#Rule the waves patch skin#
The “skin depth problem” is that you didn't achieve at least three (preferably five) skin depths so you didn't do your best to minimize loss. But if you are working on the bias circuits for high power, current-hungry solid-state amplifiers down at DC, then adding more copper can decrease the loss, as ALL of the copper is used in conduction. To clarify that obtuse statement (thanks to Sylvia), if you are working at microwave frequencies, using more than ½ ounce copper does not improve loss as you can reached the maximum surface conductivity. If you are using copper boards with half-ounce or thicker copper, you don't have to worry about skin depth problems unless you are working below 200 MHz.Five skin depths of a good conductor will keep your losses to a minimum in microstrip.This is one outcome of the skin depth effect. The loss of a branchline coupler is reduced as the square-root of frequency, given that the same substrate and metallization is used.
![rule the waves patch rule the waves patch](https://www.researchgate.net/publication/320963374/figure/fig7/AS:960230552764416@1605948212011/Patch-discretization-of-the-domain-shown-in-Sect71_Q320.jpg)
2003, Microwave Solid State Circuit Design, 2 Ed, John Wiley & Sons, New Jersey, p.377 This related rule came from John, who also supplied a reference (thanks!) The minimum noise figure of a BJT varies quadratically with frequency, up until Fmax.
![rule the waves patch rule the waves patch](https://i.ytimg.com/vi/IcPqFk3wUtY/maxresdefault.jpg)
These rules are scattered about the web site in appropriate places as well. We will keep compiling microwave rules of thumb on this page, in no particular order, and we don't guarantee that we will reorder the rules in the future. any tired references to Murphy's law will never make it to this page, so please don't feel the need to share any of this boring crap with us! We know there are a lot of OFs out there, so please send in your favorite rule of thumb and win a pocket knife (what OF could resist an offer like that?) We will acknowledge your contribution here (unless you prefer to remain anonymous). Microwave rules of thumb have been handed down to new-hires by microwave old farts for the last century.
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Obviously, you must use some discretion when you apply these rules, exact results can vary widely depending on influences you haven't considered, such as the phase of the moon. What we mean by a microwave rule-of-thumb could be an inexact but notable relationship of one or more design parameters with performance, or it could just be an easy way to remember something that other lesser people often mix up. Sadly, in some countries today women have to deal with even worse treatment. The origin of the phrase "rule of thumb" is debatable some say it was once a man's right to beat his wife with a stick no wider in diameter than his thumb.