Download - Matching Techniques and Baluns
Matching Techniquesand Baluns
INEL 5305Dr. Sandra Cruz-Pol
ECE, UPRM
Ref. Balanis sect. 9.8, 14.8
Matching Techniques
Matching over the desired frequency range
when connecting the T.L. to the antenna
Types Stub-matching /4 transformer: single or multiple
Zo (real)
ZL (complex)
Stub-matching
Zo
s
l
/4 transformer-matching: Single Section First move so that ZL is
completely real
Zo
so
4
oinx ZZZ
Zx
/4 transformer-matching: Multiple- Section- provides broader BW First move so that ZL is completely real
Zo
so
4
444
Could be designed using Dolph-Tchevy or Taylor coefficients.
Multiple sections: Quarter-wave Xmer N-sections
Can be implemented several ways Binomial Tschebyscheff
Nn
nn
nnn
N
n
njn
NjN
jjoin
CZZ
ZZ
where
e
eeef
1
1
0
2
242
21 ...)(
o
o
f
flk
24
2
Multiple sections: Quarter-wave Xmer For symmetrical Xmer,
Binomial Coefficients
n=0,1,2,…N
...)2cos(cos(2)( 12 NNef o
Njin
N
n
njNn
oL
oLN eCZR
ZR
0
22
Nn
oL
oLNn C
ZR
ZR
2
!)!(
!
nnN
NC N
n
Binomial Design for Multiple sections Quarter-wave Xmer Fractional Bandwidth:
where m= maximum value of reflection coefficient which can be tolerated within the bandwidth.
f
for
Z
m
n
N
oL
oLm
o
mo
o ZR
ZR
f
ff
f
f/1
1cos4
22
design
for
NRZ
fm
Lo
,,
Use Radians!!!
Implementing with Microstrip For Microstrip lines:
tw
hZ
r
c 8.0
98.5ln
47.1
87
Tschebyscheff Design for Multiple sections Quarter-wave Xmer
mN
mN
oL
oLNj
oNj
in
T
T
ZZ
ZZe
NNef
sec
cossec
...)2cos(cos(2)(
2
12
mNoL
oLm TZZ
ZZ
sec
1
Comparison of frequency response for matching quarter-wave network
in
of
f
0.5 1.0 1.5
Binomial
(Maximally flat)
Tschebyscheff
Matching-techniques There are other techniques for matching a
line to the antenna; T-Match Gamma Match Baluns
BalunsBALance to UNbalance Converters a passive electronic device that converts
between balanced and unbalanced electrical signals, such as between coaxial cable and dipole antenna. Present in some radars, transmitters, satellites, in
every telephone network, and probably in most wireless network modem/routers used in homes.
A 75- to 300 ohm balun:
Baluns- current distribution
Coaxial Line(unbalanced)
Currentleak|| wire
transmission line(balanced)
Balanced load
Currentdistribution
Coaxial Line(unbalanced)
Balun
Some antennas like the monopole or horn are unbalance loads, and it’s ok to use a coaxial cable to feed them.
Balanced source The source is balanced if the voltage
potential of one level is equally above ground as the other is below ground at all instants of time. Example: +50V and -50V is balanced, +30V
and +12V or +20V and 0V are NOT balanced.
Some types of baluns
Shorted to coaxial outer conductor
/4 above looks like an open circuit, therefore
the leak current is zero.
Bazooka
Shorted to coaxial outer conductor
/4 above looks like an open circuit, therefore
the leak current is zero.
/4 coax/2 coax
Ferrite Core
(toroidal)
a) Transforms Z, 4:1 or 1:4
b) Increased bandwidth but may not behave well at very hi frequencies. There are losses in iron core. Can be made 1:1 or impedance transforming such as 4:1
Feed Networks for Arrays Series feed Parallel (Corporate) Space feed
Usually one source feeds all elements in the array. Have to be careful not to affect the amplitude and phase of the feed to each element. Also the mutual impedance of neighboring elements.
Corporate Feed
b) quarter-wave Xmers
a) Tapered lines