In early 2015, MIRAD was contracted to develop two feed systems operating in X-band. One unit is to be installed in a 9m class step-track antenna, while the second unit will be equipped with TE21 monopulse coupler to provide auto-track capability. The antennas will be used for a government application, the Wideband Global Satcom (WGS). Due to these special operating conditions and requirements and the fact that multi-carrier operation in the X-Tx band can cause passive intermodulation effects, due to non-linearities in the system, the LNAs may be disturbed by such effects and signal reception will be degraded.
For this reason, MIRAD has put extra effort into PIM research and testing during the design phase to provide the best possible solution for our customers. This led to the redesign of some of our standard components and the application of special manufacturing methods to minimize the number of places where PIM can occur. After the successful design and manufacturing phase, the two feed systems were successfully validated as PIM-free by our in-house PIM measurement facility, where two HPA signal carriers of 200 W each are combined for testing purposes.
In 2017, MIRAD was asked by another customer to provide such a feed system and a corresponding antenna design for a 13m class Cassegreain antenna. After successful testing, the system has been in operation since 2019.
X-band low PIM feed back view (right), typical PIM measurement result (center and isolation measurement result (right)
Key technical challenges:
- Low PIM design requires special design methodology and manufacturing techniques
- Strict PIM level specification for IM3 and IM5
- Lowest possible losses
- High Tx/Rx Isolation >130 dB
- Integration of redundancy and LNA switching network
- X-band TX (7.900 – 8.400 GHz)
- X-band RX (7.250 – 7.750 GHz)
- Dual circular polarization (simultaneously)
- Power handling 2.0 kW per port
- Dual circular polarization in all bands
- Axial Ratio <0.55 dB
- PIM level -135 dBm (-191 dBc dual tone)