EC15 · Sem 7 · Microwave engineering

Microwave link budget

Aim: Calculate received power, SNR and capacity of a point-to-point link.

🧪 Live simulation🧊 Real-time 3D bench⚠ Simulated values, not physical measurements

🔬 Virtual lab

Starting the lab…

📘 Theory

The Friis equation adds transmit power and antenna gains and subtracts free-space path loss (20·log d + 20·log f + 92.45). Comparing with the noise floor kTB + NF gives SNR and, by Shannon, capacity.

FSPL(dB) = 20log d(km) + 20log f(GHz) + 92.45 · C = B·log₂(1 + SNR)

🧰 Apparatus (virtual)

Two dish antennas on towers
transmitter
receiver
spectrum analyser

📝 Procedure

Read the received power at 5 km, 2.4 GHz
Double the distance and see −6 dB
Raise the frequency and see more loss
Increase the antenna gain to recover the link

Observations and result (kept on this device)

🎤 Viva questions

Why do 60 GHz links work only over short distances

Path loss rises with frequency and oxygen absorbs strongly near 60 GHz.

What is the Fresnel zone

An ellipsoid around the line of sight that must stay mostly clear.

🛡️ Safety

Virtual lab. With real RF equipment, respect exposure limits, never transmit without a licence, and keep antennas away from people.