With the rapid development of wireless communication technology, wireless communication terminals have become miniaturized and multi-directional. As the import and export of wireless communications, the antenna has a great impact on the performance of wireless communications systems. The space reserved for the antenna in the design of the wireless terminal is getting smaller and smaller, and the functional requirements of the antenna are getting bigger and bigger.
The height of the integrated circuit can keep up with the demand of wireless device miniaturization, the volume of the. At present, Miniaturization, multiband and broadband are the important trend of the development of antenna design. As used as the unit of plane conformal antenna array antenna and built-in antenna of the mobile phone.
The traditional microstrip antenna has a half wavelength structure, the practical application of the antenna needs a smaller size. At the same time, the development of microwave integrated technology and the birth of a variety of high-performance materials have made the miniaturization of microstrip antenna become one of the hot researches in recent years.
The Concept And Characteristics Of Microstrip Antenna
Since Deschamps,G,A proposed the microstrip line as a radiating device in 1953, the microstrip antenna has been widely used in the field of wireless communication due to its low profile, light weight, small volume, and simple fabrication. The microstrip antenna is a type of antenna that uses a thin dielectric plate and attaches a thin layer of metal on one side of the dielectric plate as the ground, making a metal patch on the other side by the method of lithography and etching, and feeding the patch through a microstrip line or coaxial cable. The shape of the patch can be a rectangle, circle, triangle, pentagon or other shapes.
The shape of the slot is similar to the shape of the microstrip patch, it can be rectangular (wide or narrow), circular or ring. Traveling wave microstrip antenna is composed of a substrate, the chain cycle structure on one side of the substrate and the floor on the other side of the substrate. At the end of the TEM wave transmission lines matched the load, when the antenna continues to raise the wave, it can make the main bean shoot in any direction.
Compared with the commonly used microwave antenna, the microstrip antenna has the following advantages: small size, light weight, low profile, low production cost, easy mass production, linear polarization and circular polarization can be achieved using simple meal, easy to double. Dual frequency and polarization antenna, feed line and matching network can be manufactured with antenna structure. And fabricate the antenna that uses the combination of short-terminated parallel lines and the capacitor.
The microstrip antenna has many advantages, for example, low profile, easy manufacturing, easy to design structure and many other advantages, A compact microstrip antenna has gained more and more attention and research. What work to be done of microstrip antenna miniaturization is to reduce the size of microstrip antenna in fixed frequency. The short-circuit charging technique can effectively reduce the size of the antenna in the fixed frequency.
And the method we used to fabricate the antenna, this method uses the combination of parallel shorted coupled lines and a capacitor.
Loading technique of microstrip antenna
These two kings of structure are similar, the difference between them is only the width of the short circuit structure. There is a literature introduction that the resonant frequency of the circular microstrip antenna and the rectangular microstrip antenna with short pin charge is 1/3 of the antenna without charge. In other words, for a fixed frequency, the size of the antenna is reduced by 89%[6][7].
Another literature presentation on the size of an equilateral triangle microstrip antenna reduced by 94% with short-circuit loading [8].
Increase of dielectric constant
Antenna b adopted a thicker material than antenna a to provide sufficient circularly polarized antenna bandwidth. At a fixed frequency, using a ceramic substrate material instead of a conventional substrate material can reduce the antenna size by 90%.
Meandering technology
The meandering technology of the ground plane refers to the antenna miniaturization technology, which realizes the change of the current path through the slit in the ground floor. Slitting on the ground floor can achieve the same effect as slitting in the patch. Keeping the shape of the antenna patch sticking into the ground floor can lead to the bending of the current on the patch.
At the same time, due to the ground floor slotting caused a decrease in Q values of the microstrip antenna, the bandwidth of the antenna will increase accordingly. If the charging technology and meandering technology are combined effectively, the effect of the miniaturization of the antenna is better. There are some references that introduce the use of slotting and loading shorting pin method at the same time in the circular microstrip patch.
Using the structure of PIF and PIL
So make the structure of the antenna reduced to 50% of the regular antenna when the frequency is kept unchanged.
Using the end-shorted coupled lines
Let us now first look at Fig. 2.5.3, which is an end-short pair line and its corresponding PI network. With this method, the transmission line can be made as short as a few degrees, resulting in a very compact circuit.
Design Simulation, Fabrication and Measurement
The Antenna Design
The following table lists a set of data calculated using formula (2.5.9) and formula (2.5.12) for the interested reader. Setting at 80 ohms, we can calculate the characteristic impedance of the terminal shorted lines in the dashed box 1 and 2 to be 373.2 and the odd mode impedance is 56. Using the LineCal tool in the Microsoft Advanced Design System (ADS), we can obtain the length and width of the final shorted line.
And the supply line value can also be calculated by the LineCala tool in ADS. For the microstrip line impedance is set only by its width and to reduce the size of the antenna, the length of the microstrip line can be set to h=6.89mm. The antenna structure is in Fig 3.1.3 and the antenna parameter is in Table 2.
Full-Wave EM Simulation by HFSS and Optimization
Then we need to adjust the resonant frequency. the resonant frequency has changed to about 0.88 Ghz, and the most important factor affecting the resonant frequency is the value of the capacitor. According to the calculation results, the value of the capacitor is 9pF, however, in the simulation, the resonant frequency is shifted from 1Ghz to 0.88Ghz, Change some values of the capacitors, and finally find when the value of the capacitor decreases to 6.6pF, the resonant frequency can be shifted back to 1 Ghz. So capacitors of 6.6pF should be used to achieve a proper resonant frequency instead of the theoretical 9pF. The simulation results are shown in Fig 3.2.3.
By changing the capacitor the center frequency becomes 1 Ghz, but the impedance of the antenna is still very poor and still needs to be adjusted. Adjusting the slot advance also allows you to increase the and tune the impedance. Since this antenna is powered by the microstrip line, the microstrip line can produce the radiation and affect the result of the antenna. Then adjust the length and width of the shorted lines at the end and the length of the microstrip is necessary.
After optimization, we get a better result, which is shown in Figure 3.2.5. c) simulation result of E-device and H-device. This parameter can be used to calculate the size and bandwidth of many other types of microstrip antennas. From Table 3, we can see that the size of the coupled line antenna is about 10% of the circular patch and ring patch antenna and about 7% of the rectangular patch and triangular patch antenna.
Fabrication and Measurement
Since there are many elements that can affect the results of the antenna, fabricating three antennas should be better. Comparing with the simulation result, we can find that all resonance frequencies of the fabricated antennas have shifted. The reason is that the value of the bundled capacitors of the manufacturing antenna is different from that of the simulation antenna.
Use the same structure to design another small antenna at 500 MHz with the dimensions of 26 mm * 14 mm.
Conclusion
Comparison of PBG and Perfect magnetic conductor surface effect s on the performance of finite microstrip antennas IEEE Proceedings of Antenna and propagation soeicty International Symposium. Two years in our life's journey are so short, but these two years in the truest form of youth are the most innocent years, my most beautiful life. I would like to express my sincere thanks to many people who have offered me enormous help in both my studies and daily life over the past two years.
Without their generous support, it would be an impossible task for me to complete my master's studies. The word thank you can hardly express my deep gratitude to him for all he has done for my account. I would like to express my sincere thanks to the other professors in our school for their guidance and help during the last two years.
In the past two years, Professor Piao has carefully taken care of us, taking care of our lives and the health of our bodies.
![Fig 2.4.1 is the sketch map of PILA of the Microstrip line feeding[9].](https://thumb-ap.123doks.com/thumbv2/123dokinfo/10548496.0/19.774.195.587.423.843/fig-2-sketch-map-pila-microstrip-line-feeding.webp)
