Introduction

Microstrip

Microstrip is a strip-mounted wire, isolated from the ground plane by a dielectric, sitting on top of a thin insulation layer with a large ground plane underneath, making impedance control relatively difficult. . Air has a lower PCB dielectric constant, so the overall microstrip line has a lower equivalent dielectric constant (about 2-3). The transmission rate of signals on microstrip lines is faster (about 5708ps per meter). Since microstrip lines are distributed on the PCB surface, the number of layers can be saved and used for high-density wiring, but they are more susceptible to interference.

Stripline

A copper tape line placed in the middle of a dielectric between two conductive planes. The electric field of the stripline is only in the PCB range, and it is relatively easy to control the impedance. The dielectric constant of the medium around the strip line is high (about 4.4), and the signal transmission speed is relatively slow (about 7283ps per meter) Because it is inside the PCB, it is not easy to interfere.

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Think of microstrip lines as the open-road drivers of the electronic signal world. They’re kind of like a single-lane road on a circuit board. The microstrip line has a conductive strip, just sitting on top of an insulating layer, with a big ground plane underneath. It’s pretty exposed, which makes it easy to work with, but it also means it can pick up some noise.

striplines are more like the subways of signal travel. They run a conductor strip but it’s tucked away, sandwiched between two ground planes, all encased in insulation. This design is great for keeping signals clean and free from interference – it’s like traveling in a quiet, underground tunnel, away from the hustle and bustle above.

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they both serve the same purpose: getting those electronic signals from point A to point B. The choice between them often comes down to the specific needs of your project. Microstrip lines are easier to manufacture and inspect, thanks to their open design. But if you’re dealing with sensitive signals and want to minimize interference, striplines are your go-to.

Microstrip line or strip line loss, which is greater?

Stripline has greater losses compared to microstrip. Mainly due to its design and materials used. In transmission lines, there are two main types of losses we discuss: conductor losses and dielectric losses. It’s a bit like comparing the wear and tear of two different types of roads and the vehicles that use them. Think of it as the friction between your car’s tires and the road. Its expression involves the surface roughness of the conductor, its skin depth (frequency dependent), and the inherent resistivity of the material.

The reason stripline typically has greater losses than microstrip comes down to the way they are constructed. A stripline is like a completely enclosed road sandwiched between two ground planes. This design results in higher dielectric losses. This is similar to how a car might use more fuel when driving on a hilly, closed road than on a smooth, open road.

Microstrip lines are more exposed, with only one side covered by the ground plane. This openness means they tend to have lower dielectric losses, just as a car faces less resistance when traveling on a straight, open highway.

How to choose microstrip and stripline？

Deciding whether to use a microstrip line or a stripline in your product is a bit like choosing the right tool for a specific job – each has its strengths and ideal applications. Let’s break down what you should consider when making this decision:

1. Electromagnetic Interference (EMI) Susceptibility: Think of microstrip lines as being more exposed to the elements, like a road above ground. They can pick up more external noise, so if your product is in a high EMI environment, striplines, which are more like underground tunnels, might be the better choice.
2. Signal Integrity: Striplines, thanks to their sandwiched design, are better at keeping the signal intact without interference from external sources. If your product needs to maintain very clean signal paths, striplines are often preferred.
3. Cost and Complexity: Microstrip lines are generally easier and cheaper to manufacture because they’re only on the surface of the PCB. Striplines, on the other hand, require more layers in the PCB, making them more complex and costly to produce. If budget and simplicity are key, microstrip might be your go-to.
4. Size and Weight: Microstrip lines are less bulky compared to striplines since they need fewer layers in the PCB. In applications where size and weight are critical, like in aerospace or wearable technology, microstrip lines might be more suitable.
5. Frequency of Operation: The higher the frequency, the more you need to consider losses and signal integrity. Striplines generally offer better performance at higher frequencies due to their shielded nature.
6. Thermal Management: Microstrip lines are better at dissipating heat because they are exposed to air. If your product generates a lot of heat, this could be a deciding factor.
7. Flexibility in Design: Microstrip lines offer more flexibility in layout and are easier to connect to other components. If your design requires complex routing or frequent connections to other elements, microstrip lines might offer the practicality you need.

Conclusion

The world of PCB design offers fascinating choices between microstrip and stripline, each analogous to different paths in electronic signal transmission. Whether choosing ventilation height for microstrip lines or shielding depth for stripline, designers balance factors such as interference susceptibility, signal integrity, cost, and complexity. It’s a testament to the nuanced art and science of PCB design, where every decision is woven into the intricate tapestry of modern electronics. As we continue to innovate and push technology boundaries, microstrip and stripline are key choices in our quest to connect and enhance the electronic world.