Upload
syed-wahaj-ul-haq
View
252
Download
0
Embed Size (px)
Citation preview
RF & Microwave EngineeringBETE-Spring 2009
Department of Electrical EngineeringAir University
Impedance Matching
Design of Matching Networks
Lecture No. 5
RF & Microwave EngineeringBETE-Fall 2009
Basit Ali ZebDepartment of Electrical Engineering, AU
Why Impedance Matching?
• Impedance matching i.e., transforming one impedance value to another, is an immensely important part of microwave component or system design engineering.
• Why impedance matching is necessary?– Maximum power is delivered to the load when the TL is matched at both the load and source ends
– Increased sensitivity of the device– Reflected power can be harmful to some microwave devices and demands extra protection circuitry
– To avoid multiple reflections which cause amplitude and phase distortions.
RF & Microwave EngineeringBETE-Fall 2009
Basit Ali ZebDepartment of Electrical Engineering, AU
Introduction
RF & Microwave EngineeringBETE-Fall 2009
Basit Ali ZebDepartment of Electrical Engineering, AU
Impedance Matching and Tuning
RF & Microwave EngineeringBETE-Fall 2009
Basit Ali ZebDepartment of Electrical Engineering, AU
Matching a TL Circuit
Impedance matching using discrete components
Impedance matching using distributed components
RF & Microwave EngineeringBETE-Fall 2009
Basit Ali ZebDepartment of Electrical Engineering, AU
Features
Matching network should ideally be lossless to avoid
unnecessary loss of generator power
The simplest design of matching network that satisfies the
required specification is generally the most preferable.
RF & Microwave EngineeringBETE-Fall 2009
Basit Ali ZebDepartment of Electrical Engineering, AU
General Rule- Impedance Matching
In order to match a complex load impedance to a
TL of Z0, the real part of the input impedance
looking into the matching network must be Z0
while the imaginary part must be zero.
This implies that a general matching network
must have at least two degrees of freedom.
RF & Microwave EngineeringBETE-Fall 2009
Basit Ali ZebDepartment of Electrical Engineering, AU
Matching Network
Narrowband Matching
Wideband Matching
RF & Microwave EngineeringBETE-Fall 2009
Basit Ali ZebDepartment of Electrical Engineering, AU
Types of Solutions
• Solve analytically to calculate the values of required elements
In designing an impedance matching circuit, we
have two broad approaches at our disposal:
• To rely on Smith Chart as a graphical
design tool
Both methods have advantages and disadvantages
RF & Microwave EngineeringBETE-Fall 2009
Basit Ali ZebDepartment of Electrical Engineering, AU
Matching Techniques
• L Networks
• Single Stub Tuner
• Quarter Wave Transformer
Discrete component
implementation
Microstrip or stripline
Implementation
We will discuss three methods for impedance matching
in this course:
RF & Microwave EngineeringBETE-Fall 2009
Basit Ali ZebDepartment of Electrical Engineering, AU
Matching With Lumped Elements
RF & Microwave EngineeringBETE-Fall 2009
Basit Ali ZebDepartment of Electrical Engineering, AU
L-Networks
At a single frequency, any positive real complex impedance
can be matched to any other positive real complex impedance using no more than two reactive elements.
There are 8 possible L-matching circuits:
RF & Microwave EngineeringBETE-Fall 2009
Basit Ali ZebDepartment of Electrical Engineering, AU
Matching With L-Network
RF & Microwave EngineeringBETE-Fall 2009
Basit Ali ZebDepartment of Electrical Engineering, AU
The Technique
Imagine that yL =gL +jbL is at the point marked Load in the circuit for gL< 1. By adding jb we will move on the constant
g=gL circle. We select the value of b such that we land at one
of the two intersections of the g=gL circle with the r = 1 circle.
RF & Microwave EngineeringBETE-Fall 2009
Basit Ali ZebDepartment of Electrical Engineering, AU
The Technique
At this point, the impedance is 1 + jx, and the series-tuning element can be used to remove the reactive part. The
solution that demands the smallest b should normally be
chosen, because it gives the largest bandwidth.
RF & Microwave EngineeringBETE-Fall 2009
Basit Ali ZebDepartment of Electrical Engineering, AU
Smith Chart Solution
RF & Microwave EngineeringBETE-Fall 2009
Basit Ali ZebDepartment of Electrical Engineering, AU
Example - Case RL< Z0
RF & Microwave EngineeringBETE-Fall 2009
Basit Ali ZebDepartment of Electrical Engineering, AU
Solution Procedure
1. Mark the normalized load impedance point on smith chart
RF & Microwave EngineeringBETE-Fall 2009
Basit Ali ZebDepartment of Electrical Engineering, AU
Solution on Smith Chart
RF & Microwave EngineeringBETE-Fall 2009
Basit Ali ZebDepartment of Electrical Engineering, AU
Impedance Movement-Smith Chart
A general rule of thumb concerning the direction of rotation is that whenever an inductor is involved we move the impedance in the upper half of the chart while capacitance results in the movement towards lower half.
The addition of series reactance with load results in motion along constant- resistance circle.
A shunt connection produces motion along the constant-conductance circle.
RF & Microwave EngineeringBETE-Fall 2009
Basit Ali ZebDepartment of Electrical Engineering, AU
L-Matching Networks
zs
Four possible
matching networks
zL*
RF & Microwave EngineeringBETE-Fall 2009
Basit Ali ZebDepartment of Electrical Engineering, AU
Mixed Design Matching
No. of transmission line sections connected in series with
capacitors placed in parallel configuration.
Inductors are usually avoided because they tend to have
higher resistive losses than capacitors.
Placement and the component value of capacitor gives
greater tuning flexibility.
RF & Microwave EngineeringBETE-Fall 2009
Basit Ali ZebDepartment of Electrical Engineering, AU
Microstrip Line Matching Networks
• Increasing frequency means decreasing wavelength, and the effect of parasitics in discrete components becomes noticeable.
• This makes design more complicated and often the distributed elements are used.
• In mid-GHz range, matching networks usually employ combined discrete and distributed components
RF & Microwave EngineeringBETE-Fall 2009
Basit Ali ZebDepartment of Electrical Engineering, AU
Quarter Wave Transformer
RF & Microwave EngineeringBETE-Fall 2009
Basit Ali ZebDepartment of Electrical Engineering, AU
Quarter Wave Transformer- Matching
±∞===
l
radl
l
1
1
1
tan
2
4
βπβλ
RF & Microwave EngineeringBETE-Fall 2009
Basit Ali ZebDepartment of Electrical Engineering, AU
QWT Design
We can adjust Z1 such that Zin = Z0
In other words, a quarter wavelength TL section with this
particular characteristic Impedance, will present a perfect match (Γ=0) to the left hand side of TL
RF & Microwave EngineeringBETE-Fall 2009
Basit Ali ZebDepartment of Electrical Engineering, AU
Broadband QWT
RF & Microwave EngineeringBETE-Fall 2009
Basit Ali ZebDepartment of Electrical Engineering, AU
Taper Design
RF & Microwave EngineeringBETE-Fall 2009
Basit Ali ZebDepartment of Electrical Engineering, AU
Microstrip Broadband QWT
Multi-section QWT
Tapered Line QWT
RF & Microwave EngineeringBETE-Fall 2009
Basit Ali ZebDepartment of Electrical Engineering, AU
QWT Matching
DISADVANTAGES
RF & Microwave EngineeringBETE-Fall 2009
Basit Ali ZebDepartment of Electrical Engineering, AU
Adjusting TL Z0
RF & Microwave EngineeringBETE-Fall 2009
Basit Ali ZebDepartment of Electrical Engineering, AU
STUB Matching
Parallel or Series connection
SINGLE STUB TUNER
DOUBLE STUB TUNER
RF & Microwave EngineeringBETE-Fall 2009
Basit Ali ZebDepartment of Electrical Engineering, AU
Single Stub Tuner (SST)
This is an example of parallel SST. The shunt-connected
section is called the STUB
Yin = Y0 + j Bs
Yin = Y0 + j 0
We require:
At input:
RF & Microwave EngineeringBETE-Fall 2009
Basit Ali ZebDepartment of Electrical Engineering, AU
Adjustable Parameters
1. Length of the stub line section “ls”
2. Location of the stub line from the load “d”
Although not necessary, all the TL sections will be
assumed to have same
Two degrees of design freedom
RF & Microwave EngineeringBETE-Fall 2009
Basit Ali ZebDepartment of Electrical Engineering, AU
For Proper Impedance Match
RF & Microwave EngineeringBETE-Fall 2009
Basit Ali ZebDepartment of Electrical Engineering, AU
For Proper Impedance Match
RF & Microwave EngineeringBETE-Fall 2009
Basit Ali ZebDepartment of Electrical Engineering, AU
SST Design Using Smith Chart
Normalized values
Procedure:
RF & Microwave EngineeringBETE-Fall 2009
Basit Ali ZebDepartment of Electrical Engineering, AU
SST Design Example
Solution:
Question:
RF & Microwave EngineeringBETE-Fall 2009
Basit Ali ZebDepartment of Electrical Engineering, AU
The Solution
Normalized
admittance
coordinates
Two Solutions
are possible:
RF & Microwave EngineeringBETE-Fall 2009
Basit Ali ZebDepartment of Electrical Engineering, AU
Solution Contd-
Rotate wavelengths
towards generator to:
FINAL 2 SOLUTIONS:
RF & Microwave EngineeringBETE-Fall 2009
Basit Ali ZebDepartment of Electrical Engineering, AU
Short or Open Stubs?
In stripline and microstrip form, open circuited stubs are much
more popular than short circuited stubs, because they are simpler to make.
Good short circuits are difficult to make in microstrip and stripline,
but they are easy to make in coaxial line.
Series stubs cannot be made in stripline or microstrip. In coaxial
line it is possible, but mechanically difficult and therefore
expensive.
RF & Microwave EngineeringBETE-Fall 2009
Basit Ali ZebDepartment of Electrical Engineering, AU
2 GHz Power Amplifier for a cellular phone
RF & Microwave EngineeringBETE-Fall 2009
Basit Ali ZebDepartment of Electrical Engineering, AU
Printed Circuit Board Layout
RF & Microwave EngineeringBETE-Fall 2009
Basit Ali ZebDepartment of Electrical Engineering, AU
Study
• Article 5.1, 5.2, 5.3, 5.4 from the text book
• Next topic of Discussion
“Microwave Network Analysis”