Microwave Link Budget

Free-space loss

The loss between two antennas unaffected by the Earth

Fading

Refers to the variation in the signal strength at the receiver input

Scintillation

refers to the constant variation in the received signal level due to the small variations in the point index gradients of refractivity through which the signal will pass over the path

Path diversity

used to counter rain fading or attenuation

Rain Attenuation

The main contributor in frequency range used by commercial radio links

Diffraction Fading

The redistribution of energy within a wavefront when a wave encounters obstructions

Path Profile

A graphical representation of the path over which the microwave signal would travel between the two ends of a MW link

Grazing Line-of-sight

Condition when the line-of-sight between the two antennas ‘just’ clears a dominant obstacle

Dominant obstacle

the point in path profile with the least clearance from the direct ray of the MW link

Fresnel Zones

Defined as an ellipsoid surrounding the MW LOS where the interference is always constructive

Multipath Fading

Occurs when the radio signals travel in more than one path and arrive at the receiver at different times

Space Diversity

used to counter multipath fading • Multipath effects can result to flat fading in narrowband systems and frequency selective fading in wideband systems

Rayleigh fading

Multipath fading is sometimes called _____

Flat Fading

A non-frequency dependent form of fading

Frequency Selective Fading

Occurs if some of the spectral components are reduced causing distortion

dispersive fading

Frequency Selective Fading also known as _____

Slow Fading

The motion of the terminal to these distant object is small and corresponding propagation change slowly

Fast Fading

Refers to the variation in signal amplitude that changes rapidly with time

Link Budget Analysis

The process works out the percentage of time the signal will be below the threshold of the radio receiver relative to the total time period

Fade margin

difference between the nominal signal level and the receiver threshold

power budget

Adding the various gains and losses over the path from the transmitter output module to the receiver demodulator input

Link budget

Used to calculate fade margin which is used to estimate the performance of the radio link. Includes calculation of all losses and gains of the signal.

Branching loss

refers to the loss in the multiplexer circuit • May also include filter loss, combiner loss, and isolator loss

branching unit

a generic term used to describe the circuitry that interfaces the antenna to the receiver

Feedline loss

the attenuation or reduction in RF power that occurs as a signal travels through a cable between the transmitter or receiver and the antenna

Waveguide loss

Taken from the specifications expressed in dB/100 ft or dB/100 m

Connector loss

Taken from specifications - typically 0.5 dB

Coupling loss

Taken from specifications (coax to waveguide to air)

Hybrid loss

Taken from specifications - typically 1 dB (circulator loss)

Radome loss

Taken from specifications - typically 0.5 dB

Effective Radiated Power

Refers to the amount of power emitted by the antenna in the direction of the maximum antenna gain

Received Signal Level (Unfaded)

The amount of power that enters the front-end of the receiver

Receiver Threshold

The minimum wideband carrier power at the receiver input that will provide a usable baseband output

receiver sensitivity

Receiver Threshold also called as ____

System Gain and Minimum Transmit Power

the difference between the nominal output power of a transmitter and the receiver threshold