Thermal Management of High Power Amplifier (HPA)
1. Design Objective
The High Power Amplifier (HPA) used in the payload RF chain is the Mini-Circuits ZVE-3W-183+. This component amplifies the RF signal before transmission and as a result it will dissipate electrical power as heat during operation. If the generated heat is not properly managed, the amplifier temperature may increase and affect the reliability and performance of the payload subsystem.
According to the manufacturer’s datasheet, the maximum allowable base plate temperature of the HPA is 85 °C, while the recommended operating ambient temperature range is −40 °C to 55 °C. To ensure reliable operation of the payload system, the temperature of the amplifier must remain below this limit during continuous operation.
Fig [] Maximum rating table for ZVE-3W-183+
The physical dimensions of the HPA are 61.72 mm × 49.78 mm × 18.8 mm, and the aluminium housing of the device serves as the primary heat conduction path for dissipating internally generated heat. Since the amplifier will operate for extended periods during ground station transmission, it is necessary to evaluate its thermal behaviour under operating conditions.
ZVE-3W-183+ CAD Model
To assess the temperature rise of the amplifier, an experimental thermal test was first conducted by powering the HPA for a fixed duration. The measured temperature data from this experiment is later used to validate a thermal simulation model, which is then applied to evaluate the effectiveness of a heatsink design for improved heat dissipation.
2. Experimental Thermal Test
An experimental test was conducted to observe the temperature rise of the HPA during operation. The amplifier was powered using a laboratory DC power supply and operated continuously for 4 minutes which represented a typical transmission duration during ground station communication.
During the test the supply voltage and current were monitored to determine the electrical power delivered to the amplifier. The HPA was subjected to an estimated thermal load corresponding to approximately 15 W based on an applied heat flux of 4000 W/m² over the relevant surface area.
The temperature distribution of the amplifier casing was measured using a thermal imaging camera. After 4 minutes of continuous operation, the surface temperature at the centre of the amplifier reached approximately 49.6 °C, as shown in image below.
Thermal Image of HPA after 4minutes of operation
The thermal image indicates that the highest temperature occurs near the central region of the amplifier housing, where the internal amplification circuitry is located. This result provides an initial estimate of the thermal behaviour of the HPA under operating conditions.
The experimental data obtained from this test is later used as a reference to validate the thermal simulation model before designing an appropriate heatsink for improved heat dissipation.
3. Thermal Simulation
Before performing the thermal simulation, a simplified model of the HPA was required. The CAD model provided by the manufacturer represents the amplifier as a solid aluminium block which does not reflect the actual internal structure of the device. The outer housing acts as a protective casing that contains the internal electronic components.
Since the internal layout and the exact location of the heat-generating components are not available from the manufacturer the amplifier was modelled as a hollow aluminium casing while maintaining its original external dimensions. This modification allows the simulation model to better represent the physical structure of the HPA.
Hollow CAD Model used for Thermal Simulation
Illustration of the casing thickness parameter used in the simulation model
The hollow casing model shown in the above image was used as the basis for the thermal simulation. In this model, the 4mm thickness shown on the left was kept constant at 4 mm while the thickness of 3mm shown on the right was varied to approximate the internal structure of the amplifier. Three casing thickness values were evaluated: 2 mm, 3 mm and 4 mm.
The purpose of varying this parameter was to determine which simplified model best represents the thermal behaviour of the actual device. The simulation results obtained from each casing thickness were compared with the experimental temperature measurement of 49.6 °C after 4 minutes of operation. The casing thickness that produced the closest temperature prediction was then selected for the subsequent thermal analysis.
3.1 Simulation parameters
Thermal Simulation Parameters (room condition)
The thermal simulation was performed using SolidWorks to evaluate the temperature behavior of the HPA under operating conditions. The boundary conditions which were used during the simulation were selected to replicate the experimental test environment as accurately as possible.
The ambient temperature was also set to 295 K (22 °C) which corresponds to the room temperature during the experimental test. Natural convection was also applied to all external surfaces with a convection coefficient of 10 W/m²·K representing typical free convection conditions in air.
A heat flux of 4000 W/m² was also applied to the internal surface of the amplifier casing to represent the heat being generated by the internal electronic components. The simulation was conducted as a transient thermal study with a duration of 4 minutes matching the duration of the experimental test.
Thermal radiation was also included in the simulation. Surfaces with black coating (radiation 1) were assigned an emissivity of 0.95, while uncoated metallic surfaces (radiation 2) were assigned an emissivity of 0.1. The material of the amplifier housing was defined as Aluminium 6061 alloy which is consistent with the material specified for the casing.
Thermal Loads for space condition
To evaluate the thermal behaviour of the HPA under space conditions, a separate thermal simulation was performed with convection removed since heat transfer in space occurs primarily through radiation.
A heat flux of 4000 W/m² was retained to represent the heat generated within the amplifier. For external surfaces exposed directly to space, radiation boundary conditions were applied with a background temperature of 3 K to represent deep space. These exposed faces were assigned an emissivity of 0.95 and a view factor of 1, assuming direct radiative exposure to space.
This setup allows the simulation to estimate the temperature response of the HPA when radiative heat loss is the dominant cooling mechanism.
3.2 Simulation Results (HPA only at room temp)
4mm Thickness casing (318.3 Klevin, 45.1 °C)
3mm Thickness casing (322.5 Kelvin, 49.4 °C)
2mm Thickness casing (328.9 Kelvin, 55.8 °C)
| Casing Thickness | Max Temp (4min) |
|---|---|
| 4mm | 318.3 K (45.1 °C) |
| 3mm | 322.5 K (49.4 °C) |
| 2mm | 328.9 K (55.8 °C) |
Simulation results for different casing thickness
Out of the three configurations the casing with 3mm thickness produced a simulated temperature of 49.4 °C which closely matches the experimental measured temperature value of 49.6 °C after 4 minutes of operation. As a result, the 3 mm hollow casing model will be selected as the representative geometry for subsequent thermal simulations.
The simulation results also indicate that operating the HPA for 4 minutes does not cause the device temperature to exceed the maximum base plate temperature rating of 85 °C specified by the manufacturer which also aligns with the experimental conclusion. However, during prolonged operation the temperature of the amplifier may continue to rise. Therefore, a heatsink is required to improve heat dissipation and ensure that the HPA temperature remains within safe operating limits during extended transmission period of more than 4minutes;
4. Heatsink Design
A custom heatsink was designed to improve the thermal dissipation of the HPA during extended operation. The initial heatsink design in iteration 1 was a simple rectangular plate facing space but it was not an efficient use of the available volume. Iteration 2 improved structural support but increased the mass and included a cover that was later deemed unnecessary. The final design in iteration 3 retains a rectangular form but is optimized for better space usage and allows easier wire routing while maintaining effective thermal performance.
The geometry of the heatsink was designed to follow the shape of the upconverter housing allowing the heatsink to be integrated within the payload assembly without interfering with the surrounding components.
The cut-out regions along the edges of the heatsink provide clearance for RF connectors and signal wiring ensuring that the cables connecting the HPA, isolator and patch antenna can pass through the assembly without any form of obstruction. This design allows the heatsink to be mounted directly onto the amplifier while maintaining proper routing space for the RF connections.
The heatsink was designed with sufficient contact area between the amplifier base plate and the aluminium heatsink surface to enhance heat conduction away from the HPA casing. By increasing the thermal mass and surface area of the structure, the heatsink helps dissipate heat through radiation which is the dominant mode of heat transfer in space thereby reducing the operating temperature of the amplifier during prolonged operation. There are also 4x M3 clearance holes which will be connected via metal rods to the ring of the assembly.
Heatsink Drawing Design
Thermal Contact Modelling
To represent the thermal interaction between the HPA and the heatsink, a local interaction thermal resistance was applied at the contact interface in the simulation. The thermal resistance was calculated using the conduction resistance equation for a flat interface:
where R is the thermal resistance (K/W), t is the thickness of the thermal interface layer (m), k is the thermal conductivity (W/m·K) and A is the contact area between the HPA and the heatsink (m²).
Using the parameters of the thermal interface material and the contact area of the amplifier base plate, the calculated thermal resistance was 0.0068 K/W. This value will be applied as the local thermal resistance between the HPA and the heatsink in the SolidWorks thermal simulation.
4.1 Simulation results (HPA + Heatsink at room temp)
Thermal results for 4minutes operation duration (room temp)
The above image shows the temperature distribution of the HPA with the designed heatsink after 4 minutes of operation under room temperature conditions. The simulation was run for a total time of 4min with time increment of 10sec per step resulting in a total step of 24.The simulation indicates that the maximum temperature of the heatsink reaches 306.1 K (33.1 °C) at the end of the 24steps.
Compared to the case without the heatsink, where the HPA temperature reached approximately 49.5 °C, the addition of the heatsink reduces the operating temperature by approximately 16.4 °C. This demonstrates that the heatsink significantly improves heat dissipation from the amplifier during operation.
4.2 Simulation Results (HPA at space condition)
Transient thermal simulation results of the HPA without heatsink under space conditions
To evaluate the effectiveness of the proposed heatsink design, a comparative simulation was performed under the same space operating conditions without the presence of the heatsink. The simulation parameters remained identical with convection removed and heat dissipation occurring only through radiation to space.
Based on the simulation results the temperature of the HPA increases significantly in the absence of a heatsink. At step 11 which is approximately 1980 seconds of operation the maximum temperature reaches 403.7 K (130.7 °C). This value greatly exceeds the maximum allowable base plate temperature of 85 °C specified by the manufacturer.
The results clearly indicate that without a dedicated thermal management solution the HPA would rapidly exceed its safe operating temperature when operating in space conditions. Therefore, the inclusion of heatsink is necessary to effectively dissipate heat and maintain the amplifier within its allowable temperature range.
4.3 Simulation Results (HPA + Heatsink at space condition)
Transient thermal simulation of the HPA with heatsink under space conditions
A transient thermal simulation was performed to evaluate the performance of the HPA with the designed heatsink under space conditions. In this simulation, convection was removed and heat dissipation occurred only through conduction and radiation to space. The ambient radiation temperature was set to 3 K while exposed surfaces were assigned an emissivity of 0.95.
The simulation was conducted for a total duration of 3600 seconds which is 60 minutes with 20 time steps corresponding to 180 seconds per step. The results indicate that at step 11 corresponding to approximately 1980 seconds about 33 minutes of operation, the maximum temperature of the HPA reaches 351.5 K (78.5 °C). This temperature value is approaching the maximum allowable base plate temperature of 85 °C which is specified by the manufacturer.
Beyond this point continued operation would result in the temperature exceeding the recommended operating limit. As a result the simulation indicates that the designed heatsink is capable of maintaining the HPA temperature below the critical limit for approximately 32 minutes of continuous operation under space conditions.
This demonstrates that the heatsink significantly improves thermal performance and allows extended operating duration compared to the case without thermal management.
4.4 Refined Thermal Analysis Under Actual Operating Power
Refined Experimental Inputs (25Watts / 6500 W/m²)
Thermal simulation results under space condition under new thermal load of 6500 W/m² which is
The initial thermal simulations were conducted using a heat flux of 4000 W/m² and this corresponds to an approximate heat input of 15 W based on the applied surface area. This was used as a baseline case to evaluate the thermal behaviour of the system.
Upon further refinement the actual operating power of the HPA was determined to be 25 W. This corresponds to an updated heat flux of approximately 6500 W/m² and a revised simulation was carried out under space conditions with radiation as the primary mode of heat transfer.
The results show that the maximum temperature reached 76.1°C after 15 minutes of operation with the heatsink applied and this remains below the allowable limit of 85°C. Beyond this duration the temperature begins to exceed the limit but this is considered acceptable as the system is not expected to operate continuously at peak power for extended periods. The heatsink is therefore effective in delaying thermal buildup and maintaining safe operating conditions within the required operational timeframe.
4.5 Thermal Interface Pressure and Mounting Considerations
The thermal interface material used in this design is the Tgon 800 series graphite pad. Based on the datasheet a reference contact pressure of 681 kPa is used. Using the estimated contact area of the HPA the required clamping force is about 209 N. Since the HPA is mounted using 4 M2 screws this gives about 52 N per screw assuming even load distribution. This level of pressure helps reduce air gaps and improves thermal contact between the HPA and the heatsink.
5. Isolator Mount Design
The RF isolator is used to protect the high power amplifier (HPA) from reflected signals (and other incoming) from the antenna side by serving as a ‘one way valve’ for radio signals. Therefore, ensuring the isolator is securely mounted and mechanically stable is essential for both RF performance and system reliability. check with tris on this part
5.1 Design Concepts
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Two-support Beam Design & Assembly
The first concept utilizes a two-support beam structure, where the isolator is mounted along a beam supported at both ends. This design provides a simple and compact configuration, allowing for easier integration within the system. The beam geometry enables load transfer between two mounting points while maintaining structural continuity.
CAD Drawing of design
Assembly Model
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Triangular 3-Point Design & Assembly
The second concept adopts a triangular 3-point support configuration. This design distributes the load across three mounting points, forming a more rigid structural geometry. The triangular layout is expected to enhance stability and reduce deformation under loading conditions.
CAD Drawing of Design
Assembly Model
5.2 Vibration analysis & design selection
To evaluate the structural performance of both designs, a frequency (modal) analysis was conducted using SolidWorks Simulation. Each design was subjected to identical boundary conditions, with fixed supports applied at their respective mounting points.
The objective of this analysis was to determine the natural frequencies and deformation characteristics of each design, which indicate their susceptibility to vibration under operational conditions.
Frequency results for 2-Support Beam Design
Frequency results for triangular support Design
The simulation results show that the two-support beam design exhibits significantly higher natural frequencies compared to the triangular design. The first natural frequency of the two-support beam design is approximately 6.10 Hz whereas the triangular design has a first natural frequency of approximately 2.06 Hz. This represents an increase of nearly 196% indicating that the two-support beam design is substantially stiffer.
Since natural frequency is directly related to structural stiffness a higher natural frequency implies that the structure is less prone to deformation under dynamic loading. Therefore, the two-support beam design demonstrates superior resistance to vibration and a reduced likelihood of resonance within the expected operational range of the system.
In contrast, the triangular design with its lower natural frequency is more susceptible to vibration-induced deformation. This may lead to misalignment of the RF components and degradation in system performance during operation.
In addition to vibration performance, spatial constraints within the payload were also considered. The two-support beam design achieves a total assembly height of approximately 71 mm whereas the triangular design requires approximately 81 mm resulting in a space saving of 10 mm (~12.3%). This reduction in height provides additional clearance for other components and improves overall system integration.
Cable connections
Furthermore, cable management considerations were taken into account. The RF connections require coaxial cables with an estimated clearance of 20–25 mm per side. The two-support beam configuration allows the isolator to be positioned centrally, providing sufficient space for cable routing while minimizing interference with surrounding components.
Based on the combined evaluation of vibration performance, structural stiffness, and spatial efficiency, the two-support beam design was selected as the final design for implementation.
6. Future works
- Experimental Testing with actual heatsink materials
Experimental testing with the final aluminium heatsink will be carried out in future work to validate the thermal performance under actual operating conditions. This was not completed within the current timeline due to delays in the manufacturing schedule. - Full mechanical Assembly
Full assembly testing will be conducted to evaluate the structural stability and integration of all components under real operating conditions. This was not completed before the report deadline due to delays in fabrication and assembly.