请问 如何测试 各类 传输线 特性阻抗 是否为 50欧 ?

yellowtoot

大家都知道, 矢网可以测S11, 并给出相应的输入阻抗(Zin)
其中所测S11的参考面, 为校准矢网时校准件(开路,短路,匹配)所连接的位置.
此外, 矢网有一功能"electrical delay",可以用于更改上述的参考面.

目前偶遇到一个问题, 就是需测量一个 RF 连接器 是否为50欧特性阻抗的.
这个连接器一头是N头,可直接连到矢网上,而另一头是个探针,相当于一个终端开路的同轴电缆.
因此无法将这个连接器串联在矢网的两个端口之间. 而只能在其另端开路的情况下测试S11.

请问在这种测试条件下, 可否知道该连接器是否为50欧特性阻抗的?

如果是50欧的,我觉得,当通过"electrical delay",改变参考面时, SMITH圆图上的点会围着大圆转动, 毕竟终端开路点是在大圆的最右端的.

但如果不是50欧的, 同样,SMITH圆图上的点也会围着大圆转动, 只是在相同的"electrical delay"设置条件下,转动的角度不同.

我是否可以根据这个角度测量出该连接器的特性阻抗?

另外, 听说还需保证这个连接器内部各点的特性阻抗均为50欧, 我能测量出其内部各点的特性阻抗吗?

非常感谢!
[em08]

yellowtoot

还有一个问题,

当改变"electrical delay"时, 是真正地在改变参考面,还只是在推算而已?


当然,这在系统都是50欧时,两者是一样的.


但我想知道,  目前当被测件是一段非50欧的传输线时, 还可不可以利用"electrical delay"功能测试该传输线上各点的S11呢?

如果是按50欧系统进行推算,肯定不行,但如果是真正地改变参考面,就没问题啦.[em13]

yellowtoot

自已顶一个[em08]

不知有没 有明白人啊[em13]

是问题简单,还是问题太复杂,或是太无聊??[em02]

还望各大侠指点一二,

是不是只有卖矢网的人才知道啊?

康乐新村

帮顶一下，看看下面有没有帮助

http://www.52rd.com/bbs/Dispbbs.asp?boardID=8&ID=41431&page=2

awp666

不需要用电长度的方式测试非50欧姆的特性阻抗。在SMitch Chart里面可以选择X+jY显示方法。X是实际阻抗

luck_life

如果我是你的话，我就先用ADS做个理想仿真，再用网络分析仪实际测试，对比，就能判断出阻抗了

henyihgjuan

你是不是想测试那个探头是不是50欧啊?或许先把它焊接在已知阻抗的衰减器上?

yellowtoot

<DIV class=quote><B>以下是引用<I>awp666</I>在2006-9-6 10:42:00的发言：</B>
不需要用电长度的方式测试非50欧姆的特性阻抗。在SMitch Chart里面可以选择X+jY显示方法。X是实际阻抗</DIV>


非常感谢!
能再说详细点吗?

我没明白你的意思.

X+jY是输入阻抗啊, 电长度不同时,它是会跟着变化的啊.

我如何能得到特性阻抗呢?

在这里,我还是强调一下吧,输入阻抗与特性阻抗是不同的概念,前者是入射波与反射波的合成波的电压/电流,即是可测量出来的; 而后者是入射波或反射波的电压./电流, 只能根据所测到的输入阻抗或S11算出来的啊.

yellowtoot

<DIV class=quote><B>以下是引用<I>luck_life</I>在2006-9-6 11:36:00的发言：</B>
如果我是你的话，我就先用ADS做个理想仿真，再用网络分析仪实际测试，对比，就能判断出阻抗了</DIV>


谢谢回复!

请问:
"网络分析仪实际测试" 是如何测呢? 测什么?根据什么判断阻抗呢?

非常感谢!

yellowtoot

<DIV class=quote><B>以下是引用<I>henyihgjuan</I>在2006-9-6 12:49:00的发言：</B>
你是不是想测试那个探头是不是50欧啊?或许先把它焊接在已知阻抗的衰减器上?</DIV>



非常感谢你的理解, 我确实是想测那个东东是不是50欧的.

我也想过焊接到什么东东上,例如同轴电缆,以连到矢网的PORT2, 或焊50欧电阻,以使其终端匹配,或焊短路线,以实现终端短路.

但我觉得, 焊点其实是会严重影响阻抗的,到时测出来的值,根本无法说明是接头有问题,还是焊点有问题.

yellowtoot

以下为老外的回答,没看懂.

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How to measure the characteristic impedance is 50ohm or not?     

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Recently, I met a problem that the return loss is not as good as expected.

Maybe the connector on our PCB is not 50ohm.

One port of the connector is N type, the other port is not standard type, something like coaxial cable.

And I cannot connect two connectors together to form a two N type ended connector.

So I can only connect one of them to the vector network analyzer's prot1 to measure S11 or Zin. While the other port is just let open ended.

I wonder how to know if it has 50ohm characteristic impedance.

Please tell me if you know.


thank U.
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VSMVDD
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06 Sep 2006 3:06   Re: How to measure the characteristic impedance is 50ohm or   

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plugs and sockets are provided you fitted them right
50 or 75 ohms
1-1 or 1-1.5 ratio of interaction
with the feeder
around 1db insertion loss per connector
chances are its the coax thats the problem

use heliax and proper ntype for your unit

make your own patch cable to the analyzer

this is best to be shure

also use silver solder

make sure of analyzers needs
if its 75R inputs use a balun

to test if the impedance is matched between two units use a vswr meter
if the standing wave ration is 1-1.5 between your unit and the analyzer
then the input maybe is 75 R

and 50 R from your unit as expected
hence the missmatch you observe

so try that

youll need several good quality vswr meters

to get the whole system balanced and usable for testing
h**p://www.irational.org/sic/radio/tech.html#VSWR

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Gakusei
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06 Sep 2006 3:17   Re: How to measure the characteristic impedance is 50ohm or   

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The easiest way to find the characteristic impedance is to calculate it.

First measure the diameter of the outside of the inner conductor and the inside of the outer conductor. Be carefull to do this in the right place, as there are steps in the diameters to allow the connectors to fit together. You can now calculate the impedance using the following equation:

Zo = 138.1 x Log10 (Outer Dia/Inner Dia)

The impedance should be either 50 or 75 ohms. If you get a different answer, you probably measured the diameters in the wrong place.

If you can post a picture of the connector, I can probably tell you what type it is.
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VSMVDD
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06 Sep 2006 3:27   Re: How to measure the characteristic impedance is 50ohm or   

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99.9 % of analyzers use 75 R inputs

50 to 75 R = 1-1.5 ratio balun is needed

or the analyzer will missmatch

so... all the maths and i bet from a picture
you cant tell a 50 R bnc from a 75 R bnc becouse
i cant...

its a measure of the diameter of the center spike and the material the dialectric is made of in the plug only {all very strange stuff but true}

so its prob a 75R input and 50 R unit under test senario so use vswr meter to check 1-1 match


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nycheung
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06 Sep 2006 11:55   Re: How to measure the characteristic impedance is 50ohm or   

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Could you explain more about your 2 port device? Is it just a 50ohm microstrip-line?

If you guess the mismatch is caused by the connector, you can simply connector it to another known-good 50 device and measure the S11 again.

ny
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xxargs
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06 Sep 2006 13:39   Re: How to measure the characteristic impedance is 50ohm or   

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VSMVDD wrote:
99.9 % of analyzers use 75 R inputs




ehh, you mean 50 Ohm, I newer seem VNA with 75 Ohm impedance...

you must have very rare VNA from TV/FM-radio field if you have 75 Ohm inputs...


Quote:



50 to 75 R = 1-1.5 ratio balun is needed

or the analyzer will missmatch

so... all the maths and i bet from a picture
you cant tell a 50 R bnc from a 75 R bnc becouse
i cant...




75 Ohm BNC have smaller center pin compare to 50 Ohm, and if you put 50 Ohm male centerpin in 75 Ohm female centerpin one time - connectors is ruined...

but serious - NEVER USE BNC in network analyzer work, connectors is not good in VSWR/retur loss-stability - Use N-connectors or SMA.

Quote:


its a measure of the diameter of the center spike and the material the dialectric is made of in the plug only {all very strange stuff but true}

so its prob a 75R input and 50 R unit under test senario so use vswr meter to check 1-1 match




so VNA as VSWR-meter is not good enough ??  

---

you can measure objects (and connector) with different impedanse to make S-parameters on each unit and in simulator coupling togheter with rigth impedances on port and make measures.

For example i measured qrystal filters (origin for 1 Kohm//5pF impedances) to S-parameters (and filter looks very bad in 50 Ohm measure enviroment) and in simulator and rigth port impedances (1 kOhm // 5 pF) sems OK and in simulator find out this filters _need_ 5 pF paralell reactive impedanses on port to working properly.

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VSMVDD
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06 Sep 2006 13:46   Re: How to measure the characteristic impedance is 50ohm or   

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dont try to pick an argement man

just solve the guys problems and stay chilled
take a powder and sit on your hands for a while


the problem has nothing to do with his setup analyzers etc

and something you all missed
is you cannot leave open ended connections and gain a match

you must add a dummy load plug to any open ended connections

yellowtoot

接头的图片
【文件名】:0697@52RD_53K210-500_LV_d.pdf
【格　式】:pdf
【大　小】:78K
【简　介】:
【目　录】:

yellowtoot

接头的一边是N型头， 另一头是一个小柱子， 插在一块金属板里，金属板上抠一个圆孔，与小柱子一起形成一个终端开路的同轴电线结构。[upload=jpg]UploadFile/2006-9/0697@52RD_夹具上面.jpg[/upload]
[upload=jpg]UploadFile/2006-9/0697@52RD_夹具下面.jpg[/upload][br]<p align=right><font color=red>+3 RD币</font></p>

yellowtoot

好象有的矢网有一种功能叫“时域”


大概可以测量出线上任一点处的S11


估计用这个东东就可以搞定偶的问题啦


可惜偶没见过这个东东，不知哪位大侠见过，请不吝赐教[em05]