Antenna Measurement

[Class Announcemets

- Grading: Attendance 10%, Homework 30%, Mid-term. exam. 30%, Final exam. 30%

- Submit homeworks and exams on eCampus.

01-Antenna Basics 1

(Homework)

1. List three types of the wire antenna.

(Ans) 1. Dipole, 2. Helix, 3. Loop

2. List three types of the antenna beam shapes.

(Ans) 1. Omni-direcitonal, 2. Directional, 3. Fan beam

3. List ten performance parameters of an antenna.

(Ans) 1. Gain/directivity, 2. Aperture efficiency, 3. Radiation pattern & beamwidth, 4. Sidelobes, nulls & fron to back ratio, 5. Polariztion, 6. Operating frequency & bandwidth, 7. Physical size & mass, 8. Return loss/VSWR, 9. Inter-port isolation, 10. Cross-polarization discrimination

02-Antenna Basics 2

(Homework)

1. Express the received power using EIRP and free-space path loss (FSPL).

(Ans) P_r = EIRP/FSPL

2. Spell out the acronyms AESA and PESA.

(Ans) AESA (Active Electronically Scanned Array), PESA (Passive Electronically Scanned Array)

3. Write down the 3-dB beamwidth in degrees of a linear array with N elements with its main beam steered off boresight by φ degree.

(Ans) θ_3dB = (102/N)/cosφ

03-Antenna Basics 3

(Homework)

1. Plot the electrical field of the TEM mode in a coaxial cable.

(Ans)

2. Express VSWR in terms of the magnitude of the reflection coefficient | Γ |.

(Ans) VSWR = (1 + | Γ |) / (1 − | Γ |)

3. Express the radian distance from an antenna in terms of the wavelength.

(Ans) r = λ / (2π)

04-Antenna Basics 4

(Homework)

1. Write down the formula for the radiation resistance of an elementary electric dipole antenna.

(Ans) R_r = 80π² (L/λ)²

2. What is the directivity in dB of an elementary electric dipole antenna?

(Ans) 1.76 dBi

3. Write down the formula for the directivity of a direcitonal antenna in terms of the beam solid angle.

(Ans) D = 4π / Ω_A

05-Antenna Parameters 1

(Homework)

1. What is the E-plane pattern of an antenna?

(Ans) The pattern of an antenna in the cut plane containing the electric field vector E and the direction of the maximum radiation.

2. Write down the distance formula for the radiating near-field (Fresnel) region.

(Ans) 0.62 (D³/λ)^1/2 < R < 2D²/λ

3. Write down the radiation efficency formula in terms of the radiated power and the input power of an antenna.

(Ans) e = P_rad / P_in

06-Antenna Parameters 2

(Homework)

1. List three types of the antenna radiation pattern.

(Ans) 1. Isotropic, 2. Directional, 3. Omnidirectional

2. Spell out the acronym HPBW.

(Ans) HPBW (Half-Power Beamwidth)

3. Write down the formula of the gain of an antenna in terms of efficiency and directivity.

(Ans) G = eD

07-Introduction to Antenna Measurement

(Homework)

1. List three types of the antenna measurement range.

2. Spell out the acronym CATR.

3. Write down the formula for the directivity of an antenna in terms the beamwidth in the principal plane.

(Answers)

1. Isotropic, Directional, Omnidirectional

2. HPBW (Half-Power Beamwidth)

3. G = eD

08-Mid-term exam.

(Problems)

1. List ten performance parameters of an antenna.

2. Write down the 3-dB beamwidth in degrees of a linear array with N elements with its main beam steered off boresight by φ degree.

3. Plot the electrical field of the TEM mode in a coaxial cable.

4. Write down the formula for the radiation resistance of an elementary electric dipole antenna.

5. Write down the formula for the directivity of an antenna in terms the beamwidth in the principal plane.

6. Write down the formula for the directivity of a direcitonal antenna in terms of the beam solid angle.

7. Read this paper (pdf) and summarize it on a keyword basis.

(Answers)

1.

1) Gain/directivity, 2) Aperture efficiency, 3) Radiation pattern & beamwidth, 4) Sidelobes, nulls & fron to back ratio, 5) Polariztion, 6) Operating frequency & bandwidth, 7) Physical size & mass, 8) Return loss/VSWR, 9) Inter-port isolation, 10) Cross-polarization discrimination

2. θ_3dB = (102/N)/cosφ

3.

4. R_r = 80π² (L/λ)²

5. D = 4π (180/π)² / (θ₁θ₂)

6. D = 4π / Ω_A

7.

- 4D mmWave radars measure range, azimuth, elevation and velocity of targets.

- Research on 4D mmWave radars for autonomous driving: calibration, resolution improvement, signal processing

- Radar data sets: pubished datasets for algorithm developments

- Learning-based radar data enhancement: detection, reconstruction

- Perception applications: various feature extraction algorithms

- Localization and mapping applications: Doppler processing for radar performance enhancement

09-Outdoor Antenna Test Ranges

(Homework)

1. What is the arc range used for in antenna measurements?

2. Spell out the acronym OATS.

3. What is the in-situ antenna measurements?

(Answers)

1. For spherical far-field antenna measurements or near-field antenna measurements.

2. OATS (Opean Area Test Site)

3. Measurements of an antenna while it is installed in its application place.

10-Antenna Gain and Directivity Measurements

(Homework)

1. Explain the principle of the gain transfer method for the antenna gain measurement.

2. Explain the principle of the method of two identical antennas.

3. Explain the principle of the antenna directivity measurement using the measured radiation patterns of an antenna in the full angular range of a sphere.

(Answers)

1. Use a reference antenna S with known gain G_s to transmit power to be received by a receiver. The received power with S transmitting is P_S. Next replace S with an antenna under test (AUT) T and supply it with the same power. The received power with T transmitting is P_T. The AUT gain is obtained from the following equation.

G_T (dB) = P_T (dBm) − P_S (dBm) + G_S (dB)

2. Place two antennas separated by a distance R with each antenna's boresight aligned so that the power transfer is maximum. Supply one antenna with transmitting power PT. Measure the power PR received by the other antenna. Use the Friis transmission formula to calculate the gain G of the antenna from the measurement.

G = (4πR / λ)(P_R / P_T)^1/2

3.

At a far-field distance, measure the normalized magnitude of the electric field E of an antenna under test over all the angular range of a sphere (0 ≤ θ ≤ π, 0 ≤ φ ≤ 2π). Use the following relations to find the directivity of AUT.

11-Near Field Antenna Measurements

(Homework)

1. List three major scanning geometries in the near-field antenna measurement.

2. Specify the measurement interval in the planar near-field antenna measurement.

3. Compare the near-field measurment (NFM) with the far-field measurement (FFM) in the point of antenna diagnostics and analysis.

(Answers)

(Homework)

1. Planar, Cylindrical, Spherical

2. Δx = Δy = λ/2

3. Antenna diagnostics and analysis: NFM = easy, FFM = difficult

12-Antenna Mutual Coupling Measurements

(Homework)

1. Write an equation for the mutual impedance between two dipole antennas.

2. Write an equation for obtaining the mutual impedance from the measured scattering parameters S₁₁, S₁₂, S₂₁ and S₂₂.

3. Two dipole antennas have mutual coupling. Write an equation for the current of the dipole 1 in the presence of mutual coupling.

(Answers)

1. Z₁₂ = V_1,oc / I_2,sc ; V_1,oc = open-circuit voltage at dipole 1's terminal; I_2,sc = short-circuit current at dipole 2's terminal

2. Z₁₂ = 2S₁₂Z₀ / [(1 − S₁₁)(1 − S₂₂) − S₁₂S₂₁]

3. I₁ = (V_s1 − V₁₂) / (Z_g1 + Z₁₁)

13-Antenna Axial Ratio Measurements

(Homework)

An antenna has two radiated electric field components at a far-field distance. E_x = A_x cos(ωt − kz + φ_x); E_y = A_y cos(ωt − kz + φ_y)

1. Specify a condition for linear polarization.

2. Specify a condition for right-hand circular polariztion with axial ratio of 1.

3. List two major methods of antenna polarization measurement.

(Answers)

1. φ_x − φ_y = nπ (n: integer)

2. A_x = A_y and φ_x − φ_y = π / 2

3. Rotating dipole method, Dual polarized sampling antenna method

14-Small Antenna Measurements

(Homework)

1. Explain the principle of the Wheeler cap method for measuring the radiation efficency of an antenna.

(Ans) Measure the input impedance Z₁ of AUT in free space. Measure the input impedance Z₂ of AUT with the antenna placed inside a completely closed metal box. Calculate the radiation efficiency η = [Re(Z₁) − Re(Z₂)] / Re(Z₁)

2. What kind of antenna parameter measurements is good in the GTEM cell measurement?

(Ans) Antenna efficiency and matching

3. What kind of antenna parameter measurements is good in the reverberation chamber measurement?

(Ans) Antenna efficiency and matching

15-Final exam.

(Problems)

1. Explain the principle of the gain transfer method for the antenna gain measurement.

(Ans) Use a reference antenna S with known gain G_s to transmit power to be received by a receiver. The received power with S transmitting is P_S. Next replace S with an antenna under test (AUT) T and supply it with the same power. The received power with T transmitting is P_T. The AUT gain is obtained from the following equation.

G_T (dB) = P_T (dBm) − P_S (dBm) + G_S (dB)

2. Explain the principle of the method of two identical antennas.

(Ans) Place two antennas separated by a distance R with each antenna's boresight aligned so that the power transfer is maximum. Supply one antenna with transmitting power PT. Measure the power PR received by the other antenna. Use the Friis transmission formula to calculate the gain G of the antenna from the measurement.

G = (4πR / λ)(P_R / P_T)^1/2

3. Explain the principle of the antenna directivity measurement using the measured radiation patterns of an antenna in the full angular range of a sphere.

(Ans) At a far-field distance, measure the normalized magnitude of the electric field E of an antenna under test over all the angular range of a sphere (0 ≤ θ ≤ π, 0 ≤ φ ≤ 2π). Use the following relations to find the directivity of AUT.

4. Explain the principle of the Wheeler cap method for measuring the radiation efficency of an antenna.

(Ans) Measure the input impedance Z₁ of AUT in free space. Measure the input impedance Z₂ of AUT with the antenna placed inside a completely closed metal box. Calculate the radiation efficiency η = [Re(Z₁) − Re(Z₂)] / Re(Z₁)

5. Write an equation for obtaining the mutual impedance from the measured scattering parameters S₁₁, S₁₂, S₂₁ and S₂₂.

(Ans) Z₁₂ = 2S₁₂Z₀ / [(1 − S₁₁)(1 − S₂₂) − S₁₂S₂₁]\

6. What kind of antenna parameter measurements is good in the GTEM cell measurement?

(Ans) Antenna efficiency and matching

7. Read this article (pdf) and make a keyword summary.

Radars for autonomous navigation: 77-81 GHz, FMCW radar, coded radar, FFT for range, velocity and angle of a target, 4D radar, 3D radar, radar vs lidar for autonomous navigation, radar data format, deep learning based processing of radar data, radar challenges, multipath and clutter