Radio-Frequency (RF) Feeds with Integrated RF, Mechanical and Thermal Functions

Status
Completed
Status date
2022-09-19
Activity Code
5B.182P1
Objectives

The objectives of the activity are the following: 

  • To design and manufacture using metal additive manufacturing (SLM) a monolithic cluster of 13 dual-band, dual-circular polarization feed chains in Ka-band for GEO applications.

  • To extensively test the resulting Engineering Model (S-parameter measurements, radiating measurements in anechoic chamber, thermal cycling, vibration testing).

  • To perform PIM testing on a representative feed chain (using the same architecture as those included in the feed cluster) and to verify the PIM-free performance of the part and of the end-to-end manufacturing technology of SWISSto12 using silver-plating.

Challenges

The main challenges of the activity are the following: 

  • The pitch of the feed chain needed to meet the mission requirements is extremely small (22 mm). To meet this, a specific feed chain architecture is selected and several tricks are implemented, profiting from the degrees of freedom offered by additive manufacturing. 

  • The mechanical design of the final feed cluster EM is challenging for modern CAD software. The complexity of the part requires special handling to avoid software and model collapses.

  • The machining of the feed cluster EM is also very challenging, the main risk being the protection of the waveguide channels from any shavings produced during the machining process.

  • Finally, the way to implement test jigs (waveguide adaptors) suitable for performing S-parameter testing in such a compact array is not straightforward and requires a lot of effort.

Benefits

The benefits of the product are the following: 

  • Monolithic fabrication of a complex part containing 13 feed chains. The monolithic nature of the produced part is a real asset as it reduced significantly the need for assembly.

  • Very lightweight par with very low insertion losses.

  • The part has been entirely conceived and designed for 3D printing and – in particular – for vertical orientation in the printer. This gives the best tolerances and also simplifies the post-processing, as there is no need for removable support structures (the device is self-standing).

  • Extremely small pitch of the feeds in the array, allowing to meet the very stringent requirements of the baseline mission. This improvement has the advantage of reducing the focal distance of the antenna reflector used on the spacecraft, resulting in significant mass and cost reduction.

  • Easily adaptable for missions with similar but less strict requirements.

Features

The end product of this activity is a monolithic cluster of 13 feeds able to generate dual-circular polarization in Ka-band for transmit and receive. Each feed chain is based on the combination of two diplexers and a septum polarizer to generate the circular polarization. Each diplexer is composed of a low-pass filter using triangular corrugations (adapted for vertical 3D-prining based on previous IP of SWISSto12) and a high-pass filter. The septum polarizer is extremely broadband as it operates from 17.7 to 31 GHz. A very low-profile choke horn completes the design that fits in a volume of only 70x123x150 mm3 with a total mass (before metal-plating) lower than 500 gr.

As another outcome of this activity, the end-to-end manufacturing technology of SWISSto12 is proved to be PIM-free after several tests for 3rd, 7th, and 9th order PIM performed in the facilities of ValSpace.

System Architecture

The system architecture selected for the feed chain is the following:

  • Two diplexers with custom waveguide inputs for TX (17.7-21.2 GHz) and RX (27.5-31 GHz). The two diplexers are flipped so that they can be put close to one another and profit from wall sharing (mass reduction and mechanical rigidity improvement).

  • The two diplexers are connected to the two ports of a circular septum polarizer, used to generate right and left handed circular polarizations, respectively. 

  • After the septum polarizer, a very compact and low-profile choke horn (horn with axial corrugations) is connected. 

  • Not included in the scope of the activity: a waveguide harness network needs to be implemented to feed the input ports of the diplexers and to match the pitch of the feed cluster with that of the amplifiers (that is typically larger). For testing purposes, waveguide lofts to standard waveguide (adaptors) outputs are implemented as separate parts.

Plan

The project plan includes the following phases: 

  • Mission selection and requirements definition: the requirements are derived from a real GEO mission scenario, using also inputs from other relevant missions. Challenging requirements are adopted to push the limits of the technology.

  • Preliminary design phase: two feed chain architectures are investigated and compared numerically. Several de-risking parts (sub-components of the feed chains) are breadboarded to assess the performances.

  • Detailed RF and mechanical design of the feed cluster: The selected architecture is implemented in a cluster including 13 feed chains. Several iterations between RF and mechanical design are performed to guarantee compliance to the specifications.

  • Manufacturing and testing: The feed cluster EM is manufactured and extensively tested (RF, mechanical, thermal, and PIM tests) to verify the compliance to the specifications.

Current status

The project is completed with the successful manufacturing and extensive testing (thermal, mechanical, RF, PIM) of a feed cluster engineering model.

Prime Contractor