LNA-TEC Peltier Device for Telecom LNA Application

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The project aims to:
  • to assess the performance and operation of TEC elements for LNA cooling
  • to develop TEC implementation concepts on the LNAs considering accommodation constraints with minimum impact on the original LNA design, in particular, without violating the hermetic sealing of the LNA and the components inside it, while minimizing the impact on the overall power, dissipation and mass budgets
  • to demonstrate the performance of the developed concept by analysis and testing
  • to develop an Engineering Model to be tested in relevant environment (thermal vacuum and vibration), verified via functional testing for the best configuration selected.
  • to develop in parallel multiple aspects allowing the final implementation, in particular: repeatability of the attachment method for the TEC element, develop an overall control strategy for the TEC power in order to actively control the temperature on the LNA (both hardware and software)
The main challenges within the project are related to the impossibility to perform a direct thermal control on the components to be cooled inside the LNA (as to do so it would compromise the hermetic sealing and though the whole LNA assembly, verification and calibration processes) and the limitations to the design options around the LNA itself. For example, the overall design cannot impact the external interfaces of the LNA and the module on which it is mounted, the only heat sink available is the one of the LNA itself (which can reach relatively high temperatures (ca. 65°C) in operation.
With respect to standard LNA design, this architecture allows to reduce the operational temperature of the LNA components and therefore to reduce the noise on the RF signal improving the performances of the equipment. This is however achieved with a limited increase in power consumption (supplied to the TEC elements) and power dissipation, with a minimal impact on the standard architecture. This last point is also the main advantage with respect to other solutions already developed for LNA cooling which need complex design and parts for cooling (e.g. a dedicated radiator, with all the necessary interfaces, heat-pipes…). The design studied in this project allows reducing the temperatures with minimal design changes to the system architecture. The final performances achieved and measured during thermal vacuum chamber campaign allow reducing the LNA Noise Figure by 0.4dB with the interface temperature at 60°C. The LNA performances are in this case comparable to those of the same unit without cooling device, but at 25°C boundary condition. This performance is achieved with a total power consumption of the cooling solution of 2.2W plus 0.39W for the control electronics and ca. 125 grams additional mass.
The cooling system is composed by:
 Thermo-Electric Cooling element/s mounted outside the LNA hermetic sealing (in order to reduce the impact on the standard
process for qualification of the LNA itself)
 temperature sensor mounted as close as possible to one of the critical elements inside the LNA hermetic sealing to monitor the
temperature reference point and used to control the power input to the TEC system
 a control electronics, which finds allocation in the available space within the Interconnection Module behind the LNA, reading the reference temperature and then controlling the input to the TEC allowing then the temperature control of the LNA. The TEC is positioned in order to maximize its cooling capacity with respect to the elements to be cooled inside the LNA, the temperature
sensor as close as possible to the component in order to provide a perfect monitoring of the system. The electronic board is as compact as possible, although designed to be able to control the complete assembly of LNAs on the Interconnection Module (4 elements) and has a limited power consumption to reduce its impact on the overall architecture.
System Architecture

The cooling system presents the following parts impacting on the LNA system architecture:  TEC element/s mounted outside the LNA hermetic sealing: this approach does not cause any impact on the standard LNA assembly and verification process  a gluing process (instead of soldering) is preferred for the EM as it allows more freedom in the system concept definition/modification, although soldering is also possible, increasing performances but also reducing tuning activities for the EM (it can be analysed within a follow-up study)  a temperature sensor is also mounted outside the LNA not to violate the hermetic sealing  the control electronics find allocation below the LNA, inside Interconnection Module, filling the available space. The solution is almost not impacting the standard architecture in terms of volume as the control electronics finds accommodation in the empty space below the interconnection module. The solution presents a total power consumption of the cooling solution of 2.2W (for each LNA) plus 0.39W for the control electronics and ca. 125 grams additional mass.

The main project tasks are organized as follows:
 definition of project requirements;
 development of the TEC implementation concept on the LNA (starting analysing multiple ones) providing optimum performance and minimum impact on the original LNA design;
 verification of developed concept by analysis (thermal and structural);
 implementation and verification via Structural Thermal Modelling (thermal vacuum and vibrational test);
 finalization of the design and manufacturing of an Engineering Model of the LNA equipped with TEC element;
 testing of the EM in relevant environment (thermal vacuum chamber and shaker);
 post-evaluation of test results and future development plan.
Current status

Project completed in May 2016.
Final review on the 7th of June 2016.