Performance of Antenna Arrays for Satellite Navigation and Communication Installed on Aircraft

Kurzfassung

The assessment of installed performance of antennas on aircraft is a very difficult task. Experimentally, patterns can be measured by performing in-flight tests, which are very expensive and allow in general the determination of only few cuts. This costly method can be replaced by down scaling the dimensions of the aircraft and of the antenna, whilst scaling up the frequency during the measurements, so that all the electrical dimensions (in wavelengths) are kept the same. In such tests, a mock-up of the real aircraft and a scaled antenna model are necessary. The scaled antenna does not need to have exactly the same geometry as the full-scale one, but the radiation characteristics of the original antenna should be well represented. Alternatively to the aforementioned procedures, computer modelling can be used to assess installed performance of antennas. The main advantage of using simulations for this purpose is the reduction of time and costs. Moreover, some electromagnetic characteristics, such as surface current densities on the aircraft surface, can not be directly measured, but they can be accurately calculated using appropriate computer models. In order to validate numerical predictions of installed performance, simulated results are compared with measurements performed with a 1/15th mock-up of a Fokker 100 aircraft. The simulations and measurements were done for two different 4x4 microstrip antenna arrays, which served as radiation models of a smart GALILEO digital-beamforming antenna under development at the Institute of Communications and Navigation, German Aerospace Centre (DLR), in Oberpfaffenhofen. The chosen up-scaled frequency was 22 GHz, which corresponds to 1.47 GHz if the full dimensions of aircraft and antenna are considered. Two different microstrip antenna arrays have been designed to assess installed performance of the full-scale smart antenna when mounted on a real Fokker 100 aircraft and operating under different beamforming conditions. The installed performance simulations have been performed using the FEKO electromagnetic simulator. Two numerical techniques have been used: physical optics (PO), which is an asymptotic technique suitable for scattering analyses at high frequencies, and the multi-level fast multipole method (MLFMM). The latter is computationally more expensive than the former, but provides in general more accurate results. The computed surface currents will be shown in the symposium and the results obtained with both techniques will be compared. The measurements with the mock-up have been performed in DLR’s antenna testing range. The details concerning the measurement setup will also be discussed in the symposium. The comparison of computed and measured radiation patterns will be presented and discussed at the symposium. The numerical predictions are in good agreement with the measured data.