First, antenna design introduction
The specific design process and principles of the antenna, the antenna multi-frequency implementation method, how to use capacitors, inductors, etc., to match and improve the performance of the antenna, share their antenna unreasonable to everyone, including common like: snake The principles and design methods of the shape of the antenna, the pour F Antenna, PIFA antenna, LOOP antenna, gap antenna, and border antenna.
In the early days of learning antenna, at least one electromagnetic simulation software, such as HFSS, CST, ADS, etc., personal suggestions to learn HFSS, because the network is easy to find some tutorial, which is beneficial to their own learning and improvement. Not much nonsense, first talk about the principle of falling the F antenna, design an antenna, first to clarify the basic design indicators, that is, the desired operating frequency band, because the operating frequency band directly determines the size of the antenna. If it is a print antenna, consider the dielectric constant and loss angle of the dielectric plate. Here I only talk about the influence of electromechanical constants, and the loss angle correct value will be explained later.
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For example, it is now designed to design a plate-loaded WiFi printing antenna working on 2.412GHz-2.472GHz (WiFi 11N protocol), using FR4 medium, requiring gain than 1.5dBi, voltage stationer ratio VSWR<2. Let's take a look at the basic structure of the printing flyf antenna, as shown below:
The printing inverted F antennas mainly have three main structural parameters, namely the antenna resonance length L, antenna height H and feed points to the ground spacing S (in the figure), where the resonance length L is used to adjust the operating frequency of the antenna, The higher the short frequency; the antenna height H can be used to adjust the bandwidth of the antenna, the larger the band, the larger the bandwidth; S is used to adjust the input impedance of the antenna, the smaller the S, the resistance is, in other words, S can be directly The VSWR performance used to adjust the antenna.
Second, the design process
See the specific design process below:
The first step, first calculate the basic size of the antenna, with 2.45 GHz as the center frequency, the corresponding free space wavelength:
Lambda0 = v / f = 122mm, where V is the frequency of light, f is the frequency required;
In the second step, the length of the monopathic antenna is calculated. Here, it should be noted that the monopole antenna is usually used, and the monopole antenna usually uses a quarter of a wavelength, and the dipole antenna is half a Wavelength or a wavelength (related knowledge can be searched in Baidu, not too much repetition), therefore, the corresponding monopole antenna length is:
1/4 * lambda0 = 30mm;
In the third step, it is necessary to consider the influence of the FR4 dielectric plate on the antenna. As a printing antenna, the antenna is etched on the dielectric plate, and the other is exposed in the free space, so the actual length of the antenna will also receive the dielectric plate dielectric The influence of constants, when the antenna is completely in the medium, its wavelength:
Lambdae = lambda0 / (e ^ 0.5) (e represents a dielectric constant)
For the print antenna, since half of the air is in the air, half of the length of the medium is between a quarter medium wavelength and a quarter free space wavelength, the design is temporarily taken in the design. According to the calculation above, the quarter medium wavelength is 1/4 * 122 / (4.4 ^ 0.5) = 15 mm, so the initial length of the can be taken is 22 mm. According to the above, the initial length is the antenna height H and the resonance length L, we can define H = 5mm, L = 17mm, s = 5mm, antenna width W = 1mm, using HFSS to establish a three-dimensional simulation model (specific The modeling process can consult the author), the established model is as follows:
Simulate according to the initial size, resulting in the following results:
From the S11 parameter, the operating frequency of the antenna covers 2.3G-2.6G (S11<-10), reaching our expected design requirements, let's take a look at the effects of L, H, and S on antenna performance ,As shown below:
Take L1 = 17mm, L2 = 16mm, L3 = 15 mm; H1 = 5 mm, H2 = 5 mm, H3 = 3mm; S1 = 4mm, S2 = 5 mm, S3 = 6mm, from the above simulation results, can be very clearly seen three The impact of the main constant on antenna performance: that is, the resonance length L is used to adjust the operating frequency of the antenna, the higher the frequency, the higher the height H can be used to adjust the bandwidth of the antenna, the greater the band, the larger the bandwidth; The echo loss S11 performance of the adjustment antenna. The specific effect is summarized as follows:
It is important to note that the monopole antenna is present, and the antenna effect generated by the mirror is larger, and the ground plane area has a large influence, so once the antenna is determined, try not to change the area of the ground plane, Otherwise the antenna needs to re-simulate design. For details, you can simulate itself to try to analyze. Read more
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