The microstrip antenna is an antenna formed on a dielectric substrate that is formed on a metal thin layer on a back surface, and a metal radiating sheet is formed. It has a microstrip line and the same axis of these two main feed mode. The microstrip antenna excited the radiation field between the metal patch and the metal ground floor, and is radiated through the gap between the patch and the gap between the ground plates, and therefore also referred to as a slit antenna. The frequency band is narrow, the power capacity is small, the loss of the volume is large, and the performance is large, etc. is the disadvantage of the microstrip antenna. Its advantage is that the size is small, the quality, low profile, simple manufacturing, low cost, easy integration, easy to achieve dual frequency, Multi-band work, etc., is also these advantages, making the microstrip antennas working within 100 MHz ~ 50 GHz frequencies are commonly used in satellite communication, command and control systems, missile telemetry, weapon trust, environmental testing.
Radio guidelines can be used to control the arms of the weapon projectile to achieve the killing effect. The antenna belongs to a part of the lettering device for transmitting and receiving signals. Therefore, the performance of the antenna has a great impact on the work status of the letter and the killing of the weapon projectile. Since the antenna should be attached to the warhead, the general body head is mostly conical, in order to facilitate mounting the microstrip antenna in the warhead portion, this paper will design a circular microprojection of a central frequency of 7.2 GHz, The relative dielectric constant is εr = 4.4, and the loss is tangent Tan δ = 0.164 6.
1 round microstrip antenna design
1.1 media design
In an antenna design, the material and thickness of the medium substrate have a great influence on the performance of the antenna, so the material of the medium and its thickness are first required. The electrical characteristic parameters mainly considering the material selection are their relative dielectric constant εr and loss angle Tan δ. The stability of the dielectric constant is very important, and the changed dielectric constant will cause the patch frequency drift. The dielectric constant can reduce the size of the patch size, but the patch cell bandwidth is usually reduced; the dielectric constant will increase the edge field around the patch, reducing radiation efficiency. Large damage substrates often reduce antenna efficiency, increasing feedback loss, so it is necessary to consider when selecting media materials. After comprehensive consideration of this design, it is determined that the FR4 epoxy resin sheet is a medium material, and its relative dielectric constant is εr = 4.4, and the loss is tangent Tan δ = 0.164 6, which is also a material commonly used in the microstrip antenna design.
For the thickness of the substrate, the thickness of the thickness can improve the antenna mechanical strength, increase radiation power, reduce conductor loss, and broaden the frequency band;, it will also increase media loss, causing a significant excitation of surface waves. For a working frequency FM, according to the microstrip circuit theory, the thickness should be satisfied:
Where: C is the light speed; Fm is the operating frequency, and εr is a relative dielectric constant. Usually h / fm< 0.1 ensures that there is no obvious excitation of surface waves.
This design is based on the FR4 plate as a medium substrate. According to the design requirements, the initial value of the medium thickness is 2 mm based on the expansion of the frequency band, and reducing the volume requirements of the antenna.
1.2 radiation patch design
For known dielectric substrates, the radius of the circular microstrip antenna is: at a given operating frequency FR = 7.20 GHz:
Where: fr is the operating frequency; εr is a relative dielectric constant; H is the thickness of the medium substrate.
1.3 Antenna feed and input impedance
This design uses coaxial feed to change the input impedance by varying the position of the feed point on the radiation patch, allowing the antenna to obtain impedance matching. A general microwave device is generally a 50 Ω system, so it is necessary to reach an input impedance of 50 Ω by changing the position of the feed point. Calculate the input impedance of the antenna, requires several aspects of dielectric loss, radiation loss, conductor loss, surface wave loss, can not be considering a certain factor unilateral, otherwise it will cause a large error. QR, QC, QD, QS are radiation loss, conductor loss, dielectric loss, and surface wave loss caused by respective Q values.
The antenna works in the main model, that is, TM11:
Where: TAN δ is the loss of the medium, TAN δ = 0.1646; Gr = 1.54 × 104.
Due to the design of ideal conductors, QC = 0 is used. so:
Antenna resonant resistance:
Where: J1 is a first-order Besi ear function. Let R = 50 Ω, into the equation (8), can estimate the position L of the feeder point L, that is, feed the input of the circular patch center L, ie the antenna reaches 50 Ω input impedance.
The inner core radius is temporarily set to 0.6 mm, and a circular hole is excavated on the ground plate as a signal input port, and the inner core is surrounded by a coaxial line, the radius is about 1.5 mm, and the impedance of the port is 50 Ω.
Through the above analysis, the initial value of the antenna parameters is obtained: the radiation radius of the circular radiation: A = 5.39 mm; medium substrate thickness: h = 2.00 mm; medium substrate radius 2 * a; feed point position: l = 1.96 MM; inner core radius: n = 0.6 mm; outer core radius: m = 1.5 mm.
2 use HFSS software for antenna simulation
Modeling analysis of the antenna based on ANSOFT HFSS 3D simulation software. The simulation flow is shown in Figure 1.
Creating an antenna initial model is shown in Figure 2 based on the initial size and HFSS antenna design requirements.
The simulation of the initial value by HFSS is known that the current initial value does not completely reach the antenna to 7.2 GHz, and the performance indicators of the antenna will not meet the requirements. Then, you need to use the HFSS's sweep analysis and optimization design functions to optimize the parameters of the antenna, so that the performance of the filling antenna is reached.
2.1 Optimization Design of Antenna
(1) Make a sweep analysis near the resonant frequency through the HSFF software, and the radius of the circular patch is corrected. The value of the corresponding patch radius A can be obtained at 7.2 GHz is 5.216 mm.
(2) Analyze the effects of dielectric substrate thickness on antenna performance. With HFSS, the effects of thickness of different dielectric substrates on the antenna return loss are obtained. According to the changes of the echo loss with the thickness of the medium substrate and the thickness of the different dielectric substrates, the value of the thickness of the medium substrate can be analyzed by the value of H = 2.021 mm.
(3) Analyze the impact of the position of the feed point on the performance of the antenna. This part is mainly to analyze the relationship between different feed positions and echo loss and input impedance. And by scanning the feed point position L, select the feeding point L = 1.863 mm.
(4) Use the HFSS software to design the standard of the antenna, and then automatically optimize the various parameters of the antenna, calculate the value of each parameter in accordance with the conditions. The results obtained are as follows:
Round radiation patch radius: a = 5.216 mm; dielectric substrate thickness: h = 2.021 mm; medium substrate radius 2 * a; feed point position: l = 1.863 mm; core radius: n = 0.516 mm; outside Core radius: m = 1.854 mm.
2.2 results analysis
The stepping of S11, SIMTH circle, gain under optimized sizes is given by HFSS software, as shown in Figures 3 to 5.
As can be seen from Figure 3, the resonance frequency of the design antenna is 7.2 GHz, and the echo loss at this time is -33.037 9 dB, and the design requirements of the antenna are reached.
Figure 4 shows that when the frequency is 7.2 GHz, the normalization impedance of the antenna is (0.977 5 + 0.037 9i) Ω, which shows that the antenna has reached a good impedance matching state.
Figure 5 is a gain direction view of the antenna on the XZ and Yz section. The figure shows that the radiation direction is φ = 0 °, θ = 0 °, and the gain is 5.486 dB.
Figure 6 is a three-dimensional gain pattern of antenna.
3 conclusion
This paper is based on the design of the microstrip patch antenna based on its application in wireless. This design is changed to a circular medium of the conventional microstrip antenna in order to facilitate the use of the letter. From several simulation results maps from the middle antenna, it can be seen that the center frequency of the antenna is 7.2 GHz, and the antenna echo loss, input impedance, gain direction map, and other technical parameters have reached the requirements. The results show that the performance of the antenna is good.
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Source: Wiku Electronic Market Network
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