U型寄生贴片微带天线,原文的.doc

Analysis and Design of A Novel Small Microstrip Patch AntennaABSTRACT:Microstrip antennas have been widely used in communication systems.Design and analysis of a wideband U-shaped parasitic Microstrip Patch Antenna which is coupled by the main patch and U-shaped parasitic patches is presented in this paper.Two parasitic elements are incorporated into the radiating edges of a rectangular patch whose length and width are and , respectively,in order to achieve wide bandwidth with relatively small size.The proposed antenna is designed and fabricated on a small size ground plane () for application of compact transceivers. The measured bandwidth is 1.5 GHz (4.786.28 GHz) with two separate resonant frequencies at 5.12 and 6.08 GHz. The measured radiation patterns are similar to those of a conventional patch antenna with slightly higher gains of 6.4 dB and 5.2 dB at each resonant frequency.KEYWORD:Parasitic patch antenna, U-shaped parasitic patches, wide bandwidth.1. INTRODUCTION In high-performance aircraft, spacecraft, satellite, and missile applications, where size,weight, cost, performance, ease of installation, and aerodynamic profile are constraints,low-profile antennas may be required. Presently there are many other government and commercial applications, such as mobile radio and wireless communications, that have similar specifications. To meet these requirements, microstrip antennas 138 can be used. These antennas are low profile, conformable to planar and nonplanar surfaces, simple and inexpensive to manufacture using modern printed-circuit technology,mechanically robust when mounted on rigid surfaces, compatible with MMIC designs,and when the particular patch shape and mode are selected, they are very versatile in terms of resonant frequency, polarization, pattern, and impedance. In addition,by adding loads between the patch and the ground plane, such as pins and varactor diodes, adaptive elements with variable resonant frequency, impedance, polarization,and pattern can be designed 18, 3944. Demand for compact and multifunctional wireless communication systems has spurred the development of multiband and wideband antennas with small size. Microstrip patch antennas are widely used in this regard as they offer compactness, a low profile, light weight, and economical efficiency. However, the microstrip patch antenna is limited by its narrow operating bandwidth. There are numerous and well-known methods to increase the bandwidth of antennas, including increase of the substrate thickness1 the use of a low dielectric substrate 1,the use of various impedance-matching and feeding techniques2the use of multiple resonators37, and the use of slot antenna geometry 8.However, the bandwidth and the size of an antenna are generally mutually conflicting properties, that is, improvement of one of the characteristics normally results in degradation of the other.Recently, several techniques have been proposed to enhance the bandwidth. In 911, utilizing the shorting pins or shorting walls on the unequal arms of a U-shaped patch, U-slot patch, or L-probe feed patch antennas, wideband and dual-band impedance bandwidth have been achieved with electrically small size.In this work, a wideband microstrip patch antenna employing parasitic elements is investigated. Two U-shaped parasitic elements are incorporated along the radiating edges of a probe fed rectangular patch antenna so as to obtain wideband operating frequency. In addition, the antenna is relatively small in comparison with the conventional parasitic patch antenna described in 4, 5. Performance of the proposed antenna is calculated and measured. The methods of analysis for microstrip antennas is given in Section 2. The proposed antenna geometry is described in Section 3. The fabricated antenna and experimental validations are presented in Section 4.2. METHODS OF ANALYSIS There are many methods of analysis for microstrip antennas. The most popular models are the transmission-line 16, 35, cavity 12, 16, 18, 35, and full wave(which include primarily integral equations/Moment Method) 22, 26, 7174.The transmission-line model is the easiest of all, it gives good physical insight, but is less accurate and it is more difficult to model coupling 75. Compared to the transmission-line model, the cavity model is more accurate but at the same time more complex. However, it also gives good physical insight and is rather difficult to model coupling, although it has been used successfully 8, 76, 77. In general when applied properly, the full-wave models are very accurate, very versatile, and can treat single elements, finite and infinite arrays, stacked elements, arbitrary shaped elements, and coupling. However they are the most complex models and usually give less physical insight. In this chapter we will cover the transmission-line and cavity models only.However results and design curves from full-wave models will also be included. Since they are the most popular and practical, in this chapter the only two patch configurations that will be considered are the rectangular and circular. Representative radiation characteristics of some other configurations will be included.3. ANTENNA DESIGNFig. 1. Geometry of the proposed microstrippatch antenna with U-shaped parasitic elements. Fig. 1 depicts the top and side views of the proposed antenna. The proposed antenna consists of a probe fed half-wavelength rectangular patch and two U-shaped parasitic elements incorporated around the radiating edges of the rectangular patch. In general, the length and width of the rectangular patch antenna are close to half-wavelength. However, the length ()and width () of the main patch vary from the proposed design. In order to maintain the inherent resonant length with smaller size, is reduced toand is defined as about,whereis the guided wavelength.Probe feeding is accomplished by a vertical via hole through the substrate material.The proposed antenna has two parasitic elements to obtain wide impedance bandwidth. Using the geometrical feature of the U-shaped patch, the size of the antenna can be miniaturized. Notable, although two parasitic patches are positioned in the proximity of the radiating edges of the main patch, all of the radiating and nonradiating edges of the main patch are surrounded by U-shaped parasitic elements. Electromagnetic coupling between the main patch and parasitic patches is realized across either horizontal () or vertical gaps (). In addition, the resonant length of the U-shaped patches can be controlled by adjusting its length () and width ().The proposed antenna is designed to operate in the 5 to 6 GHz region. The length and width of main patch are close to and at a center frequency of 5.5 GHz.The distance between bottom radiating edge of main patch and center of feed via is 0.084and the total length of the U-shaped parasitic patch(d) is 1.05The geometrical parameters of the proposed antennas are ,and .An FR4 substrate, whose permittivity is 4.3 with a thickness (h) of 4mm, has been used in this work. . The radius of the feed via is 0.4 mm and the length is same as the substrate thickness. The ground and substrate size of the proposed antenna is defined asfor compact transceiver application.4. CALCULATION AND MEASUREMENT The resonant properties of the proposed antenna have been predicted and optimized using a frequency domain three- dimensional full wave electromagnetic field solver (Ansoft HFSS) and the characteristics of the fabricated antenna have been measured with a vector network analyzer and a far field measurement system. Fig. 2 shows a photograph of the fabricated antenna on a FR4 substrate, and Fig. 3 compares the calculated and measured return loss characteristics of the proposed antenna. The specific values of the resonant frequency and relative bandwidth are summarized in Table I,where and represent the first and second resonant frequencies, respectively.The calculated result shows two neighboring resonant frequencies (5.32and 6.11 GHz), and the frequency band ranges from 4.84 to 6.28 GHz(1.44 GHz).The bandwidth is 26.2% at 5.5 GHz. The measured bandwidth is 1.5 GHz (4.786.28 GHz) with two separate resonant frequencies at 5.12 and 6.08 GHz. The measured as predicted antenna performance show excellent agreement. Fig. 4 presents the calculated currents distributions at each resonant frequency. As shown in Fig. 4(a), the amplitudes of the currents around non-radiating edges of main patch are strong, and the effect of the parasitic patches is not significant at 5.32 GHz. Therefore, the low resonant frequency is determined by the length of main patch (LR). In addition, there are strong currents flowing around gaps between the main patch and U-shaped parasitic elements at 6.11 GHz as shown in Fig. 4(b). It means that the radiation at high resonant frequency is mainly contributed by strong electromagnetic coupling between three patches. Therefore, the width of horizontal and vertical gaps (GH, GV) and the total length of U-shaped parasitic element(d) are directly related to the wideband impedance matching performance. This shows the reason how U-shaped parasitic patches can extend the bandwidth. The calculated and measured normalized radiation patterns at the first and second resonant frequencies are plotted in Fig. 5, where the “Co (C),” “Co (M),” “Cross (C),” and “Cross (M)” indicate calculated co-polarization, measured co-polarization, calculated cross-polarization, and measured cross-polarization, respectively. As shown in Fig. 5, the designed antenna displays good broadside radiation patterns in the E-plane (XZ plane) and H-plane (YZ plane) at each resonant frequency. It can be seen that the beam peaks of the E-plane are slightly shifted in a right direction due to the feeding position on the main patch, which means that they experience phase difference at each radiating edge of main patch. The measured co-polarization radiation patterns are almost identical to the calculated radiation patterns, while the cross polarization level is somewhat higher than that of the calculated results due to various error mechanisms in measurement, such as multipath in the chamber, positioning error between standard gain horn antenna and antenna under test (AUT). In addition, the higher cross polarization level in H-plane atis caused by y-directed currents flowing on the U-shaped parasitic patches as shown in Fig. 4(b). Notable, the radiation characteristics of the proposed antenna are nearly identical to those of the conventional patch antenna. The measured maximum gains of the fabricated antenna are 6.4 and 5.2 dB at 5.12 and 6.08 GHz, respectively. Fig. 2. Three-dimensional view of the fabricated antenna.Fig. 3. Comparison of calculated and measured results.Table 1.Calculated and measured characteristic of the proposed antennaFig. 4. Calculated currents distribution: at (a) 5.32 GHz and (b) 6.11 GHz.5. CONCLUSION In this paper, a novel wideband microstrip parasitic patch antenna has been proposed, where U-shaped parasitic elements are incorporated close to the radiating edges of a reduced size main patch so as to achieve wideband characteristics, and those two parasitic patches are excited by proximity coupling from the main patch. The wideband impedance matching can be achieved by adjusting either horizontal or vertical gaps between the main patch and parasitic elements. The size of the radiating elements including parasitic elements is , and the overall dimensions of the designed antenna with ground plane and substrate are . The measured resonant frequencies are 5.12 and 6.08 GHz, and the bandwidth is 1.5 GHz,which is 27.3% at 5.5 GHz (center frequency). In addition, the radiation patterns of the fabricated antenna are almost identical to those of a conventional microstrip patch antenna at each resonant frequency with more than 5 dB gain. From these results, it can be concluded that implementation of the U-shaped parasitic patch on the radiating edges of the reduced main patch is an effective means of realizing a wideband microstrip antenna having a finite substrate and ground plane.REFERENCES1 D. H. Schaubert, D. M. Pozar, and A. Adrian, “Effect of microstrip antenna substrate thickness and permittivity: Comparison of theories and experiment,” IEEE Trans. Antennas Propag., vol. AP-37, pp. 677682,Jun. 1989.2 H. F. Pues and A. R. Van De Capelle, “An impedance-matching technique for increasing the bandwidth of microstrip antennas,” IEEE Trans. Antenna Propag., vol. AP-37, no. 11, pp. 13451354, Nov.1989.3 D. M. Pozar and D. H. Schaubert, Microstrip Antennas. New York:IEEE press, 1995, pp. 155166.4 G. Kumar and K. C. Gupta, “Broad-band microstrip antennas using additional resonators gap-coupled to the radiating edges,” IEEE Trans