CTE CTE Wireless & RF Engineering 1 — Questions and Answers
Question 1: What is the Friis transmission equation used to calculate in RF engineering?
- Signal attenuation due to rain
- Received power in a line-of-sight link given transmit power and antenna gains (Correct answer)
- Noise figure of a receiver chain
- Impedance mismatch between antenna and feedline
Correct answer: Received power in a line-of-sight link given transmit power and antenna gains
The Friis transmission equation calculates received power as a function of transmit power, antenna gains, wavelength, and free-space path distance.
Question 2: Which modulation scheme provides the highest spectral efficiency in a wireless link?
- BPSK
- QPSK
- 16-QAM
- 256-QAM (Correct answer)
Correct answer: 256-QAM
256-QAM encodes 8 bits per symbol, giving the highest spectral efficiency among the listed schemes, though it requires a high SNR.
Question 3: What does VSWR measure in an antenna system?
- Antenna gain over an isotropic radiator
- Impedance mismatch between transmission line and antenna (Correct answer)
- Doppler shift at the receiver
- Effective radiated power
Correct answer: Impedance mismatch between transmission line and antenna
Voltage Standing Wave Ratio (VSWR) quantifies impedance mismatch; a VSWR of 1:1 indicates perfect match with no reflected power.
Question 4: In cellular network planning, what is the primary purpose of frequency reuse?
- To reduce transmit power in each cell
- To increase network capacity by using the same frequencies in non-adjacent cells (Correct answer)
- To eliminate multipath fading
- To comply with FCC band allocation rules
Correct answer: To increase network capacity by using the same frequencies in non-adjacent cells
Frequency reuse assigns the same frequency channels to geographically separated cells, multiplying overall network capacity.
Question 5: Which multiple access technology does LTE use on the downlink?
- TDMA
- CDMA
- OFDMA (Correct answer)
- FDMA
Correct answer: OFDMA
LTE downlink uses Orthogonal Frequency Division Multiple Access (OFDMA), which divides bandwidth into sub-carriers assigned to different users.
Question 6: What is the typical frequency range for the C-band used in fixed satellite services in the United States?
- 500 MHz – 1 GHz
- 1 GHz – 2 GHz
- 3.7 GHz – 4.2 GHz (downlink) / 5.925 GHz – 6.425 GHz (uplink) (Correct answer)
- 10 GHz – 12 GHz
Correct answer: 3.7 GHz – 4.2 GHz (downlink) / 5.925 GHz – 6.425 GHz (uplink)
Fixed satellite service C-band uses 3.7–4.2 GHz for downlink and 5.925–6.425 GHz for uplink in the United States per FCC allocations.
CTE CTE Wireless & RF Engineering 1
What is the Friis transmission equation used to calculate in RF engineering?