4) RF Fundamentals β Waves, Power and Decibels
π Theory β 4) RF Fundamentals β Waves, Power and Decibels
I. The Radio Wave
β’ Electromagnetic wave: Ξ» = c / f.
β’ Polarisation β linear (H/V) or circular (RHCP/LHCP).
β’ Propagation at speed of light.
II. Frequency Bands
β’ L, S, C, X, Ku, Ka.
β’ Higher frequency = more bandwidth, worse propagation.
β’ Lower frequency = larger antennas, better penetration.
III. Power in Decibels
β’ dB = 10 logββ(Pβ/Pβ).
β’ dBW β power relative to 1 W.
β’ dBm β power relative to 1 mW.
β’ dBi β antenna gain relative to isotropic.
IV. Gain and Loss
β’ Amplifiers add gain (dB).
β’ Cables, filters, feeders add loss (dB).
β’ Total is a sum of dB contributions.
V. Noise
β’ Thermal noise: N = kTB.
β’ Noise figure β degradation of SNR.
β’ Noise temperature β equivalent input noise.
β’ G/T β figure of merit for a receiving station.
VI. Antennas
β’ Parabolic reflector β gain β (ΟD/Ξ»)Β².
β’ Beamwidth β Ξ»/D.
β’ Efficiency 55β70% typical.
β’ Phased arrays β electronic steering for LEO.
π Level 1
β 0 points
π Advanced Essay (AI-Marked)
Critically analyse the RF fundamentals underpinning satellite communication. Discuss propagation, the decibel system, the concepts of gain and loss, and the noise characteristics that constrain link performance.
π Practice MCQs (15)
Q1: How does DB differ from alternatives?
Q2: Why is Parabolic antenna important?
Q3: What are the limitations of Noise temperature?
Q4: How does Polarisation differ from alternatives?
Q5: Explain Noise figure in satellite communication.
Q6: Explain Gain in satellite communication.
Q7: What are the limitations of Loss?
Q8: How does DBW differ from alternatives?
Q9: What is DBm?
Q10: What are the limitations of Wavelength?
Q11: How does Parabolic antenna differ from alternatives?
Q12: What is DBi?
Q13: What are the limitations of Polarisation?
Q14: What are the limitations of DBW?
Q15: Why is Gain important?
Module score: 0/0