In PCB design, microstrip line and stripline are two common transmission lines used to transmit signals, respectively. Although they are similar in many ways, there are great differences in their physical structure, transmission rate, characteristic impedance, etc.
This article will introduce the basic concepts, characteristics, and application scenarios of microstrip line and stripline, and compare their advantages and disadvantages to help designers choose the right transmission line when designing PCB circuits.
Microstrip lines (bottom line traces)
Microstrip is a transmission line that separates metal channels from ground planes, and due to its miniaturization and ease of integration, microstrip lines are widely used in high-speed digital, radio frequency and microwave circuits. The main component of the microstrip line is a narrow width and relatively small thickness of single and double metal channels, usually designed to be stacked on the surface or inside the PCB.
The characteristic impedance of the microstrip line changes with the change of wire diameter and dielectric constant, and the change of its characteristic impedance can be achieved by adjusting the width of the microstrip line, board thickness, or dielectric constant.
For microstrip lines, in general, higher characteristic impedances and transmission rates can be achieved through using independent hierarchical or layered techniques, which can eliminate magnetic field interference between channels, which is the main advantage of microstrip lines.
Striplines (inner traces)
A stripline is also a transmission line that uses metal conductors and is one of the common structures in PCB circuits. The structure of the strip line differs from the microstrip line and consists of a metal path made of metal foil with a large width. Compared to microstrip line, board with stripline has a simpler structure and can be achieved by designing a printed circuit board (PCB) with only one layer.
The characteristic impedance of the stripline changes with the change of wire diameter and dielectric constant, and its characteristic impedance can be achieved by adjusting the width, height, or distance from the ground plane of the stripline.
Due to the simple structure of the transmission line of the stripline, relatively few processing processes are required in the circuit design and production, which makes the stripline easier to produce than the microstrip line, and at the same time relatively low-cost.
Comparison of microstrip line and stripline
Microstrip line and stripline may have some differences in characteristic impedance, transmission rate, structure, and performance. Several advantages and disadvantages of microstrip line and stripline comparisons are listed below:
The characteristic impedance of the microstrip line changes relatively large, and it is easy to electromagnetic interference between nearby lines, so some special techniques are needed to overcome these problems. The characteristic impedance change of the stripline is small, and the anti-interference ability is strong, which is often used in the design of high-density circuit boards (HDI PCB).
Under the same conditions, microstrip lines can usually achieve higher transmission rates. Because the structure of the microstrip line can reduce the signal-to-noise ratio and cross-interference, this is especially important for high-speed digital and high-frequency RF circuits. Striplines have a lower transmission rate than microstrips.
The structure of the microstrip line is more complex, because the transmission line structure of the microstrip line is layered, so it requires designers to spend more energy to design and manufacture. In contrast, the structure of the stripline is simple, easy to handle and produce, and also saves some problems in terms of cost and process handling.
Microstrip line has good anti-electromagnetic interference ability, high characteristic impedance and better transmission rate, which is suitable for high-speed digital and high-frequency RF circuits. Striplines have small characteristic impedance changes, are easy to handle and produce, and are more suitable for low-speed digital and analog circuits.
It should be noted that when selecting a transmission line, it should be selected according to the design and application needs. In addition to microstrip line and stripline, transmission lines such as shaft cables, parallel cables, etc. can also be selected. For general board design, microstrip line and stripline are one of the most commonly used and reliable solutions, and designers must weigh their advantages and disadvantages and choose them according to actual needs.
From this, we can conclude that microstrip line and stripline are two commonly used PCB transmission lines, although they have great differences in structure, characteristic impedance, transmission rate, anti-interference ability and manufacturing cost, but they all have their own advantages and application scenarios. When selecting a PCB transmission line, microstrip line or stripline should be selected according to the requirements and special needs of the actual application environment, so as to achieve better results for the high-speed, high-quality and high-reliability transmission of the circuit.