Noise Figure And Receiver Sensitivity Explained: Practical RF Design For Low-Noise Systems

Understanding receiver sensitivity starts with grasping noise figure (NF), a critical but often misunderstood concept in RF and microwave engineering. Sensitivity defines the minimum input signal a receiver can reliably detect, directly impacting communication range, radar detection, and system performance. While NF is frequently associated with amplifier performance, front-end losses—such as those from antennas, cables, or passive components—often dominate sensitivity degradation.

A receiver’s dynamic range balances the ability to detect both high-power and low-power signals, requiring careful consideration of linearity, gain, and noise contributions. Thermal noise from antennas and components sets a fundamental noise floor, below which signals cannot be reliably detected. Amplifiers cannot distinguish between signal and noise, so any added noise is amplified alongside the desired signal.

Optimally designed receivers alternate gain stages and lossy elements to maintain signal integrity without causing distortion or saturation. Cascaded NF, described by Friis’ formula, highlights the importance of a high-gain, low-noise amplifier (LNA) at the front end to preserve overall sensitivity. Modern LNAs, including Marki Microwave’s ultra-low power designs, achieve excellent noise performance with minimal current consumption, making them ideal for compact, power-constrained systems such as phased arrays or airborne platforms.

Front-end architecture also requires trade-offs between noise figure, linearity, and survivability. Limiting devices, impedance matching, and proper amplifier selection ensure that receivers can handle both weak signals and strong interferers. By understanding noise figure, system loss, and amplifier behavior, engineers can design RF front ends that maximize sensitivity while maintaining practical size, power, and cost constraints.