國際電信聯(lián)盟0001

1、ITU-R P.838-2 建議書預(yù)測方法所用的特定雨衰模型(1992-1999-2003 年)ITU-R 201/3號研究課題國際電聯(lián)無線電通信全會，考慮到a有必要用的降雨率計算因降雨引起的衰減，建議1采用以下程序。采用幕律關(guān)系由降雨率 Rmm/h得出特定雨衰：(1)R =kR：線極化水平：H，垂直：V 水平通路的頻率依從系數(shù) k和a在表1中給出。表1中的各值經(jīng)測試說明，對于最高不超過55 GHz頻率的衰減預(yù)測具有足夠的準(zhǔn)確度。系數(shù)k和a作為頻率的函數(shù)，也可用以下公式確定。這兩個公式是通過由散布計算得出的幕律系數(shù)的 曲線擬合導(dǎo)出的：-fl expFklog f g(2)-ai exp -ml

2、ogf c;.Ci(3)式中：f :頻率GHzk :或者kH或者kV:或者:-H或者:V°表1采用公式4、 5和1估算特定衰減時所用的頻率依從系數(shù)頻率(GHz)kVOHa10.00003870.00003520.91220.88011.50.00008680.00007840.93410.890520.00015430.00013880.96290.92302.50.00024160.00021690.98730.959430.00035040.00031451.01850.992740.00064790.00058071.12121.074950.0011030.00098291.

3、23381.180560.0018130.0016031.30681.266270.0029150.0025601.33341.308680.0045670.0039961.32751.312990.0069160.0060561.30441.2937100.010060.0088531.27471.2636120.018820.016801.21681.1994150.036890.033621.15491.1275200.075040.068981.09951.0663250.12370.11251.06041.0308300.18640.16731.02020.9974350.26320

4、.23410.97890.9630400.35040.31040.93940.9293450.44260.39220.90400.8981500.53460.47550.87350.8705600.70390.63470.82660.8263700.84400.77350.79430.7948800.95520.88880.77190.7723901.04320.98320.75570.75581001.11421.06030.74340.74341201.22181.17660.72550.72571501.32931.28860.70800.70912001.41261.37640.693

5、00.69483001.37371.36650.68620.68694001.31631.30590.68400.6849其他系數(shù)在表2和表3中給出。公式2和3用于水平極化時的系數(shù)abcmkckm ac aj = 10.33641.12740.29161.9925-4.412320.75201.66440.51753-0.94662.84960.4315i=10.55640.77410.4011-0.080160.899320.22371.40230.34753-0.19610.57690.23724-0.022192.29590.2801表3公式2和3用于垂直極化時的系數(shù)abcmkckm a

6、c aj=10.30231.14020.28261.9710-4.453520.77901.67230.56943-1.00222.94000.4823i=10.54630.80170.3657-0.070590.875620.21581.40800.36363-0.16930.63530.21554-0.018952.31050.2938對于線極化和圓極化以及對于所有通道格式，可用以下公式從表1中的值計算出公式1的系數(shù):(4)k =kH kV (kH -kV) cos2 v cos 2 ./2a =kHaH kVaV 亠kH aH -kVav cos2 v cos2 . / 2k式中0為通道仰角，T為相對于水平方向的極化傾角圓極化 T =45 °。為方便起見，與表1中的頻率不同的k和a值可用圖1至4快速估算。圖1水平極化系數(shù)k隨頻率的變化 k隨頻率的變化kH 數(shù) 系1.401.351.301.251.201.151.101.051.00H數(shù) 0.95系 0.900.850.800.750.700.650.60(、/1f、1、圖2水平極化系