Fresnel Zone calculation

Microwave communication is kind of Line of Sight communication (LOS) and Transmitting power without obstacle.

 Radio Microwave Link determines below parameters:

-          Flat Fading Margin (FFM) or System Operating Margin (SOM): relate to Transmitting Power, Type of Antenna Disk ​ Lenght Coaxial and distance.​ It is calcaulated to ensure if tramsitting power is enough.

-           Free Space Loss (FSL) : determines transmitting power in space

-          Fresnel Zone Clearance (FZC) : Height antenna

-          Antenna Bearing, Antenna down tilt and Antenna down tilt coverage radius :

Calcaulation of Link Budget and Fresnel Zone Clearance

1/ Link Budget

            Principle of Link budgett is ​path length with signal level and ​Receive signal level determines Fading margin.

Factor for calculating Fading margin is Free-Space loss:

Fomular:

Receiver Signal Level = P_tx – L_tx + G_tx – L_fs+ G_rx – L_rx

            Where is:

                        P_tx: transmitter output power

                        L_fs: free space path loss

                        G_tx: transmitter antenna gain

                        G_rx: receiver antenna gain

                        L_tx: transmitter feeder loss

                        L_rx: receiver feeder loss

-          Free-Space Loss        

L_fs = 32.4 + 20*log₁₀ F + 20* log₁₀ D         

                        L_fs= free space loss in dB

                        F = frequency (MHz)

                        D = path length, in kilometers (Km) 
                   -          ​Flat Fade Margin
                        We receive

Flat fade margin = Receive signal level – Receiver sensibility threshold           

2/ Fresnel Zone Clearance

F  radius of Fresnel Zone is the most important to calcalate the antenna height to make sure  to transmit signal radio frequency without obstacle.

Fresnel Zone calculation depends on:

-          Transmitting frequency

-          The distance covered

-          ​If Radius of First Fresnel Zone has obstacle between both stations

Radius of First Fresnel Zone

F = 12.75x[(d₁xd₂)/(f xD)]^1/2

Where is

f : transmitting frequency GHz

d_1​ and d₂distance compare with obstacle point between both stations Km

D distance between both stations Km

F​ is Radius of First Fresnel Zone  m

-          Radius of First Fresnel Zone without obstacle between both stations

F = 17.3x(D/4f)^1/2

                ^{Where is:}

F​ Radius of First Fresnel Zone m

D distance between both stations Km

f transmitting frequency  GHz

3/ Microwave Antenna height

            Microwave Antenna height is bigger than Radius of First Fresnel Zone plus ​obstacle between both stations

Radius of First Fresnel Zone(m)+Obstruction Height(m) ≤ Microwave Antenna Height(m)