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.
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.
The feed chain developed in the frame of the present project shows excellent performances, compliant with target requirements and in line with the targeted application. The tests performed on the Advanced EM model, fully representative for RF design and technology implementation, showed an excellent agreement between measured and predicted performances, providing substantial validation of the design solutions proposed.
Target customers could be all worldwide L-band Telecom Satellite manufacturers and their target users, although the first accessible target customer is Airbus DS who has been one of the main satellite suppliers for Inmarsat constellations in the past decades.
Currently, Airbus DS has not such equipment in the product portfolio and the scope of Airbus Italia was to fill this gap and create a European alternative to the worldwide monopolistic suppliers.
The project enabled Airbus Italia to achieve performances in line or better than those proposed by the major competitors, including non-European suppliers, for similar applications. The developed product actually represent a valid European alternative for future MSS L-band missions, as well as Navigation (GNSS, G2G, etc.) and LEO constellations Telecom missions.
Key feature of the L-band feed chain are summarized here:
Cup-loaded crossed-dipoles (Short Back Fire) radiating element ▪ Integrated feeding network in strip-line technology ▪ Extended L-band operation (1518–1559 MHz Tx, 1626-1675 MHz Rx) ▪ Dual circular polarization (RH & LH) ▪ High directivity (>10.3 dBi @ Tx) and radiation efficiency (>98%) ▪ Low cross polarization (AR<1.5 dB) ▪ Integrated diplexers in coaxial technology ▪ Avoidance of tuning screws on Tx channel ▪ High Tx/Rx Isolation (>90 dB) ▪ Temperature compensation for optimum phase and gain tracking ▪ Coaxial RF interfaces: standard SMA (Rx), hi-power TNC (Tx) ▪ High power handling (125W average per pol., >1250 W continuous at array level) ▪ Multipaction free and low PIM (<-145 dBm - 5th order) ▪ Reduced mass ▪ Compatible with cluster arrangements (~1l element spacing, triangular lattice) ▪ Space qualified materials and flight proven and technologies ▪ Advanced EM manufactured, fully representative of RF design and implementation technology ▪ Performance tests in stand-alone and embedded sub-array configurations ▪ State-of-the-art performances in excellent agreement with design predictions
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.
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.
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.