Given an amplifier’s frequency range (noise bandwidth), gain, noise factor or noise figure, and the amplifier’s temperature if substantially different from room ambient, then the noise floor at the output of the amplifier can be calculated.

The level of the noise floor calculated using thermal noise (kTB) and noise figure represents the noise at frequencies away from the signal (far from carrier). Thermal noise is flat (f⁰) with frequency. In the presence of a carrier signal, the noise level near the carrier is no longer constant, but is increased. Random noise in electronic systems exhibits the characteristic of increasing near the carrier. “Flicker” noise or “pink” noise has a slope of f^-1 versus frequency. This “1/f” or “one over f” noise is attributed to electron motion caused by the signal.

(F_c is called the corner frequency and varies depending upon the technology)

The phase noise of a signal through an amplifier is increased by the flicker noise, referred to as the amplifier’s residual phase noise. This is an interesting result, in that it means that not only is the noise floor is increased by gain and noise figure of an amplifier, but that the phase noise of a signal through the amplifier is also increased.

Note that there may be other undesired energy in the spectrum of the signal due to interference, intermodulation frequency products (both active and passive) or various spurious signals coupled through power supplies, cross-talk or radiation. The presence of this unwanted energy may be detrimental to the performance of the system, and generically called “noise”, but are separate phenomena, and can be removed or mitigated by filtering, shielding and isolation techniques.

Spanawave/Giga-tronics microwave power amplifiers have lower noise figure than most other microwave power amplifiers in their class, and with the GaAs parallel-MMIC technology, the root mean square (RMS) residual phase noise is less than that of cascaded single device designs.

Due to careful design and construction, the use of the highest quality cables and connections along with well-filtered power supplies, Spanawave/Giga-tronics amplifiers exhibit low spurious and excellent immunity to interference.

Noise Considerations in Broadband Microwave Power Amplifiers