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On The Communication And Navigation Antennas For The Special Applications

Posted on:2015-06-04Degree:DoctorType:Dissertation
Country:ChinaCandidate:C X ChengFull Text:PDF
GTID:1108330464468887Subject:Electromagnetic field and microwave technology
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The research works are made with scientific projects. The design problem of conformal antenna for communication, handheld terminal navigation antenna and multi-band/multi-polarized communication antennas are discussed in this dissertation.The research works involved can be divided into four parts: the design and development of the wearable conformal vest antenna arrays constitute the first part; the second part represents the scheme of the design of handheld terminal navigation antenna; the third part represents the design and development of broadband navigation antenna with high phase center stability; the engineering samples of several communication antennas with multi-band and multi-polarization are proposed in the fourth part, which includes high-isolation dual-frequency orthogonally polarized patch antenna, polarization diversity antenna and tri-band omnidirectional circularly polarized antenna. The main research works of the dissertation are outlined as follows:1. Research on the wearable vest of conformal antenna. Combined with the design requirements, the software Ansoft HFSS is used to design the wearable vest of conformal antenna. On the basis of simulation, the antenna prototype is fabricated. The measured results show that the antenna prototype can be completely conformal with the garment and has a VSWR of less than 2 and a gain of 6d B in the working frequency band. Its radiation pattern is omnidirectional(out-of-roundness≤5d B) in azimuth plane and "∞" in the elevation plane with forward beamwidth narrower than the backward. All the results can satisfy the design requirements.2. In the design of handheld terminal antenna, three and five antennas schemes are compared. The comparison results show that the VSWR and gain of three antennas scheme can satisfy the design requirements, but its isolation( about 10 d B) cannot satisfy the design requirement(≥15d B) and its 3d B beamwidth(≥72°) and axial ratio(≤8.4d B) within 3d B beamwidth cannot satisfy the design requirement. The VSWR, gain and isolation of five antennas scheme can satisfy the design requirements, but its 3d B beamwidth( ≥81°) cannot satisfy the design requirement( ≥120°) and its axial ratio( ≤10.5d B) within 3d B beamwidth cannot satisfy the design requirement( ≤5d B); Therefore, five antennas scheme is chosen to be further optimized in the following design. The optimized antenna has a VSWR of less than 1.6, a gain of more than 2.7d Bat the normal direction in the Beidou band, a gain of more than-2.8d B at an elevation of 15 degrees in the Beidou band, a gain of more than 3d B at the normal direction in the S band, a 3d B beamwidth of more than 120°, an axial ratio of less than 5d B within the 3d B beamwidth and an isolation of more than 15.9d B, which all satisfy the design requirements.3. Combined with the design requirements of multi-mode satellite navigation antenna, a antenna with high phase center stability is proposed. It can cover L1 and L2 bands of GPS and B1 and B2 bands of BDⅡ. On the basis of simulation, the antenna prototype is fabricated and measured. The measured results illustrate that within the operating band, the proposed wideband antenna with high phase center stability has a VSWR of less than 1.8, a gain of more 0.2d B and an axial ratio of less than 2.9d B at an elevation of 90°, a gain of more-5d B and an axial ratio of less than 5.7d B at an elevation of 20°, a front-to-back ratio of more than 15.1d B, a phase center of less than ±2mm and a size of 120mm×76mm×15.3mm, which all satisfy the design requirements.4. In the design of high-isolation dual-frequency orthogonally polarized patch antenna, using two coupling microstrip feed lines to excite two orthogonal fundamental modes in the dual-band. Modified rectangular radiation patch and multilayer configuration contribute to size reduction. The high isolation is achieved by embedding two novel EBG filters underneath the two feed lines to reject the incoming signal from the opposite line. The total size is only quarter of multilayer rectangular radiation patch antenna using common EBG filters with the same performance. The results show that the proposed method improved isolation by more than 20 d B.5. In the design of polarization diversity antenna, a switchable power divider is used to design a polarization reconfigurable antenna operating in 2.4GHz band. The radiation patch is composed of four triangle-shaped elements with T slits. Each triangle-shaped element is fed by one output port of the switchable power divider. The switchable power divider is composed of three Wilkinson power dividers and interconnected with PIN diodes. By controlling the states of the diodes, the antenna can produce different polarization. Its bandwidth especially circularly polarization bandwidth is wider than those of the reference antennas.6. In the design of tri-band omnidirectional circularly polarized antenna, a top-loadedmodified Alford loop dielectric resonator antenna is proposed. The design is based on the principle that when the fields of the electric monopole and magnetic dipole are equal in amplitude with phase quadrature, omnidirectional CP(circular polarized) fields can be obtained. In the proposed antenna, the DRA(dielectric resonator antenna) fed by an axial probe radiates like a vertically polarized electric monopole, and the top-loaded Alford loop provides an equivalent horizontally polarized magnetic dipole. By modifying the top-loaded Alford loop, a tri-band omnidirectional circularly polarized antenna can be achieved.
Keywords/Search Tags:communication antenna, navigation antenna, conformal, wearable, wideband, high phase center stability, dual-band orthogonally polarized, high isolation, polarization reconfigurable, omnidirectional circularly polarized
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