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A high performance omnidirectional microstrip antenna design and analysis

In Electronic Infomation Category: A | on April 12,2011

In the field of mobile communications, full-high-gain antenna to have a wide range of applications. Microstrip antenna as a cross-stream of high-gain omnidirectional antenna, its simple structure, matching easy, convenient and MAX1686HEUA datasheet and low cost advantages of mass attention. The general stream of the microstrip antenna shown in Figure 1 cross, this structure in the simulated and MAX1686HEUA price and measured in a more serious pattern distortion, antenna VSWR is relatively poor. Literature gives an improved program that will make the ground ladder microstrip antenna structure, shown in Figure 2. Which to some extent, improve the antenna performance. This paper gives the structure of the antenna of the test results of simulation and MAX1686HEUA suppliers and in-kind to the proposed microstrip with the omnidirectional antenna for comparison. In this paper, the proposed omnidirectional microstrip antenna shown in Figure 3. In addition to the gradient of the antenna structure with microstrip matching converters and inductors, are still top of the antenna loaded g / 4 short-circuit matching minor. Simulation and test show that the antenna with the antenna proposed in the literature compared with the better voltage standing wave ratio and higher gain, is a high performance omnidirectional microstrip antenna.


Figure 1 Schematic diagram of microstrip antenna, cross-time around

1 microstrip antenna cross-stream of the basic principles

Microstrip antenna cross-stream of the basic structure shown in Figure 1. Each microstrip transmission line to the ground as the outer coaxial conductor, the conduction band as the conductor of coaxial line, with the traditional COCO antenna has a similar structure. Similarly, the microstrip antenna is also cross time around by a number of g / 2 unit of the cascade from the microstrip antenna of the ground and the conduction band in the dielectric substrate placed alternately on both sides, to take advantage of cross-connections to achieve phase inversion. As cross-connection points of discontinuity form of radiation, making this structure there are two modes, transport mode and radiation modes. For the transmission mode, due to the wave along the conduction band and then transfer the inner surface of the floor, and the microstrip transmission line is uniform, so the analysis does not consider the space radiation. And radiation modes, is due to take the floor of the alternating voltage at the source of radiation from the current incentive exists in the ground plane of the inner and outer surfaces to form the radiation. As with the COCO antenna, microstrip antenna is a cross-array antenna time around. From the basic theory of array antenna known for far-field area, the antennas normalized directional function


gain antenna


Where, is the antennas radiation efficiency; D is the antenna directivity.

2 cross stream of microstrip antenna design and analysis

Cross-stream of the basic microstrip antenna shown in Figure 1, experiments show that the structural distortion of the antenna pattern is quite serious and in-band VSWR is not ideal. In order to improve the performance of the antenna, the antenna structure of the floor designed trapezoidal, and the conduction band in each cell in the middle of the microstrip load a rectangular patch, is used to tune the antenna, when the antenna structure shown in Figure 2, which to some extent, improve the antenna impedance. Load equivalent to a rectangular patch inductors. Assuming that the inductor length l, width w, then the equivalent circuit inductance L as shown in Eq (3) below.


Which, h as the medium thickness; t is the thickness of the conductor; Kg for the correction factor, the empirical formula for the


From (3) can be seen in the media panel parameter to determine the circumstances, rectangular patch of the inductance value determined mainly by the width of the w.


Figure 2 Schematic diagram of the top of the antenna is not loaded

Microstrip antenna with cross-stream of COCO antenna has a similar structure and the same principle, so they have a similar equivalent circuit. Figure 2 shows the antenna, each microstrip element equivalent circuit shown in Figure 4, where, R is the equivalent radiation resistance; C for the equivalent capacitance; L is the equivalent inductance. L inductance of the unit itself, including microstrip and loading inductance. They form a RLC resonant circuit. Not loaded rectangular patch antenna, before rendering its characteristic impedance larger capacitance, therefore, by adjusting the width of the rectangular patch to change the size of load inductance, in order to achieve the best S11.


load short-circuit in Figure 3 matches the top minor cross stream of microstrip antenna diagram


Figure 4, the top minor short circuit is not loaded when the antenna equivalent circuit

Figure 5 shows the different values ??of the antenna of the S11. After optimization, when w = 6, the time matching the antenna with the best performance. At this time the band antenna S11 <-15 dB.


Figure 5, when the top is not loaded with different W values ??corresponding to the antenna S11

Order to further reduce the energy of the antenna reflector to improve the radiation characteristics of the antenna, the antenna top loaded g / 4 minor short match, when the antenna structure shown in Figure 3. Loaded at the top of the antenna, each microstrip element equivalent circuit shown in Figure 6, the equivalent of a parallel microstrip unit admittance. Where, R1 is equivalent to the radiation resistance of microstrip unit; C1 is the equivalent capacitance; L1 equivalent inductance; Y equivalent to the top of minor short-circuit admittance.


Figure 6, the top loaded antenna equivalent circuit

Minor short-circuit admittance Y match the antenna impedance matching of the play a regulatory role. Learned from the Smith chart, the top antenna is not loaded g / 4 minor short match, in the 2 400 ~ 2 483.5 MHz, the real part of antenna impedance between 37 ~ 46 between the minor load matching, the antenna characteristics the real part of impedance at between 47 ~ 58 . And the imaginary part of antenna impedance have significant changes in the required band, the value closer to 0. Figure 7 and Figure 8 shows the two antenna simulation software CST received by the real and imaginary part of impedance versus frequency curve. It can be seen from the figure, the antenna top loaded g / 4 minor short match, the significant increase in the real part of antenna impedance, the imaginary part is not loaded than when reduced. Figure 9 shows the top of the load short matches at different w minor impact on the antenna S11. From the figure we can see that when w is 6, in the required band, the antenna S11 <-20 dB.


Figure 7, the real part of antenna impedance versus frequency curve


Figure 8, the imaginary part of antenna impedance versus frequency curve


Figure 9 is not loaded at different W values ??corresponding to the antenna S11

Antenna top loaded g / 4 minor short match, the antenna current distribution will be changed. When the waves from the antenna to the top through the g / 4 unit, resulting in 90 phase shift, after a short circuit, the resulting 180 phase shift, and then after g / 4 the ground, they produce 90 phase shift. After a minor short-circuit current after the match, resulting in a 360 phase shift. After the current in phase with the original after the excitation current has the same phase, current compensation and thus play the role of the antenna to keep the antenna on the current balance.

Physical antenna shown in Figure 10. Antenna with a thickness of 1.5 mm, relative dielectric constant of 2.65 in the medium plate, the bottom of the feed with 50 SMA joints. In the actual production, the length of slightly less than the simulation time around the antenna length, which is caused by the loss of the material. In general, the bottom edge of the antenna length of the ground ladder


Figure 10 Antenna

kind

Table 1 and Figure 11 shows the two antennas were measured gain and S11 of the contrast. It can be seen, the antenna top loaded short match, the antenna gain increases 1 ~ 1.3 dBi. This is because the top match the minor load short-circuit, the impedance matching the antenna to improve performance, increase the antennas radiation efficiency, reduce energy reflections on the antenna, so that each unit of microstrip radiation power obtained the largest full use of the antenna aperture efficiency, thereby increasing the gain of the antenna.



Figure 11 top loading and top non-loaded antenna measured

3 Conclusion

Two antennas of the CST simulation results and experimental results are consistent. Actual test results compared with the simulation results found that the measured antenna gain are slightly higher than the gain obtained by the simulation software, which was mainly due to the impact of the earth caused by the antenna. The top of the antenna loading g / 4, after minor short match, further reducing the antenna VSWR, gain increased. Microstrip antenna physical unit with 7 cascaded, the total height of

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