MICROWAVES DEEC Introduction to Laboratory Classes · Introduction to Laboratory Classes MEEC, ......
Transcript of MICROWAVES DEEC Introduction to Laboratory Classes · Introduction to Laboratory Classes MEEC, ......
MICROWAVES Introduction to Laboratory Classes
MEEC, 1st semester 2011/2012
Custódio Peixeiro
DEEC
Laboratory Classes
• 4 Sessions
• T1 – Contact with a microwave bench
• T2 – Matching on an impedance load
• T4 – Measurement of the S-parameters of a waveguide “T”-junction
• T5 – Measurement of dielectric properties of materials
• Classes concentrated in 4 weeks (separated 4 weeks)
• T1 – 19-23 September
• T2 – 17-21 October
• T4 – 14-18 November
• T5 – 12-16 December
2
• Maximum duration: 3 hours
• 2 students per group (few exceptions with 3 students)
• 5 groups per class (5 benches)
• On-line registrations in Fénix (from 15h30 September 13 until 23h59 September 15)
• Support to students on the days of the laboratory classes, 15h30-17h00, room 11.24 North Tower (ext. 2167)
• Classes start next week (19 September)
3
Evaluation Marks
• Final Mark = 70% Written Exam Mark + 30% Laboratory Mark
Laboratory Mark = 50% Oral Evaluation Mark +
50% Written Report Mark
Witten Exam Mark – individual (0 to 20)
Oral Evaluation Mark – individual (0 to 10)
Written Report Mark – group (0 to 10)
4
Microwave Bench
• Students use a microwave didactic bench (X band: 8-12 GHz) with rectangular metallic waveguide
5
6
Reports Editor
• Use of the desktop computer available in each bench to write the session report
• Fixed template for each session report
• The templates follow the laboratory guide (Portuguese version available in “Secção de Folhas”, AEIST)
• Report printing at the end of the class
• Report marks given two weeks after the last class of each
session
7
Important Notes
• It is absolutely necessary to prepare the laboratory sessions
by reading the corresponding guide. If you don’t do that
usually you will not be able to finish the session.
• Always follow thoroughly the safety recommendations given
in the first session
• Although low power is used (10 mW) microwaves radiation
hazards must be avoided
• Always follow the handling recommendation given in the first
session to handle the components and equipment with care
• Very expensive and fragile equipment
8
• Take a USB flash drive to each class to store the report
• Register in paper all the results obtained
• Download the evaluation record sheet file from the Fénix web
page, print it and take it (with name and photo of each
student) for the first session
• Take a calculator for every session
• The classes start at the indicated time (08h00 or 17h00) and
FINISH at the indicate time (11h00 or 20h00)
9
Transmission Line Basics
• As already indicated the microwave bench uses metallic
rectangular waveguide components
• TE (transversal electric) and TM (transversal magnetic) modes
are defined for the metallic rectangular waveguide
• The fundamental mode of the metallic rectangular waveguide
(ab) is the TE10 (a > b). The corresponding cutoff frequency
is
10
a2
cf
10TEc
2z
a2
λ1
λλ
10TE
11
• Each waveguide mode can be represented by equivalent
voltage and current (fictitious) distributions
• Transmission line theory can be used to study the field
distribution along the microwave bench
12
Zg
Vg Z0
I1 I2
Zc V1 V2
z -l 0
zkj2
zkj2 eVreVi(z)Vr(z)Vi(z)V
)eVreVi(Z
1(z)Ir(z)Ii(z)I zkj
2zkj
2o
θj
2
2 e|Γ|Vi
VrΓ Load (voltage) reflection coefficient
)eΓe(Vi(z)V zkjzkj2
)eΓe(Z
Vi(z)I zkjzkj
o
2
)Γ1(Z
ViZ)Γ1(ViIZV
o
2c22c2
1y
1yΓΓ
y1
y1
1z
1zΓ
Γ1
Γ1
Z
Zz
c
cI
c
c
c
c
o
cc
13
14
l)(ktanZjZ
l)(ktanZjZZ
eΓe
eΓeZ
l)z(I
l)z(VZ
co
ocolkjlkj
lkjklj
o1
)(tan1
)(tan11
lkzj
lkjz
Z
Zz
c
c
o
zk2j
zkj2
zkj2 eΓeVi
eVr
Vi
Vr(z)Γ
Reflection coefficient along the line
Voltage standing wave ratio (VSWR)
[,[1VSWR10,|Γ|1VSWR
1VSWR|Γ|
|Γ|1
|Γ|1
V
VVSWR
min
max
In space and time
θ)]zktω(cos|Γ|)zktω(cos[Vit)(z,V 2
Download VSWR.EXE from Fénix web page
Smith Chart
15
xjrz1z
1ze|Γ|Γ c
c
cθj
bjgy
1y
1ye|Γ|Γ c
c
cθjII
I
πθθ|Γ||Γ| II
Re ( or I)
Im ( or I)
1
(r + j x)
I (g + jb)
or I
16
Example Zc = 25 + j 50 Zo = 50 zc = 0.5 + j 1 yc= 0.4 – j 0.8
π0.46je0.62Γ
dB4.15)(0.62log20|Γ| dB
VSWR = 4.27
Impedance Matching with Stub
Goal is y- = 1 + j 0 (perfect matching)
17
Zc Z0
Z0
ls
d
z 0
)(z'ylimy
(z)ylimy
(z)ylimy
slz's
left)(fromdz
right)(fromdz
s
)b(bj)gg(
)bjg()bjg(
yybjgy
ss
ss
s
0bb
1gg
s
s
bb
1g
s b)l(kcotanb ss
18
Example Zc = 25 + j 50 Zo = 50 zc = 0.5 + j 1 yc= 0.4 – j 0.8
Two solutions (a, b) da / = (0.115+0.178)=0.293 lsa / = (0.340-0.250) = 0.090 db / = (0.115+0.322)=0.437 lsb / = (0.250+0.160)=0.410
19
Solutions a and b
• are equivalent (|| = 0 = - dB, VSWR = 1) at central frequency
• (but) have different bandwidths (BW)
For VSWR 2 (|| -9.54 dB)
Solution a BW = 16.2 %
Solution b BW = 8.1 %
-40
-35
-30
-25
-20
-15
-10
-5
0
0,7 0,8 0,9 1 1,1 1,2 1,3
Inp
ut
Re
fle
ctio
n C
oe
ffic
ien
t [d
B]
Normalized Frequency
Solution a Solution b
20
1
1,5
2
2,5
3
3,5
4
4,5
5
0,7 0,8 0,9 1 1,1 1,2 1,3
VSW
R
Normalized Frequency
Solution a Solution b
Several other specifications may be used
VSWR 1.5 || 0.2 -14 dB
VSWR 3 || 0.5 -6 dB
RF Virtual (Software Tool)
• Down load the software tool from the Fénix web page
• Basic setup (T1)
• Choose frequency and type of load
• Include (or not) slide screw tuner
• Visualization of the VSWR meter measurement
• Can be very useful to prepare T1 and T2
21
22
VSWR Meter
• It is a dedicated equipment to measure directly the VSWR in
the slotted waveguide
• Tuned (1 kHz) amplifier and voltmeter
• Calibration needed each time the load conditions are changed
• Pointer deflection (stronger voltage) clockwise
• Very important to learn you to use it
23
24
25
VSWR Measurement Procedure
1. Move the probe carriage to the right limit of the slotted waveguide (closest to the load)
2. Move the probe carriage slowly to the left until you find a maximum
3. Adjust the gain (use the buttons for 10 dB steps and the knob for continuous adjustment) until the meter indicates 1.0 on the upper scale
4. Move the probe carriage to a minimum
• Move to the right if in 2 you have passed a minimum and to the left otherwise
• Do not change the gain
26
27
5. Read the VSWR directly in the upper scale (1 - )
6. If VSWR > 4 then increase the gain 10 dB and read the VSWR in the second scale (3.2 – 10)
7. If VSWR > 10 then increase the gain 10 dB again, read the VSWR in the first scale and multiply by 10
8. If VSWR > 40 then increase the gain 10 dB again, read the VSWR in the second scale and multiply by 10
9. You can continue this increase of gain and change of scale procedure if needed (VSWR > 100)
10. The third (red) scale is used to obtain more accurate measurements when VSWR 1.3. In that case you need to press the (red) “EXPAND” button.