PAGE CONTENTS
Objectives
The objective of the activity is the development of an L-band High-Power Dual Polarization Feed Chain, mainly intended to be a valid European alternative for future Mobile Satellite Services (MSS) satellite antennas.
The rising congestion in the L-Band spectrum calls for the development of dual-polarization MSS antenna systems, while the need for higher throughput is expected to consistently drive the power handling requirements higher. Considering this scenario, the key design target in the frame of the present project is to develop an integrated feed chain, including radiating element and diplexers, compatible with cluster arrangements in large multiple-beam array-fed reflector antenna architectures (INMARSAT-like). The feed shall be able to operate in both transmit and receive mode in dual polarization, handling high levels of RF power and ensuring low PIM and Multipaction free operation.
A possible extension of the developed technologies is also envisaged toward the development of similar radiating elements and diplexers/filters for Navigation (GNSS, G2G, etc.) and future LEO constellations Telecom missions.
Challenges
The main challenges of the development are related to the implementation of the dual-polarization operation and high power handling requirements.
Two diplexer units must be integrated in each feed chain trying to fit the stringent accommodation requirements imposed by the minimum array spacing. Dedicated design solutions and proper selection of technologies are required to achieve very low-PIM and Multipaction free operation. Stringent RF performances must be guaranteed within severe thermo-mechanical conditions imposed by launch and space environment. Mass and dimensional constraints become extremely critical for large array applications, as well as amplitude and phase tracking among similar units.
System Architecture
The feed chain is designed to be compatible with cluster arrangements in large, multiple-beam, array fed reflector antenna architectures (INMARSAT-like). Both single feed per beam and multiple feeds per beam feed array operation are considered as reference scenario.
Each feeding chain is an assembly composed of:
- A radiating element with integrated feeding network for CP operation
- Two diplexers for Tx/Rx operation in both the polarizations
- A Support frame, to be customized for specific cluster configurations
The radiating element is composed of a main back reflector and a small circular sub-reflector, forming an open cavity resonator with radiation normal to the sub-reflector plane. The cavity is excited by two crossed dipoles fed by Γ-shaped baluns and coaxial lines. A parasitic circular disc is placed proximity of the crossed dipoles. An integrated feeding network composed of a branch-line hybrid coupler in strip-line technology (TEM) generates the dual CP. The transmit and receive signals are separated by two diplexers realized in coaxial TEM cavity technology. 6th order generalized Chebyshev filters with one transmission zero ensure the required rejection in both Tx and Rx channels. Temperature compensated resonators are implemented to achieve stringent amplitude and phase tracking performances.
Plan
The project plan is articulated over two phases with the primary objective to design and test the L-band feed chain up to EQM level:
a) Phase 1: design development and tests up to EM level;
b) Phase 2: complementary activities, covering manufacturing and qualification tests of EQM model.
Current Status
Phase 1 of the project has been completed.
The design has been validated through an Advanced EM model fully representative for RF design and technology implementation, successfully manufactured and tested. The achieved design is ready for full space qualification, including high-power tests.
Based on the recent evolutions of the market, the development of the EQM and relevant qualification campaign is actually postponed to a future reprise of market interests for this kind of applications. Therefore, the Phase 2 of the study will be not carried out.
