me1300 lab04 (fieldfox) antenna gain measurement - v2.06

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ME1300 Antenna and Propagation

Lab 4

Antenna Gain Measurement

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Objectivei) To perform antenna gain measurement

Equipment Requiredi) ME1300 Training Kitii) Agilent N9912A FieldFox RF Analyzeriii) Agilent 85033E Standard Mechanical Calibration Kit (optional)iv) A pair of dipole antennasv) A pair of ceramic antennas

Accessories Requiredi) 1 x 5 V power adapterii) 1 x Type A-to-Type B USB cable iii) 2 x SMA(m)-to-SMA(m) RF coaxial cableiv) 1 x LAN cablev) A PC running Microsoft® Windows 2000/XP/Vista® with a minimum of 1 GB RAM, and pre-

installed with setup prerequisites and the RadPat ver0.01 software (Refer to the ME1300 Quick Start Guide for the installation procedures)

ME1300 Antenna and Propagation Lab 4 - 1/10


1. Introduction

Gain, G is the intensity of an antenna in a given direction to the isotropic antenna with an amount of power equal to the power accepted by the antenna (whereas directivity assumes there is no loss).

Antenna measurement takes place in the far-field region. When the phase difference of the incident wave is less than o/16 (where o is the wavelength of antenna) between the outer edge and the center of the receiving antenna, the field is considered a far field at a distance r which is the distance between the transmitting and receiving antennas. This requires that r 2D2/o, where D is the largest dimension of the receiving antenna (D = o/2). However, the main source of errors in antenna measurement is the reflection from nearby obstacles and the ground. To reduce the reflection, the minimum height above ground must be h D2/d, where d is the largest dimension of the transmitting antenna.

Several methods have been introduced to measure the antenna gain. The first method will be the Two-Antenna Method. In this method, two identical antennas are used for the measurement. The relation between the received power PR at the receiving antenna and the transmitted power PT at the transmitting antenna is:

where GT is the gain of the transmitting antenna and Aer is the effective area or aperture of the receiving antenna. It is generally valid that Aer = Go

2 / 4. It follows that:

If the two antennas are identical, this formula reduces to:

Therefore, the gain of two identical antennas can be further simplified as:

The second method is the Gain Transfer Method. Under this method, a set of reference antennas is set up to measure the received power. This received power will be used as a reference power which is Pref with a known Gain, Gref. After that, another receiving antenna will be used to replace the reference antenna. The replaced antenna will be treated as an antenna-under-test (AUT). The received power PAUT of the antenna-under-test (AUT) is obtained with identical measurement conditions. The difference between the two received powers (PAUT & Pref) is the difference between the antenna gains. Therefore, the gain of the antenna-under-test (AUT) can be obtained using the equation below:

where

The third method is the Three-Antenna Method. There can be any three antennas. Two antennas — one as the transmitting antenna and the other as the receiving antenna — are set up to measure the received power and obtain the gain at the same time. This is repeated for all three antenna combinations. Let the



three measured powers be PR1, PR2, PR3 and the antenna gains are GA, GB, and GC. The path-gain factor, F is assumed to be 1, which means there is no reflection from the ground.

… (1) … (4)

… (2)

… (3) … (5)

Replace (4) and (5) into (2), and solve for GA:

… (6)

Finally, replace (6) into (4):

Then replace (6) into (5):

Thus, the three antenna gains are obtained.



2. Two-Antenna Method

Note:To get the best accuracy, you should perform calibration before making any measurements on your network analyzer. The recommended calibration kit is the Agilent 85033E. Please refer to Appendix B for the calibration procedure.

1. Mount a 2.4 GHz 2 dipole antenna on the top connector of the fixed antenna holder on the transmitter module (TX). This is the transmitting antenna.

2. Orientate the antenna for horizontal polarization and broadside to the other antenna-under-test (AUT). The orientation of antenna is shown in Figure 1.

Figure 1 – Orientation of Receiving and Transmitting Antennas for Horizontal Polarization3. Use an RF coaxial cable to connect the RF OUT connector of the N9912A FieldFox RF analyzer

to the RF IN connector of the transmitter module (TX).4. Mount another 2.4 GHz dipole antenna (AUT) on the top connector of the rotatable antenna

holder on the receiver module (RX). This is the receiving antenna.5. Orientate the receiving antenna broadside to the transmitting antenna as shown in Figure 1 for

horizontal polarization and maximum reception. 6. Use another RF coaxial cable to connect the RF OUT connector of the receiving antenna (RX) to

the RF IN connector of the N9912A.7. Press Meas Setup (button #4) on the N9912A, and select High for the Output Power. This will

set the transmitted power, PT to 5 dBm.8. Adjust the distance between the antennas to 50 cm and make sure that they are in the far-field

region. Record the distance and the heights of the antennas in the corresponding record form as given in Appendix A.

9. Open the RadPat software, select the desired PC ComPort under Settings > ComPort tab.10. Set Baud Rate to 57600 under Settings > ComPort tab. Click the Instrument tab followed by

Load SCPI File to select the desired instrument Standard Commands for Programmable Instruments (SCPI) file. If the N9912A is used for testing, load the N9912A.scp file from the installed RadPat > SCPI folder. Select the Enable Instrument option.

11. Set the start frequency to 2300 MHz and the stop frequency to 2500 MHz under RF (Frequency Range).

12. Set Frequency of Interest to 2400 MHz. This is the frequency of the antenna-under-test (AUT).13. Click Connect to bring the rotator back to its home position and configure the N9912A settings.14. After the homing operation and the N9912A configuration have completed, align the receiving

antenna in broadside to the transmitting antenna and observe the maximum insertion loss, S21 from the N9912A.

15. Record the results in the corresponding record form as given in Appendix A and calculate the antenna gains. Assuming there is no reflection from the ground, the path-gain factor F = 1.


TX

AUT (RX)


3. Gain Transfer Method1. Repeat the procedure in Section 2 by replacing the receiving dipole antenna with a ceramic

antenna. 2. Orientate the ceramic antenna broadside to the transmitting antenna for horizontal polarization

and maximum reception.3. Record the results in the corresponding record form as given in Appendix A.4. Use the gain you obtained from Section 2 as the reference gain, Gref in order to calculate the gain

of the ceramic antenna.

4. Three-Antenna Method1. Use the results from Section 2 and 3 to form the first and second sets of results respectively with

this method.2. Repeat the procedure in Section 2 by replacing the transmitting dipole antenna with the ceramic

antenna to obtain the third set of results.3. Record the results in the corresponding record form given in Appendix A and calculate the three

antenna gains.

5. Discussions1. What is the theoretical gain (in dB or ratio) of a /2 dipole antenna? How close is the measured

value (from the two-antenna method or three-antenna method) compared with it? 2. The three-antenna method separates the gains of the two /2 dipoles. How much is the difference

(in dB) between the gains? How do these gains compare with the gain from the two-antenna method?

Appendix A



Two-Antenna Method Gain Measurement Record Form(Two /2 Dipole Antennas)

f = Hz

= m

r = m (horizontal distance between two antennas)

h1 = m (height of antenna 1, TX)

h2 = m (height of antenna 2, RX)

PT = dBm = mW

PR = dBm = mW

PR /PT = dB = ratio)

Polarization: vertical horizontal

The observed value on FieldFox is in the form of Insertion Loss (dB) = where PR is the

received power and PT is the transmitted power.

F = (F = path-gain factor = 1 for free-space propagation)

= (ratio) = dB



Gain-Transfer Method Gain Measurement Record Form(/2 Dipole Antenna and Ceramic Antenna)

G (dipole) = dB

PR (dipole) = dBm

PR (ceramic) = dBm

Gain = PR (ceramic) – PR (dipole)

= dB

G (ceramic) = G (dipole) + Gain

= dB



Three-Antenna Method Gain Measurement Record Form(/2 Dipole Antenna A, /2 Dipole Antenna B, and Ceramic Antenna)

Antenna A = dipole antenna AAntenna B = dipole antenna BAntenna C = ceramic antenna

f = Hz

= m

r = m (horizontal distance between two antennas)

h1 = m (height of antenna 1, TX)

h2 = m (height of antenna 2, RX)

Polarization: vertical horizontal

The observed value on FieldFox is in the form of Insertion Loss (dB) = where PR is the

received power and PT is the transmitted power.

F = (F = path-gain factor = 1 for free-space propagation)

PT = dBm = mW

Antennas A-B: PR1 = dBm = mW

Antennas B-C: PR2 = dBm = mW

Antennas C-A: PR3 = dBm = mW

=

=

=

= (ratio) = dB

= (ratio) = dB

= (ratio) = dB



Appendix B

Tips on How to Calibrate the N9912A FieldFox RF Analyzer

S11 Calibration

Figure 2 – Calibration Setup for S11

1. Set up the connections as shown in Figure 2, and then connect the calibration kit to the SMA connector. The suggested calibration kit for the following calibration procedure is the Agilent 85033E.

2. Press Cal (button #5) on the N9912A front panel. Use the softkeys to select [O,S,L] for the Calibration Type.

3. Select Start Cal and press the corresponding softkey Open –F–.4. Connect the OPEN CIRCUIT calibration kit to the RF OUT connector of the SMA connector and

press Measure.5. Upon completing the measure, press the corresponding softkey Short –F–.6. Connect the SHORT CIRCUIT calibration kit to the RF OUT connector of the SMA connector and

press Measure.7. Upon completing the measure, press the corresponding softkey Load –F–.8. Connect the TERMINATION calibration kit to the RF OUT connector of the SMA connector and

press Measure.9. Upon completing the measure, press Finish to complete the O,S,L calibration. The calibration

can be repeated again at any time in the event that the calibration kit was not properly connected during the calibration process.



S21 Calibration

Figure 3 – Calibration Setup for S21

1. Set up the connections as shown in Figure 3.2. On the N9912A front panel, press Mode. Use the softkey to select NA, then select S21.3. Press Cal (button #5) on the N9912A front panel. Use the softkey to select Norminal.4. Then, select Thru and connect the RF OUT and the RF IN port with a short coaxial cable as figure

shown on the N9912A screen.5. Select Measure after completed the setup.6. Upon completing the measure, press Finish to complete the Norminal calibration. The calibration

can be repeated again at any time in the event that the calibration kit was not properly connected during the calibration process.


me1300 lab04 (fieldfox) antenna gain measurement - v2.06

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