In high-frequency circuit design, Rogers PCBs have long been recognised as the industry standard thanks to their outstanding performance. With their stable dielectric properties and low-loss characteristics, they are virtually indispensable core materials in high-end fields such as 5G communications, millimetre-wave radar and aerospace.
As the key medium for signal transmission, the choice of transmission lines—particularly microstrip and stripline—directly determines the signal integrity, interference immunity and overall cost-effectiveness of the design. Many engineers tend to fall into the trap of thinking solely in terms of ‘performance first’ or ‘cost first’ when selecting components, overlooking how well these factors align with the characteristics of Rogers materials.
A rational selection process not only fully leverages the material advantages of Rogers PCBs but also effectively reduces design costs and shortens debugging cycles; this is precisely the key to enhancing product competitiveness in high-end PCB manufacturing.
Unlike standard FR4 boards, Rogers PCBs utilise a specialised hydrocarbon ceramic laminate that maintains excellent dielectric stability even in high-frequency scenarios above 500 MHz. Characteristics such as a low coefficient of thermal expansion, high thermal conductivity and low outgassing provide a reliable guarantee for the stable operation of microstrip and stripline structures.
Microstrip and stripline are the two most commonly used transmission line structures on Rogers PCBs; it is not simply a matter of one being ‘superior’ to the other, but rather that each has its own specific applications. The core differences lie in structural design, signal transmission characteristics, manufacturing complexity and cost control. The key to selection lies in ‘scenario adaptation + material matching’, rather than blindly pursuing a single performance metric.
Microstrip and Stripline: Key Structural Differences on Rogers PCBs
The microstrip structure on a Rogers PCB is very simple, consisting solely of the top-layer signal copper foil, the Rogers dielectric substrate in the middle, and the full ground plane on the bottom layer; the signal traces are exposed on the substrate surface and require no additional shielding.
The advantage of this structure lies in its ease of fabrication, as it eliminates the need for complex internal routing and interlayer alignment. This helps to reduce the manufacturing costs of Rogers PCBs and facilitates subsequent signal debugging and component soldering. Thanks to the uniform material structure and stable dielectric constant of Rogers PCBs, microstrip lines can achieve precise impedance control.
In actual production, the selection of microstrip lines on Rogers PCBs is often concentrated in high-frequency applications where cost is a key consideration and shielding requirements are not particularly stringent. However, due to structural limitations, the electromagnetic field of a microstrip line cannot be fully confined within the dielectric; some field lines extend into the air, resulting in a quasi-TEM wave propagation mode. Consequently, there is a certain degree of radiation loss, and resistance to external electromagnetic interference is relatively weak—in millimetre-wave high-frequency scenarios, this loss becomes increasingly pronounced as frequency rises.
Striplines, on the other hand, embed the signal conductor within the inner layers of the Rogers PCB, with complete ground planes above and below. The signal conductor is fully enclosed by two layers of dielectric material and two ground planes, forming a structure similar to a flat coaxial cable. This enclosed structure confines the stripline’s electromagnetic field entirely between the upper and lower ground planes, resulting in a pure TEM wave propagation mode with virtually no radiation loss. It also offers excellent resistance to external electromagnetic interference, with crosstalk control far superior to that of microstrip lines.
For Rogers PCBs, their low thermal expansion coefficient and excellent interlayer adhesion effectively prevent issues such as delamination and signal displacement during the manufacturing and use of striplines. Consequently, ribbon traces on Rogers PCBs are better suited to applications with extremely high signal integrity requirements.
However, ribbon traces are more difficult to manufacture, requiring precise control of the inner conductor positioning and interlayer thickness. This places higher demands on the manufacturing process of Rogers PCBs, resulting in higher production costs compared to microstrip lines. Furthermore, post-production debugging and maintenance are inconvenient, as direct access to the signal conductors is not possible.
Overall, microstrip lines better leverage the advantages of ease of fabrication and cost control, making them suitable for low-to-mid-frequency applications with modest interference requirements; conversely, ribbon lines fully utilise the interlayer stability and low-loss characteristics of Rogers PCBs, making them suitable for high-frequency, high-interference-resistance and high-reliability applications.
Key Considerations for Selecting Rogers PCBs
Frequency Requirements
The advantages of Rogers PCBs are particularly evident in high-frequency applications, where the loss characteristics of microstrip and stripline differ significantly at different frequencies. When the design frequency ranges from 500 MHz to 20 GHz and there are no stringent requirements regarding signal radiation or interference, microstrip is the preferred choice. For example, in a 5G base station antenna board (3.5 GHz) using Rogers RO4350B material, a microstrip line width of just 0.8 mm is sufficient to achieve a 50 Ω impedance, meeting signal transmission requirements whilst reducing manufacturing costs.
However, when frequencies exceed 20 GHz, particularly in millimetre-wave applications (such as 77 GHz automotive radar), radiation loss becomes a key factor affecting signal quality. In such cases, the enclosed structure of striplines helps to reduce losses; when combined with low-loss materials from the Rogers RO3000 series or RT/Duroid series, stable signal transmission can be ensured. It should be noted that when using microstrip lines in the millimetre-wave band, thinner Rogers PCB materials should be selected to reduce radiation losses and suppress the generation of spurious modes.
Signal Integrity
Where designs demand high levels of low loss, low crosstalk and high shielding performance—such as in aerospace and defence radar applications—striplines are the obvious choice. Rogers PCBs’ low dielectric loss and uniform material structure further enhance the signal integrity of striplines, whilst their enhanced plated-through-hole reliability effectively protects interlayer connections, preventing signal drift caused by temperature variations.
For applications such as consumer electronics and standard RF modules, where signal integrity requirements are moderate and cost control is a priority, microstrip lines can meet basic requirements. When paired with the more cost-effective Rogers RO4000 series materials, a balance between performance and cost can be achieved. For example, when designing Wi-Fi 6E circuit boards (6 GHz) using microstrip lines, optimising trace corners (by employing 45° chamfers or rounded transitions) can effectively reduce return loss and meet signal transmission requirements.
Manufacturing Costs and Lead Times
Microstrip structures are simple, requiring no internal routing or complex interlayer alignment. The manufacturing process is straightforward, helping to shorten the production cycle and reduce manufacturing costs for Rogers PCBs, making them particularly suitable for small-batch production or rapid prototyping.
In contrast, stripline requires precise control of the position of internal conductors and interlayer thickness, demanding higher manufacturing precision and a more complex process. This not only increases manufacturing costs but also extends the production cycle, making it more suitable for high-volume, high-reliability products.
Furthermore, the manufacturing difficulty varies across different Rogers material series. For example, the RT/Duroid series, which is based on PTFE material, has higher process requirements; if combined with ribbon traces, the increase in manufacturing costs must be taken into account.
Number of PCB Layers and Layout Space
In single-layer or double-layer Rogers PCBs, microstrip is the only viable transmission line option. Its surface-layer routing structure does not require additional layers, which helps to control PCB thickness and cost.
In multi-layer Rogers PCBs, the choice can be made flexibly according to layout requirements: if dense routing is required whilst avoiding signal interference, sensitive signals can be routed using striplines embedded in the inner layers, whilst non-sensitive signals can be routed using microstrip lines on the surface layers, thereby achieving a dual improvement in space utilisation and signal quality.
For example, in multi-layer millimetre-wave radar Rogers PCBs, the core signal transmission lines are typically designed as striplines, whilst peripheral auxiliary lines are designed as microstrip lines. This ensures the stability of the core signals whilst reducing the overall design complexity.
In the practical application of high-frequency design for Rogers PCBs, the choice between microstrip and striplines is not a simple either/or decision, but rather a careful balancing act involving performance, cost, manufacturing processes and specific application scenarios. The degree to which both are suited to the characteristics of the Rogers PCB material directly determines whether the design can achieve the optimal balance between signal quality, manufacturing efficiency and overall cost.
