Overview
Currently, the implementation process for installing antennas on aircraft results in high costs and long timescales. There are errors in the coupling calculations used to obtain isolation between antennas on opposite sides of the fuselage, the design phase uses unverified computational modelling and there is a frequency gap in the computational software used. Scaled model measurements used to bridge this gap are expensive and time consuming. In-flight trials have severe limitations and the erroneous siting of antennas results in massive time and cost implications to the whole programme.
The purpose of the programme was to improve computer-aided engineering design and evaluation capabilities (computational and measurement methods) for the installation of antennas on aircraft structures. This was to be achieved by bridging the frequency gap in computational electromagnetic tools using refined hybrid and multi-domain methods and the development of fast solver methods for solving full-wave integral equation methods in the frequency domain.
The performance of antennas on non-metallic and hybrid materials such as GLARE were investigated and more accurate coupling calculations based on measurements were derived empirically. This led to an improved prediction of performance of antennas and interoperability, with consequent contributions to operational safety and on-board Internet access.
The feasibility of radiation pattern measurements on full-scale aircraft using an innovative airborne platform were investigated. This is based on near-to-far-field transformations adapted to cope with irregular spatial sampling.
There were five technical Work Packages consisting of:
- Characterisation of antenna data.
- Improvements in computational tools, which including hybridisation (of low and high-frequency codes), multidomain, Fast Multipole methods, asymptotic techniques, application to hybrid structures.
- Verification of tools through measurements on flat panels, metal cylindrical tubes and scaled aircraft models, as well as verification of inverse methods for use in the validation of the ANTF (airborne near field facility). Additionally, empirical formulas were derived for more accurate calculations of the coupling between antennas and a CAD cleaning tool developed for reducing the number of wire segments (and hence the CPU time) for MoM tools.
- Full-scale measurements and modelling on real aircraft or full-scale mock-ups.
- Production of codes of practice for the design and qualification phases of antenna siting on aerostructures.
Funding
Results
The final success and achievements of the IPAS project can be briefly stated in two ways; firstly the successes and achievements of the modelling aspects of the project and secondly the successes and achievements of the measurement programme.
Modelling
IPAS has achieved its primary goal of extending the ability to accurately predict installed antenna performance. In particular, the accuracy, the range of applicability and the ease of use of computer modelling have been improved to the extent that numerical modelling has overtaken scale model measurements as the most effective prediction and qualification approach over a wide range of frequencies.
A key to success in cost-effective numerical modelling is to get a model that eliminates unwanted detail but captures the essential physics. IPAS has made significant contributions here: improved CAD-to-mesh software has helped get good vehicle models. Development of simplified antenna models combined with calibration measurements has made accurate simulation of gain and coupling of quite complicated production antennas on full aircraft feasible. Improvements in multi-domain and fast solver methods have extended the range of frequencies accessible to numerical modelling.
The validation of method-of-moment (MoM), fast multipole (FMM) and multi-domain (MD) software against measurements for antennas on canonical body, on scale model and on full-scale aircraft has demonstrated electromagnetic software is now sufficiently mature to replace scale models as the tool of choice for installed performance assessment. Improved meshing and knowledge captured from the validation work has made the software accessible as everyday engineering design tools.
Measurement programme
The qualification and certification process was accomplished by mock-up and in-flight measurements on a real aircraft with coupling and radiation patterns. In IPAS, the prediction of computer models have been compared with measurements performed under known and real conditions. IPAS achieved the measurement part while proposing bases model for comparison with codes. Several measurement parameters have been identified as being affecting results and need to be taken into account for the calculation code improvement.
In order to bring bases model for comparison, measurements on both mock-up and full-scaled model have been performed. Three aircraft families (ATR42, Fokker100 and IPAS-1) have been necessary to demonstrate the reliability of the code pred