Noise & Distortion in Microwave Systems

Thermal Noise by Components & DevicesAtmosphere and Interstellar RadiationMan-made InterferenceExternal EnvironmentInternal CircuitNoise : Random Process!

1 Thermal NoiseThermal NoiseRandom motion of charge carriersPassive circuit element contains LossAtmospheric attenuation & Interstellar Background RadiationShot NoiseRandom motion of charge carriers in Electron tubes & solid-state devicesFlicker Noise1/f NoiseIn Solid-state & Vacuum tubeQuantum NoiseIn quantized nature of charge carriers & photonsPlasma NoiseIn ionized gas or sparking electrical contacts

Noise Voltage and Power of Resistor RR: Resistor at T: TemperatureMean ValueRMS Value

TeB2 Noise Temperature & Noise FigureEquivalent Noise Temperature:

Measurement of Te: Direct measurement: difficult to measure small level of noiseY-factor Method:G,B,T

1. X20dB1GHzYT1290KN1-62dBmT277KN2-64.7dBmTs450KdBm

Noise Figure

Noise Figure of a Lossy Line:For Thermodynamic Equilibrium

Noise Figure of Cascaded Components

2.NikTABTA150K20dB?T05010MHzFf1 dB

3 Noise Figure of Passive NetworksFor Thermodynamic Equilibrium

Application to a Mismatched Lossy Line

Application to a Wilkinson Power Divider

4 Dynamic Range & Intermodulation DistortionNonlinear:At very Low Power Level due to Noise Effects.At very High Power Level due to device nonlinearitiesLinear outputDC outputSquared output

Gain Compression

Intermodulation Distortion

IP3: Third-Order Intercept Point:Input IP3Output IP3

Dynamic RangePin(dBm)Pout(dBm)Input P1dBOutput P1dBInput IP3Output IP3Linear Dynamic Range ( DRl )SFDR: Spurious-free Dynamic Range ( DRf )DRl DRf

Intercept Point of Cascaded Components

3.20dB322dBm6dB313dBm

5 Passive Intermodulation PIMGenerated by passive nonlinear effects in any Metal-to-metal Contact: Cable, Connectors, Antenna, etcCaused by Poor mechanical contact Oxidation Junctions between Ferrous-based metalsContamination of conducting surface at RF junctionsUse of Nonlinear Material, such as Fiber composites or Ferromagnetic materialPIM only significant when HIGH PowerCellular Telephone BS TransmitterPout=30-40 dBm , PIM < -125dBm