按类别存档： sma接头常识

您对于sma头功率容量知道多少，如果您想了解sma头的功率容量想相关知识，看完这篇稿子就应该差不多了。

同轴电缆/接头功率处理是一个复杂的课题，但它可以分解成两种现象。高峰值功率会导致电弧引起的故障，而高平均功率会导致由于热导致的故障。

射频接头的功率承受与尺寸和材料有关，一般不能直接计算。同一种接头，使用材料不同，功率承受也不一样。

一般来说，接头的功率承受随信号频率变高而降低。对同一频率的射频信号，尺寸大的接头的功率承受大。比如一般的SMA接头，在2GHz的功率承受约为500W，在18GHz下的功率承受不到100W。BMA和SMA差不多，N接头的功率承受约为SMA的3-4倍。以上所述功率承受指连续波功率。如入射功率为脉冲则功率承受还要高些。注意如果传输过程的匹配不好，驻波过大，则接头上承受的功率有可能大于入射功率。一般为安全起见，在接头上加载的功率不应超过其极限功率的1/2。

Peak power handling

This section was greatly improved for August 2017.

Power handling of air coax is a topic that is related to atmospheric breakdown.

Once breakdown occurs, a short circuit is provided across the coax, and Hell breaks loose.

Arcing is caused when the electric field E exceeds a critical value which we will denote Ed for electric field at discharge. In air, the critical field is about 1,000,000 volts/meter, in PTFE it is raised to about 100,000,000. These numbers are approximate, there’s no sense trying to be exact in calculating breakdown, just be sure you avoid it by an order of magnitude or more and you’ll have little to worry about.

The electric field of a coaxial transmission line varies as a function of position along the radial line from the outer conductor to the inner conductor (denoted “ρ” in the radial coordinate system). You’d have to use calculus to derive this, but we just looked it up in Pozar’s Microwave Engineering.

Here, “b” is D/2 and “a” is d/2, the radii of the outer and inner conductors. The peak E-field obviously occurs right at the surface of the center conductor. If this isn’t obvious to you, consider becoming a program manager!

Rearranging the equation for the maximum peak voltage when breakdown occurs,

For fixed “b”, the magic ratio of b/a for highest voltage handling turns out to be exactly “e”, or 2.718… you can prove this easily by taking the derivative of the above equation and setting it to zero (ewww, calculus!) Note that the magic b/a=e ratio for maximum voltage does not change when dielectric is introduced into the coax.

Now, let’s recall a shortcut equation for coax impedance… the “60” in the equation is a close approximation of η0 (the impedance of free space, ~377 ohms) divided by pi. The equation is accurate to at least three decimal places.

At the max voltage condition, ln(b/a)=ln(e)=1. Thus the impedance of air coax that can handle the highest voltage is 60 ohms and the impedance of any coax with any dielectric that can handle the most voltage is 60/SQRT(ER).

The peak power you can put into a coax under well-matched conditions (low VSWR) is calculated from the peak voltage it can withstand:

The 2 in the denominator is necessary because we were considering peak voltage, not RMS.

Plugging the Z0 equation into the Pmax equation yields:

Taking the derivative with respect to “a” and setting it to zero, yields a different magic ratio for maximum power: (b/a) for max power=e^0.5, as opposed to (b/a)=e^1 for maximum voltage. Using the maximum power b/a ratio, you will find that impedance for maximum power is 30/SQRT(ER). Thus, for air coax, Z0=30 ohms optimum for power. For PTFE-filled cables (ER=2.2), Z0 is 20.2 ohms for maximum power.

Now that we have the final equation for maximum peak power handling of coax, we are ready to do some analysis. Remember that this result is only true for a matched load. If you accidentally broke a connection to a high-power transmitter, you’d see a very high VSWR, in that case the peak voltage could double. If you need to consider this type of mishap, you want to further de-rate your power handling by 6 dB.

Now let’s look at some coax examples… how about the air dielectric 50-ohm connectors? The breakdown strength of air 3,300,000 volts/meter according to Wikipedia, but that is at “dry air” at standard temperature and pressure, between spherical electrodes. Let’s use 1,000,000 volts/meter.

How about PTFE-filled coax? The breakdown field strength of PTFE is about 10,000,000 volts per meter! So “049” cable (0.049 inches “D”, 0.015 inches “d”) can withstand 2260 volts and pass almost 50,000 watts peak. This seems to good to be true, doesn’t it? It is. The problem is that with voltage breakdown, the limitation of the weakest link in the chain is what you need to focus on. Your semi-rigid cable might be able to pass thousands of watts, but as soon as that signal crosses a path where the PTFE dielectric fill is interrupted by air, it will spark. At the end of the cable, where the connector is soldered on, there is surely going to be a gap in the dielectric. You need to revise the calculation for air dielectric, in which case you’ll see 256 volts is the maximum voltage, 358 watts is the maximum power into a good load, and 89 watts is the maximum into an unmatched load. Note that at this interface the coax presents 71 ohms impedance.

Before we move on to average power handling of coax, let’s look at power handing as a function of line impedance for air coax, which is part of the “coax compromise” that led to the fifty ohm standard. If you allow the center diameter freedom to move away from 50 ohms, you’ll see that maximum peak power handling occurs at ~30 ohms.

By the way, if anyone wants a copy the spreadsheet that generated this curve, just ask. Eventually we will put it into our download area, it still needs some clean up and comments…

New for August 2017: additional thoughts on this. Peak power handling of air coax may not be at 30 ohms, if you consider another limitation. Suppose you are operating very close to the cut-off of the unwanted TE11 mode. Heck, let’s assume you want to operate exactly at TE11 cut-off. TE11 cuts off when (b+a)*pi is equal to operating wavelength. To cut to the punch line, at TE11 cut-off, 44 ohms carries the most power. You can find this fun fact and many more in Introduction to Microwaves by Gershon J. Wheeler, dating back to 1963.

For September 2017, we created a new page and posted the math behind the 44 ohm absolute maximum peak power handling calculation, it included two solutions: one is brute force, the other is elegant. At least they agree!

Average power handling

Average power causes failure due to heat, as opposed to arcing. Cable vendors provide some guidance on average power handling, but there is a lot of voodoo involved. Basically, you don’t want the center conductor to heat up so much that it compromises the integrity of the cable. In the old days, cable vendors might have derived power handling ratings experimentally.

The dissipated power per length is the variable you need to consider, and you will need to note that dissipation is a function of frequency, with the metal loss term being proportional to SQRT(f). Thus, a cable that can handle 100 watts at 4 GHz is only good for 50 watts at 16 GHz.

You must consider how the cable is cooled, i.e. is there forced air, convection, conduction and/or radiation? What is the air temperature? (It can be much higher than room temperature if it is inside a housing or chassis).

If average power handling is a concern, we are going to recommend that you (or someone who knows what they are doing) perform a thermal analysis using finite-element techniques. If anyone has an example average power handling study, please sent it!

本文由德索五金电子运营团队编辑整理，文章来源于网络，如有侵权，请及时联系我们，进行删除。若需采购sma连接器相关产品，请拨打我们的热线电话：0769-81153906，专业工程师辅助您的采购工作。德索五金电子，是一家主做射频连接器的厂家，有着十三年的历史，产品均通过了ISO认证，符合国际上的环保要求，一年内可享受免费质保的服务，欢迎前来采购。

sma转接头，也被人们称作sma适配器，它是转换连接器型号的一种元件，起到了一个桥梁的作用，是射频连接器中比较热门的一款产品之一。关于sma转接头的市场发展情况，是没有办法单独的去分析的，它的市场发展会跟随射频连接器的发展发展，下面我们来看看射频连接器的市场发展情况吧。

德索工程师指出，早在60年代开始，我国便能研制生产RF连接器。直到80年代初达到国际标准研制生产国际通用系列产品，当时主要以国营和集体企业为主，随着经济活跃，开始出现一些民营、合资和外资企业。一步步发展到现在，国内RF连接器生产厂家已过几百家，通用连接器的生产水平已与国外不相上下。未来小型化、高频化、多功能、低驻波、大容量是主要方向和发展趋势。所以sma转接头也是随着连接器市场一样继续发展!

关于sma转接头的市场发展情况分析就介绍到这了，更多与sma转接头相关的文章，我们的射频工程师会陆续整理发布在射频技术频道。如果您需要采购sma转接头系列的射频产品，请拨打我们的热线电话：400-6263-698，专业工程师辅助您的sma转接头采购工作顺利进行。

德索电子，是一家专业的射频连接器厂商，我们所生产sma转接头、sma连接器产品种类较多，备受市场的追捧。我们在长达14年的时间里，一直专注于射频产品的研发，逐渐开发出性价比超高的连接器模式，长期服务于全球多家知名企业，凭借着产品品质在客户心中留下量越好的口碑，致使德索射频连接器持续增长。

有谁知道sma接头的正确安装方法是什么，sma接头的正确安装，可以延长sma接头产品的使用寿命，降低维护成本，因此了解一些sma接头的安装方法十分必要。下面德索五金电子工程师就来为您讲解一下如何正确的安装sma接头，您可以要看好了，步骤不可乱，六步走轻松完成。

1、电缆内芯焊接在内针上

2、再把冷压管和热缩管穿在电缆上

3、焊好内针的线缆从接头小的那一端穿过

4、将线缆屏蔽层抱住焊线孔

5、冷压管从电缆端往接头端推入，压进屏蔽层

6、用压线钳将冷压管压紧。

网友观点：外围的脚接地，中间的脚接模块的信号输入点，信号输入点你可以根据内置天线的焊点来判断，sma-kwe同轴电缆接头不是为PCB专用的，可以按照普通同轴电缆封装BNC标准库画法。

sma接头的正确安装方法是什么就介绍到这里了，更多sma接头方面的内容请阅读频道其他技术文档。SMA接头好产品，尽在德索五金电子，快来与我们开展一次愉快的合作吧，让您的采购工作完美进行。多款sma接头系列优质产品，在我们官网上可以进行查询，快进去看看吧，不要犹豫了。每一款sma接头均通过ISO认证，符合国际上的环保要求，值得您的信赖。

深度好文分享，关于sma连接器的选择要求及其电缆性的介绍，感兴趣的朋友可以来阅读一下这篇文章，读完之后可以让你对于SMA连接器选择要求及电缆性有一个更深入的了解。德索电子是专业sma接头、sma接口、SMA连接器生产厂家，各种规格SMA连接器，更多未列出SMA产品，请联系我们索取更详细资料。

选择射频连接器考虑的因素，其中配接电缆和使用频率范围是主要的因素。在工程实践中，小和电缆直径尽可能相近，以最大限度地减少反射。电缆直径和连接器直径之间的区别越大，性能越差。

SMA射频连接器的选择既要考虑性能要求又要考虑经济因素 性能必须满足系统电气设备的要求经济上须符合价值工程要求。

在选择SMA射频连接器原则上应考虑以下四方面：

1、连接器接口(SMA、SMB、BNC等)

2、电气性能、电缆及电缆装接

3、端接形式(PC板、电缆、面板等)

4、机械构造及镀层(工防、商用)

SMA射频连接器电缆性：

1)电视电缆因其屏蔽性能低，通常用于只考虑阻抗的系统，一个典型的应用是电视天线。

2)电视软电缆为电视电缆的变型，它有相对较为连续的阻抗及较好的屏蔽效果能弯曲、价格低 广泛用于电脑业，但不能用于要求有较高屏蔽性能的系统。

3)屏蔽软电缆消除了电感及电容主要用在仪器和建筑上。

4)软性同轴电缆由于其特殊的性能而成为最普遍的密闭传输电缆。同轴意味着信号和接地导体在同一轴上，外导体由细致的编织线构成 ，所以又称编织同轴电缆。此电缆对中心导体有良好的屏蔽效果其屏蔽效果，取决于编织线类型和编织层厚度。除有耐高压特。

5)性外此电缆亦适应在高频及高温条件下使用。

6)半刚性同轴电缆用管状外壳取代了编织层，有效地弥补了编织电缆在高频时屏蔽效果不佳的缺点，频率很高时通常都使用半刚性电缆。

SMA射频连接器电缆装接：

SMA射频连接器安装方法主要有两种：(1)焊接中心导体，旋接屏蔽层。(2)压接中心导体，压接屏蔽层。其它方法部由以上两种方法派生出来，如:焊接中心导体，压接屏蔽层。

SMA射频连接器方法(1)用于没有特殊安装工具的场合;由于压接式装接方法工作效率高，端接性能可靠，且专用压接工具的设计可确保装接出来的每个电缆蛆件部是相同的，所以随着低造价装接工具的发展，焊接中心导体压接屏蔽层将日益受到欢迎。

德索五金电子专业的sma连接器生产厂商，至今已有十六年的sma连接器生产经验，每一款关于sma的连接器产品均通过了ISO认证，符合国际环保要求，并且承诺每一位客户一年内免费享受质保，有需要的用户可以拨打电话：400-6263-698联系我们进行采购。

以下内容整理自客户发来的邮件，询问的是关于sma接头与tnc接头承受功率方面的问题，在这里德索编辑部进行了一个汇编整理，供大家查阅。德索tnc接头咨询电话：0769-81153906，欢迎前来咨询。

问题描述：

SMA的接头可以用到18GHz,TNC的接头可以用到11GHz，有谁知道SMA接头和TNC接头能承受的功率是多少啊?(额定值和正常的使用值)

工程回答：

客户朋友，您好！不知道您需要多大的一个功率?SMA接头的承受功率相较TNC接头的较小，这是由于线缆决定的，而是不接头。具体的你可以看看线缆的功率容量。11G，18GHz 的功率，你也做不了多大。

如果您有还有关于SMA与TNC接头的其他问题，也可以向我们发送邮件咨询，我们会安排工程师及时给您答复。德索电子生产的SMA接头、TNC接头通过ISO认证，符合国际环保要求，并且承诺一年内质保服务，让您购后无忧。

德索五金电子，专注于射频连接器的生产研发与销售，有着十三年的经验积累，可熟练解决各种生产设计方面的难题，并且提供定制服务，满足您的特殊需求。在德索采购SMA接头、TNC接头产品，无需排单，我们有自己的工厂，可以确保及时交货。