| Wireless communication technology brings about rapid development of the antenna industry. Among many kinds of antennas, microstrip antennas arouse more and more attention because of its many advantages such as light weight, thin profile, low cost, easy and conformal integrated with the active circuitry and so on. New structure of microstrip antennas have been widely used in aircraft antenna, missiles and telemetry, satellite communications, mobile communications, radar, communications and surveillance in battlefield, electronic countermeasures, remote sensing, meteorology and astronomy, biological medicine and many other fields.In recent years, the spectrum resources become more and more shortage, in order to increase the number of channel, we often require introduce new bands, and also need take into account the compatibility of the equipment, so dual-frequency and multi-frequency antennas are needed. Mobile communications, satellite communications, radar, electronic countermeasures, electronic surveillance and interference, and other fields require circularly polarized antennas with high performance. Although microstrip antenna is one dimension compact antenna, in some low-frequency applications, the size of traditional half-wavelength microstrip patch antenna is still too large. Therefore, the study of dual-frequency, dual circular polarization and compact technology on microstrip antenna become the emphasis of this thesis.The first part of the thesis the historical background, features and applications of microstrip antenna is introduced, and the technological research and development actuality of microstrip antenna is recited in details. Mainly cover the following four areas:(1) The compact technology of microstrip antenna;(2) The dual-frequency technology of microstrip antenna;(3) The wide-band technology of microstrip antenna;(4) The circular-polarization technology of microstrip antenna.The second part of the paper presents the definition, structure and radiation mechanism of microstrip antenna, introduces three theoretical analysis methods such as the transmission line model theory, cavity model theory and full-wave analysis theory. Three numerical analysis methods of microstrip antenna as Method of moments(MOM), finite element method (FEM)and the Finite Difference Time Domain(FDTD) are analyzed and compared.Currently, the new designs of antenna are usually based on the above theory, and use the electromagnetic simulation software to amend the size and optimize its performance. This paper chooses Ansoft HFSS 10 which is a high frequency electromagnetic simulation software of three-dimensional electromagnetic structure. The text briefly overviews the principles and simulation steps of the software, designs two types of dual-frequency microstrip antennas by the software. The design methods and the simulation results analysis of the antennas are given in Chapter 3 and Chapter 4.After studying and comparing several current popular technological methods of dual-frequency, this paper designs two novel dual-frequency microstrip antennas: the compact dual-frequency microstrip antenna and the dual-frequency dual-circular polarization microstrip antenna. The antenna structure and theoretical calculation method of specific parameters are introduced in detail. The models are simulated and optimized by Ansoft HFSS. The charts of S-parameters, gain, impedance characteristics, axial ratio are given. And the regularity how the antenna parameter of the structure influences the antenna performance is summarized up.The compact dual-frequency microstrip antenna receives dual frequencies by slotting in the edge of the rectangular patch. The patch surface current has changed because of the slots, at the same time, the antenna size is reduced. By groups of tests on the length, the width, the number of slots, the following conclusions can be got:(1) Slot length is the main factor in impacting the resonant frequency of the antenna.(2) Width of the slots little effects on the performance of the antenna.(3) Increase the number of slots will bring the antenna gain reduction and the pattern deterioration at high-frequency.Based on the above analysis, an L-band and C-band compact dual-frequency microstrip antenna is designed in this paper, the simulation results indicate that: the antenna gets dual resonant frequencies at 2.74 GHz and 5.18 GHz, at the same time the S11 parameters were lower than -20 dB at two frequencies. The antenna was single-point feed by a coaxial probe. The impedance matching is good and the bandwidth and gain of the antenna is guaranteed by adjusting the location of the feed point.An L-band circularly-polarized stacked microstrip antenna is designed in Chapter 4. The antenna is circularly-polarized by double-fed at two orthogonal edges of square patch which is on the down substrate. Dual-frequency covering can be achieved with two layer substrates. The results simulated by Ansoft HFSS10 are presented. The relative impedance bandwidth of this microstrip antenna reaches up to 13% under the condition that VSWR is less than 2.And the 3dB axial-ratio bandwidth is about 74%.Elevation angles from -54°to 54°was well covered with AR<3dB. The antenna has a maximal gain of nearly 9 dBi and the isolation reaches 21 dB. Dual-polarized can be got by adjusting the phase of dual-port excitation current. At the same time, the structure of the antenna is simple and easy processing and debugging, and it can be carried out as a unit element in antenna array.In this paper, the dual-frequency microstrip antenna technology is studied in detail. Two practical design methods of novel dual-frequency microstrip antennas are given; techniques of slot loading and stack-up are studied; the single point of coaxial probe and dual-port microstrip line feed is used in two antennas respectively; linear-polarization and circularly-polarization are both designed, especially the stack-up dual-frequency microstrip antenna also achieves double-circularly polarization, the methods are currently popular dual-frequency technology and have great engineering applications value. |
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