European Space Agency

SSPA with European GaN Devices

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Objectives

The main objective is to evaluate last improvements of the European commercial 0.5μm (GH50) and 0.25μm (GH25) GaN HEMT  technologies from United Monolithic Semiconductors Foundry. These two GaN technologies studied in the frame of the GREAT² ESA contract have reached a satisfactory level of maturity that makes them the good candidates for space applications from L-band to Ku-band.

Main proposed activity is to design, manufacture and test:

  • 1 hybrid HPA module (two iterations) at L-band and based on the UMS GH50 technology
  • 1 MMIC HPA module at Ku-band and based on the UMS GH25 technology

To ensure maximum power added efficiency (PAE), the HPA module relies on the design of an optimal inverted class F working mode. The optimization of the output combiner has to be managed in order to match as close as possible the optimum output load including 2nd harmonic with minimum of losses..

The introduction of the GaN technology in SSPA equipment and the objective to use GaN SSPA equipment with more stringent thermal specification are inducing an increase of component temperature and high heat flux density to be managed at the interface between the units and the spacecraft panel.

To demonstrate that high level of compression could be used for flight operation, RF step stress measurements on HPA modules are performed in order to identify the safe operating area.

Challenges

To answer to the requirements imposed by the technical aspects described above, the development of HPA modules are  based on the following techniques and solutions:

  • For an optimal RF performance prediction (Pout/PAE/Linearity) of L-band and Ku-band HPA modules, active devices (transistors and power-bars) have been characterized and modelled through harmonics load-pull measurements campaign.
  • To ensure maximum power added efficiency (PAE), the HPA relies on the design of an optimal inverted class F working mode. The optimization of the output combiner has to be managed in order to match as close as possible the optimum output load including 2nd harmonic with minimum of losses. For Ku-band applications, HPA modules based on Doherty architecture have also been evaluated.
  • In order to manage the important heat flux under GaN devices, new material with high thermal conductivity has to be privileged for the baseplate of the micro-package.

Regarding the high compression level required to achieve maximum power added efficiency, RF step stress measurements are performed to identify safe operating area.

Benefits

The L-band HPA module designed, manufactured and tested in the frame of this study has proven its ability to deliver high output power at L band over 50W with efficiency above 60%. These excellent performances made it a perfect candidate to high power SSPA equipment dedicated to Telecom applications. Thus, based on this L-band GH50 HPA module,  EM GaN SSPA equipment brings many benefits compared to LTWTA solution and GaAs SSPA solution:

  • Improved electrical performances with multi-carrier signal
  • Higher operating temperature: 85°C instead of 65°C
  • Mass reduction of 66% compared to a L-band LTWTA solution
  • Footprint reduction of 65% compared to a L-band LTWTA
  • Simplified implementation during payload integration
  • Cost reduction compared to LTWTA solution

This competitive EM GaN SSPA equipment is able to address the entire renewal market of constellations of mobile communications satellites.

For Ku-band applications, the introduction of Ku-band GH25 HPA module developed in this study, has been analysed on two types of equipment: SSPA and LC-SSPA

Regarding a 20W Ku-band SSPA based on a single GaN HPA module developed in this study, the comparison between GaAs and GaN SSPA equipment versions shows important improvements and points to be addressed further:

  • Improvement of PAE performance: +7 to 10 points
  • Footprint reduction : -28%
  • Mass reduction: -20%
  • Cost reduction estimation: -17% in comparison with the 20W Ku-band GaAs SSPA using 2 HPA modules.

Regarding a 160W Ku-band LC-SSPA based on 8x GaN HPA modules  and low loss space combiner technique, the comparison with LC-TWTA show mitigate results for LC-SSPA in particular for electrical performance. It is then clear that a GH25 based LC-SSPA presents insufficient electric performances (low PAE and reduced frequency bandwidth) and that a technological breakthrough is required to increase this performance (Pout/PAE/NPR/Instantaneous frequency bandwidth).

Features

The GaN HPA module based on UMS GH50 power bar is using a novel hermetic high dissipative package with Metal-Diamond material.

The measurements are excellent and are showing that output power is over 50 W in CW with more than 60% of PAE at hot temperature. RF step stress measurement performed on three HPA modules up to 10dB compression have demonstrated that high the level of compression (6,5dBc) required for high efficiency performance could be used for flight operation. 

In Ku-band, for the inverted class F working mode GH25 HPA version, performance results are in line with the electrical simulations, thus, validating the NL transistor model established during the study.

Regarding the GH25 Doherty HPA version and due to specificity of the targeted linearity (NPR=15dB corresponding to 2-2,5dB OBO), the performance obtained in term of Pout/PAE/NPR (multicarrier mode) show similar results compared to the previous version. Due to the complex architecture of this Doherty HPA module (2 stages using 8x transistors in parallel for output stage), ‘’Doherty effect’’ is limited at low OBO.

System Architecture

L-band GaN SSPA equipment using HPA-1 module brings many benefits compared to LTWTA solution

  • Mass reduction of 66% compared to a L-band LTWTA solution
  • Footprint reduction of 65% compared to a L-band LTWTA

Solution

  • Simplified implementation during payload integration
  • Cost reduction compared to LTWTA solution

Plan

The activities are dedicated to the development and the tests of  L-band and Ku-band GaN HPA.

Phase 1:

  • Study of SSPA equipment for space-borne Telecom applications
  • Baseline design of L-band GH50 HPA module
  • Run-1 Manufacture of GH50 transistors and power-bars
  • Run-1 Non-linear modelling and performance validation
  • Run-1 Detailed design of L-band GH50 HPA module
  • Run-1 Manufacture and test of L-band GH50 HPA module

Phase 2:

  • Run-2 Manufacture of GH50 transistors and power-bars
  • Run-2 Non-linear modelling and performance validation
  • Run-2 Detailed design of L-band GH50 HPA module
  • Run-2  Manufacture and test of L-band GH50 HPA module
  • Baseline design of Ku-band GH25 HPA module
  • GH25 Non-linear modelling and performance validation
  • Detailed design of Ku-band GH25 HPA module including Doherty versions
  • Manufacture of GH25 MMIC
  • Manufacture and test of Ku-band GH25 HPA modules

Current status

All key reviews have been held successfully. The L-band GaN HPA was fully tested with the expected performance. Benefits of the introduction  of the L-band GaN HPA module into SSPA equipment dedicated to Telecom applications are demonstrated.  

Regarding Ku-band HPA module with GH25 technology, different architectures (Class AB and Doherty) were tested. Through two kind of measurements during RF step campaign, the reliability on the Ku HPA has been validated. 

The contract is now closed.

Contacts

ESA Contacts

Status date

Monday, August 5, 2019 - 11:43