X-Band and Ka-Band Low Noise Block Downconverter

Figure 1.  Low noise block downconverter

Requirements imposed on modern receivers used in ground and mobile terminals of satellite communications are increasingly more complex in order to achieve light weight and greater communication capacity under various interfering signals. A typical low noise block downconverter used in these receivers consists of (1) limiter (2) low noise amplifier (LNA) (3) image rejection filter (4) local oscillator and (5) IF amplifier.

Limiters are required to protect LNAs from large interfering signals and must be placed between the antenna and LNA. Losses in the limiters directly contribute to degradation of overall system noise figure. The LNA is the primary component that establishes noise figure of the system, but traditional transistors, such as GaAs- or InP-based HEMTs, are low-voltage devices and prone to damage even under small interfering signals. Low-loss image rejection filters are necessary to remove noise and signals in the image band. Without the filters, the system will suffer from increased noise figure by 3 dB and by not being able to discriminate signals in the image band. A high-quality local oscillator will provide stable and clean power that is typically generated by a phase-locked loop.

Balanced Solution:

Deliver a GaN LNA that can provide dual functionality: signal amplification and receiver protection.

With the recent emergence of wide bandgap semiconductor devices, particularly GaN HEMTs, LNAs may operate with low noise figure, high gain, and high breakdown voltages.  This enables receivers to remove front-end protection circuitry (i.e., limiters) improving system noise figure by 0.5 dB or more.