G卡方位=29-25lgφ
上面的公式适于计算天线口径的直径与波长之比大于100，增益大于48dB的大型卡塞格伦天线。如果天线口径直径与波长之比小于100，增益小于48dB，方位增益计算公式如下
G卡方位=52-10lg（D/λ）-25lgφ
上式中，D是天线口径面直径，λ是工作波长，粗算时λ取工作频段中心频率的波长。
以上为卡塞格伦天线方位增益的一般算法。如果存在干扰，双方需进行技术协调，并且认为通过上式计算的干扰量若超过规定的标准，则两网络之间有产生有害性干扰的可能性，这时，需对干扰量进行更为精确的计算，计算天线方位增益也需要取得较为精确的数值。下面就主波束增益、主波束宽度、主波束方位增益、第一次波束增益、第一次波束宽度、第一次波束方位增益以及第一个次波束以外的方位增益计算方法进行具体的分析讨论。
对大口径天线，主波束增益为 G主=（Dπ/λ）2η
上式中，D是天线口径面直径；η是天线工作效率，标准天线的η=0.75。主波束一边宽度为
φ半=20（λ/D）G主?G1次
上式中， G主是天线主波束增益；G1次是天线第一个次波束增益，单位均为dB。主波束方位增益为
-32
G主方位=G主-2.5×10×（Dφ/λ）
上式中，φ是在天线主波束范围内的射线方位角。第一个次波束增益为
G1次=2+15lg（D/λ） 第一个次波束宽度为
-0.6
φ1次=15.85（D/λ）-φ半
-0.6
上式中，15.85×（D/λ）是第一个次波束离主波束轴最远的一边与主波轴之间的夹角。第一个次波束的对称半波束宽度是φ1次/2。由于第一个次波束宽度很窄，计算干扰一般不计算它的方位增益，而使用它的最大增益。第一个次波束以外的方位增益的计算方法如下：当第一个次波束离主
-0.6
波束轴最远边的方位角度在15.85×（D/λ）到48°之间时，可用上面介绍的一般算法计算方位增益；当方位角度在48°到180°之间时，在此范围内方位增益一律取-10dB。
例5：设天线口径面直径D=10m，工作效率f=4000MHz。试计算北天线的G主、G1次、φ半、G主方
位和φ1次的值。
89
解：f=4000MHz，λ=3×10/4×10=0.075m，η=0.75，D=10m
2
G主=[3.14159×（10/0.075）]×0.75=131594.5031=51.1924dB G1次=2+15lg（10/0.075）=33.8741dB
φ半=20?(0.075/10)?51.1924?33.8741=0.6242° 在0～0.6242°范围内，设φ=0.5°，则 G主方位（0.5°）=51.1924-2.5×10-3×(-0.6
10?0.52)=40.0813dB
0.075 φ1次=15.85（10/0.075）-0.6242°=0.8415°-0.6242°=0.2173°
0.8415°是第一次波束离主波束轴最远的一个边与主波轴之间的夹角。第一个次波束的对称半波束宽度是0.2173°/2=0.1087°。
小口径天线G主、G1次、φ半、G方位的计算公式与大口径天线相同。φ1次=100×（λ/D），第一个
次波束方位增益用其最大增益计算。φ1次～48°方位增益的计算公式为
G方位=52-10lg（D/λ）-25lgφ
48°～180°方位增益为
G方位=10-10lg（D/λ）
例5：如卫星置于东经135°，另一网络地球电台天线波束主轴指向东经120°，且D/λ=70。计算地球电台天线的G主、G1次、φ半、G主方位和φ1次的值。同时，计算地球电台天线对东经135°卫星和70°卫星的干扰增益。
2
解：G主=（3.14159×70）×0.75=36270.7349=45.5956dB G1次=2+15lg（70）=29.6765dB
φ半=20（70）×45.5956?29.6765=1.14°
G方位（0.5°）=45.5956-2.5×10×（70×0.5）=42.5331dB φ1次=100×（λ/D）=100×（1/70）=1.4286°
G方位（135°-120°）=52-10lg70-25lg15=4.1467dB G方位（135°-70°）=10-10lg70=-8.45dB
知道了方位方向性系数和方位增益后，我们就能估算卫星与地面微波站间的干扰。如图4.29所示，设A、B、C为三个地面微波站，双向传输。“o”为卫星接收站。天线主波束方向与OA、OB、OC之间的夹角为x、y、z，OA与OB、OB与OC、OC与BC的夹角分别为α、β、γ。则接收站收到信号电平P卫星和收到地面微波干扰信号电平P干扰的计算公式如下
P卫星=（EIRP）S-LD+GS 图4.29 接收干扰的计算 P干扰=（EIRP）M-（GM-G1）-LDA+G2+FS 上式中，（EIRP）S为卫星下行等效全向辐射功率；LD为卫星与地面接收站间的传输损耗；GS为地
面接收天线的增益；LDA为微波站与地面卫星接收站间的传输损耗；GM为微波站天线增益； （EIRP）M为微波站主波束全向等效辐射功率；G1为地面微波站天线对卫星接收站方向的增益；G2为卫星接收站天线对地面微波站
G1 方向的增益；FS为接收站对微波站
1 3 方向的屏蔽系数。
接卫星接收机 LNA 功率合成器 干扰判断：
(1) 对于同频干扰（包括镜频干2 G2 扰）信号，要求在图像质量上达到
干扰 可变衰减器 R 不能察觉的程度，则P卫星-P干扰＞30dB。一般情况只要P卫星-P干扰＞20dB，就不会产生明显有害的干扰。
移相电缆 可变移相 前置放大器 (2) 对于非同频干扰，由于接收
机的选频作用，允许干扰电平大于信号电平。但条件是不能使高频头图4.30接收干扰的估算
-3
2
饱和（接收机输入电平范围-20～-60dBmW），也不能使信号电平低于最低工作电平。
克服干扰的几种方法：
(1) 利用地形地物消减干扰。
(2) 加带通滤波器消减干扰。一般将带通滤波器插接在前置放大器和下变频器之间，其带宽要保证电视信号全部通过。对于有可能使前置放大器饱和的极强干扰，滤波器要加在LNA与馈源之间。滤波法虽然简单，但只适用于非同频干扰。
(3) 采用相位抵消法克服微波干扰。相位抵消法是在卫星接收系统中，另用一副专门接收微波干扰的天线，把收到的干扰与从卫星接收天线上收到的混有微波干扰的信号进行叠加，改变干扰的相移和幅度，使其与混在电视信号中的干扰反相，从而消减干扰，其原理如图4.30所示。相位抵消法对于干扰信号，实质是振幅可调的反相分集式接收，它能有效地消减干扰幅度而不损害有用信号。由于干扰信号的相位是不断变化的，因而不可能做到完全抵消干扰信号。实践证明，此种方法可压制干扰电平10～15dB。主观评价等级可改善1.5级，克服干扰的效果十分明显。
3.无线电通信系统中的EMC标准
随着无线通信的发展，无线电通信系统内和系统间的电磁兼容问题也十分突出。为此，我国和国际电联制定了大量的有关无线电通信业务的电磁兼容标准，下列分别列出了这些标准：
（1）我国有关无线电通信业务电磁兼容的国家标准与行业标准 GB 6364-1986 航空无线电导航台站电磁环境要求
GB 6830-1986 电信线路遭受强电线路危险影响的容许值
GB/T 7432-1987 同轴电缆载波通信系统抗天线电广播和通信干扰的指标 GB/T 7433-1987 对称电缆载波通信系统抗天线电广播和通信干扰的指标 GB/T 7434-1987 架空明线载波通信系统抗天线电广播和通信干扰的指标 GB/T 7495-1987 架空电力线路与凋幅广播收音台的防护间距 GB 9254-1998 信息技术设备的无线电骚扰限值和测量方法 GB 12638-1990 微波和超短波通信设备辐射安全要求
GB 13421-1992 无线电发射机杂散发射功率电平的限值和测量方法 GB 13613-1992 对海中远程无线电导航台站电磁环境要求 GB 13614-1992 短波无线电测向台（站）电磁环境要求 GB 13615-1992 地球站电磁环境保护要求 GB 13616-1992 微波接力站电磁环境保护要求
GB 13617-1992 短波无线电收信台（站）电磁环境要求 GB 13618-1992 对空，情报雷达站电磁环境防护要求 GB/T 13619-1992 微波接力通信系统干扰计算方法
GB/T 13620-1992 卫星通信地球站与地面微波站之间协调区的确定和干扰计算方法 GB 15540-1995 陆地移动通信设备电磁兼容技术要求和测量方法 GB 17618-1998 信息技术设备抗扰度限值和测量方法 YD/T 968-1998 电信终端设备电磁兼容性限值及测量方法 YD/T 983-1998 通信电源设备电磁兼容性限值及测量方法 YD/T 1003-1999 卫星通信VSAT地球站电磁干扰的测量方法 YD/T 1103-2001 无绳电话的电磁兼容性要求及测量方法
YD 1138-2001 固定无线链路设备及其辅助设备的电磁兼容性要求和测量方法
YD 1032-2000 900/1800MHzTDMA数字蜂窝移动通信系统电磁兼容性限值和测量方法 第一部分：移动台及其辅助设备
YD 1139-2001 900/1800MHzTDMA数字蜂窝通信系统电磁兼容性限值和测量方法 第二部分：基站及其辅助设备
（2）国际电联（ITU）有关无线电通信业务的电磁兼容标准 Rec.ITU-R SM 327-7 Spurious Emissions
Rec.ITU-R SM 337-4 Frequency and Distance Separations
Rec.ITU-R SM 433-5 Methods for the Measurement of Radio Interference and the
Determination of Tolerable Levels of Interference
Rec.ITU-R SM 669-1 Protection Ratios for Spectrum Sharing Investigations Rec.ITU-R SM 853-1 Necessary Bandwidth
Rec.ITU-R SM 856-1 New Spectrally Efficient Techniques and Systems Rec.ITU-R SM 1045-1 Frequency Tolerance of Transmitters Rec.ITU-R SM 1047 National Spectrum Management
Rec.ITU-R SM 1049-1 A Method for Spectrum Management to be Used for aiding Frequency
Assignment for Terrestrial Services in Border areas
Rec.ITU-R SM 1055 The Use of Spread Spectrum Techniques Rec.ITU-R SM 1056 Limitation of Radiation from Industrial, Scientific and Medical(ISM)
Equipment
Rec.ITU-R SM 1132 General Principles and Methods for Sharing between Radio Services Rec.ITU-R SM 1134 Inter-modulation Interference Calculations in the Land-Mobile
Services
Rec.ITU-R F 1108-2 Determination of the Criteria to Protect Fixed Services from the
Emissions of Space Stations Operating in Non-Geostationary Orbits in Shared Frequency Bands
Rec.ITU-R F 1190 Protection Criteria for Digital Radio-Relay Systems to Ensure
Compatibility with Radar Systems in the Radio-determination Service
Rec.ITU-R F 1334 Protection Criteria for Systems in the Fixed Service Sharing the
Same Frequency Bands in the 1 to 3 GHz Range with the Land Mobile Service
Rec.ITU-R F 1402 Frequency Sharing Criteria between a Land Mobile Wireless Access
System and a Fixed Wireless Access System Using the Same Equipment Type as the Mobile Wireless Access System
Rec.ITU-R F 302-3 Limitation of Interference from Trans-Horizon Radio-Relay Systems Rec.ITU-R F 752-1 Diversity Techniques for Radio-Relay Systems
Rec.ITU-R F 760-1 Protection of Terrestrial Line-of-Sight Radio-Relay Systems
against Interference from the Broadcasting-Satellite Service in the Bands 20 GHz
Rec.ITU-R F 1093-1 Effect of Multi-path Propagation on the Design and Operation of
Line-of-Sight Digital Radio-Relay Systems
Rec.ITU-R F 1095 A Procedure for Determining Coordination Area between Radio-Relay
Stations of the Fixed Service
Rec.ITU-R F 1096 Methods of Calculating Line-of-Sight Interference into Radio-Relay
Systems to Account for Terrain Scattering
Rec.ITU-R F 1097 Interference Mitigation Option to Enhance Compatibility between
Radar Systems and Digital Radio-Relay Systems
Rec.ITU-R PL 372-6 Radio Noise
Rec.ITU-R P 452-8 Prediction Procedure for the Evaluation of Microwave Interference
between Stations on the Surface of the Earth at Frequencies above about 0.7GHz
Rec.ITU-R P 619-1 Propagation Data Required for the Evaluation of Interference between
Stations in Space and Those on the Surface of the Earth
Rec.ITU-R P 620-3 Propagation Data Required for the Evaluation of Coordination
Distance in the Frequency Range 0.85～60GHz
Rec.ITU-R PL 842-1 Computation of Reliability and Compatibility of HF Radio Systems Rec.ITU-R PL 844-1 Ionospheric Factors Affection Frequency Sharing in the VHF and
UHF Bands (30MHz～3GHz)
Rec.ITU-R PL 1060 Propagation Factors Affecting Frequency Sharing in HF Terrestrial
Systems
Rec.ITU-R M 218-2 Prevention of Interference to Radio Reception on Board Ships Rec.ITU-R M 589-2 Interference to Radio-Navigation Service from Other Services in
the Frequency bands between 70 and 130kHz
Rec.ITU-R M 691-1 Technical Characteristics and Compatibility Criteria of Maritime
Radio-Location Systems Operating in the Medium Frequency Band and Using Spread-Spectrum Techniques
Rec.ITU-R M 831 Frequency Sharing between Services in the Band 4～30MHz
Rec.ITU-R M 1039-1 Co-Frequency Sharing between Stations in the Mobile Service below
1 GHz and FDMA Non-Geostationary-Satellite Orbit(NON-GSO)Mobile Earth Stations
Rec.ITU-R M 1044-1 Frequency Sharing Criteria in the Amateur and Amateur-Satellite
Services
Rec.ITU-R M 1072 Interference due to Inter-Modulation Products in the Land Mobile
Service between 25 and 3000MHz
Rec.ITU-R M 1086 Determination of the Need for Coordination between Geostationary
Mobile Satellite Networks Sharing the Same Frequency bands
Rec.ITU-R M 1087 Methods for Evaluating Sharing between Systems in the Land Mobile
Service and Spread-Spectrum Low-Earth Orbit(LEO)System in the Mobile-Satellite Services(MSS) below 1GHz
Rec.ITU-R M 1089 Technical Consideration for the Coordination of Mobile-Satellite
Systems Supporting the Aeronautical Mobile-Satellite(R) Service(AMS(R)S)
Rec.ITU-R M 1141-1 Sharing in the 1～3GHz Frequency Range between Non-Geostationary
Space Stations Operating in the Mobile-Satellite Service and Stations in the Fixed Service
Rec.ITU-R M 1142-1 Sharing in the 1～3GHz Frequency Range between Geostationary Space
Stations Operating in the Mobile-Satellite Service and Stations in the Fixed Service
Rec.ITU-R M1143-1 System Specific Methodology for Coordination of Non-Geostationary
Space Stations (Space-to-Earth)Operating in the Mobile-Satellite Service with the Fixed Service
Rec.ITU-R M 1171-1 Techniques for Measurement of Spurious Emissions of Radar Systems Rec.ITU-R M 1179 Procedures for Determining the Interference Coupling Mechanisms
and Mitigation Options for Systems Operating in Bands Adjacent to and in Harmonic Relationship with Radar Stations
Rec.ITU-R M 1183 Permissible Levels of Interference in a Digital Channel of a
Geostationary Network in Mobile-Satellite Service in 1～3GHz Caused by Other Networks of This Service and Fixed-Satellite Service
Rec.ITU-R M 1186 Technical Considerations for the Coordination between Mobile
Satellite Service(MSS)Networks Utilizing Code Division Multiple Access(CDMA)and Other Spread Spectrum Techniques in the 1～3GHz Band
Rec.ITU-R M 1185-1 Method for Determining Coordination Distance between Ground Based
Mobile Earth Stations and Terrestrial Stations Operating in the 148.0～149.9MHz Band
Rec.ITU-R M 1231 Interference Criteria for Space-to-Earth Links Operating in the
Mobile-Satellite Service with Non-Geostationary Satellite in the 137～138MHz Band
Rec.ITU-R M 1232 Sharing Criteria for Space-to-Earth Links Operating in the
Mobile-Satellite Service with Non-Geostationary Satellite in the 137～138MHz Band
Rec.ITU-R M 1314 Reduction of Spurious Emissions of Radar Systems Operating in the
3GHz and 5GHz Bands
Rec.ITU-R M 1318 Interference Protection Evaluation Model for the Radio Navigation
Satellite Service in the 1559～1610MHz Band
Rec.ITU-R M 1388 Threshold Levels to Determine the Need to Coordinate Between Space
Stations in the Broadcasting-Satellite Service (Sound) and Particular Systems in the Land Mobile Service in the Band 1452～1492MHz