When designing antennas for communication terminal products, the electromagnetic simulation software is used to model and design antennas, and the results are often very different from the actual ones. Many theoretical scholars spend a lot of time on software modeling when receiving antenna design projects. After getting the ideal antenna pattern, the proofing will be a problem, wasting precious project time. Today I will tell you why when you design antennas on real electronic products, you only do computer HFSS, CST and other simulation designs to directly determine the antenna is not reliable.
First we need to understand the principles of computer HFSS, CST and other simulation software. The working principle of this type of software is to import the 3D model of the desired design product into the computer simulation software, or create a 3D model that simulates the actual product on the software, and then set the material of the model to a universal material The antenna design is completed on the basis of which the technical parameters of the antenna are calculated by software.
HFSS antenna simulation interface
Based on the above principles, we can know that there are many inaccurate factors in computer software simulation, and these factors will lead to inaccurate simulation results.
1、 Difference between 3D model and final real product
Many times the 3D model is a simplified model created by the simulator itself based on the customer's product. There is a difference between this simplified model and the actual product, and this difference will directly lead to deviations in the simulation results. Even if the real dimensions of the customer's real shell 3D drawing and the circuit board drawing are imported for simulation, the internal structure of the accessories in the customer's product, the drawing file and the actual deviation are unknown, and the results of natural simulation cannot be accurate.
2、 Differences between general material parameters and real product material parameters
This is also a very common situation. After completing the above 3D model, the simulator needs to determine the parameters (including dielectric constant and loss) of the materials of the various components in the model. Many customers themselves cannot accurately know the material parameters of the products they use. How do the simulation personnel determine? At this time, the simulator usually sets the material to a common material, such as metal uniformly set to PEC (ideal conductor), plastic uniformly set to general plastic parameters, and so on. However, in fact, there are various materials such as iron, aluminum, and copper, and the dielectric constant of different plastics ranges from 2.8 to 4.0. The actual parameters of these seemingly similar materials are very different, and it is necessary to simply set them Bring differences between simulation parameters and real products.
3、 Differences in accuracy of the simulation software itself
Everyone who has done antenna simulation knows a phenomenon. If the same model is imported into different simulation software for antenna simulation, the simulation results are different. This is because the algorithm and accuracy of different software will cause different results of the operation simulation. The software calculation results are also different from the actual product situation.
Taking into account the above differences, how can the results of software simulation antenna design be consistent with the antenna parameters of real products? So how much is the difference between the simulation result and the actual product?
Take a customer as an example. What he wants to design is a built-in on-board PCB antenna for WiFi. The antenna and the circuit are co-boarded and there is a casing and a battery. The results of the simulation design completed by the antenna simulator showed that the resonant frequency of the simulated antenna fell exactly at 2450MHz, and the VSWR index was less than 2.0, indicating that the impedance of the antenna performed well in the simulation software and met the built-in antenna design standards. After the customer completed the production of the product according to the size board provided by the simulator, the customer found that the communication distance of this antenna was very poor. The RF solution can normally have a communication distance of more than 200 meters, but his product communication distance is less than 30 meters.
VSWR simulation results
This customer gave us the simulation model and the manufactured product. We tested the antenna of the product with the special antenna equipment and found that the antenna is at a high frequency (> 5.0) at the working frequency of 2.4-2.5GHz. In this way, the mismatch between the antenna and the device is very different from the simulation result. Therefore, the poor use of this antenna is natural.
Antenna based on simulation
Antenna Dedicated Network Analyzer
Different from these computer simulation designs, the antenna design we provide is to connect a real complete product to a special instrument (network analyzer) specifically designed to test the antenna. After the antenna is designed, it is tested using a completely real product environment. Accurate antenna parameters and repeated modification until the actual parameters of the antenna meet the antenna design standards. Because it is designed on a real product, the product model differences and material parameter differences mentioned above do not exist at all. We use professional instruments to test the actual antenna parameters. There is no calculation process, so there is no calculation error. So our test results are real antenna performance. This design method is also the standard antenna design method of major antenna manufacturers and professionals. Here are the 2.4GHz antennas we designed for our customers.
The simulation results are actually just a reference data, and professionals in antenna design know this. As long as the customer is making the actual product, we will advise the customer to provide a complete antenna environment and customize the appropriate antenna.