california state university, sacramentoathena.ecs.csus.edu/.../newlabs/spring2018/lab8don.docx ·...

Dr. Milica Markovic’ Applied Electromagnetics Laboratory page 1

EEE 161 Applied ElectromagneticsLaboratory 8

Patch Antenna TestingI ObjectiveIn this laboratory exercise you will learn how to use a network analyzer. You will measure and display measurement results for a one-port passive circuit, i.e. an antenna. A Network Analyzer can display input impedance s11. S11 is also called refection coefficient, or return loss.In this lab we will also measure antenna radiation pattern with a scalar network analyzer set up to measure s12 between a source antenna built into the anechoic chamber, and your Antenna Under Test (AUT).

II What is an antenna?According to IEEE Standard Definitions of Terms for Antennas IEEE Std 145-1993, antenna is defined as that part of a transmitting or receiving system that is designed to radiate or to receive electromagnetic waves. Antenna is a shell, made most commonly of metal, that helps the signal in the cable “escape" the cable and continue moving forward in air.In lieu of a Lab final exam we will have a culminating final project where each student does a take home final. The final will be due finals week into SACCT

III General InstructionsAfter Lab 7 each lab group will make a patch antenna. The patch antenna and matching network will be on a 4” square substrate. Each group will attach a feed connector at the end of the matching network. Each group bring a thumb drive to get the data from the anechoic chamber computer “Quiet” or move the output file to your folder on Gaia. The antenna data file names include the date and time measured.Antenna measurements will be taken in Santa Clara 1119D Antenna Lab during lab time or by special appointment with the lab instructor.Each lab group has 1 hour split between impedance and antenna pattern tests.

IV Impedance Measurement instructionsNetwork Analyzer Safety In Power Laboratory we are usually concerned about student safety. In microwave lab, we are concerned about student safety as well, but it will be very difficult for you to get hurt, because the signals that we are using are of the order of several milliwatts (mw) and frequency of operation is usually very high. Therefore, we are mostly concerned about instrument safety in this case. Network analyzer is a very sensitive piece of equipment. This is an experimental part of the lab, where you calibrate the network analyzer, then measure the calibration standards and some other circuits as well. Network Analyzers are very expensive. Please be careful and read the list of the instrument-safety precautions. ● Do not bend semirigid cables, they are very expensive. If the cable is broken, we will not be able to buy new ones. However, flexible cables can be bent.● Do not touch the inside pin of the connectors, and do not force the connectors together. Only male and female connectors of the same type can mate. Study the connector types listed before. Align them carefully, and then use the wrench from the calibration kit.

California State University Sacramento EEE161 revised: 18. April, 2018


● put a wrist-strap on (if available).Inside Network Analyzer Network Analyzer measures and displays the antenna return loss, the ratio of the reflected voltage and a known incident voltage expressed in dB. It is different than the spectrum analyzer because the spectrum analyzer displays an unknown signal generated by another piece of equipment or device under test (DUT). Network analyzer generates its own incident signal, sweeps the signal over the frequency range that you specify, then measures the reflected (and transmitted signal) and displays the ratio of reflected and incident signal (or ratio of transmitted and incident signal).

Reflection (S11) MeasurementsMeasure the reflection coefficient of the antenna at its resonance near 2 GHz. Be sure that the antenna points away from metal objects.

1. Use the guided set up button to set up the network analyzer to measure electrical (not optical) reflected power.

2. Set the frequency sweep for 1 GHz to 3 GHz.

3. Connect your antenna to the incident/reflected port.

4. Use markers 1, 2, & 3 to observe and note the lower frequency 10 dB return loss (dBrl) point, the center frequency and return loss, and the higher frequency 10 dBrl point respectively.

5. Plot the reflected power if possible or take a screen photo.

Why do we calibrate Network Analyzers? There are three types of errors in any measurementsystem: systematic errors that are predictable; random errors; and drift errors that occur dueto changes in the system after the calibration has been performed, such as temperature change.Network analyzer calibration is performed to remove systematic errors, and set the reference plane for measurements at the Device Under Test (DUT). For Lab 8 the network analyzer will be calibrated before the beginning of the lab, and will be sufficient for the duration of the lab.


Figure 1 HP8702 Network Analyzer

Markers 1, 2, & 3


V Antenna Pattern informationThe standard spherical coordinate system for antenna systems from IEEE Standard Test Procedures for Antennas, ANSI/IEEE Std 149-1979 is shown in figure 2.The antenna measured in figure 3 is aligned with the x axis, that is θ = 90⁰ and φ = 0⁰.

An antenna radiates most power in a certain direction in space. The exact distribution of this power in space is called an antenna pattern. We will measure antenna patterns in the Antenna Lab, Santa Clara 1119D. The pattern of an antenna is usually drawn on x-y plane as power on y-axis as a function of degrees on X- axis, as shown in Figure 3. The shape of the radiated power in 3-D space looks like a beam and it is called antenna beam.


Figure 2 E plane is electric field. H plane is magnetic field

Elevation bottom to top to bottom

Azimuth around equator


Beamwidth Beam width is the measure of antenna beam in degrees. It shows how many degrees away from the axis of the antenna most power is concentrated in. We define the point at which the beam-width in degrees is calculated as the point where the antenna power falls off to ½ of the maximum power, -3 dB is ½ of the power. The H-plane beamwidth of Patch D at 2 GHz is 110⁰; the E-plane beamwidth of Patch D at 2 GHz is 80⁰.

Directivity Directivity is the measure of the narrowness of the antenna beams. The higher the directivity the narrower the beam is. The formula to estimate directivity is

D = 4π/(φ θ) θ, φ in radians (2)The angle φ is the beamwidth in the azimuth xy plane and θ is the beamwidth in the elevation xz plane. Both θ and φ angles are converted to radians by multiplying the degree reading by π/ 180 . Directivity is usually quoted in decibels. To find directivity in decibels, use the formula below:

DdB = 10log (D) (3)Gain is measured in dB isotropic (dBi) by comparing the AUT to an antenna with known gain. Gain and directivity are related by equation 4 where η is the efficiency.

G = D η (4)Isotropic is a theoretical antenna that radiates equally in all directions.The gain of patch D at 2 GHz is 1.8 dBi. The directivity from (3) is 6.7 dBi. The difference expressed in dB is 1.8 - 6.7 = -4.9 dB. This low efficiency (~32%) is due to several factors including:

Mismatch lossConductor loss, i.e. I²RBeam pointing errorHigh sidelobes and backlobesCross polarization andEquation (2) assumes that beam widths θ & φ are measured through the actual beam peak in

both directions.It is necessary to have more than principal plane measurements to evaluate these losses. For instance the highest gain may not appear in the principal plane as assumed above.


-30

-27

-24

-21

-18

-15

-12

-9

-6

-3

0

3

6

-180 -150 -120 -90 -60 -30 0 30 60 90 120 150 180

Gain

dBi

& d

irecti

vity

φ⁰ Azimuth

Patch D VV_180330 date_162551 time

1.91.9522.052.1Isotropic

F. GHz

-30

-27

-24

-21

-18

-15

-12

-9

-6

-3

0

3

6

-180 -150 -120 -90 -60 -30 0 30 60 90 120 150 180

Gain

dBi

& d

irecti

vity

θ Elevation⁰

Patch D HHc_180403 date_143348 time

1.91.9522.052.1Isotropic

F. GHz

Directivity = 6.7 dBiGain = 1.8 dBi

Figure 3A, H-plane 3B, E-plane


Laboratory setupThe antenna laboratory measurement setup is shown in Figure 4 and 5.

WindowsDesktop Computer

USB

HP8757C Scalar Network Analyzer (SNA)_16&17

ABCRHPIB (8757 System Interface)POS Z BlankSweep in 0-10vStop Sweep

HPIB#16

r

Cable 1

Cable 2

HP 8340B Sweeper_19

HPIB#19

POS Z Blank-Sweep out/in-Stop Sweep-

Po

Agilent 82357B USB/GPIB Interfacefor Windows

HPIB

USB

.

AUTSource Antenna

LLNA

HP85025 detector

SA 4131 Positioner Controler

HPIB #1

Figure 4 Antenna Measurement Block diagram

HP 8757C Scalar Network Analyzer measures S21 amplitude only

Scientific Atlanta SA4131 Positioner Controller

HP8304B Signal Generator

Computer


Figure 5 Antenna Measurement Equipment Rack


VI Antenna Pattern Measurement instructions1. To measure antenna pattern first rotate the positioner to 0⁰ with the SA4131 in manual

mode set on its front panel. 2. Secure the AUT Vertically in the anechoic

chamber as shown in figure 6 and align the antenna with the 0⁰ position mark.

3. Rotate the angle in the reverse direction past -180⁰ to ~+175⁰ with the SA4131.

4. Plug in the Preamplifier power supply5. Set the source antenna to Vertical as

shown in figure7. This will be a VV pattern for V transmit & V receive polarization, an H-plane test

6. Open the antenna control software in \\gaia\ruckerd\Anechoic chamber\Antenna Lab 2017, a LabVIEW instrument type file.

7. The LabVIEW main window will appear briefly then the antenna control window shown in figure 8 will appear.

8. Set the Start Frequency to the lower frequency of your antenna. Set the Stop

Frequency to the higher frequency of your antenna.

9. Set the number of frequency Points to 3.10. Leave the default Start Angle at -180⁰11. Leave the default Stop Angle at 180⁰12. Leave the default Step Angle at 10⁰13. Leave the default Source Power at 10

dBm14. Click the run arrow at upper left; it will fill

in to black while the antenna pattern is running

15. The current angle, last angle measured, and distance travelled in degrees will display during the test for observing test progress.

16. After each measurement the values measured will appear in the graph when three or more frequencies are selected.

17. While the test is running make a note of the current settings being run such as the


Figure 6 AUT Set Up

Figure 7 Source Antenna, Control Screen, & Port Holes


time, polarization, your antenna name, the set up alignment (VV, HH, or VH) and any other pertinent information so you can manually add it to your data in post processing. The time will help you find the data file name to save the correct identification.

18. At the end of the test a data dialog box will appear as shown in Figure 9. Click OK to save the data.

19. Then a rewind dialog box will appear as shown in Figure 10. Click REWIND. 20. The antenna will be rewound and be ready for the next test.

21. The data will be saved in an .xls text file as “antenna data_##_##” (## date & ## time). The frequencies


Figure 8 antenna measurement Front Panel

Start ArrowStart frequencyStop frequency# FrequenciesStart angleStop angle Step AnglePower

Figure 9 OK Dialog Box


and angles measured will automatically be stored as column and row headings respectively.

22. Leave the front panel settings as they are, and change the source polarization to Horizontal.

23. Change your AUT alignment to Horizontal, and align it with +90⁰ to have the data coordinated with the standard coordinate system.

24. Click the start arrow and repeat the process for an E plane test. This will provide an Elevation pattern. Refer back to figure 2, Azimuth is the XY plane. Elevation is from -Z to +Z & back to -Z at any Azimuth, the XZ plane in our test.

25. Set the source polarization back to Vertical but leave the AUT as is. This will check the AUT cross polarization (VH cut).

26. Note the Isotropic level in dBi at your center frequency from the calibration chart posted on the test equipment rack.

27. When opening your data file you need to select yes to have it open as a spread sheet. You may want to save it as an .xlsx file for convenient data manipulation, or print it for manual data manipulation, or paste the data into another graphic application.

Data Post-Processing Take Home FinalCopy and paste all the data in Excel .xlsx. Select Graph x-y plot. Plot each pattern.Your final report must be individual (1 per student) and include:

1. A one paragraph summary in your own words of your observations from Lab 7.2. A description of your patch & matching network design.3. A photo of your group’s antenna.4. The center frequency and reflection coefficient photo or graph from the impedance (s11) test in

part IV above.5. Plots of azimuth, elevation, & cross polarization patterns (s12) from the .xls text files generated

in the anechoic chamber computer.6. Calculation of directivity and gain in dBi and a comparison between them.


Figure 10 Rewind Dialog Box

california state university, sacramentoathena.ecs.csus.edu/.../newlabs/spring2018/lab8don.docx ·...

Documents