Modified rain attenuation model for tropical regions for Ku‐Band signals

Abstract

SUMMARYAttenuation measurement on Ku-band satellite signal in a tropical site, Fiji is presented. Rain-attenuation prediction by ITU-R and the Crane Global models showed noticeable deviation to the measured values. Unlike the monotonic decrease predicted by these models, exceedance of rain-rate and attenuation in Fiji and other tropical regions showed the presence of breakpoints. For Suva, the breakpoint in rain-rate and attenuation were at 58 mm/h and 9.4 dB with exceedances of 0.009 and 0.018%, respectively. Modifications to the ITU-R model are proposed in this paper, for adopting it in the tropics. These modifications are based on the properties that in the tropics (i) the accumulation time factor at the breakpoints is an invariant (ii) for elevation angles 5608 and at high rain rates multiple rain cells intersect the slant path. The attenuation exceedance is predicted by two expressions similar to the ITU-R model, one for rain-rates lower than the breakpoint rain-rate and the other above it. The modified prediction model show remarkable agreement with the measured Ku-band attenuation in seven tropical sites.

Some of the atmospheric influences on microwave propagation through atmosphere

“…The difference between measured and standard prediction model is the existence of "break point" in the exceedence curve. The presence of such break point in the exceedance curve was reported by several authors (Pan et al, 1994;Ramchandran and Kumar, 2007;Mandeep and Allnutt, 2007). The break point here refers to the point at which the trend gets reversed (Kumar et al, 2006;Bryant et al, 2001).…”

Rain Attenuation Predictions at Ku-Band in South East Asia Countries

“…The orientation of the receiver antennas is horizontal polarized. The output signal of the LNB, at the dish, was connected to a data logger via personnel computer (PC) at USM, ITB and AdMU whereas at USP, was connected to a spectrum analyzer, which was interface to a computer via a labVIEW interfacing card [12]. For all measurement sites labVIEW software was used and programmed to record the peaks of sixty successive samples each of 1 ms duration.…”

“…These recordings were then repeated every 10 s giving six averaged peak values in a minute. To account for any variation in the satellite signal strength due to orbital variations, the average clear day signal strengths on the day prior to and after the rainy day(s) were used in the computation of the rain attenuation [12].…”

“…The cumulative distributions of the measured rain attenuation were compared with five tropical regions prediction models known as [18][19][20][21][22] and [12]. Fig.…”

“…Rain in these regions is mostly of stratiform structure, which is generally 'light' with relatively large rain cell diameters. However, in the tropics, rain at times is from convective rain cells, with relatively small diameter [12] often resulting in 'heavy' down pours for short periods [13]. The precipitation observed over the globe often are a combination of the two rather than simply one or the other, however, the frequency of a particular rain structure may dominate a region [14].…”