What are striplines and microstrip lines? Reference planes and transmission lines

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A pair of conductors can form a transmission line , The signal travels between the pair of conductors in the form of electromagnetic waves . These two conductors , One is called “ Signal path ”, The other is called “ Reference path ” or “ Return path ”. The forms of transmission lines are varied , such as PCB Routing in 、 Coaxial cable, etc .

In our traditional sense , The signal is generated from the transmitter , after “ Signal path ” Reach the load , And then from the load along the ground line, that is, along “ Reference path ” Back to the transmitter , Form a loop .

But in the concept of transmission lines ,“ Reference path ” It has nothing to do with grounding , Even if the “ Reference path ” It's a floating metal conductor , It can also form a transmission line , yes , we have PCB The power plane is taken as the reference plane in the design . It's a bit like EMC In question , A metal enclosure for shielding , Whether the metal shell is grounded , Will have a different impact on the shielding effect . Besides , In the concept of transmission lines , As long as the transmitter just generates a signal ,“ Reference path ” There will be an accompanying return current at the same time , Not in the traditional concept , After the signal passes through the load, it flows back through the ground wire , This point will be described in detail later .

The process of transmitting a signal on a transmission line , It is a process of continuously establishing electromagnetic field , Establish an electromagnetic field when the signal changes , The signal is stable before and after the signal changes , There is no electromagnetic field .

Another important difference is , Traditional signal propagation model , It is regarded as a lumped parameter model , This model assumes that the signals at various positions on the transmission cable are the same , That is, the signal will be transmitted from the transmitter to the receiver soon . In the transmission line , The signal propagation model is a distributed parameter model , That is, the signals at various positions on the transmission cable are different , The signal is transmitted forward step by step , The following is the schematic diagram of lumped parameter model and distributed parameter model .

A pair of conductors meeting the above characteristics can form a transmission line , stay PCB Routing , Generally, a complete plane is used for “ Reference path ”, We used to call it a reference plane , For occasions with high signal requirements , The signal will have two reference planes , Even the left and right have accompanying holes .

These reference planes form a good transmission line model , The impedance can be controlled , Avoid reflection , Improve signal transmission efficiency , At the same time, it also plays a good shielding role .

We often hear about the concepts of microstrip line and stripline , What is a microstrip line and what is a stripline ？

Some people say that the surface line is a microstrip line , Memory routing is stripline , In fact, this answer has a big problem , Quite inaccurate . This is based on a specific internal company , Answer by conventional or habitual way .

The concept of microstrip line is a transmission line with only one reference plane , The stripline has two reference planes , But we only have a reference plane on the second layer when we route the surface layer , Meet the concept of microstrip line ; And the inner wiring , Due to the characteristics of the laminated structure , The signal line can have two reference planes , Satisfy the concept of stripline . therefore , Everybody just said , The surface route is the microstrip line , The inner line is the strip line , There is no problem in daily communication , But when you answer questions in an interview or written examination , Pay attention to the distinction between the two .

 

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