducing the antenna’s backward gain and improving the forward gain.The quadruple feed network which was coplanar with the excited patch was applied to expand the axial ratio bandwidth through sequential rotation technology,and obtain a symmetrical circular polarization pattern for the antenna.The test results show that|S₁₁|is lower than–10 d B and the axial ratio is less than 3 d B within the frequency band of 884～969MHz.The antenna gain is 8.3 d Bic at the designed center frequency of 915 MHz.The antenna gets the advantages of excellent performance,compact structure and convenient processing.（2）A power division and phase-shifting feed network applied to the phased array was designed,which was used for beam forming and beam scanning control of the phased array.It included a miniaturized four-way unequal power division feed network and four analog phase shifters.The design of the power divider realized the miniaturization of the power branch circuit by loading the compensation capacitor,and used the stepped impedance converter to realize the miniaturization of the output branch circuit.SMV1763 varactor diodes were used in the design of the analog phase shifter,and the phase shift range of the phase shifter was widened by the cascade method.The power divider and phase shifter were integrated and processed into a feed network.The test results show that in the 850～950 MHz frequency bands,|S₁₁|is lower than-10 d B as the control voltage changes.The output amplitude of the feed network meets the excitation requirements of the antenna array.In the voltage range of1.7 to 5.35 V,the phase variation of the feed network at the center frequency of 915MHz is238 degrees.（3）A four-element nonuniform diamond antenna array was designed,whose array elements adopted the proposed novel quadruple feed microstrip antennas.The antenna array was a diamond-shaped structure with nonuniform space,whose direction of the array axis was equal to three array elements.This not only ensured the beam scanning angle but also relieved the working pressure of the phase shifter.Two array elements were placed side by side in the middle of the array axis.When scanning a large angle,it ensured good circular polarization performance of the antenna array.The amplitude distribution of 1:2:2:1 was adopted in the array for beam forming.The sidelobe level was reduced by this distribution method.At the same time,it avoided the situation that the feeder line width was too thin due to high power division ratio.The coaxial cables were used to combine the power division and phase-shifting feed network and the antenna array,and finally a phased array was obtained.The test results show that during the beam scanning process,|S₁₁|is lower than-10 d B in the frequency range of 867～1012 MHz.This shows that the phased array has superior impedance matching performance.At the center frequency of 915 MHz,the phased array achieves the beam scanning in the range of 48 degrees and the gain at the maximum radiation direction is greater than 10 d Bic.At the same time,the axis ratios at vertex of the main beam are all lower than 3d B,which shows that the phased array has superior circular polarization performance.