ELEC273 Lecture Notes Set 11 AC Circuit Theorems Homework on phasors and impedance. The course web site is: http ://users.encs.concordia.ca/~trueman/web_page_273.htm Final Exam (confirmed): Friday December 15, 2017 from 9:00 to 12:00 (confirmed)
ELEC273 Lecture Notes Set 11 AC Circuit Theorems
Homework on phasors and impedance.
The course web site is: http://users.encs.concordia.ca/~trueman/web_page_273.htmFinal Exam (confirmed): Friday December 15, 2017 from 9:00 to 12:00 (confirmed)
Network Theorems:
Chapter 10 Sinusoidal Steady State Analysisβ’ Superpositionβ’ Theveninβs Theoremβ’ Nortonβs Theorem
Chapter 11 AC Power Analysisβ’ The Maximum Power Transfer Theorem
Theveninβ s Theorem for AC Circuits
Theveninβs TheoremAny two-terminal network consisting of voltage sources, current sources, dependent sources, inductors, capacitors and resistors is equivalent to a voltage source ππππ in series with an impedance ππππ.
Procedure to find the Thevenin Equivalent Circuit:1.Open-circuit test: terminate the circuit with an open circuit and find the open-circuit voltage, ππππππ.2.Short-circuit test: terminate the circuit with a short circuit and find the short-circuit current, πΌπΌπ π ππ. 3.The Thevenin equivalent voltage source is ππππ = ππππππ.4.The Thevenin equivalent impedance is ππππ = ππππππ
πΌπΌπ π ππ.
Note that ππππ can also be found as the impedance of the βdead circuitβ with the independent sources set equal to zero.
TwoTerminal Circuit
ππππ
ππππ
Example: Theveninβ s Theorem
1)Find the Thevenin Equivalent Circuit at a frequency of ππ=3 rad/sec. Use phasors relative to βsineβ.
2)Find the voltage across a load consisting of a 1 ohm resistor in series with a capacitor of value C=0.16667 F, using: β’ The Thevenin equivalent circuitβ’ The original circuitThe answer must be the same in both cases!
2 Ξ©
1 Ξ©
12
H10 sin 3π‘π‘
A
B
Find the Thevenin Equivalent Circuit.
1) Find the open-circuit voltage.2) Find the short-circuit current.
Convert the circuit to phasors and impedance.The impedance of the inductance is ππππππ = j3x 1
2=
πππ.5 ohms
In this example I have written my phasors relative to βsineβ.
Hence 10 sin 3t becomes phasor 10 angle zero.
However, we must remember to convert phasors back to βsineβ.
Thus phasor ππ = π΄π΄ππππππ converts to time functionπ£π£ π‘π‘ = π΄π΄ sin(πππ‘π‘ + ππ)
2 Ξ©
1 Ξ©
12
H10 sin 3π‘π‘
A
B
2 Ξ©
1 Ξ©πππ.5 Ξ©10
A
B
+ππππππβ
Find the open-circuit voltage
015.12
10=ββ
β ocococ VjVV
01
65.1
62
106 =βββ ocococ Vj
jVjVj
064)10(3 =βββ ocococ jVVVj
064330 =βββ ocococ jVVjVj
jjVV ococ 3094 =+
Β°β =β =β
β =
+= 24046.34182.0046.3
153.1849.9571.130
9430
jjVoc
Β°β == 24046.3ocT VV
2 Ξ©
1 Ξ©πππ.5 Ξ©10
A
B
+ππππππβ
2)Find the short-circuit current
Β°β == 052
10scI
2 Ξ©
1 Ξ©πππ.5 Ξ©10
A
B
πΌπΌπ π ππ
3)Find the impedance
Β°β = 05scIΒ°β = 24046.3ocV
Β°β == 24046.3ocT VV
2477.05565.00.246092.005
0.24046.3 jIVZ
sc
ocT +=β =
β β
==
The reactance of 0.2477 ohms is equivalent to an inductor of value ππππ = 0.2477 so ππ = 0.2477ππ
= 0.24773
= 0.08257 H
This phasor is written relative to sine so the time function is 3.046 sin(πππ‘π‘ + 24Β°)
ππππ = 3.046β 24Β°
ππππ = 0.5565 + πππ.2477 Ξ©
ππππ = 3.046β 24Β°
0.5565 Ξ© 0.08257 H
The impedance of the capacitor is πππΆπΆ = 1π½π½πππΆπΆ
= 1ππ3ππ0.16667
= βππ2 ohms
Draw the circuit in the frequency domain using phasors and impedances.
2)Find the voltage across a load consisting of a 1 ohm resistor in series with a capacitor of value C=0.16667 F, using: β’ The original circuitβ’ The Thevenin equivalent circuit
Using the original circuit:
πππ.5 Ξ©
2 Ξ©
1 Ξ©
12
H10 sin 3π‘π‘
A
B
1 Ξ©
0.16667 F
2 Ξ©
1 Ξ©10
B
1 Ξ©
βππ2 Ξ©
Using the original circuit, find πππΏπΏ:
02115.12
10=
ββββ
βj
VVjVV LLLL
Write a node equation:
210
2115.12=
β+++
jVV
jVV LLLL
( ) ( ) ( )( ) 5
21)5.1(221)5.1(2212215.1=
β+β+β+β
jjjjjjjVL
536
5.311=
++
jjVL
Β°β =++
= 9.8906.25.311
365jjVL
Do we get the same answer using the Thevenin Equivalent Circuit?
πππ.5 Ξ©2 Ξ©
1 Ξ©10
B
1 Ξ©
βππ2 Ξ©
πππΏπΏ
2477.05565.00.246092.0 jZT +=β =
Find the load voltage using the Thevenin Equivalent Circuit. Define πππΏπΏ = 1 β ππ2 Ξ©
Β°β == 24046.3ocT VV
0=ββ
L
L
T
LT
ZV
ZVV
T
T
LTL Z
VZZ
V =
+
11
T
T
LT
LTL Z
VZZ
ZZV =
+
LT
TLL ZZ
VZV+
=
21 jZL β=
)21(2477.05565.0)0.24046.3)(21(jj
jVL β++β β
=
7523.15565.1)0.24046.3)(4.63236.2(
jVL β
β ββ =
8.48343.2)0.24046.3)(4.63236.2(
ββ β ββ
=LV
Β°β = 915.8906.2LV
Β°β = 9.8906.2LVThis agrees with the answer obtained above of
Note that this equation is simply a voltage divider between ππππ and πππΏπΏ.
ππππππππ
πππΏπΏ
βππ2 Ξ©
1 Ξ©
Nortonβs Theorem for AC Circuits.
Nortonβs TheoremAny two-terminal network consisting of voltage sources, current sources, dependent sources, capacitors, inductors and resistors is equivalent to a current source πΌπΌππ in parallel with an admittance ππππ.
Procedure to find the Norton Equivalent Circuit:1.Open-circuit test: terminate the circuit with an open circuit and find the open-circuit voltage, ππππππ.2.Short-circuit test: terminate the circuit with a short circuit and find the short-circuit current, πΌπΌπ π ππ. 3.The Norton equivalent current source is πΌπΌππ = πΌπΌπ π ππ.4.The Norton equivalent susceptance is ππππ = πΌπΌπ π ππ
ππππππ.
Note that ππππ can also be found as the admittance of the circuit with the independent sources set equal to zero.
Two TerminalCircuit
A
B
A
B
πΌπΌππ ππππ
Norton Equivalent from the Thevenin EquivalentFind the open-circuit voltage ππππππ and the short-circuit current πΌπΌπ π ππ.
Thevenin: ππππ = ππππππππππ =
πππππππΌπΌπ π ππ
Norton:πΌπΌππ = πΌπΌπππΆπΆππππ = πΌπΌπ π ππ
ππππππ
We can change The Thevenin Equivalent Circuit to the Norton Equivalent Circuits using:ππππ = 1
ππππandπΌπΌππ = πΌπΌπππΆπΆ = ππππ
ππππ
ππππ
ππππ
πΌπΌππ ππππ
ππππ
ππππ
πΌπΌπππΆπΆ =ππππππππ
Example: Find the Norton Equivalent Circuit
Find the Norton Equivalent Circuit at a frequency of ππ=3 rad/sec.
Method:1.Find the open-circuit voltage.
2.Find the short-circuit current.
3.Find the Norton Equivalent Circuit:πΌπΌππ = πΌπΌπππΆπΆππππ = πΌπΌπ π ππ
ππππππ
We found the Thevenin Equivalent Circuit earlier in this set of notes.
Open-circuit βloadβ.
Short-circuit βloadβ.
2 Ξ©
1 Ξ©12
H10 sin 3π‘π‘
A
B
2 Ξ©
1 Ξ©12
H10 sin 3π‘π‘
A
B
+ππππππβ
πΌπΌπ π ππ10 sin 3π‘π‘
2 Ξ©12
H1 Ξ©
A
B
Find the open-circuit voltage:
1) Find the open-circuit voltage
015.12
10=ββ
β ocococ VjVV
Convert the circuit to phasors and impedance.The impedance of the inductance is ππππππ = j3x 1
2= πππ.5
Β°β == 24046.3ocT VV
We solved for the open-circuit voltage and the short-circuit current when we found the Thevenin equivalent earlier in these notes.
2 Ξ©
1 Ξ©
12
H10 sin 3π‘π‘
A
B
2 Ξ©
1 Ξ©πππ.5 Ξ©10
A
B
+ππππππβ
Find the short-circuit current:
Β°β == 052
10scI
2 Ξ©
1 Ξ©πππ.5 Ξ©10
A
B
πΌπΌπ π ππ
3)Find the admittance:
Β°β = 05scIΒ°β = 24046.3ocV
Β°β == 05scN II
Β°ββ =β β
== 0.24641.10.24046.3
05
oc
scN V
IY
2 Ξ©
1 Ξ©πππ.5 Ξ©10
A
B
A
B
πΌπΌππ ππππ
Norton Equivalent, example #2:
β’ Find the Norton Equivalent Circuit at 60 Hz.β’ Convert the Norton Equivalent to the Thevenin Equivalent Circuit.
Procedure to find the Norton Equivalent Circuit:1.Open-circuit test: terminate the circuit with an open circuit and find the open-circuit voltage, ππππππ.2.Short-circuit test: terminate the circuit with a short circuit and find the short-circuit current, πΌπΌπ π ππ. 3.The Norton equivalent current source is πΌπΌππ = πΌπΌπ π ππ.4.The Norton equivalent susceptance is ππππ = πΌπΌπ π ππ
ππππππ.
Convert to phasors and impedances:
Voltage source:π£π£π π π‘π‘ = 110 cosπππ‘π‘ becomes phasor πππ π = 110 volts
At ππ =60 Hz the radian frequency is ππ = 2ππππ = 377 r/s
ππππππ = ππππ3πππππ.3πππ10β3 = ππ2 ohms
ππππππ = ππππ3ππππ10.62ππ10β3 = ππ4 ohms
1πππππΆπΆ
= 1ππππ377ππ133ππ10β6
= βππ2 ohms
1.Find the open-circuit voltage:
ππππππ5 + ππ28 β ππ2 = 110
ππππππ = 1108 β ππ25 + 2ππ
ππππππ = 1108.25β β 14.0Β°5.39β β 21.8Β°
ππππππ = 168.4β β 35.8Β°
110 β ππππππ1 + ππ2 β
ππππππ1 + ππ4 β
ππππππβππ2 = 0
ππππππ1
1 + ππ2 +1
1 + ππ4 +1βππ2 =
1101 + ππ2
ππππππ1 + ππ4 βππ2 + 1 + ππ2 βππ2 + (1 + ππ2)(1 + ππ4)
(1 + ππ2)(1 + ππ4)(βππ2) =110
1 + ππ2
ππππππ1 + ππ4 βππ2 + 1 + ππ2 βππ2 + (1 + ππ2)(1 + ππ4)
(1 + ππ4)(βππ2) = 110
ππππππβ2ππ + 8 β 2ππ + 4 + 1 + ππ2 + ππ4 β 8
βππ2 + 8 = 110
ππππππ5 + ππ28 β ππ2 = 110
ππππππ
+
-
ππππππ
2.Find the short-circuit current:
πΌπΌπ π ππ =110
1 + ππ2 = 22 β j44 = 49.19β β 63.4Β°
πΌπΌπ π ππ
3 and 4.Find the Norton Equivalent Circuit:
Β°ββ == 4.6319.49scN II
6.272921.08.354.1684.6319.49
ββ =Β°ββ Β°ββ
==oc
scN V
IY
πΌπΌπ π ππ =110
1 + ππ2= 22 β j44 = 49.19β β 63.4Β°
ππππππ = 168.4β β 35.8Β°
Siemens
Amps
A
B
πΌπΌππ ππππ
Check by finding the dead-circuit impedance:
ππππ
ππππ
1 + ππ4 β₯ βππ2 = 1+ππ4 βππ21+ππ4βππ2
= 0.8 β ππ3.6 ohms
ππππ = 1 + ππ2 β₯ 0.8 β ππ3.6 =1 + ππ2 0.8 β ππ3.61 + ππ2 + 0.8 β ππ3.6
ππππ = 3.034 + ππ1.586 = 3.423β 27.6Β° ohms
ππππ = 1ππππ
= 13.423β 27.6Β°
= 0.2920β β 27.6Β° Siemens
This agrees with the value found on the previous slide:
6.272921.0 ββ ==oc
scN V
IY
Convert the Norton Equivalent to the Thevenin Equivalent Circuit:
Β°ββ = 4.6319.49NIΒ°ββ = 6.272921.0NY
ππππππ = πΌπΌππππππ
= 49.19β β63.4Β°0.2921β β27.6Β°
= 136.6 β ππππ.51 = 168.4β β 35.8Β° volts
ππππ = ππππππ = 98.51 = 168.4β β 35.8Β°ππππ = 1
ππππ= 1
0.2921β β27.6Β°= 3.423β 27.6Β° ohms
+ππππππ-
The Superposition Theorem for AC Circuits
The Superposition Theorem is exactly the same for AC circuits as for DC circuits.
The response of a circuit ππ0 with two sources πππ π 1 and πππ π 2 acting together is equal to the sum of:β’ the response ππ01 with source πππ π 1 acting alone and πππ π 2=0, β’ plus the response ππ02 with source πππ π 2 acting alone and πππ π 1=0,ππ0 = ππ01 + ππ02.
Two sources acting together. Source #1 acting alone. Source #2 acting alone. Two sources acting together. Source #1 acting alone. Source #2 acting alone.
πππ π 1 πππ π 2
+ππππ β
Linear Circuit πππ π 2
+ππππ2 β
Linear Circuitπππ π 1
+ππππ1 β
Linear Circuit
Superposition: DC Sources and AC Source
Use Superposition to separate this problem into:1)The DC response to the DC sources ππ2 = 3 volts and πΌπΌ1 = 1 amp2)The AC response to the AC source π£π£1 π‘π‘ = 0.1 cos(πππππ‘π‘) volts at ππ=1000 r/s
In the circuit below there are two DC sources, ππ2 = 3 volts and πΌπΌ1 = 1 amp. There is also an AC source, π£π£1 π‘π‘ = 0.1 cos πππππ‘π‘ volts.
Use Superposition to find the voltage across the current generator π£π£ π‘π‘ .
The component values are π π 1 = 1 Ξ©, π π 2 = 2 Ξ©, πΆπΆ1 = 500 microFarads, πΆπΆ2 = 40 microFarads, ππ = 1 mH.
0.1 cos πππππ‘π‘
πΆπΆ1 = 500 ππF
π π 1 = 1 Ξ©
πΆπΆ2 = 40 ππF π π 2 = 2 Ξ© ππ = 1 mH
5π£π£ππ+π£π£ππβ
ππ2 = 3 voltsπΌπΌ1 = 1 amp+π£π£β
π£π£(π‘π‘)
Solve with the DC sources:
β’ The AC source is set to zero.β’ The capacitors become open circuits.β’ The inductor becomes a short circuit. β’ Since πΆπΆ1 and πΆπΆ2 are open-circuits at DC, there is zero DC current in π π 1 and
so π£π£ππ = 0β’ Then the dependent source is zero: 5π£π£ππ = 0
Node equation:
βπ£π£ β 3
2 β 1 = 03 β π£π£ β 2 = 0
π£π£ = 1 volt at DC
Draw the DC circuit:β’ AC source becomes zero volts = short circuitβ’ Capacitor: ππ = πΆπΆ ππππ
ππππ= 0, Cβs become open
circuits. β’ Inductor: π£π£ = ππ ππππ
ππππ= 0, Lβs become short
circuits.
+π£π£ππβ
5π£π£ππ 12 Ξ©
3+π£π£β
3 volts0.1 cos πππππ‘π‘
πΆπΆ1
π π 1
πΆπΆ2 π π 2 ππ
5π£π£ππ+π£π£ππβ
1 amp+π£π£β
π£π£(π‘π‘)
Solve with the AC source: use phasors and impedance.
Draw the AC circuit.
0.1 cos πππππ‘π‘
πΆπΆ1 = 500 ππF
1 Ξ©
πΆπΆ2 = 40 ππF 2 Ξ© 1 mH
5π£π£ππ+π£π£ππβ
Use Superposition to separate this problem into:1)The DC response to the DC sources ππ2 = 3 volts and πΌπΌ1 = 1 amp2)The AC response to the AC source π£π£1 π‘π‘ = 0.1 cos(πππππ‘π‘) volts at ππ=1000 r/s
+π£π£β
0.1 cos πππππ‘π‘
πΆπΆ1 = 500 ππF
π π 1 = 1 Ξ©
πΆπΆ2 = 40 ππF π π 2 = 2 Ξ© ππ = 1 mH
5π£π£ππ+π£π£ππβ
ππ2 = 3 voltsπΌπΌ1 = 1 amp+π£π£β
π£π£(π‘π‘)
Use phasors and impedance:Draw the AC circuit: β’ The DC sources are set to zero.β’ π£π£1 π‘π‘ = 0.1 cos(πππππ‘π‘)
becomes phasor ππ1 = 0.1β’ The frequency is ππ = 1000 r/s.β’ 1
πππππΆπΆ1= 1
ππππ1000πππ00ππ10β6= βππ2
β’ 1πππππΆπΆ2
= 1ππππ1000ππ40ππ10β6
= βππ2πβ’ ππππππ = πππππππππππππ10β3 = πππ
Node equations:
0.1 β ππππβππ2 β
ππππ1 β
ππππ β ππβππ2π = 0
ππππ β ππβππ2π β 5ππππ β
ππ2 + ππ = 0
0.1 cos πππππ‘π‘
πΆπΆ1 = 500 ππF
1 Ξ©
πΆπΆ2 = 40 ππF 2 Ξ© 1 mH
5π£π£ππ+π£π£ππβ
0.1
βππ2
1 Ξ©
βππ2π 2 Ξ© πππ
5ππππ+ππππβ
ππππ ππ
+ππβ
Solve the equations for V:Node equations:0.1 β ππππβππ2
βππππ1βππππ β ππβππ2π
= 0
ππππ β ππβππ2π
β 5ππππ βππ
2 + ππ= 0
Multiply the 1st equation by (-j2)(-j25):βππ2π 0.1 β ππππ β βππ2 βππ2π ππππ β (βππ2)(ππππ β ππ) = 0βππ2.5 + ππ2πππππ + 50ππππ + ππ2ππππ β ππ2ππ = 0+50 + ππ2π ππππ β ππ2ππ = ππ2.5
Multiply the 2st equation by (-j25)(2+j):2 + ππ ππππ β ππ β βππ2π 2 + ππ 5ππππ β βππ2π ππ = 02 + ππ ππππ β 2 + j ππ β βj50 + 25 5ππππ + ππ2πππ = 02 + ππ + ππ2ππ β 125 ππππ + (β2 β ππ + ππ25)ππ = 0β123 + ππ2ππ ππππ + (β2 + ππ24)ππ = 0
Solve the equations for V:First Equation:+50 + ππ2π ππππ β ππ2ππ = ππ2.5
ππππ =ππ2ππ + ππ2.550 + ππ2π
Second equation:β123 + ππ2ππ ππππ + (β2 + ππ24)ππ = 0
Substitute ππππ = ππ2ππ+ππ2.ππ0+ππ27
to get:
β123 + ππ2ππππ2ππ + ππ2.550 + ππ2π + (β2 + ππ24)ππ = 0
β123 + ππ2ππ (ππ2ππ + ππ2.5) + (50 + ππ2π)(β2 + ππ24)ππ = 0β123 + ππ2ππ ππ2ππ + 50 + ππ2π β2 + ππ24 ππ = β β123 + ππ2ππ ππ2.5βππ24π β 502 ππ + β100 + πππ2ππ β πππ4 β 648 ππ = ππ307.5 + 627.5β502 β ππ24π ππ + β748 + ππππ4π ππ = 627.5 + ππ3ππ.5β1250 + πππππ ππ = 627.5 + ππ3ππ.5
ππ =627.5 + ππ3ππ.5β1250 + πππππ = β0.2139 β πππ.4001 = 0.4π3πβ β 118.1Β°
Superposition: add the DC solution to the AC solution.
DC Solution:
π£π£ = 1 volt
AC Solution:ππ = 0.4π3πβ β 118.1Β°π£π£ π‘π‘ = 0.4536 cos πππππ‘π‘ β 118.1Β° volts
With both the DC sources and the AC source active: π£π£ π‘π‘ = 1 + 0.4536 cos πππππ‘π‘ β 118.1Β° volts
+π£π£ππβ
5π£π£ππ 12 Ξ©
3+π£π£β
0.1βππ2
1 Ξ©
βππ2π 2 Ξ© πππ5ππππ
+ππππβ
ππππ ππ
+ππβ
3 volts0.1 cos πππππ‘π‘
πΆπΆ1
π π 1
πΆπΆ2 π π 2 ππ
5π£π£ππ+π£π£ππβ
1 amp+π£π£β
π£π£(π‘π‘)
Superposition with two frequencies:
An antenna receives two signals at the same time, one at frequency , ππ1 = 1 GHz and the other at frequency ππ2 = 2 GHz. The antenna is modelled with two voltage sources in series. The circuit uses two ideal op-amps. The component values are π π = 1 ohm, π π 1 = 1ohm, πΆπΆ = 1 pF and ππ = 6.333 nH.
Use Superposition to find the output voltage π£π£4(π‘π‘).
π£π£π π 1 π‘π‘ = 0.1 cosππ1π‘π‘
π£π£π π 2 π‘π‘ = 0.1 cosππ2π‘π‘
50 Ξ©50 Ξ©
π π
π π 1
π£π£4π£π£3
+π£π£4(π‘π‘)β
πππΆπΆπ£π£2π£π£1
Analysis of the first stage:π£π£π π 1 + π£π£π π 2 β π£π£1
50βπ£π£1 β π£π£2
50= 0
The op-amps are ideal with infinite gain and very high input impedance. Consider π£π£1 to be a virtual ground, so π£π£1 = 0. Then
π£π£π π 1 + π£π£π π 250
+π£π£250
= 0
π£π£2 = β π£π£π π 1 + π£π£π π 2
The output of the first stage is the sum of the two voltages.
π£π£π π 1 π‘π‘
π£π£π π 2 π‘π‘
50 Ξ©50 Ξ©
π£π£2
π£π£1 β 0
β 0
π£π£π π 1 + π£π£π π 2
Use phasors to analyze the second stage at some frequency ππ:
Write a node equation at ππ3:
ππ2 β ππ3
π π + ππ ππππ β 1πππΆπΆ
βππ3 β ππ4π π 1
= 0
Amplifier input ππ3 is a virtual ground, ππ3 = 0
ππ2
π π + ππ ππππ β 1πππΆπΆ
+ππ4π π 1
= 0
phasor
Drive the circuit with a generator at frequency ππ:π£π£π π π‘π‘ = π΄π΄ cosπππ‘π‘
The phasor isπππ π = π΄π΄ππππ0
The output of the first stage is ππ2 = βπππ π
ππ4 = π π 1πππ π
π π + ππ ππππ β 1πππΆπΆ
π£π£π π π‘π‘ = π΄π΄ cosπππ‘π‘
50 Ξ©50 Ξ©
π π
π π 1
ππ4ππ3 β 0
+ππ4β
ππππππ1πππππΆπΆ
ππ2ππ1 β 0
πππ π = π΄π΄
β 0 β 0
At frequency ππ1 = 1 GHz, ππ1 = 2ππππ1 = 6.2π3ππ109:
π π = 1 ohm, π π 1 = 1 ohm, πΆπΆ = 1 pF and ππ = 6.333 nH, πππ π = 0.1
ππ1ππ β1
ππ1πΆπΆ= 6.2π3ππ109πππ.333ππ10β9 β
16.2π3ππ109πππππ10β12 = 39.79 β 159.15 = β119.36
ππ4 = π π 1πππ π
π π +ππ ππ1πΏπΏβ1
ππ1πΆπΆ
= 0.11βππ119.36
= 8.3ππππ10β4β ππ.5 degrees
π£π£4 π‘π‘ = 8.3ππππ10β4 cos ππ1π‘π‘ + 89.5Β°
π£π£π π π‘π‘ = 0.1 cosππ1π‘π‘
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π π
π π 1
ππ4ππ3 β 0
+
ππ4 = π π 1πππ π
π π + ππ ππ1ππ β1
ππ1πΆπΆβ
ππππ1ππ1ππππ1πΆπΆ
ππ2ππ1 β 0
πππ π
β 0 β 0
At frequency ππ2 = 2 GHz, ππ2 = 2ππππ2 = 1.2ππππ1010:
π π = 1 ohm, π π 1 = 1 ohm, πΆπΆ = 1 pF and ππ = 6.333 nH, πππ π = 0.1
ππ2ππ β1
ππ2πΆπΆ= 1.2ππππ1010πππ.333ππ10β9 β
11.2ππππ1010πππππ10β12 = 79.54 β 79.55 = β0.01 β 0
ππ4 = π π 1πππ π
π π + ππ ππ2ππ β1
ππ2πΆπΆ=
0.11 + πππ = 0.πβ π degrees
π£π£4 π‘π‘ = 0.1 cos ππ2π‘π‘
π£π£π π π‘π‘ = 0.1 cosππ2π‘π‘
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π π
π π 1
ππ4ππ3 β 0
+
ππ4 = π π 1πππ π
π π + ππ ππ2ππ β1
ππ2πΆπΆβ
ππππ2ππ1ππππ2πΆπΆ
ππ2ππ1 β 0
πππ π
β 0 β 0
Superposition with two frequencies:
By superposition, with both sources active:π£π£4 π‘π‘ = 8.3ππππ10β4 cos ππ1π‘π‘ + 89.5Β° + 0.1 cos ππ2π‘π‘
The design of the circuit makes ππππ β 1πππΆπΆ
=0 at 2 GHz.Then the circuit βpassesβ 2 GHz but βrejectsβ 1 GHz.The circuit behaves as a βfilterβ to recover the 2 GHz signal from the two signals received by the antenna.
π£π£π π 1 π‘π‘ = 0.1 cosππ1π‘π‘
π£π£π π 2 π‘π‘ = 0.1 cosππ2π‘π‘
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π π
π π 1
π£π£4π£π£3
+π£π£4(π‘π‘)β
πππΆπΆπ£π£2π£π£1