The Effect of PCB Structure on the Efficiency of Millimeter Wave Radar

The Effect of PCB Structure on the Efficiency of Millimeter Wave Radar
The printed circuit board is made of ordinary composite materials, mainly using glass fiber as the filler of the dielectric layer. However, the special braided structure of glass fiber changes the local dielectric constant of the PCB Especially at the millimeter wave frequency, the glass braiding effect is more obvious than that of thin laminates. The local non-uniformity of Dk leads to significant changes in the efficiency of RF circuits and antennas We use (1) 00mm thick glass braided PTFE laminate to study the effect of PCB structure on transmission line efficiency, depending on the type of glass braided structure. It is found that the dielectric constant of PCB is 0.01-0.2 (2). The results fluctuate between the two In order to study the effect of various glass braid structures on antenna efficiency, a series fed microstrip patch array antenna was constructed on Rogers commercial laminate RO4835 and RO4830 thermosetting laminate The experimental results show that according to the conventional tolerance, the power efficiency of the antenna treated with RO4830 laminate is more consistent with the calculated value, with less variation, and the reflectivity and aiming gain efficiency are improved
PCB board

At present, autonomous vehicles are being studied, while drivers and pedestrians can avoid fatal accidents and require high reliability, and autonomous vehicles, that is, drivers and pedestrians, are currently being studied Help people avoid fatal accidents and require high reliability Therefore, these component circuits must be highly reliable The millimeter wave radar has a compact design and high environmental detection sensitivity, providing a reliable target detection solution for automatic driving For commercial millimeter wave radar systems with a frequency range of 76 to 81 GHz, the cross fed microstrip antenna has simple design, compact structure, mass production and low production cost
(1).  The higher the frequency, the shorter the wavelength. In summary, the size of transmission lines and antennas operating at millimeter wave frequency is smaller than that at low frequencies In order to ensure the perfect efficiency of automobile radar, it is necessary to study the influence of PCB on transmission line and microstrip antenna For millimeter-wave frequency circuits that work under the external environment (affected by temperature and humidity) for a long time.
(2).  When selecting PCB circuit laminates, the first thing to consider is the consistency of data performance indicators However, copper foil, glass fiber reinforced materials, ceramic fillers that make up the laminate, and other materials have a significant impact on the consistency of the indicator at high frequencies get up. Therefore, these component circuits must be highly reliable
Composition of laminate
Laminates are usually made by combining glass fiber cloth and polymer remain to form a dielectric layer, and then cover both sides with copper foil The typical dielectric constant (Dk) of glass cloth is relatively high, about 6.1, while The dielectric constant Dk of low loss polymer resin is 2.1-3.0 Figure 1 shows the microscopic top view and cross section of the glass braided fiber in the laminate Due to the high content of glass fiber, the periphery of the "knuckle bundle" has a high Dk. Due to the high resin content, the periphery of the "bundle" has a high Dk In addition, the minimum value is low. Many factors, such as the thickness of the glass cloth, the distance between the fabrics, the method of leveling the fabric, and the glass content of each axis, will affect the effectiveness of the glass cloth
Impact on transmission line chain
This test uses a transmission line diagram of a microchip with a 1 mm terminal connector.  The connector is first connected to a 50 ohm ground coplanar wave (GCPW) and converted to a high-impedance microcircuit transmission line through an impedance converter.  The length of the microstrip transmission line is 2 inches This enables the experimental scheme to test the effect of glass texture structure The solution uses a layer of copper and glass cloth, and is treated with a thin layer of polytetrafluoroethylene glass (PTFE) In order to compare the effects of different glass structures, we created a transmission line diagram using three different PCB laminated structures 1080 glass fiber PTFE polytetrafluoroethylene fabric, 1078 glass fiber PTFE polytetrafluoroethylene ceramic fabric filled PTFE laminate, 1080 glass fiber fabric Carefully check the processed circuit, display the appropriate transmission line for testing, and measure the amplitude and phase angle characteristics The phase angle (the phase value after opening), the group delay (based on the change of the phase angle with frequency) and the propagation delay (calculated by the phase angle) are the three parameters that determine the constant dielectric constant of the laminate.
In summary
The structure of the laminate affects the performance of the transmission line and antenna.  The construction method of glass fiber cloth changes the dielectric constant of the circuit, reduces the product efficiency and affects the product quality Compared with RO4835 laminate, the antenna made of RO4830 laminate has better refractive index efficiency compatibility The improvement of antenna efficiency and process production is mainly due to the combination of composite materials: flat glass fabric, low glass content (conductor away from glass fiber), thick coating, etc The antenna efficiency is related to the electrical efficiency of data (such as RO4830 laminate), with low dielectric constant and low loss tangent Therefore, the efficiency and compatibility of the antenna made of Rogers RO4830 laminate using low wavelength millimeter wave radar are better than those made of RO4835 laminate

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