RF/Microwave PCB Design and Layout GuidePosted on 2022-04-22
射频 (RF) 和微波 PCB 是需要特殊设计和布局的流行 PCB。在本指南中，您将了解构成成功射频/微波PCB 设计的要素，包括设计注意事项、材料选择、集成组件等。
射频和微波电路板处理从手机到军用雷达的通信中常用的兆赫兹到千兆赫兹（极低频到极高频）频率范围内的信号。在布局、制造和组装建议方面，RF 和微波 PCB 是一回事。
传输线是将能量从一个点传输到另一个点的导线或导体。这些是铜结构，可通过 PCB 传输电信号而不会中断或干扰，并防止电磁干扰 (EMI)。
Surface microstrip (copper traces will run across the surface)
Strip line from edge to symmetrical
Strip lines are usually embedded, and microstrips are located on the surface. Coplanarity is another type of transmission line.
All transmission line structures will carry the impedance.
The exact components will vary depending on the specific PCB, but the following list details the important components commonly found in RF/Microwave PCB designs:
Layout techniques and strategies
You need to know the impedance of the transmission line, which is also directly related to the PCB material you choose. The engineer will help determine what type of power line is required.
The RF/Microwave PCB layout is typically a transmission line on top, copper traces followed by a dielectric material. The second layer is the ground or force plane. All this directly affects the impedance of the transmission line, the width of the copper tracks and the height of the material on the board.
Noise is one of the most important problems in RF/Microwave circuits. These types of circuit boards are often made from digital power supplies, which means they can be noisy. It is important to isolate the RF part of the circuit to avoid such interference. In some cases, you can protect your circuit from cosmic noise; other times you need a grounded barrier or shield around the circuit.
Materials and Board Stacks
RF and microwave printed circuit boards are often manufactured using advanced composite materials with very specific properties of dielectric constant (Er), loss tangent and coefficient of thermal expansion (CTE).
High frequency circuit materials with low stable Er and loss tangent allow high speed signals to pass through the PCB with lower impedance than standard FR-4 PCB materials. These materials can be mixed in one package for optimum performance and economy.
It is important to consider impedance calculations, which are closely related to material selection. Dual layer boards are relatively simple, but multilayer PCBs can be more complex. For example, in a stack of RF/Microwave printed circuit boards, the transmission lines and ground planes must be adjacent to each other. If separated by two layers, engineers use software to help design the correct stack to determine the height and weight of all layers.
Some materials are more suitable for RF/MW PCBs than others, but this depends on the frequency. For example, Teflon is ideal for high frequency printed circuit boards due to its low loss tangent.
Skin effect and loss tangent
Skin effect refers to the noise picked up on the board by the copper traces. The loss tangent is a measure of the dielectric loss caused by electromagnetic energy. High frequency circuit materials with low stable Er and loss tangent allow high speed signals to pass through the PCB with lower impedance than standard FR-4 PCB materials.
RF/Microwave printed circuit boards typically use materials with lower loss tangents.