RF Antenna Interview Questions and Answers

This page provides top RF Antenna interview questions and answers to help interviewees succeed in their job interviews for RF Antenna engineer positions. These RF Antenna questions are written by specialists in the RF Antenna domain.

Question 1: What is the function of an RF Antenna?

Answer: The main function of an RF antenna is to radiate electromagnetic (EM) waves in the desired direction into the air and to receive EM waves from the air into the RF receiver circuits. This is achieved by impedance transformation between the antenna ports and the air medium. Air has an impedance of about 377 Ohms.

Question 2: What is the difference between the Near Field Region and the Far Field Region of an antenna?

Answer:

• Near Field Region: The region close to the antenna (i.e., up to $2D^2/\lambda$) is known as the near-field region. Here, $D$ indicates the antenna diameter, and $\lambda$ indicates the wavelength. The near-field region is further divided into the reactive region (up to $3\lambda$) and the Fresnel region (above $3\lambda$ and up to $2D^2/\lambda$).

• Far Field Region: The region beyond $2D^2/\lambda$ is known as the far-field region. This region is also referred to as the Fraunhofer region.

Question 3: What is the difference between linear polarization, circular polarization, and elliptical polarization?

Answer:

• Linear Polarization: In this polarization, the amplitude of the electric (E) field varies at the radio frequency rate, and the direction is constant.
• Circular Polarization: In this polarization, the amplitude of the E-field is constant, and its direction rotates synchronously with the radio frequency.
• Elliptical Polarization: In this polarization, the amplitude and direction of the E-field vary synchronously with the radio frequency.

Question 4: Explain terms related to the antenna radiation pattern.

Answer: Common terms associated with the antenna radiation pattern include the main lobe, side lobes, 3 dB beamwidth, squint, boresight, and so on. Let’s understand the definitions of these terms.

• Main Lobe: The direction of the lobe having a larger field strength than other parts.
• Side Lobes: Parts of the pattern other than the main lobe are called side lobes.
• Bandwidth: The frequency range over which an antenna can transmit/receive EM waves is called its bandwidth.
• 3 dB Beamwidth: The range between two points located at one-half of the maximum power on the radiation pattern is called the 3 dB beamwidth.
• Squint: The main beam of the radiation pattern is shifted from its normal position. This degree of shift is called squint.
• Boresight: The direction where there will be maximum gain is called boresight.

Question 5: What is G/T of an RF antenna?

Answer: It is referred to as the figure of merit of an antenna. It is expressed as the ratio of antenna gain and system noise temperature.

$G/T \text{ in dB/K} = \text{Receiver Antenna Gain} - 10 \cdot \log(\text{System Noise Temperature})$

Question 6: Mention common types of RF antennas and describe their functions.

Answer: Here are common types of RF antennas and their functions:

• Dipole Antenna : A basic antenna with two conductive elements, used for omnidirectional radiation.
• Monopole Antenna : A single element antenna over a ground plane, commonly used in mobile communications.
• Yagi Uda Antenna : A directional antenna with multiple elements, used in TV reception and point-to-point communication.
• Patch (Microstrip) Antenna : A compact, planar antenna used in mobile and satellite communications.
• Parabolic Reflector Antenna : A high gain antenna with a parabolic dish, used in satellite and radar systems.
• Helical Antenna : A coil shaped antenna providing circular polarization, used in satellite and GPS applications.
• Log Periodic Antenna : A multi element antenna with a wide frequency range, used in TV and broadband communication.
• Horn Antenna : A waveguide-based antenna with directional radiation, used in microwave and radar applications.
• Loop Antenna : A closed loop conductor used for AM radio and RFID applications.
• Slotted Waveguide Antenna : A waveguide with slots for directional radiation, used in radar and aircraft communication.
• Fractal Antenna : A space efficient, multi band antenna used in modern wireless applications.
• Dielectric Resonator Antenna (DRA) : A non metallic antenna used in high frequency applications like 5G and radar.

Question 7: Mention the Parabolic Reflector Antenna Gain Equation.

Answer: The following is the gain equation for a parabolic reflector antenna.

Question 8: Which Antenna is used for TV signal transmission and reception?

Answer: Different indoor and outdoor antenna types are used for TV signal reception. Indoor antennas include loop antennas and half-wave dipoles. Outdoor antennas include Yagi antennas, log-periodic antennas, and phased array antennas. Nowadays, parabolic dish antennas have become very popular for satellite TV channel receptions.

Question 9: What is the difference between antenna efficiency and antenna directivity?

Answer: The ratio of total radiated power to the input power of the antenna is called efficiency. The ability of an antenna to focus energy in a particular direction while transmitting and receiving is called directivity.

Question 10: What is the relation between wavelength and frequency of Electromagnetic wave?

Answer: The following equation denotes the relationship between wavelength and frequency.

Question 11: What is the difference between dBi and dBd?

Answer: dBi refers to the calculation of the gain of an antenna compared to an isotropic radiator. dBd refers to the calculation of directional gain compared to a dipole antenna.

Question 12: What are the different types of cell tower antennas?

Answer: Here are different types of cell tower antennas and their functions:

• Omnidirectional Antenna : Radiates signals in all directions, commonly used in urban areas for uniform coverage.
• Sector Antenna : Covers a specific sector (e.g., 120° or 90°) to provide directional coverage in cellular networks.
• Panel Antenna : A flat, rectangular antenna used for directional signal transmission in mobile networks.
• Yagi Antenna : A high-gain directional antenna used in rural areas for long-distance cellular connectivity.
• Dipole Antenna : A simple, omnidirectional antenna used in base stations for local coverage.
• Small Cell Antenna : Compact antennas used for boosting coverage in high-density areas like stadiums and malls.
• Microwave Dish Antenna : A parabolic antenna used for backhaul communication between cell towers.
• Distributed Antenna System (DAS) : A network of smaller antennas improving indoor and dense area coverage.
• MIMO Antenna : Uses multiple antennas to enhance data speed and network capacity in LTE and 5G.
• Base Station Antenna (BSA) : General antennas used in cell towers for transmitting and receiving mobile signals.

This set of RF Antenna interview questions and answers is useful for freshers and experienced job positions.