Objectives

The objective of this activity is to design and develop a high voltage power transformer in planar technology for Electronic Power Conditioning Units (EPC) used to drive travelling wave tubes.

The aim is to develop a novel transformer design solution not existing today in Europe for up to 8kV class of EPCs (with research of margin up to 10kV). 

A transformer engineering model is designed, manufactured and tested in a  representative environment to validate the developed concept for space application.

The main intermediate objectives of this project are: 

• To establish a detailed requirement specification for the high voltage planar transformer,

• To define a program (in Excel), based on the build-up in order to compute the tracks size of primary and secondary windings, the leakage inductance, the copper losses of the secondary and primary windings, the core losses, the resonant push-pull losses and rectifier losses,

• To define thermal and electrical models of the High Voltage Planar technology,

• To review and de-risk the available technologies and processes available in accordance with the technical requirements defined,

• To minimise the manufacturing complexity and to ease flexibility during production aiming at a short time to delivery.

Challenges

The main technological challenges are the management of the high electrical fields inside the planar transformer assembly, and the thermal management of the transformer.

The chosen design needs to manage high voltage design rules in PCBs, while at the same time using a more complex build-up than high voltage PCBs currently used.

Thermal design needs to be optimized by using innovating solutions such as optimizing the transformer build-up and improving thermal interfaces with the structure.

System Architecture

Resonant transformer topology working at high frequency.

The Planar transformer technology is based on a high voltage multilayer PCB equipped with its ferrites, thermal conductive material and mechanical fixations.

The secondary side is a single or multiple windings and the primary side is a push-pull type so double windings with a common point.

Plan

The project’s work plan is based on the following methodology:

1. Based on the state of the art of the Travelling Wave Tube Amplifier, to build the definition of a detailed technical requirement specifications for planar transformer,

2. To study suitable technologies to achieve a high voltage transformer in planar technology based on a technical trade-off and specific de-risking evaluation activities as High Voltage withstanding aspect,

3. To study and optimize the electrical and thermal concept of such technological assembly. This step includes detailed calculation and optimization of magnetics tools (including software calculation tools),

4. After the manufacturing of an Engineering Model (Elegant Bread Board – EBB), to test the High Voltage Planar technology in a realistic EPC environment. The tests sequence includes a Thermal Vacuum test sequence covering GEO mission needs.

Current Status

The main achievements are: 

In the frame of the project Requirements Review (RR):

• The feasibility study to address the technology to the following TWT tubes has been validated: 150W Ku, 40W Q, 250W Ka, 170W Ka, 300W Ku, 150W C, 75W C, Dual 70W Ka and Compact Dual Ka/Ku TWT’s (80W RF) and for multi-tube constellations market, 

• The confirmation of implementation feasibility has also been successfully performed ; this study included the following tasks: definition of the preliminary mechanical architecture of the technical solution, planar losses optimization, PCB build-up, preliminary thermal analysis and preliminary electrical fields analysis.

In the frame of the project Technical Design Review (TDR):

• Several electrical optimizations have been performed including parasitic capacitors computations and leakage inductance distribution,

• Based on these optimizations, the development of the Planar/PCB build-up has been pushed including thermal and Electrical field analysis,

• The derisking of the PCB technologies including incoming tests definition, High Voltage ageing behavior (with the definition of a specially dedicated representative test vehicle) and materials performances such as outgassing tests and dielectric strength.

In the frame of the project Preliminary Design Review (PDR): 

• The definition of the Elegant Breadboard (EBB) ; designed taking into account the challenge to establish a compromise between high voltage insulation properties and sufficient thermal drain capabilities of the HV planar transformer technology studied in the frame of this project.  The demonstrator definition was based on Quadral EPC adapted to the selected TWT’s, i.e. 170W Ka. Detailed calculation and optimization methods for magnetic, electrical and thermal designs have been performed. The design took into account manufacturing and assembly properties in order to minimize the manufacturing complexity and to ease flexibility during production aiming at a short time to delivery. 

In the frame of the project Final Review (FR) : 

• The planar transformer technology has been exposed to space representative environment. After a first step covering the ground test sequence, a TVAC sequence of 130 thermal cycles has been successfully performed in order to verify the high voltage design and environment effect (including the effect of the local increase of pressure). 10 cold starts at -40°C have also been performed. The test has then been pursued with success with a HV life test at +70°C base plate in order to reach a total test duration of 1500 hours. The test sequence also included thermal characterization under vacuum in order to validate the thermal model related to the evaluated technology.

Companies

Thales Alenia Space Belgium

http://www.thalesgroup.com

Belgium

Objectives

The achievement of high output power requires a higher energetic electron beam. Technological bricks are more and more challenging, developments for components and materials are getting marginal.

In order to achieve a high electronic flow, with reduced geometrical dimensions, an advanced new electron emission device (MMC) is needed, for a constant high beam current density. This MMC device shall be capable for 5 A/cm² electronic flow through the TWT interaction range. Obviously, the electron ejection has to function constantly for more than the 15 years of the cosmic mission life.

The MMC emitter is developed from actual MM-type technology, at THALES as a new high current density electronic source. It allows an increase of the current density by lowering the extraction energy for electronic emission.

The new MMC emitter-design is already in use in telecommunication tubes on ground, for high power TWT’s. The non-terrestrial qualification includes a complete batch of MMC-devices, further specific test vehicles and qualification tubes in order to verify the performance of the MMC devices either by accelerated or standard life testing.

Based on a successful qualification, the MMC emitters will serve THALES’ actual and new development projects, where the high emission current density is mandatory.

Challenges

The development of the MMC emitter for 5 A/cm² with 15 years life time can be considered as an evolution out of the well approved and reliable MM-type technology. By lowering the extraction energy for electronic emission, the MM-technology could be systematically improved and verified. Consequently, the MMC device for non-terrestrial application represents the follow-on for the MM-type emitter, including a general process update, while maintaining the reliability aspects of the actual MM–type emitter. In detail, prior to the qualification of the MMC-emitters a further optimisation step for increasing performance and reliability is done by adjusting the manufacturing processes.

System Architecture

The electron beam is generated by the MMC emitting device. By increasing the current density the electron beam becomes more powerful and a higher output power of the TWT can be reached.

High power TWTs are designed such, that they can handle maximum microwave energy, which is automatically correlated to the tube efficiency. So, – under the consideration of a sufficient margin – the following main parameters are adjusted to their physical / material optima: 

• Temperature

• Thermo-mechanical stress

• Thermal gradients

• Thermal conductivity

• Electrical field strength

• Long-term stability

The MMC electron source has to fulfil all of the above criteria, which sometimes need to choose a compromise on materials and processes. Therefore, the selected materials and processes play an outstanding role in this assembly and need to be chosen very carefully.

Plan

The project is divided into three blocks, each finalized by a dedicated milestone.

The first is focused on the process engineering updated and closed by the Preliminary Design Review (PDR/TRR). 

Followed by qualification tests on subassembly level and specific test vehicles, which were finalized by the Critical Design Review (CDR).  Finally, the qualification test on tube level for a 170W Ku-band TWT THL12170C+ was successfully performed and evaluated for the final review.

Current Status

The qualification campaign of the MMC cathode was successfully performed with real improvements for THALES and their customers. With a significant increase of the permissible emission current density up to 5A/cm² future gun designs can be improved with reduced beam compression and therefore improved beam focusing. The customer can expect improved live time behaviour, due to the fact that a chromium-doped MM cathode will ensure improved barium coverage over a long life time. The cathode size can be potentially reduced due to increased current density or kept constant to replace MM cathodes with improved life time behaviour.

Related Links

• Building Blocks for High Power and High Frequency TWTs
• 500W S-band traveling wave tube
• Ku-Band Developments Including High Power

Companies

Thales Deutschland GmbH

http://www.thalesgroup.com

Germany

Objectives

Starting point for this activity was the EM design of a combined Tx-Rx Ka band feed chain for user application, developed in a previous program.

This feed chain was further developed and qualified as EQM in a scalable feed cluster. Therefore, beside the RF performance, mass and dimensions were important design drivers. The feed cluster in this program consists of a waveguide panel, designed as beam forming network, carrying 16 horn-polariser assemblies.

Challenges

The design of the Ka band feed chain needs to allow the application in a scalable feed cluster to be used as feed for a multi spot beam antenna. To be able to achieve narrow beam spacing and a compact feed size, the outer diameter of the feed chain was chosen to be 30mm. To achieve a good RF performance with such accommodation constraint, while fulfilling the environmental requirements was the main challenge of this program.

Plan

The project started with the mechanical analysis of the EM feed chain model of the previous program. Design iterations to balance RF performance and mechanical properties followed.

In parallel a waveguide panel with an integrated distribution network was designed. Both designs were performed under the constraint of scalability with respect to the number of feeds in the cluster.

After the detailed design phase all components were manufactured, integrated and tested according to the requirements.

Current Status

The project is completed successfully. 

Companies

Airbus Defence and Space GmbH

Germany

Airbus Defence and Space (UK)

http://www.airbus.com

United Kingdom

Objectives

Describe in less than 200 words the objectives of the project. 

The satellite communication market is evolving towards medium-volume production of antennas and associated front-ends. Indeed, in GEO applications, complex focal plane arrays of hundreds of antenna-feed chains and BFNs are required to implement Tbps VHTS systems. In LEO and MEO applications, constellations of several hundreds or even thousands of low-cost small satellites are already in operation or will be deployed soon. 

In this framework, additive manufacturing (AM) technologies are being steadily investigated and exploited for the development of RF equipment for satellite communication payloads. Indeed, AM technologies provide several advantages with respect to conventional machining, among which are free-form capability and fit-for-purpose design. These two specific aspects of AM enable the integration of different functionalities in a single monolithic part, thus reducing the number of parts, costs, lead time, and MAIT activities. 

The present project aims at developing through AM a monolithic K/Ka-band dual-circular-polarization antenna-feed system with integrated RF, thermal and mechanical functionalities, intended for GEO High Throughput Satellites.

Challenges

Additive manufacturing technologies offer several advantages in the development of highly integrated RF systems with additional functionalities. However, they also present critical aspects in terms of dimensional accuracy and surface roughness, when RF equipment working at K/Ka bands and in dual-circular polarization are targeted. In this view, one of the main challenges of the present project deal with the RF, mechanical and thermal co-design of the antenna-feed system capable of minimizing the impact of the manufacturing process on the performance. In parallel, challenges apply also on the manufacturing process in order to optimize the production parameters for the intended application.

System Architecture

The K/Ka-band dual-circular-polarization antenna-feed chain developed in the present project consists of a smooth-wall feed-horn and an asymmetrical feeding-network. 

Since a dense focal plane array is considered, the relevant feeding network has to fit within the radiating aperture of the feed horn. Moreover, it was considered the additional goal to minimize the transversal dimension of the feeding network to make feasible its potential application to arrays with smaller lattice steps. Indeed, asymmetric configurations lead to very streamlined geometries, compatible with lattice steps of the focal-plane array in the order of 20 mm, although at some expense in terms of performance (primarily, port-to-port isolation in polarization and XPD). To understand the applicability of these configurations, three different architectures were investigated.

The mechanical design of the EM integrates the adapters towards the standard measurement setup. The design of the thermal circuit integrated in the feeding network was carried out by considering a requirement of thermal dissipation equal to 2.5 W. After a trade-off study and considering the minimum tube dimensions, a Mechanically Pumped Fluid Loop (MPFL) system was selected.

Plan

The project plan consists of one phase, including the following milestones:

• Requirements Review (RR), focused on requirements at system, antenna and antenna-feed chain level, regarding RF, thermal and mechanical aspects.

• Mid-Term Review (MTR), focused on the preliminary RF design of the antenna-feed system and bread-boarding of key building blocks.

• Critical Design Review (CDR), aimed at the consolidation of the RF, thermal and mechanical co-design and additive manufacturing route of the EM.

• Test Readiness Review (TRR), focused on manufactured EM, test plan, and measurement setups and procedure.

• Test Review Board (TRB), aimed at the discussion on the comparison among predicted and measured performance of the EM, including RF, thermal and mechanical responses/properties.

• Final Review (FR), including all the activities carried out during the project and discussion on lessons learnt and follow-on activities.

Current Status

The project was successfully completed. Indeed, the tests performed on the EM confirm the validity of the RF, thermal and mechanical co-design and manufacturing approach and pave the way for a continuation of activities aimed at obtaining a higher TRL.

Related Links

• Pasquali Microwave Systems web page
• VEGA Composites web page

Companies

Pasquali Microwave Systems Srl

http://www.pasquali-microwavesystems.com/

Italy

CNR - IEIIT

https://www.ieiit.cnr.it

Italy

Politecnico di Torino

http://www.polito.it/

Italy

Argotec

https://www.argotecgroup.com

Italy