Quick RF Tips for General Reference

传送门：http://www.microwavetools.com/rf-tips-to-make-you-look-smart/

全文搬运过来的，本篇文章并未有其它意义和目的，仅作为个人参考笔记，我会标出认为有趣的部分并进行粗糙的翻译

了解这些规则可以用来快速评估射频产品的可行性，

• Electromagnetic energy such as microwave radiation travels one foot in one nanosecond in free space
• Linear passive devices have noise figure equal to their loss. Expressed in dB, the NF is equal to -S21(dB).
• Noise figure is dependent on the first gain stage. If there is 20 dB gain in a receiver LNA, the noise figure contribution of the subsequent stage will likely be insignificant.
• 噪声系数取决于增益放大的第一阶
• The third-order intercept point of an amplifier is generally 10 dB higher than its one-dB compression point, when measured at the output (9 dB higher at the input).
• 通常功放的3阶交调点会比它的1dB压缩点高10dB？
• Nepers? To convert neperts to decibels, multiply by ~8.68. (just use 9 for really quick conversions)
• The isolation of a Wilkinson is limited to 6 dB better that the return loss of the common port match.
• Metal loss is proportional to square-root frequency.
• 金属损耗与频率的平方根成比例
• Dielectric loss is proportion to frequency.
• 介质损耗与频率成比例
• The P1dB point of a mixer at its RF input is often about 6 dB less than its LO drive level.
• The noise figure of a mixer is approximately equal to the magnitude of its conversion loss.
• 混频器的噪声系数约等于其转换损耗的幅度
• N-way resistor power dividers are very lossy, power is transferred as (1/N)^2 compared to a lossless power divider which transfers power at (1/N).
• The number of elements in a phased array antenna can be used to estimate the total gain of the array. A 30 dB gain array needs ~1000 elements and a 20 dB gain array needs ~100, 10 dB needs ~10.
• 相控阵天线中的单元数目可以用来估计整个天线阵的增益，一个30dB增益的阵列大概需要1000个单元
• If your circuit does funny things when you close up the box, it’s oscillating!
• 如果你的射频电路安装到盒子里后发生了奇奇怪怪的事情那么它可能自激振荡了！
• A Wilkinson power splitter can be made in sections to increase bandwidth. To determine how many sections are needed divide the center frequency by the lowest frequency; i.e. 1-10 GHz, plan on 5 to 6 sections (5.5 is not an integer).
• You can electrically measure the approximate length of a transmission line by analyzing the frequency separation between the dips in VSWR.
• If you forget to build image rejection into your receiver design, you are probably adding 3dB to your receiver’s noise figure.
• 如果你忘了在接收器设计中加入镜像抑制，接收器的噪声系数可能会增加3dB
• Make sure you have more gain than you need, it is easier to change an attenuator than to add more gain to the final design. (With good designs oscillations should not be to much of a problem, but be weary of just adding gain, do a proper loss budget first!)
• For microstrip, you can cut metal losses by ~1/2 by doubling the dielectric thickness.
• The coupled port on a microstrip or stripline directional coupler is closest to the input port because it is a backward wave coupler.
• For stripline and microstrip, the attenuation factor always decreases almost linearly with characteristic impedance is reduced, lower impedance = lower loss.
• 对于带状线和微带线，衰减因素的的减少总是与特征阻抗的减小呈线性相关，低阻抗=低损耗
• A microstrip board height should never exceed 1/10 of a wavelength at the maximum frequency of it usage.
• Metal enclosures should have a height of less than 1/4 wavelength to attenuate radiated signals and avoid other weird things from happening. You can also buy materials designed to absorb RF signals, we prefer magnetic RAM but there are several other methods.
• Metal covers should be greater than 6 times the height the substrate thickness.
• 金属覆盖层的面积应大于基板厚度的6倍。？
• An acceptable voltage droop for a power amplifier during pulsed operation is 5%, which will drop the power by a similar amount (5%, or about a quarter of a dB). This should be used to determine the amount of capacitance needed.
• When designing a phase shifter multiple stages should be used for bits which induce more than 90° of delay. If designing a bit with more than a 90° phase shift use two elements, it is best to use one high pass element and one low pass element.
• E-plane of a wave-guide is “easy to bend” and the H-plane in rectangular waveguide is hard to bend.
• 波导的E-plane很容易弯曲，矩形波导的H=plane则很难弯曲
• The WR number a waveguide is simply the dimension of the broad wall in mils, divided by 10.
• The Bragg frequency is when a artificial transmission line stops acting like a transmission line. This often occurs when the artificial transmission lines unit cell is longer than 1/3 of a wavelength.
• For silicon, 110 degrees C is the maximum junction temperature for reliable operation.
• For SiGe, 110 degrees C is the maximum junction temperature for reliable operation.
• The return loss of a circulator is very nearly equal to its isolation.
• 环形器的回波损耗几乎与其隔离相等