| The research works are made on the basis of scientific projects.Researches on communication smart antenna and antennas for special applications are presented in this dissertation.This dissertation consists of two main parts: First one presents the communication smart antenna,which utilizes new calibration method to achieve wide bandwidth of the circular array for communication smart antenna application.The second part is concerned with the development of antennas for special applications,including missile-borne miniaturized wideband widebeam dual-polarization antennas as well as two wideband circularly polarized antennas and two wideband planar Yagi antennas.The author's major contributions are outlined as follows:1.Wideband circular array for communication smart antenna applicationAccording to the requirements of wide bandwidth and high gain for the smart antenna circular array,we present the design of substituting calibration element for calibration network to achieve wideband property.The proposed array antenna consists of 15 array elements and a center calibration element.An omnidirectional high-gain double-sided printed dipole is used as the array element,while a conventional rotational symmetrical dipole is employed as the calibration element.After beam forming,stable array gains and side lobe levels could be obtained.Based on the studies above,the prototype of the array antenna,the antenna radome for the array antenna and one-to-fifteen coaxial radial waveguide wideband power divider are fabricated.Measurement results reveal that the proposed array element can provide an impedance bandwidth of 38.3%,while the impedance bandwidth of the calibration element is 15.4%.Within the required operating bandwidth of 12.8%,the 3-dB beamwidths and the horizontal deviation angles in elevation planes of the radiation pattern for the array element are greater than 25° and less than 6°,respectively.Meanwhile,the element gains are greater than 7 dBi.The phase and amplitude matching of the coupling coefficients between the calibration element and 15 array elements are less than 7.2° and 1.2 dB,respectively.In addition,when the array antenna works as an omnidirectional transmitter,the gain variations and gains in azimuth planes of the radiation pattern are less than 3.1 dB and greater than 3.1 dB,respectively.All of the resuls meet the design requirements.2.Missile-borne miniaturized wideband widebeam dual-polarization antennasMiniaturized wideband widebeam dual-polarization antennas applied to missile-borne installment environment include two S/C-band transmitting/receiving antennas and two X-band transmitting/receiving antennas,which are both with the transition section of missile cabin,while locating in separate bulkheads with different cone angles.According to the requirements of miniaturization,low profile,broad bandwidth,wide beam as well as strong ability to resist vibration and pressure,four transmitting/receiving antennas operating at S/C-band and X-band and their antenna radomes are designed and fabricated respectively.Measurement results reveal that the proposed S/C-band transmitting/receiving antennas have VSWRs of less than 2.6 within the required operating bandwidth of 78.7%,and the circular polarization gains are greater than-5.0 dB across both ±60° beam coverage in rolling planes and 20°~110° beam coverage in elevation planes.Meanwhile,the proposed X-band transmitting/receiving antennas have VSWRs of less than 1.9 within the required operating bandwidth of 40%,and the circular polarization gains are greater than-4.9 dB across both ±60° beam coverage in rolling planes and 30°~110° beam coverage in elevation planes.Additionally,the proposed S/C-band and X-band antennas have heights of 26 mm and 26.2 mm respectively,and they are installed in a metal cavity which is sturdy in structure to meet the requirement of strong ability to resist vibration,and their antenna radomes meet the requirement of strong ability to resist pressure simultaneously.All of the resuls meet the design requirements.3.Wideband and miniaturized CPW-fed circularly polarized square slot antennaThe proposed wideband and miniaturized coplanar waveguide-fed(CPW-fed)circularly polarized square slot antenna consists of a stepped feeding strip,a modified grounded L-shaped radiating patch,an inverted-L grounded strip and an asymmetric ground with an L-shaped slot as well as two horizontal slots.By loading tapered structures on two ends of the grounded L-shaped radiating patch,the AR bandwidth can be greatly enhanced.Meanwhile,a meandered line is etched on the grounded L-shaped radiating patch to provide a slightly longer pathway for the current,which equivalently miniaturizes the antenna size.Measurement results reveal that the proposed antenna can provide an impedance bandwidth of 106.3%(2.3-7.52 GHz)and a 3-dB axial ratio(AR)bandwidth of 90.2%(2.25-5.95 GHz).The proposed antenna can not only be used in the Wi-Fi(2.4/5.2/5.8 GHz)and WiMAX(2.5/3.5/5.5 GHz)systems,but also provide the potential to implement multiservice transmission in wideband wireless communication systems.4.Wideband circularly polarized SIW cavity-backed antennaThe proposed wideband circularly polarized substrate integrated waveguide(SIW)cavity-backed antenna is designed to be double-layered stacked structure,consisting of a modified inverted-T feeding stripline,an improved circular SIW cavity and a conventional perturbed circular patch radiator.The proposed antenna employs indirect stripline-to-SIW feeding transition structure,hereby exciting the perturbed circular patch radiator with proximity coupling method.Furthermore,the horizontal portion of the inverted-T stripline employs tapered structure,which significantly enhances the AR bandwidth of the proposed antenna.Measurement results reveal that the proposed antenna can provide an impedance bandwidth of 22.1%(4.94-6.17 GHz)and a 3-dB axial ratio(AR)bandwidth of 18.7%(5-6.03 GHz).The proposed antenna can not only meet the need for certain Wi-Fi(5.2/5.8 GHz)and WiMAX(5.5 GHz)band communication application,but also be applied in wideband wireless communication systems.5.Planar wideband and miniaturized double-sided printed quasi-yagi antennaThis design substitutes conventional balun for microstrip-to-slotline transition balun to achieve wider bandwidth and relatively smaller size for the proposed planar quasi-Yagi antenna.The proposed planar quasi-Yagi antenna consists of a conventional feeding balun,a concave arc-shaped reflector,a modified driver with stacked structure and two directors.The driver dipole is designed to be double-layered stacked structure,which greatly improves the impedance and pattern bandwidths of the proposed antenna.Meanwhile,a concave arc-shaped reflector is employed instead of a conventional straight reflector,which facilitates the miniaturization of the proposed antenna.The proposed antenna achieves a measured operating bandwidth of nearly 100%(2.02-6.05GHz).6.Wideband and miniaturized microstrip magnetic dipole Yagi antennaThe proposed wideband and miniaturized microstrip magnetic dipole Yagi antenna consists of a reflector,a driver with backed soldered SMA connector,a coupling microstrip line with three rectangular slots and three modified directors.By symmetrically loading three pairs of metal shorting walls on the three-stage director,both impedance and pattern bandwidths are greatly enhanced.Meanwhile,three rectangular slots are symmetrically loaded on the coupling microstrip line so as to further enhance the impedance bandwidth.The proposed antenna achieves a measured operating bandwidth of 19.2%(4.95-6GHz). |
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