Transmission media can be categorized in two ways,

傳輸媒體可以通過兩種方式進行分類：

Guided Transmission Media

引導傳輸媒體

Unguided Transmission Media

非引導傳輸媒體

1)非引導傳輸媒體 (1) Unguided Transmission Media)

It is also called wireless communication or unbounded transmission, they transmit electromagnetic waves without using a physical conductor. In this medium signals are radiated through the air (or, in a few cases, water) and therefore, are reaching to anyone with a device capable of accepting them.

也稱為無線通信或無限制傳輸，它們無需使用物理導體即可傳輸電磁波。 在這種介質中，信號是通過空氣(或在少數情況下是水)輻射的，因此會通過能夠接收信號的設備到達任何人。

We can categorize wireless transmission into the following groups,

我們可以將無線傳輸分為以下幾類：

Radio waves

無線電波

Micro waves

微波

Infrared waves

紅外波

a)無線電波 (a) Radio Waves)

Radio waves are electromagnetic waves and are omnidirectional. When an antenna transports radio waves they are propagated in all directions in free space which means the sending and receiving antennas do not have to be aligned that is any receiving antenna can receive that transmitted wave.

無線電波是電磁波，是全向的。 當天線傳輸無線電波時，它們會在自由空間的所有方向上傳播，這意味著發送天線和接收天線不必對齊，因為任何接收天線都可以接收該發射波。

The frequency of radio waves about 30 hertz (Hz) to 300 gigahertz (GHz) and like all other electromagnetic waves radio waves travel at the speed of light in vacuum.

無線電波的頻率約為30赫茲(Hz)至300吉赫茲(GHz)，與所有其他電磁波一樣，無線電波以真空中的光速傳播。

Applications of Radio waves

無線電波的應用

• These waves are omnidirectional so they are useful for multicasting in which one sender but many receivers.

  這些波是全向的，因此它們對于一個發送者但很多接收者的多播很有用。

• Examples of radio waves are television, AM and FM radio, cordless phones, and paging.

  無線電波的示例是電視，AM和FM廣播，無繩電話和尋呼機。

Advantages and disadvantages

的優點和缺點

• Radio waves are easy to generate and penetrate buildings also can travel long distances.

  無線電波很容易產生，并且穿透建筑物也可以傳播很長的距離。

• Radio waves cover a large area and can penetrate the buildings. By this, an AM radio can receive signals inside a building.

  無線電波覆蓋的面積很大，可以穿透建筑物。 這樣一來，AM收音機就可以接收建筑物內部的信號。

• This can also be disadvantageous because we cannot isolate a communication just inside or outside a building. Cause of this, governments strictly legislate the use of radio transmitters.

  這也可能是不利的，因為我們無法隔離建筑物內部或外部的通信。 因此，政府嚴格立法使用無線電發射器。

b)微波 (b) Micro Waves)

Micro Waves includes a line of sight transmission that is the sending and receiving antennas that need to be properly aligned with each other. The distance is directly proportional to the height of the antenna which is covered by the signal. In mobile phone communication and television distribution, these are majorly used.

微波包括一條視線傳輸線，該傳輸線是需要彼此正確對準的發送和接收天線。 該距離與信號覆蓋的天線高度成正比。 在移動電話通信和電視發行中，主要使用這些。

Applications of Micro Waves

微波的應用

Due to the unidirectional properties of Micro Waves, they are very useful when unicast (one-to-one) communication is needed between the sender and the receiver. Cellular phones, satellite networks, and wireless LANs are using Micro Waves.

由于微波的單向特性，當發送方和接收方之間需要單播(一對一)通信時，它們非常有用。 蜂窩電話，衛星網絡和無線局域網正在使用微波。

Microwave Transmission

微波傳輸

Two types of Microwave Transmission are as follows,

微波傳輸的兩種類型如下：

Terrestrial Microwave

地面微波

Satellite Microwave

衛星微波

(i) Terrestrial Microwave

(i)地面微波

The frequency of Electromagnetic waves between 300 MHz and 300 GHz are called microwaves. These waves are unidirectional. Whenever through an antenna microwave are transmitting, they can be narrowly focused. That is the sending and receiving antennas need to be aligned.

300 MHz至300 GHz之間的電磁波頻率稱為微波。 這些波是單向的。 每當通過天線發射微波時，它們都可以狹窄地聚焦。 也就是說，發送和接收天線需要對齊。

Characteristics of microwaves

微波爐的特性

• It is inexpensive for short distance expensive as it requires a higher tower for a longer distance.

  對于短距離的昂貴，它是廉價的，因為它需要更長的塔，距離更長。

• Due to environmental conditions and antenna size attenuation (loss of signal) occurs.

  由于環境條件和天線尺寸的衰減，會發生信號丟失。

• There is a capacity in very high-frequency microwaves that they cannot penetrate walls. This characteristic can be a disadvantage of microwaves if the receiver is inside the buildings.

  高頻微波具有無法穿透墻壁的能力。 如果接收器在建筑物內部，則此特性可能是微波的缺點。

Advantages

優點

• Microwave transmission is cheaper than using cables.

  微波傳輸比使用電纜便宜。

• It does not require any land for the installation of cables that is free from land acquisition.

  它不需要任何土地來安裝免征土地的電纜。

• Microwave transmission provides easy communication.

  微波傳輸可輕松進行通訊。

Disadvantages

缺點

• Bandwidth is limited in microwave transmission.

  微波傳輸帶寬有限。

• A signal can be moved out of phase and any environmental change such as rain, wind can distort the signal so these signals are susceptible to weather conditions.

  信號可能會異相，并且任何環境變化(例如雨，風)都會使信號失真，因此這些信號容易受到天氣條件的影響。

• Cause of eavesdropping insecure communication occurs in which any user can catch the signal in the air by using its antenna.

  發生監聽不安全通信的原因，其中任何用戶都可以使用其天線捕獲空中信號。

(ii) Satellite Microwave

(ii)衛星微波

A satellite is an entity that revolves around the earth at a certain height. Satellite communication offers more flexibility than fiber optic and cable systems. We can transmit signals from any point on the globe by using satellite transmission.

衛星是在一定高度繞地球旋轉的實體。 衛星通信比光纖和電纜系統具有更大的靈活性。 我們可以使用衛星傳輸來傳輸來自全球任何一點的信號。

How does a Satellite work?

衛星如何工作？

The satellite receives the signal that is transmitted from the earth station, and it amplifies these signals. It is retransmitted the amplified signal to another earth station.

衛星接收從地球站發送的信號，并放大這些信號。 它會將放大的信號重新傳輸到另一個地球站。

Satellite transmission is much like the line-of-sight transmission in which one of the stations is a satellite orbiting the earth. The principle is the same as the terrestrial microwave. Signals still travel in straight lines in satellite transmission.

衛星傳輸與視線傳輸非常相似，在視線傳輸中，一個站是環繞地球運行的衛星。 其原理與地面微波相同。 在衛星傳輸中，信號仍沿直線傳播。

Features of Satellite Microwave

衛星微波的特點

• It provides transmission capability to and from any location on earth.

  它提供往返于地球上任何位置的傳輸能力。

• Deployment of Satellite microwaves for orbiting satellites is difficult.

  用于軌道衛星的衛星微波的部署是困難的。

Advantages of Satellite Microwave

衛星微波的優點

• High-quality communication available to undeveloped parts of the world without requiring a huge investment in the ground-based infrastructure.

  高質量的通信可用于世界上不發達的地區，而無需在地面基礎設施上進行大量投資。

• It is used in a variety of applications such as radio/TV signal broadcasting, weather forecasting, radio/TV signal broadcasting, mobile communication and mobile, and wireless communication applications.

  它用于各種應用程序，例如無線電/電視信號廣播，天氣預報，無線電/電視信號廣播，移動通信和移動以及無線通信應用。

• The coverage area of a terrestrial microwave is less than the terrestrial microwave.

  地面微波的覆蓋面積小于地面微波。

Disadvantages of Satellite Microwave

衛星微波的缺點

• The manufacturing cost is very high of satellite and very expensive to launch a satellite.

  衛星的制造成本非常高，而發射衛星的成本非常高。

• Transmission can go down in bad weather.

  在惡劣的天氣下，傳輸會中斷。

c)紅外波 (c) Infrared Waves)

The frequency of Infrared waves is about 300 GHz to 430 THz, which can be used for short-range communication. Infrared waves of high frequencies cannot penetrate walls. This characteristic of Infrared waves prevents interference between one system and another. This means a short-range communication system in a room cannot be affected by another system in the adjacent room.

紅外線的頻率約為300 GHz至430 THz，可用于短距離通信。 高頻紅外線無法穿透墻壁。 紅外線的這一特性可防止一個系統與另一個系統之間的干擾。 這意味著一個房間中的短距離通信系統不會受到相鄰房間中另一個系統的影響。

If we are using the infrared remote control, we do not interfere with the use of the remote by our neighbors. However, by this characteristic, infrared signals become useless for long-range communication. Also, we cannot use infrared waves outside a building because the sun's rays contain infrared waves that can interfere with communication.

如果我們使用紅外遙控器，則不會干擾我們的鄰居使用該遙控器。 但是，由于該特性，紅外信號對于遠程通信變得毫無用處。 另外，我們不能在建筑物外使用紅外線，因為太陽光線中的紅外線會干擾通訊。

Characteristics of infrared waves

紅外線的特征

• This type of wide bandwidth can be used to transmit digital data with a very high data rate.

  這種寬帶寬可用于以很高的數據速率傳輸數字數據。

• The Infrared Data Association (IrDA) has established standards for using these signals for communication between devices such as keyboards, mouse, PCs, and printers and it is also responsible for sponsoring the use of infrared waves.

  紅外數據協會(IrDA)已經建立了使用這些信號在鍵盤，鼠標，PC和打印??機等設備之間進行通信的標準，并且還負責贊助使用紅外波。

• This type of communication provides better security with minimum interference.

  這種類型的通信以最小的干擾提供了更好的安全性。

References:

參考文獻：

• Transmission medium

  傳輸介質

• Radio Wave

  無線電波

• Microwave

  微波

翻譯自: https://www.includehelp.com/computer-networks/unguided-transmission-media.aspx

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