外文翻译--天线的选择

Lee Kong Haw,华为技术有限公司 天线的选型 在移动通信网络中，天线的选择是主要的一部分，应根据网络的覆盖要求、话务量、干扰和网络服务质量等实际情况来选择天线。天线选择得当，可以增大覆盖面积，减小干扰，改善服务质量。由于天线的选型是与覆盖要求紧密相关的，根据地形和话务量的分布要求可以把天线使用的环境分为城区、郊区、农村和公路四种类型。 1、 天线使用中存在的问题 （ 1） 较少考虑实际的地形与天线方向图的关系，而仅仅考虑覆盖的话务量分布来选择天线。比如在全向天线的选择方面，全网都使用同一种型号的全向天线，天线高低 较高时，由于垂直面波束很窄，造成“塔下黑”的现象。 （ 2） 在使用天线时，如果机械倾角很大，方向图就畸变，造成覆盖或干扰的问题。仿真表明，真对不同增益的天线，应该有不同的下倾角限制要求。 （ 3） 过于追求天线的高增益性能，而忽略了高增益天线的一下缺点。导致几乎全网使用的天线增益都很高，高增益天线的缺点表现为体积大、重量大、副瓣高、零瓣深和垂直面波束窄。 （ 4） 没有考虑到双极化天线和垂直极化天线在使用中的区别，只是从安装角度考虑使用双极化天线。 2、 城区基站天线应用原则 （ 1） 在城区，由于基站分布密集，要求单个基站覆盖范围小，尽量减少越区覆 盖，减少基站之间的干扰，提高频率复用率，原则上对天线有以下几方面的要求。 1. 天线水平半功率波束宽度的选择 由于城区天线基站分布数量一般较多，重叠覆盖和频率干扰成为网络中一个恒严重的问题。为减少相邻扇区的重叠区，降低基站之间的可能干扰，天线的水平半功率波束宽度应该小一些，通常选择水平半功率波束宽度为 65 的天线 2. 天线增益的选择 由于市区基站一帮不要求覆盖大的范围，因此建议使用中等增益天线， 这样天线垂直面波束可以变宽，可以增加覆盖区内的覆盖效果。同时，天翔体积和重量可以变小，有利于安装并降低成本。对于目前天 线型号，建议市区天线增益选择 15dBi(900MHZ)15-18dBi(1800MHZ)。 对于城市边缘基站，如果要求覆盖范围扩大，可选用高增益天线如 17dBi和 18dBi. 原则上，在城区实际基站覆盖时，应选择具有固定电下倾角的天线，下倾角的大小根据具体情况而定（建议 6 9 ）。 在城区，为了提高频率利用率，减小越区干扰，可以选择上第一副瓣抑制、下第一零点填充的赋形技术天线。 由于市区基站天线安装空间往往存在限制，一般建议选用双极化天线。在相同货相近电气指标下，应选用尺寸较小的天线。 3、 郊区基站天线应用原 则 在郊区，情况差别比较大，可以根据需要的覆盖面积来估算大致需要的天线类型。一般可以遵循以下几个基本原则。 可以根据情况选择水平半功率波束宽度为 65 或 90 的天线。当周围的基站比较少时，应该优先选用水平半功率波束宽度为 90 的天线。 若周围基站天线分布很密集，可以参考城区基站天线选择原理进行处理。 考虑到将来的平滑扩容，一般不建议采用全向天线。 4、 乡村基站天线应用原则 在乡村环境下，一般话务量较小，而且较分散，部分站点要求覆盖广，天线应用时应遵循以下原则。 考虑到建设成本，对覆盖要求小、话务量低的站点建议采 用全向基站覆盖。但是全向基站天线由于增益低，覆盖距离不如定向天线远。当基站要去覆盖距离较远时，则需要采用定向天线来实现覆盖。建议采用水平半功率波束宽度为 90 ，且增益较高的垂直极化天线。 需要注意的是，如果基站位置过高，而需要覆盖的区域位置较低（倾角大于 5 ），当采用全向天线时，可以考虑采用预置下倾或零点填充特性的全向天线来改善这些地区的覆盖，避免可能出现的“塔下黑”现象和覆盖不均匀而产生的信号波动现象。 5、 公路覆盖天线应用原则 对于公路覆盖地区，天线的选用原则如下： 对以覆盖铁路、公路沿线为目标的基站，可以 采用窄带波束的定向天线； 如果覆盖目标为公路及周围零星分布的村庄，可以考虑采用全向天线； 如果覆盖目标仅为高速公路，则可以考虑勇 8 字型天线，这样可以节约基站的数量，实现高速公路的覆盖。 如果是对公路以及公路一侧城镇的覆盖，可以根据情况考虑用水平半功率波束宽度为 210 的天线来进行覆盖。 建议在进行高速公路的覆盖上有限考虑 8 字型天线和 210 天线。图 4 1 和图 4 2 分别是两种天线的应用示意图。 图 4 1 210 天线示意图 图 4 2 8 字型天线示意图 6、 天线应用的其它考虑 上面主要给出了不同场合下天 线选用的基本原则。实际上，天线的选用还要考虑到将来的扩容因素和设备的基本性能问题。 举一个简单的例子说明： 加入在一个小镇附近的公路覆盖选用 210 的天线，采用单小区满足覆盖。就要考虑该地区为来话务量是否会增加，是否需要增加载频数量来满足扩容需求。在一般情况下，基站增加负载往往会伴随合路方式的改变以及合路损耗的增大，因此扩容后将会导致覆盖距离下降，在天线选型时要遇见到这些问题，在天线增益的选取合站型选择上做好前期规划。 7、 天线选用参考 天线选用参考见表 4 2 表 4 2 天线选用参考 地形 站型 天线选择建议 城区 定向站型 一般选择低或中等增益、预置电下倾天线，主要取决于基站的密度，也可以选择电调天线或机械下倾天线 郊区 定向站型 一般采用高增益天线，可以是电调下倾、机械下倾 平原农村 定向站型 一般选用 90 天线，最好采用垂直单极化天线 全向站型 首选零点填充天线，不考虑下倾角 高速公路 定向站型 受限考虑 8 字型天线，再考虑采用公分器 定向全向站型 首先考虑 210 天线，其次才考虑定向天线全向天线的组合。 山区 全向站型 受限考虑有零点填充的天线，其次考虑低增益的天 线，然后考虑加下倾角 定向站型 首先考虑低增益、垂直波束宽的天线，然后才考虑 加下倾角 Lee Kong Haw. Huawei Technologies Co., Ltd. 公司内部资料 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