CTE CTE Wireless & RF Engineering 2 — Questions and Answers
Question 1: What is the purpose of a Low Noise Amplifier (LNA) placed at the front-end of a receiver?
- To filter out-of-band interference
- To boost the received signal before it degrades in the receiver chain (Correct answer)
- To convert RF to baseband
- To match antenna impedance to 50 ohms
Correct answer: To boost the received signal before it degrades in the receiver chain
An LNA amplifies the weak received signal before further processing, minimizing noise added by subsequent stages and improving overall receiver sensitivity.
Question 2: In RF propagation, what phenomenon causes a signal to arrive at the receiver via multiple paths of different lengths?
- Atmospheric ducting
- Multipath fading (Correct answer)
- Ionospheric scintillation
- Diffraction
Correct answer: Multipath fading
Multipath fading occurs when reflected, scattered, or diffracted copies of a signal arrive with different delays, causing constructive or destructive interference.
Question 3: What is the link budget's 'fade margin' designed to account for?
- Equipment manufacturing tolerances
- Expected signal strength variations due to propagation anomalies and fading (Correct answer)
- Regulatory EIRP limits
- Antenna pointing errors only
Correct answer: Expected signal strength variations due to propagation anomalies and fading
Fade margin is extra dB added to the link budget to maintain the required SNR even when the signal fades due to weather, multipath, or other propagation impairments.
Question 4: Which antenna type has a toroidal (doughnut-shaped) radiation pattern ideal for omnidirectional coverage in the horizontal plane?
- Parabolic dish antenna
- Yagi-Uda antenna
- Dipole antenna (Correct answer)
- Horn antenna
Correct answer: Dipole antenna
A dipole antenna radiates equally in all horizontal directions with nulls at the tips, producing the classic toroidal pattern used for omnidirectional coverage.
Question 5: In the context of 5G NR, what does 'beamforming' enable that traditional antennas cannot?
- Wider coverage with fewer base stations
- Spatially targeted transmission that increases gain toward specific users (Correct answer)
- Automatic frequency switching between bands
- Reduced handover latency
Correct answer: Spatially targeted transmission that increases gain toward specific users
Massive MIMO beamforming uses phase-shifted arrays to concentrate energy toward individual users, improving throughput and reducing interference.
Question 6: What is the purpose of the Guard Interval (Cyclic Prefix) in OFDM systems?
- To prevent adjacent channel interference
- To absorb inter-symbol interference caused by multipath delay spread (Correct answer)
- To synchronize carrier frequencies
- To increase peak data rate
Correct answer: To absorb inter-symbol interference caused by multipath delay spread
The cyclic prefix is a copy of the end of each OFDM symbol prepended to the beginning, giving the receiver time for multipath echoes to settle before sampling.
CTE CTE Wireless & RF Engineering 2
What is the purpose of a Low Noise Amplifier (LNA) placed at the front-end of a receiver?