天線增益與回波損耗有什么關(guān)系(急)

各位大蝦:  
        請(qǐng)問(wèn)天線增益與天線結(jié)構(gòu)中什么因素有關(guān)？天線增益與回波損耗有什么關(guān)系呢？  

網(wǎng)友回復(fù):

天線增益與天線結(jié)構(gòu)沒(méi)啥關(guān)系的.

網(wǎng)友回復(fù):

有一定的關(guān)系，這個(gè)要看你是在設(shè)計(jì)什么樣的天線的，天線的集合繞射和反射等都會(huì)給天線的增益有一定的損失的，個(gè)人理解

網(wǎng)友回復(fù):

天線的增益和天線形式有關(guān)的，內(nèi)置天線和環(huán)境有關(guān)如天線地的大小與地遠(yuǎn)近 
有關(guān)還和支架的介電常數(shù)有關(guān)。回波損耗和匹配程度有關(guān)，匹配越好回波損耗 
越大，即反射越小。

網(wǎng)友回復(fù):

內(nèi)置天線,,有時(shí)受環(huán)境的影響,,回?fù)p好了,增益不一定好的...現(xiàn)在看回?fù)p也是只是一個(gè)參考值而已...

網(wǎng)友回復(fù):

sonnet 給出的天線增益和回波損耗的概念是這樣的: 
Directive Gain (dB) 
 
Directive gain is defined as the radiation intensity from an antenna in a given direction divided by the uniform radiation intensity for an isotropic radiator with the same total radiation power.[2]  
 
The far field viewer calculates the directive gain based on the total power radiated by your circuit. The far field viewer calculates the total power by using all the theta and phi points to integrate over the entire surface. Therefore, the more theta and phi points calculated, the more accurate the values provided for directive gain. A Figure of Merit (F.O.M.) appears in the Gain section of the legend when directive gain is selected to provide you with an idea of how accurate is the data (100% is perfect). If this figure is too low, try recalculating using more theta and phi data points. If this figure is too high, that is an indication that the problem is over calculated. i.e., angles are being analyzed twice. In this case, check for duplicate angels such as theta = 180 and theta = -180. 
 
Relative to: You select a reference point from which the gain is calculated. For power gain, there are three choices: Isotropic, Arbitrary and Max. 
 
Isotropic: Normalizes the data to a theoretical isotropic antenna in free space. 
 
Arbitrary: Normalizes the data to an arbitrary value which you enter in the Reference Value text entry box. 
 
Max: Normalizes the data by using the maximum value of radiation for the plot as the 0 dB point.  
 
Reference Value: This value provides the reference point in dB for the normalization when using the Arbitrary setting. 
 
 
 
Gain (dB) 
 
The power gain is defined as the radiation intensity divided by the uniform radiation intensity that would exist if the total power supplied to the antenna were radiated isotropically[1].  
 
Include Reflection: Select this checkbox to base the gain calculation on the total available power at the source rather than the total power delivered to the load. 
 
Relative to: The reference points available for gain are the same as those described above for directive gain. 
 
Reference Value: This value provides the reference point in dB for the normalization when using the Arbitrary setting. 
 
 
 
 
Calculation of the far field antenna pattern: The Sonnet far field pattern viewer 
calculates the far field pattern of the antenna from the analyzed current density and 
displays the antenna gain in 2D Cartesian or polar format. You can normalize the 
pattern to show the directive gain or the antenna gain. 
 
If you choose to display the directive gain (also known as directivity), the radiated 
power is normalized to an ideal, isotropic radiator that radiates the same total power. 
The output is the far field pattern of the antenna. Please note that any antenna 
losses will not be taken into account. 
 
If you choose to display the gain (also known as power gain), the radiated power is 
normalized to the input power. All dielectric and metallic losses are taken into 
account. The gain is therefore always smaller than the directive gain. 
 
If you want to take antenna losses into account, you have to choose “gain” as 
normalization (Graph > Normalization... > Gain). An additional option is to take 
mismatch losses into account as well. This means that any mismatch (input 
reflection) will reduce the antenna gain. The following two screenshots below show 
the same theta-cut plots as above, but now for the normalization “gain”. It can clearly 
be seen that the antenna gain is much smaller than the directive gain, due to the 
losses. 
看看最后三個(gè)"if you",大概的意思就應(yīng)該清楚了. 

網(wǎng)友回復(fù):

定義上講，增益是假設(shè)匹配良好的前提的，也就是認(rèn)為回波損耗很小。考慮上回波損耗之后，就跟實(shí)際測(cè)量的情況一樣了，回波損耗大，測(cè)到的增益肯定偏低。

網(wǎng)友回復(fù):

 
顯然有關(guān)系吧！ 

網(wǎng)友回復(fù):

有關(guān)系，有很大關(guān)系。。 
 
唉唉，書上都講了啊 
回去好好看書去

網(wǎng)友回復(fù):

但有些時(shí)候在HFSS仿真中 天線增益挺好 駐波大 怎么解釋呢

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