外文翻譯--天線的選擇

Lee Kong Haw,華為技術有限公司 天線的選型 在移動通信網(wǎng)絡中，天線的選擇是主要的一部分，應根據(jù)網(wǎng)絡的覆蓋要求、話務量、干擾和網(wǎng)絡服務質量等實際情況來選擇天線。天線選擇得當，可以增大覆蓋面積，減小干擾，改善服務質量。由于天線的選型是與覆蓋要求緊密相關的，根據(jù)地形和話務量的分布要求可以把天線使用的環(huán)境分為城區(qū)、郊區(qū)、農村和公路四種類型。 1、 天線使用中存在的問題 （ 1） 較少考慮實際的地形與天線方向圖的關系，而僅僅考慮覆蓋的話務量分布來選擇天線。比如在全向天線的選擇方面，全網(wǎng)都使用同一種型號的全向天線，天線高低 較高時，由于垂直面波束很窄，造成“塔下黑”的現(xiàn)象。 （ 2） 在使用天線時，如果機械傾角很大，方向圖就畸變，造成覆蓋或干擾的問題。仿真表明，真對不同增益的天線，應該有不同的下傾角限制要求。 （ 3） 過于追求天線的高增益性能，而忽略了高增益天線的一下缺點。導致幾乎全網(wǎng)使用的天線增益都很高，高增益天線的缺點表現(xiàn)為體積大、重量大、副瓣高、零瓣深和垂直面波束窄。 （ 4） 沒有考慮到雙極化天線和垂直極化天線在使用中的區(qū)別，只是從安裝角度考慮使用雙極化天線。 2、 城區(qū)基站天線應用原則 （ 1） 在城區(qū)，由于基站分布密集，要求單個基站覆蓋范圍小，盡量減少越區(qū)覆 蓋，減少基站之間的干擾，提高頻率復用率，原則上對天線有以下幾方面的要求。 1. 天線水平半功率波束寬度的選擇 由于城區(qū)天線基站分布數(shù)量一般較多，重疊覆蓋和頻率干擾成為網(wǎng)絡中一個恒嚴重的問題。為減少相鄰扇區(qū)的重疊區(qū)，降低基站之間的可能干擾，天線的水平半功率波束寬度應該小一些，通常選擇水平半功率波束寬度為 65 的天線 2. 天線增益的選擇 由于市區(qū)基站一幫不要求覆蓋大的范圍，因此建議使用中等增益天線， 這樣天線垂直面波束可以變寬，可以增加覆蓋區(qū)內的覆蓋效果。同時，天翔體積和重量可以變小，有利于安裝并降低成本。對于目前天 線型號，建議市區(qū)天線增益選擇 15dBi(900MHZ)15-18dBi(1800MHZ)。 對于城市邊緣基站，如果要求覆蓋范圍擴大，可選用高增益天線如 17dBi和 18dBi. 原則上，在城區(qū)實際基站覆蓋時，應選擇具有固定電下傾角的天線，下傾角的大小根據(jù)具體情況而定（建議 6 9 ）。 在城區(qū)，為了提高頻率利用率，減小越區(qū)干擾，可以選擇上第一副瓣抑制、下第一零點填充的賦形技術天線。 由于市區(qū)基站天線安裝空間往往存在限制，一般建議選用雙極化天線。在相同貨相近電氣指標下，應選用尺寸較小的天線。 3、 郊區(qū)基站天線應用原 則 在郊區(qū)，情況差別比較大，可以根據(jù)需要的覆蓋面積來估算大致需要的天線類型。一般可以遵循以下幾個基本原則。 可以根據(jù)情況選擇水平半功率波束寬度為 65 或 90 的天線。當周圍的基站比較少時，應該優(yōu)先選用水平半功率波束寬度為 90 的天線。 若周圍基站天線分布很密集，可以參考城區(qū)基站天線選擇原理進行處理。 考慮到將來的平滑擴容，一般不建議采用全向天線。 4、 鄉(xiāng)村基站天線應用原則 在鄉(xiāng)村環(huán)境下，一般話務量較小，而且較分散，部分站點要求覆蓋廣，天線應用時應遵循以下原則。 考慮到建設成本，對覆蓋要求小、話務量低的站點建議采 用全向基站覆蓋。但是全向基站天線由于增益低，覆蓋距離不如定向天線遠。當基站要去覆蓋距離較遠時，則需要采用定向天線來實現(xiàn)覆蓋。建議采用水平半功率波束寬度為 90 ，且增益較高的垂直極化天線。 需要注意的是，如果基站位置過高，而需要覆蓋的區(qū)域位置較低（傾角大于 5 ），當采用全向天線時，可以考慮采用預置下傾或零點填充特性的全向天線來改善這些地區(qū)的覆蓋，避免可能出現(xiàn)的“塔下黑”現(xiàn)象和覆蓋不均勻而產生的信號波動現(xiàn)象。 5、 公路覆蓋天線應用原則 對于公路覆蓋地區(qū)，天線的選用原則如下： 對以覆蓋鐵路、公路沿線為目標的基站，可以 采用窄帶波束的定向天線； 如果覆蓋目標為公路及周圍零星分布的村莊，可以考慮采用全向天線； 如果覆蓋目標僅為高速公路，則可以考慮勇 8 字型天線，這樣可以節(jié)約基站的數(shù)量，實現(xiàn)高速公路的覆蓋。 如果是對公路以及公路一側城鎮(zhèn)的覆蓋，可以根據(jù)情況考慮用水平半功率波束寬度為 210 的天線來進行覆蓋。 建議在進行高速公路的覆蓋上有限考慮 8 字型天線和 210 天線。圖 4 1 和圖 4 2 分別是兩種天線的應用示意圖。 圖 4 1 210 天線示意圖 圖 4 2 8 字型天線示意圖 6、 天線應用的其它考慮 上面主要給出了不同場合下天 線選用的基本原則。實際上，天線的選用還要考慮到將來的擴容因素和設備的基本性能問題。 舉一個簡單的例子說明： 加入在一個小鎮(zhèn)附近的公路覆蓋選用 210 的天線，采用單小區(qū)滿足覆蓋。就要考慮該地區(qū)為來話務量是否會增加，是否需要增加載頻數(shù)量來滿足擴容需求。在一般情況下，基站增加負載往往會伴隨合路方式的改變以及合路損耗的增大，因此擴容后將會導致覆蓋距離下降，在天線選型時要遇見到這些問題，在天線增益的選取合站型選擇上做好前期規(guī)劃。 7、 天線選用參考 天線選用參考見表 4 2 表 4 2 天線選用參考 地形 站型 天線選擇建議 城區(qū) 定向站型 一般選擇低或中等增益、預置電下傾天線，主要取決于基站的密度，也可以選擇電調天線或機械下傾天線 郊區(qū) 定向站型 一般采用高增益天線，可以是電調下傾、機械下傾 平原農村 定向站型 一般選用 90 天線，最好采用垂直單極化天線 全向站型 首選零點填充天線，不考慮下傾角 高速公路 定向站型 受限考慮 8 字型天線，再考慮采用公分器 定向全向站型 首先考慮 210 天線，其次才考慮定向天線全向天線的組合。 山區(qū) 全向站型 受限考慮有零點填充的天線，其次考慮低增益的天 線，然后考慮加下傾角 定向站型 首先考慮低增益、垂直波束寬的天線，然后才考慮 加下傾角 Lee Kong Haw. Huawei Technologies Co., Ltd. 公司內部資料 Antenna Selection The antenna selection is a very important part in a mobile communication network. The antenna must be selected according to the actual conditions, such as coverage requirement, traffic volume, interference, and the quality of service of the network. A proper antenna can enlarge coverage area, reduce interference, and improve the quality of service. Because antenna selection is closely related to coverage requirement, the antenna application environment can be divided into four types according to landforms or traffic distribution. They are: urban area, suburban area, rural area, and highroad. 1、 Problems Present in Antenna Selection This section introduces the problem present in antenna application from the following perspectives: The antenna is selected only based on the covered traffic distribution, but little consideration is given to the relationship between landforms and antenna directional diagram. For example, if all antennas used in a network are of the same type, when the antenna is installed at a high position, the phenomenon of blind under tower” will be present because the width of the beams in vertical plane is narrow. Too large antenna mechanical tilt angle results in the distortion of the directional diagram. In this case, coverage problem or interference problem will occur. Emulation shows that the restrictions on tilt angles must vary in accordance with the antennas with different gains. Too much attention is focused on the high gain performance of the antenna but little attention is given to its drawbacks. As a result, the gains of almost all the antennas used in a network are quite high. A high gain antenna has many drawbacks, including large size, great weight, high side lobe, deep zero lobe, and narrow vertical beams. No consideration is given to the difference between the vertical polarization antenna and dual polarization antenna in terms of application. The dual polarization antenna is selected from the perspective of installation. 2、 Principles for Selecting Base Station Antenna in Urban Areas Base stations are densely distributed in urban areas. Therefore, it is required that the coverage area of each base station is as small as possible so as to reduce cross coverage and interference among base stations, and enhance frequency reuse rate as well. In this case, an antenna must meet the following requirements in principle. I. Selection of antenna horizontal half power beam width Because a large number of base stations are distributed in urban areas, overlapping coverage and frequency interference rises as serious problems in a network. To reduce the overlapping areas of neighbor sectors and the interference between base stations, you can set the beam width of the antenna horizontal half power to a smaller value. Generally, antennas whose horizontal half power beam width is 65 are selected, but antennas whose horizontal half power beam width is above 90 are not selected. II. Selection of antenna gain The base stations in urban areas are not required to cover a large area, so the antennas with medium gain are recommended. Thus the antenna vertical beam can be wider, which can improve the coverage quality within the areas to be covered. In addition, the size and weight of the antenna with medium gain are small, which is helpful for installing the antenna and reducing cost. According to present antenna specifications, antennas with a gain of 15dBi (900MHz) and 15-18 dBi (1800 MHz) are recommended in urban areas. For the base stations on the outskirt of a city, if it is required to cover a large distance, you can select the antennas with higher gains, such as 17dBi and 18dBi. In principle, when designing base station coverage in urban areas, you should select the antennas with a fixed electrical tilt angle. The degrees of the electrical tilt angle can be set according to actual conditions (the recommended value is 6 to 9). In urban areas, to enhance frequency reuse rate and reduce cross interference, you can select the shaped-beamed antenna with the first upper side lobe suppressed and the lower side lobe filled. Because space restriction is present in the antenna installation in urban areas, the dual polarization antenna is recommended. And it is better to select the antenna with a smaller size when the electrical specifications of the antennas are the same or nearly the same. 3、 Principles for Selecting Base Station Antenna in Suburban Areas Because the environment is suburban areas are largely different from that in urban areas, antennas used in suburban areas can be selected according to the required coverage area. Generally, in suburban areas, an antenna can be selected according to the following principles: The antennas whose horizontal half power beam width is 65 or 90 can be selected according to actual conditions. If base stations are sparsely distributed, the antennas whose horizontal half power beam width is 90 is first considered. If the base stations are densely distributed, the antennas are selected by referring to the principles for selecting base station antenna in urban areas. Omni antennas are not recommended for the purpose of smooth expansion in the future. 4、 Principles for Selecting Base Station Antenna in Rural Areas In rural areas, traffic volume is small and base station are sparsely distributed, so some base stations are required to cover a large area. In this case, the antennas are selected based on the following principles: Considering the construction cost, you are recommended to select an omni antenna for the base stations whose coverage area is small and traffic volume is low. However, because the gain of the omni antenna is low, the coverage of an omni antenna is shorter than that of a directional antenna. When the base station is required to cover a long distance, the directional antenna must be selected to realize the coverage. Generally, a high gain vertical polarization antenna whose horizontal half power beam width is 90 is recommended. One point needs to be noted. That is, if the base station antenna is installed at a high position, but the area needs to be covered lies in a low location (the depression angle is greater than 5), when an omni antenna is used, the kind with a preset tilt angle or with zero point filling function are recommended to improve the coverage quality of this area. In this case, the phenomenon of “blind under tower” and the signal fluctuation caused by uneven coverage can be avoided. 5、 Principles for Selecting Base Station Antenna along Highroads The principles for selecting antennas along highroads are as follows: For the base stations designed to cover the areas along railways and highroads, a directional antenna with narrow beams can be selected. For the base station designed to cover the highroads and the villages scattered around the highroads, an omni antenna can be selected. For the base station designed to cover highroads only, an 8-shaped antenna can be selected, because the 8-shaped antenna help realize the highroad coverage with only a few base stations. For the base station designed to cover the highroads and the towns on both sides of the highroads, the antenna whose horizontal half power beam width is 210 can be selected according to actual conditions. It is recommended to give the priority to the 8-shaped antenna and the 210antenna for highroads coverage. Figure 4-1shows the application of a 210 antenna. Figure 4-1 Application of a 210 antenna Figure 4-2 shows the application of an 8-shaped antenna Figure 4-2 Application of an 8-shaped antenna 6、 Other Considerations for Antenna Selection Apart from the basic principles for selecting the antenna in different places are provided in the previous parts, other factors, such as system expansion and equipment performance, must be considered for antenna selection. Hereunder is an example: If the 210 antenna and used to cover the highroads nearby a small town, and only a cell is used to promise the coverage requirements, you should consider whether the traffic of this area will increase in the future and whether to meet the expansion requirements by adding carriers. Generally, once a carrier is added to the base station, the combiner loss will increase, so the coverage distance will decrease after the expansion. Therefore, when selecting an antenna, you should consider these problems beforehand and work out a good plan for the selection of antenna gain and base station type. 7、 Antenna Selection Reference 1 li