英文翻譯外文文獻(xiàn)翻譯23畢業(yè)設(shè)計外文英文翻譯射頻與微波應(yīng)用-wenkub.com
2024-11-27 20:00 本頁面
【正文】 在建筑物內(nèi)，利用射頻 /微波可以很容易地構(gòu)成無線局域網(wǎng)，使之與電話、計算機(jī)和其他局域網(wǎng)互連 。 遙感 在此應(yīng)用中，會用到許多衛(wèi)星，用于連續(xù)觀察地球狀況和探索自然資源，如氣候、臭氧層、土壤濕度、農(nóng)業(yè)、農(nóng)作物受凍情況、森林、雪層的厚度、冰山等。光通信適用于傳輸大量不同頻率的信號且受外界電磁輻射干擾小的情形。 電視與無線電廣播 在電視與無線電廣播通信中，將射頻 /微波用做音頻和視頻的載波。還有一些其他的領(lǐng)域，例如遙感，加熱（工業(yè)提純和烹飪等）等，這些都將在下一節(jié)中介紹。在雷達(dá)中使用微波的另一個優(yōu)點(diǎn)是：給定天線尺寸后，增大信號頻率可以獲得更大的天線增益，這是因為天線的增益與天線的電尺寸成正比，在微波頻段隨 著頻率的增大而增大。此外，與低頻信號不同，微波信號不會經(jīng)電離層彎曲或反射。 從以上討論中可得如下重要結(jié)論：當(dāng)系統(tǒng)的波長與電路尺寸相比大得多、小得多或者可比擬時，只要進(jìn)行適當(dāng)?shù)暮喕?，麥克斯韋方程就可對任何頻率下的任何系統(tǒng)提供統(tǒng)一的分析理論。 當(dāng)信號頻率很高以至于波長要比器件或電路尺寸小很多時，對應(yīng)頻率軸上另一端的光場。這是因為元件的尺寸和波長具有可能性，這意味著，電信號（電流或電壓）的相位將會隨著所通過的設(shè)備或元器件的尺寸顯著變化。所有這些，都使得射頻 /微波成為一個非常有用和熱門的研究領(lǐng)域。 從 1897 年到 1936 年，正當(dāng)人們差不多已忘記波導(dǎo)時， ATamp。 接下來，馬可尼試圖以更低的頻率實(shí)現(xiàn)長距離通信，并使之商品化，但由于他所有的工作都涉及到商業(yè)利益，所以這不是純科學(xué)行為。海維賽德在其發(fā)表的論文中將麥克斯韋方程進(jìn)一步簡化。麥克斯韋將人類所掌握的電磁學(xué)知識歸結(jié)為一組由四個一致相干的方程構(gòu)成的方程組，以次描述經(jīng)典電磁場的特性。 the molecular, atomic, and nuclear resonance of conductive materials and substances when exposed to microwave fields. This property creates a wide variety of applications. For example, because almost all biological units are posed predominantly of water and water is a good conductor, microwave technology has tremendous importance in the fields of detection, diagnostics, and treatment of biological problems or medical investigations (., diathermy, scanning, etc.). There are other areas in which this basic property would create a variety of applications such as remote sensing, heating (., industrial purification and cooking) and many others are listed in a later section. Reasons for Using RF/Microwaves Over the past several decades, there has been a growing trend toward use of RF/microwaves in system applications. There are many reasons among which the following are prominent: Wider bandwidths due to higher frequency Smaller ponent size leading to smaller systems More available and less crowded frequency spectrum Lower interference due to lower signal crowding Higher speed of operation Higher antenna gain possible in a smaller space On the other hand, there are some disadvantages to using RF/microwaves, such as: more expensive ponents, availability of lower power levels, existence of higher signal losses, and use of highspeed semiconductors (such as GaAs or INP) along with their corresponding lessmature technology (relative to the traditional silicon technology, which is now quite mature and less expensive). In many RF/microwave applications the advantages of a system operating at these frequencies outweigh the disadvantages and propel engineers to a highfrequency design. RF/Microwave Applications The major applications of RF/microwave signals can be categorized as follows: Communication This application includes satellite, space, longdistance telephone, marine, cellular telephone, data, mobile phone, aircraft, vehicle, personal, and wireless local area work (WLAN), among others. Two important subcategories of applications need to be considered: TV and radio broadcast, and optical munications. TV and radio broadcast In this application, RF/microwaves are used as the carrier signal for audio and video signals. An example is the Direct Broadcast System (DBS), which is designed to link satellites directly to home users. Optical munications In this application, a micro
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