本文翻译自Microwaves101 | Microwave Rules of Thumb，汇总了一些微波电路中的经验法则（Rules of Thumb），所谓经验法则，就是一些长期总结出来的规律，多数情况下适用，但并不是任何时候都适用，请读者自行斟酌。
Electromagnetic radiation at frequencies higher than light (such as x-rays) can cause cell damage (ionizing radiation). EM radiation below
light (such as microwaves) don't damage cells, they only cause heating
(which can cause injury as well, but is easy to avoid because it causes
pain!)比光频率高的电磁辐射（例如x射线）会导致细胞损伤（电离辐射），比光频率低的电磁辐射（例如微波）不会损伤细胞，只会导致热效应（虽然也会造成伤害，但容易避免，因为会感觉疼痛！）
This additional info came from John (thanks!)以下附加信息来自John：
I would like to add some important information pertaining to
microwave rule of thumb 51. Specifically the rule states that
non-ionizing radiation injury is easy to avoid because the heat it
generates causes pain.我想就微波经验法则第51条增加一些重要信息，该条特别指出非电离辐射伤害容易避免，因为产生的热会导致疼痛。
Exposure to microwave radiation at power levels below the pain
threshold does cause heating in the lens of the eye producing cataracts.
Heating denatures proteins in the crystalline lens of the eye (in the
same way that heat turns egg whites white and opaque) faster than the
lens can be cooled by surrounding structures. The lens and cornea of the
eye are especially vulnerable because they contain no blood vessels
that can carry away heat. The damage is accumulative and over time
degrades vision. High power levels will produce discomfort that includes
irritation of the eye however; levels of power well below the average
person’s pain threshold will induce cataracts over time. It should be
noted that frequencies whose wavelength more closely match the size of
the eye (X-band freqs with wavelengths in the 2-4 centimeter range) are
particularly dangerous.暴露在功率电平低于疼痛阈值的微波辐射中仍然会导致眼球产生热效应进而引发白内障。热效应导致眼睛晶状体中的蛋白质变性（跟鸡蛋清受热变白不再透明同理）的速度比眼球被其他周围结构降温更快。眼球与眼角膜特别容易受损，因为它们没有血管散热。这种损伤是可以累积的，逐渐导致视力下降。高功率的电磁辐射会导致包括眼睛刺激感在内的不适症状，但功率远低于人体平均痛觉阈值的电磁辐射长时间仍会导致白内障。需要注意的是，对应波长与眼睛尺度更接近的频率（X波段波长2-4cm）更是极度危险！
Also, there has been some infomation in the news on terahertz waves, which are purported to unzip DNA molecules. Stay tuned! - UE此外，还有一些关于太赫兹电磁波的新闻报道，据称可以导致DNA分子断裂。
When measuring S-parameters to get group delay, you should pick the frequency interval to achieve about 10 degrees S21 phase difference between frequency points. Less than this will make the measurement jumpy, greater than 10 degrees might mask some real problems in group delay flatness. How do you know in advance what frequency interval to pick? Excuse us while we go think up a formula for this...通过测量S参数来计算群时延，应将频率间隔设置为相邻频点S21的相位差约10deg，如果相差小于10deg可能导致测量结果容易跳动，而如果相差大于10deg则可能导致忽略掉群时延平坦度中隐含的一些真实问题。若你要问怎么计算频率间隔，很抱歉得等我们想个公式出来……
If you divide the switch element Figure of Merit by 10 (FOM=(1/(2
pi*Ron*Coff)), you will arrive at the highest frequency that the device can be made to perform as a switch. Thus MESFET switches will work up to about 26 GHz, PHEMTs will work up to 40 GHz, and PIN diodes will work up to 180 GHz.如果将开关元件的性能系数除以10（性能系数FOM=(1/(2pi*Ron*Coff)），你就得到了该元件能用于作为开关的最高工作频率。因此MESFET开关最高能工作到大约26GHz，PHEMT开关大约工作到40GHz，PIN二极管开关可以工作到约180GHz。作者注：简言之，开关元件的Ron*Coff值越小越好。
When you are counting the number of squares in a meandering resistor to determine its value, the squares at each bend should be counted as 1/2 square.数方块数来计算蛇形弯折电阻的阻值时，每个拐角应算作1/2个方块。
Switch isolation is often limited by package isolation. If you design a 60 dB switch, you should think carefully about how to package it!开关的隔离度通常都是受限于封装的隔离度，如果你设计一个60dB的开关，你应该仔细考虑如何封装！
Linear passive devices have noise figure equal to their loss. Expressed in dB, the NF is equal to -S21(dB). Something with one dB loss has one dB noise figure. But wait, as Gene points out, there is more to consider! This statement is true only if the passive linear device is at room temperature. You'd best analyze the problem using noise temperature.线性无源器件的噪声系数等于其损耗，以dB来计算，NF=S21(dB)。损耗为1dB的器件噪声系数就是1dB。且慢，正如Gene指出，还有更多需要考虑的因素！上面的论述当且仅当该线性无源器件在室温条件下才成立。你最好用噪声温度来分析这个问题。
If you have 20 dB gain in your LNA or receiver, the noise figure contribution of the subsequent stage will be small (unless the noise figure of the next stage is horrendous!)如果你的LNA或者接收机有20dB增益，那么后级贡献的噪声系数就很小了（除非后级的噪声系数大到可怕！）
Twenty dB of image rejection is about all you need before you can neglect image noise foldover. Worst case, image noise foldover can degrade receiver noise figure by 3 dB.只要20dB的镜像抑制基本上就可以忽略掉镜像折叠噪声。最坏情况下镜像折叠噪声会导致接收机噪声系数恶化3dB。
The minimum width for a stripline that is encased by metal on the edges is 5 times the line width, in order for the impedance to calculate with the "normal" closed form equations.带状线两侧边沿被金属覆盖的最小宽度为5倍线宽时，才能以“常规”闭合形式的方程来计算阻抗。
The angular beam width of a parabolic reflector can be estimated from the diameter of the dish and the frequency of operation as: angular beam width (degrees)=70 degrees/(D/lambda). Corrected thnks to Vincenzo!抛物面反射天线的角波束宽度可以用天线的直径D和工作频率（波长lambda）估算：角波束宽度(deg)=70deg/(D/lambda)。
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