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Post date: May 17, 2020 5:51:55 AM
Satellite Digital Audio Radio Service's (SDARS) reception over 2320-2345MHz can be blocked by cellular transmissions in the neighbouring bands. In vehicles, the blocking is exacerbated by SDARS sharing a common radome with cellular aerials. Considering the SDARS satellites are ~40,000km away, this is an extreme example of the near-far problem.
Among cellular services, the Wireless Communications Service's (WCS) 2305-2320MHz and 2345-2360MHz bands are the most disruptive because they sandwich SDARS without any guard band.
As SDARS aerial on the car roof is connected to the receiver through a long coaxial cable, an outboard low noise amplifier (LNA) is necessary to overcome cable loss. A compact LNA is required because of the small radome.
Conventionally, a band-select filter before the LNA (pre-filter), is used to defend against blockers, but the filter's insertion loss can significantly degrade the overall noise figure. Furthermore, the space constraint necessitates a miniature filter which accentuates the loss. To reject WCS, the filter must possess narrow fractional bandwidth (~1%) and steep skirts.
To reduce component count, we integrated amplifiers, biasing, impedance matching and filters into a 5×5mm 2 multi-chip on board (MCOB) module. The conflicting requirements for low noise and blocking immunity are satisfied by relocating the filter to mid-LNA. In conclusion, this design achieves previously unattainable miniaturization and blocking performance.
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