The Challenges with RF PCB Design

As RF PCBs, radio frequency PCBs, can be found in a large variety of commercial products, most of which are handheld wireless devices for medical, industrial, and communications applications, it is important that we understand the challenges that designers can face within RF PCB design.??

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There are many new challenges for PCB designers when handling RF board. Among them, the top four factors are:?

1. RF is far more sensitive to noise, incurring ringing and reflections, which must be treated with great care.?
2. Impedance matching is extremely critical for RF. And, the higher the frequency, the smaller the tolerance becomes. Practically, only if the total length of the trace from the driver to the receiver is greater than 1/16th of the wavelength of the signal, then impedance control of that trace is required (1/16th of the wavelength is called the critical length of the signal). For example, if you are routing a 1GHz signal and its total length is greater than 425 mils, then that trace needs to be impedance controlled.?
3. The return loss must be minimized. At very high microwave frequencies, the return signal takes the path of least inductance. As a result, without good PCB design, the return signal will go through power planes, through a PCB’s multi-layers or through some other route, and it will no longer be an impedance-controlled signal.?
4. Crosstalk is a major issue in high frequency designs. This is because crosstalk is directly proportional to the edge rates of the active line. In this case, the coupled energy from the active line will be superimposed on the victim line. When the board densities increase, the problem of cross talk becomes more critical.?

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Tips about RF PCB design for designers:?

Now that we know what some of the challenges are, let us look at some design tips. ? To achieve more reasonable design and better anti-interference ability for high frequency PCB (Microwave RF PCB), design engineers should consider the tips as following:

1. Use inner layer as power ground layer, which will have the effect of shielding and even decreasing spurious inductance, shorten length of signal wire, reducing cross interference between signals.?
2. Circuit layout must be turn with 45-degree angle, which will help to reduce high frequency signal emission and coupling between each other.?
3. The shorter the better for length of circuit layout.?
4. The less the better for through holes.?
5. Layout between layers should be in vertical direction, top layer as horizontal direction and bottom layer as vertical direction, because this will help to reduce the signal interference.?
6. Increasing copper on ground layer to reduce the signal interference.?
7. Do package for important signal traces can obviously improve signals anti-interference ability. Of course, we can also do package for interference sources to avoid interference on other signals.?
8. Signal traces layout should avoid loop, but should layout according to chrysanthemum link.?
9. In the power section of integrated circuit, bridging decoupling capacitor.?

Get it right from the start – download our PCB design guidelines?

To prevent getting it wrong from the start, we have put together our design guidelines, to use as a checklist.?

Download our design guidelines

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