CHAPTER 3 DESIGN AND DEVELOPMENT OF REFLECTION TYPE PHASE...
Transcript of CHAPTER 3 DESIGN AND DEVELOPMENT OF REFLECTION TYPE PHASE...
68
CHAPTER 3
DESIGN AND DEVELOPMENT OF REFLECTION TYPE
PHASE SHIFTER FOR WIRELESS APPLICATIONS
3.1 PREAMBLE
Reflection type phase shifter or branch line hybrid coupled phase
shifter with semiconductor diode control has been reported widely in the
literature. Most of the studies reporting on the branch line hybrid coupled
phase shifter assume that the coupler is ideal and concentrate on the analysis
and design of a reflective phase-shifting network. Some studies that combine
the performance of the coupler with that of the reflective network have also
been made (Koul and Bhat 1991 b). Any desired phase shift with wideband
response can be achieved by approximately choosing the elements of the
network and the corresponding design formulas are reported (Graver 1972).
J.F.White indicates that a reflective line phase shifter can provide a wide
bandwidth for pulse phased-array radar applications (White 1974). A phase
shifter incorporating hybrid coupled circuits for 90 and 180 phase bits are
reported (Burns et al 1974).
The optimization of matching network for a hybrid coupler phase
shifter for a smaller phase error and greater bandwidth are described (Piotr
1977). Branch-line–hybrid coupled phase shift circuits Characterized using S
parameters are presented (Katsumi and Susumu 1979). During 1980, Atwater
studied the Reflection coefficient transformations for phase-shift circuits
(Harry 1980). A procedure for obtaining the impedance transformer to
produce a prescribed pair of reflection coefficients for reflective type phase
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shifter is dealt (Harry 1981). A complete branch-line hybrid coupled phase
shifter circuit, along with the coupler is analyzed and presented (Kori and
Mahapatra 1987). An 180 phase bit is realized using reflective type phase
shifter is reported (Jan 1998).
A complete analysis and fabrication of 4 bit branch line hybrid
coupled phase shifter for phased array antenna operated in Blue tooth access-
point is described (Salonen and Sydanheimo 2002). Miniaturized Phase
shifters have been reported using MEMS technology (Malczewski et al 1999),
MMIC technology (Ellinger et al 2001, Ellinger et al 2002) and metamaterials
(Siso et al 2007). The concept of metamaterials has been used to reduce the
size of antenna (Baliarda et al 2000). But, the concept of fractals has not been
used for miniaturizing phase shifter. The space filling curves like Moore,
Sierpinski and Minkowski are used to miniaturize the rat-race branch-line and
coupled –line hybrids are reported (Ghali and Moselhy 2004a). The
performance of the space filling hybrids is as effective as that of the
corresponding conventional structures (Ghali and Moselhy 2004b). Design of
fractal rat–race coupler with better phase performance and design equations
for different space filling curves are reported (Ghali and Moselhy 2004a).
A compact wide band rat-race hybrid using space filling curves with the
performance same as that of conventional one is presented (Caillet et al
2009). Also the usage of KOCH fractal in miniaturizing a branch line coupler
and a hybrid coupler is reported (Annaram et al 2008). Miniaturization of
fractal-shaped branch-line couplers without altering the bandwidth are
reported (Chen and Wang 2008).
3.2 REFLECTIVE LINE PHASE SHIFTER
3.2.1 The Structure
Reflective line phase shifter consists of 3dB 900 hybrid coupler and
terminated transmission lines at the coupled ports of the coupler. By changing
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the electrical plane of the impedance matching transmission line suitably,
differential phase shift is achieved.
The hybrid coupled phase shifter shown in Figure 3.1 uses two
identical, symmetrically placed reflective terminations at the coupled ports of
3dB 900 hybrid coupler. Signal at input port gets divided equally except the
quadrature phase at the two coupled ports. These signals reflect from a pair of
switched loads and combine in phase at the phase shifter output, as long as
the loads are identical in reflection coefficient.
Figure 3.1 Reflective type phase shifter
The required properties of hybrid coupler is that it must provide a
3-dB power split for the two output arms and there must be a 900
phase
differences in its output signals. Given these properties, it is possible to show
(using a scattering matrix) that reflections from symmetric terminations on the
3-dB arms exits at the fourth (normally decoupled) port of the hybrid. Thus
the reflective nature of the control termination is converted to matching
transmission operation for the phase shifter bit.
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3.2.2 Design of Conventional Reflective Type Phase Shifter
In the design of a reflective type phase shifter, the impedance and
the electrical length of hybrid coupler is known, that is, the impedance of the
main arm is oZ / 2 and that of the shunt arm is Z0.The electrical length of all
arms is 90°. The design of an impedance matching transmission line (Kori
and Mahapatra 1987, Jan 1998) which matches the impedance between the
50 microstrip feed and diode plays an important role. The phase shift is
achieved between the two bias states of the diode.
Figure 3.2 Matching network
Figure 3.2 shows a matching network consisting of a transmission
line with a length of T and impedance of ZT. The purpose of the transmission
line is to generate the desired phase shift between the two bias states for the
diode
The normalized driving port admittance at point A in the forward
bias state is
D
c T FF D
T F T
Z Z X tanb
Z X Z tan (Piotr 1977), (3.1)
and in reverse bias state,
D
c T R TR D
T R T T
Z Z X tanb
Z X Z tan (3.2)
ZT , T
ATo hybrid
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In Equations 3.1 and 3.2, Zc is the impedance of the hybrid, T is
the electrical length of the matching transmission line, ZT is the impedance of
the matching transmission line, D
FX and D
RX are the diode reactances at
forward and reverse bias.
The phase shift is given by
1 1
F R F R2 tan b 2 tan b (3.3)
After substituting the equations (3.1) and (3.2), in (3.3) yields
4 2 3 D D 2
T T T T F R TZ h tan Z h (X X ) tan Z2 2
D D 2 2 2 2
c F R T F R CZ (X X )(1 h ) tan (X X Z )2
2 D D 2 2 D D
T C T F R C T F RZ Z h (X X ) tan Z h X X tan 02 2
(3.4)
where T Th tan , T is the electrical length of the matching transmission line.
Equation (3.4) can be solved in two different ways:
i) By calculating ZT for an assumed T ,
ii) By calculating T for the desired ZT.
For T = 900 Equation 3.4 simplifies significantly to
D D4 2 2 D Dc F R
T T C F R
Z (X X )Z Z Z X X 0
tan / 2 (3.5)
Equation (3.5) is a second-order equation in 2
TZ with four existing
solutions for ZT because ZT must be real and positive, and only one of these
four solutions may be used in the design for < 1800.
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D D D D 2 D D 2
C F R F R F R
T
Z (X X X X ) 4X X tan / 2Z
2 tan / 2(3.6)
to calculate T for some desired ZT
2 4 2 D D 2 D D
T T T C F R C F Rh Z tan Z Z (X X ) Z X X tan2 2
D D 2 2 2
T T F R T C Th Z (X X )(Z Z ) tan Z2
D D 2 D D
C F R C F R[Z (X X ) (Z (X X )) tan ] 02
(3.7)
Equation (3.7) is a second order equation, and it is written as
2
T
b b 4ach
2a (3.8)
2
T
b b 4actan
2a (3.9)
21
T
b b 4actan ( )
2a (3.10)
where a = 4 2 D D 2 D D
T T C F R C F RZ tan Z Z (X X ) Z X X tan2 2
b = D D 2 2 2
T F R T C TZ (X X )(Z Z ) tan Z2
c = D D 2 D D
C F R C F R[Z (X X ) (Z (X X )) tan ]2
Solving the Equation (3.6) to Equation (3.10), the impedance ZT
and electrical length T of the matching line for the desired phase shift for
a given diode can be calculated.
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Figure 3.3 90 Conventional reflection type phase shifter
3.3 ISSUES WITH CONVENTIONAL REFLECTIVE TYPE
PHASE SHIFTER
Figure 3.3 shows the layout of conventional reflective type phase
shifter. In the reflective type phase shifter, the branch line coupler and the
matching transmission line has a dimension of quarter wave length by quarter
wave length at the centre frequency. Because of these large electrical lengths
of the transmission line elements, the conventional branch line hybrids and
matching line occupy a significant amount of circuit area and leave the
interior area unoccupied. To reduce the circuit size of the branch line coupler
many compact designs have been proposed. The lumped and quasi lumped
approaches are proposed in (Chiang and Chen 2001,Liao and Peng 2006) and
these techniques consider the combinations of shunt-lumped capacitors and
short high impedance transmission lines. In those cases, metal-insulator-metal
capacitor is needed for the monolithic microwave integrated circuits which
increase cost and complexity of fabrication. Photonic Band Gap structure is
another way to miniaturize the circuits (Shun et al 2001,Sung et al 2004).
However, the existence of many defected cells on the ground plane may limit
the use of this technique. Compact couplers are achieved by adding artificial
transmission line, which consists of microstrip lines periodically loaded with
open stubs (Eccleston and Ong 2003, Sun et al 2005) or simply T-shaped
stubs (Sakagami et al 1999, Liao et al 2005). In (Ghali and Moselhy 2004 b,
Awida et al 2006) just by meandering the microstrip lines according to space
filling curves of different iteration orders, fractal-shaped and meandered
couplers achieved a great size reduction.
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3.4 FRACTAL BASED SINGLE BIT REFLECTIVE TYPE
PHASE SHIFTERS
3.4.1 Fractals in Coupler Design
In by employing outwards space filling curves to utilize vacant
space outside the conventional coupler(Ghali and Moselhy 2004 b), and by
employing inwards KOCH fractal lines to utilize vacant space inside the
conventional coupler, the fractal shaped branch line couplers achieved a
maximum of 75.3% and 70% reduction respectively and the phase- shifting
phenomenon are observed(Awida et al 2006).
3.4.2 Design of KOCH Fractal Based Reflective Type Phase Shifter
The KOCH fractals are applied to the matching transmission line
and bias line of the conventional reflective type phase shifters as shown in
Figure 3.4(a) ,(b) and (c) for various phase shifts namely 90 , 180 and 270
with 0.2 and 0.4 iteration factor with iteration order of 1 as discussed in
section 2.3.2 and 2.3.3. All other transmission lines including coupler arms do
not satisfy the KOCH Fractal criteria and hence cannot be iterated.
(a) 90 . (b) 180
(c) 270
Figure 3.4 KOCH reflection type phase shifters
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3.5 RESULTS AND DISCUSSION
3.5.1 Design and Simulation of 90° KOCH Reflective Type Phase
Shifter
Specifications
Frequency of operation (f) = 2.45 GHz
Desired Phase shift is ( ) = 90
Bandwidth = 80MHz (2.4 - 2.48GHz)
Z0 =50 and = 90
A 90 conventional phase shifter is designed and simulated for
specifications. The line dimensions are tabulated in Table 3.1. The KOCH
fractals are applied to the matching and bias transmission lines of the
conventional 90 reflective type phase shifter. The simulation layout of 90
KOCH reflective type phase shifter is shown in Figure 3.5 along with the
discrete components like dc blocking capacitors and p-i-n diodes is simulated
using Agilent’s ADS(Advanced Design Suit) software . The simulation is
performed for diode OFF condition by supplying a bias voltage of -20V and
diode ON condition by supplying a bias voltage of + 1.5 V to the bias circuit.
Table 3.1 Calculated design data of 90 conventional reflective type
phase shifter
Description of the
line
Characteristic
impedance of
the line in
Electrical
length of the
line in
Length of
the line in
mm
Width of
the line in
mm
Coupler series arms 35.356 90 15.94 5.025
Coupler shunt arms 50 90 16.408 2.908
Coupler feed lines 50 90 16.408 2.908
Matching lines 85.4559 90 17.192 0.956
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Figure 3.5 Simulation of 90 KOCH reflective type phase shifter
2.2 2.3 2.4 2.5 2.6 2.7 2.8
-35
-30
-25
-20
-15
-10
-5
0
S-p
ara
met
er (
dB
)
Frequency (GHz)
S11
OFF
S11
ON
S21
OFF
S21
ON
Figure 3.6(a) Simulated return loss and insertion loss of 90 KOCH
reflective type phase shifter
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Simulation results of 90 KOCH reflective type phase shifter is
given in Figure 3.6(a) and 3.6(b).The simulated return loss remains less than -
17dB in both ON and OFF conditions whereas the average insertion loss
varied with -2.8dB between ON and OFF conditions over 2.4-2.48GHz band.
Over the band 2.4-2.48GHz, the phase for on and off condition is linear.
2.2 2.3 2.4 2.5 2.6 2.7 2.8
-200
-150
-100
-50
0
50
100
150
200
S21(d
eg)
F requency (G H z)
S21
O FF
S21
O N
Figure 3.6(b) Simulated phase plot for 90 KOCH reflective type phase
shifter
3.5.2 Design and Simulation of Equivalent Circuit of 90 KOCH
Reflective Type Phase Shifter
The equivalent circuit model parameters are calculated using the
standard formulae given in section 2.4. The same diode MA4P789-287 is
used for simulation and the parameters given by the manufacturer are used.
Table 3.2 gives the equivalent circuit parameter values of 90 KOCH
reflective type phase shifter. Figure 3.7 gives the schematic of the equivalent
circuit of 90 KOCH reflective type phase shifter
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Figure 3.7 Simulation of equivalent circuit of 90 KOCH reflective type
phase shifter for ON condition
The simulation result for the equivalent circuit in Figure 3.8(a)
shows that the return loss is less than -12dB for both ON and OFF conditions
and the insertion loss remained less than - 2.4dB for both on and off condition
over the desired band 2.4-2.48GHz.
Table 3.2 Calculated values of equivalent circuit model for 90 reflection
type Phase shifter
Sl. No Component Value
1.L73-L80,L85-92,L61-L68,L18-L25,L28-L33,L36
,L37,L53-L60,L8914nH
2.L107-L110,L43-L47,L95-L102,L43-L47,L95-
L102,L38-L42,L106-L11113nH
3.C90-C93,C98-C101,C56,C70,C68,C58,C82-C85,C43,
C78-C81,0.4pF
4.C86-C89,C43-C45,C47,C52,C54,C55,C57,C83,C82,
C94-C105,C74-C770.5pF
5. C39,C40,C9,C30,C34,C35,C39,C40 0.3pF
6. C33,C32 .35pF
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Table 3.2 (Continued)
Sl. No Component Value
7. L4,L3 12nH
8. C18,c17 420nF
9. C7,C5,C8 0.1pF
10. L2,L1 11nH
11. L17 8.27nH
12. C1-C3 0.2pF
13. C31 3.32pF
14. C21,C27 0.01pF
15. C20, 0.05pF
16. C23,C29 0.1pF
17. L13,L15 0.7nH
18. L14 0.65nH
19. C72,C71 0.13pF
20. C22,C28 0.015pF
21. R2 1.5ohms
2.2 2.3 2.4 2.5 2.6 2.7 2.8-30
-25
-20
-15
-10
-5
0
S-p
ara
met
er
(dB
)
Frequency (GHz)
S11
ON
S21
ON
S11
OFF
S21
OFF
Figure 3.8(a) Simulated return loss and insertion loss for equivalent
circuit model of 90 KOCH reflective type phase shifter
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2 .4 0 2 .4 1 2 .4 2 2 .4 3 2 .4 4 2 .4 5 2 .4 6 2 .4 7 2 .4 8 2 .4 9 2 .5 0-1 8 0
-1 3 5
-9 0
-4 5
0
4 5
9 0
1 3 5
1 8 0
S2
1(d
eg)
F r eq u en cy (G H z )
S21
O N
S21
O F F
Figure 3.8(b) Simulated phase plot for equivalent circuit model of 90
KOCH reflective type phase shifter
From the phase plot shown in Figure 3.8 (b) it is observed that the
linearity of phase response is effective up to the mid of the band 2.45GHz and
after that it deviates.
3.5.3 Fabrication of 90 KOCH Reflective Type Phase Shifter
To validate the design and simulation results, a 90° KOCH
reflective type phase shifter is fabricated on a FR-4 substrate (thickness of 1.6
mm; dielectric constant r of 4.6, loss tangent of 0.011) using a copper etching
process. The fabricated prototype is shown in Figure 3.9. The p-i-n diodes
(MA4P789-287 with SOT-23 package), capacitors and SMA connectors are
soldered. The p-i-n diodes are grounded through via holes using PTH. The
RF performance measurements are done using Agilent ENA series E5062A
vector network analyzer.
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Figure 3.9 Fabricated prototype of 90 KOCH reflective type phase
shifter
As observed from Figure 3.10(a), the measured return loss remains
less than -10dB in both ON and OFF conditions of the diodes whereas the
average insertion loss varied -2.0dB between ON and OFF conditions over
2.4-2.48GHz band.
2.2 2.3 2.4 2.5 2.6 2.7 2.8
-30
-25
-20
-15
-10
-5
0
S-p
ara
met
er (
dB
)
Frequency (GHz)
S11
OFF
S11
ON
S21
OFF
S21
ON
Figure 3.10(a) Measured return loss and insertion loss of 90 KOCH
reflective type phase shifter
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2.40 2.41 2.42 2.43 2.44 2.45 2.46 2.47 2.48 2.49 2.50
-180
-135
-90
-45
0
45
90
135
180
S21(d
eg)
Frequency (GHz)
S21
OFF
S21
ON
Figure 3.10(b) Measured phase plot of 90 KOCH reflective type phase
shifter
The phase remains linear over the desired band 2.4-2.48GHz, in
both ON and OFF condition of the diodes as shown in Figure 3.10(b). The
measured RF performance at the centre frequency of 2.4 GHz is tabulated in
Table 3.3. Figure 3.10(c) shows the measured phase shift of the fabricated
reflective type phase shifter.
2.40 2.41 2.42 2.43 2.44 2.45 2.46 2.47 2.48 2.49 2.50
-180
-135
-90
-45
0
45
90
135
180
Ph
ase
sh
ift
(deg
)
Frequency (GHz)
Figure 3.10(c) Measured phase shift of 90 KOCH reflective type phase
shifter
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Table 3.3 90 Measured results of KOCH reflective type phase shifter at
2.45 GHz
Phase
S11 S21Phase
shift
( )
Phase
error
Area in
mm2Magnitude
In dB
Magnitude
In dB
Phase
in
degrees
90ON -12.54 -2.15 -71.03
-91.34 -1.34 3451.41OFF -21.2 -2.36 20.31
3.5.4 Design and simulation of 180° KOCH Reflective Type Phase
Shifter
A 180° conventional phase shifter is designed and simulated for the
same specifications as given in section 3.5 and the line dimensions are
tabulated in Table 3.4. The KOCH fractals are applied to matching
transmission line and bias network transmission line. The simulation layout of
KOCH reflective type phase shifter is shown in Figure 3.11 and RF
performance plots are shown in Figure 3.12 (a) to (c).
Table 3.4 Calculated design data of 180 conventional reflective type
phase shifter
Description of
the line
Characteristic
impedance of
the line in
Electrical
length of
the line in
degrees
Length of
the line in
mm
Width of
the line in
mm
Coupler series
arms35.356 90 15.94 5.025
Coupler shunt
arms50 90 16.408 2.908
Coupler feed
lines50 90 16.408 2.908
Matching lines 62. 1337 90 16.72 1.954
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Figure 3.11 Simulation of 180 KOCH Reflective Type Phase Shifter
From Figure 3.12(a) it is observed that the simulated return loss is
less than -15dB in both ON and OFF conditions whereas the average insertion
loss is -1dB for ON condition and -1.4dB for OFF condition over
2.4-2.48GHz band.
2.2 2.3 2.4 2.5 2.6 2.7 2.8
-30
-20
-10
0
S-p
ara
met
er
(dB
)
Frequency (GHz)
S11
ON
S11
OFF
S21
ON
S21
OFF
Figure 3.12(a) Simulated return loss and insertion loss of 180 KOCH
phase shifter
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2 .2 2 .3 2.4 2.5 2 .6 2 .7 2.8
-180
-90
0
90
180
S21
(deg
)
Frequen cy (G H z)
S21
O N
S21
O FF
Figure 3.12(b) Simulated phase plot of 180 KOCH phase shifter
From the phase plot, shown in Figure 3.12 (b), it is observed that
over the desired band of 2.4 - 2.48GHz, the phase for ON and OFF condition
of the diodes is linear.
2.40 2 .41 2 .42 2 .43 2 .44 2 .45 2 .46 2 .47 2 .48 2 .49 2 .50
-180
-90
0
Ph
ase
Sh
ift
(deg
)
F requency (G H z)
Figure 3.12 (c) Simulated phase shift of 180 KOCH phase shifter
Also the phase shift gives ±2 variation for the bandwidth of
15MHz and rest of the band ±12 variations are seen from Figure 3.12 (c).
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3.5.5 Fabrication of 180 KOCH Reflective Type Phase Shifter
Figure 3.13 Fabricated prototype of 180 KOCH reflective type phase
shifters
To validate the simulation results a 180º reflective type phase
shifter is fabricated as shown in Figure 3.13.From the S-parameter plot shown
in Figure 3.14(a) and (b) it is observed that the return loss is less than -13dB
in both ON and OFF condition of the diodes whereas the average insertion
loss is -1.9dB for ON condition and -2.95dB for OFF condition over 2.4-
2.48GHz band.
2.2 2 .3 2.4 2.5 2 .6 2 .7 2 .8-30
-25
-20
-15
-10
-5
0
S-p
ara
met
ers
(dB
)
F requency (G H z)
S11
O N
S11
O F F
S21
O N
S21
O F F
Figure 3.14(a) Measured return loss and insertion loss of 180 KOCH
phase shifter
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2.2 2.3 2.4 2.5 2.6 2.7 2.8
-180
-90
0
90
180S
21
(deg
)
Frequency (GHz)
S21
O N
S21
O FF
Figure 3.14(b) Measured phase plot of 180 KOCH phase shifter
From the phase plot shown in Figure 3.14 (b), it is observed that,
over the desired band 2.4-2.48GHz, the phase for ON and OFF conditions is
linear.
2.40 2 .41 2.42 2.43 2.44 2.45 2 .46 2 .47 2.48 2.49 2.50
-180
-90
0
Ph
ase
sh
ift
(deg
)
Frequency (G H z)
Figure 3.14(c) Measured Phase Shift of 180 KOCH Phase Shifter
89
From Figure 3.14(c), it is observed that the phase shift has ±2
variation for the bandwidth of 12MHz and for rest of the band ±15 variation
is maintained.
Table 3.5 180 Measured results of KOCH reflective type phase shifter
at 2.45 GHz
Phase
S11 S21Phase
shift
( )
Phase
error
Area in
mm2Magnitude
In dB
Magnitude
In dB
Phase
in
degrees
180ON -13.92db -1.85db -57.578
-182.6 -2.6 3184.85OFF -26.703 -2.97db 125.02
3.5.6 Design and simulation of 2 Bit 270 KOCH Reflective Type
Phase Shifter
A 270 KOCH reflective type phase shifter is a cascaded
combination of 90 and 180 KOCH reflective type phase shifter. A 270
KOCH reflective type phase shifter is designed for the specification given in
section 3.5. The simulation of the 270 KOCH layout is done using ADS and
is shown in Figure 3.15.
Figure 3.16(a), (b) shows that the simulated return loss is less than -
13dB in all four phase bits whereas the average insertion loss is less than, -
2dB, -2.6dB, -2.8dB and -3.3dB for 11, 10, 01 and 00 phase bits respectively
over 2.4-2.48GHz band.
90
Figure 3.15 Simulation of 270 KOCH Reflective Type Phase Shifter
2.40 2.41 2.42 2.43 2.44 2.45 2.46 2.47 2.48 2.49 2.50-45
-40
-35
-30
-25
-20
-15
-10
-5
0
S-p
ara
met
er (
dB
)
Frequency (GHz)
S11
(00)
S11
(01)
S11
(10)
S11
(11)
S21
(00)
S21
(01)
S21
(10)
S21
(11)
Figure 3.16(a) Simulated return loss and insertion loss of 270 KOCH
phase shifter
91
2.40 2.41 2.42 2.43 2.44 2.45 2.46 2.47 2.48 2.49 2.50-270
-180
-90
0
90
180
270
S21
(deg
)
Frequency (GHz)
S21
(00)
S21
(01)
S21
(10)
S21
(11)
Figure 3.16(b) Simulated phase plot of 270 KOCH phase shifter
Figure 3.16(b) depicts the phase variation over the desired band
2.4-2.48GHz where the phase of all four phase bits remains linear.
2.40 2.41 2.42 2.43 2.44 2.45 2.46 2.47 2.48 2.49 2.50
-270
-180
-90
0
Ph
ase
sh
ift
(deg
)
Frequency (GHz)
S21
(01)
S21
(10)
S21
(11)
Figure 3.16(c) Simulated phase shift of 270 KOCH phase shifter
92
As shown in Figure 3.16 (c), the 90 phase bit has ±2 phase
variation over the bandwidth 27MHz and for rest of the band ±8 phase
variation is maintained. On the other hand, the 180 phase bit provides ±2
phase variation for the bandwidth of 12MHz and for rest of the band ±16
phase variation is observed. On the whole, the 270 phase shifter satisfies ±2
phase variation for 9MHz and for rest of the band ±20 phase variation is
maintained.
3.5.7 Fabrication of 2 Bit 270 KOCH Reflective Type Phase Shifter
Figure 3.17(a) shows the fabricated prototype of 2 bit 270 KOCH
reflective line phase shifter which is fabricated for validation of the design
procedure and simulated data.
Figure 3.17(a) Prototype of 270 KOCH phase shifter
93
2.40 2.41 2.42 2 .43 2.44 2.45 2.46 2.47 2.48 2.49 2.50-45
-40
-35
-30
-25
-20
-15
-10
-5
0
S-p
ara
met
er (
dB
)
F requency (G H z)
S11
(0 0)
S11
(0 1)
S11
(1 0)
S11
(1 1)
S21
(0 0)
S21
(0 1)
S21
(1 0)
S21
(1 1)
Figure 3.17(b) Measured return loss and insertion loss of 270 KOCH
phase shifter
The measured return loss is less than -10dB in all four phase bits
whereas the average insertion loss is less than- 3.2dB, -4.3dB, -5dB and -6.5dB
for 11, 10, 01 and 00 phase bits respectively over the desired 2.4-2.48GHz
band as seen from the S-parameter plots, which is shown in Figure 3.17(b).
2 .4 0 2 .4 1 2 .4 2 2 .4 3 2 .4 4 2 .4 5 2 .4 6 2 .4 7 2 .4 8 2 .4 9 2 .5 0
- 2 7 0
- 1 8 0
- 9 0
0
9 0
1 8 0
2 7 0
S21
(deg)
F r e q u e n c y ( G H z )
S2 1
(0 0 )
S2 1
(0 1 )
S2 1
(1 0 )
S2 1
(1 1 )
Figure 3.17(c) Measured phase plot of 270 KOCH phase shifter
From the Figure 3.17(c), it is noticed that over the desired band of
2.4-2.48GHz, the phase of all the four phase bits is linear.
94
2.40 2.41 2.42 2.43 2.44 2.45 2.46 2.47 2.48 2.49 2.50-360
-270
-180
-90
0
Ph
ase
sh
ift
(deg
)
Frequency (GHz)
S21
(01)
S21
(10)
S21
(11)
Figure 3.17 (d) Measured phase shift of 270 KOCH phase shifter
From the phase shift plot shown in Figure 3.17(d), it is noticed that
the 90 phase bit measures ±2 phase variation for the bandwidth of 11MHz
and for rest of the band ±10 phase variation is measured. The 180 phase bit
measures ±2 phase variation for the bandwidth of 9MHz and for rest of the
band ±20 phase variation is measured. But for the 270 phase bit satisfies ±2
phase variation for 6MHz bandwidth and for rest of the band ±30 phase
variation is noted.
Table 3.6 270 Measured results of KOCH reflective type phase shifter
at 2.45 GHz
Phase
S11 S21 Phase
shift
( )
Phase
error
Area in
mm2Magnitude
In dB
Magnitude
In dB
Phase in
degrees
-12.96 -6.34 62.91 - -
6845.137
90 -10.32 -5.28 -28.17 -91.08 -1.74
180 -19.41 -3.58 -110.65-
173.55-0.85
270 -13.98 -3.75 151.69-
271.22-0.56
95
3.6 RF PERFORMANCE OF KOCH REFLECTIVE TYPE
PHASE SHIFTERS
The simulated and measured phase shift responses of KOCH phase
shifter for various phase shifting namely 90 , 180 and 270 show good
agreement as shown in Figure 3.18(a)-3.20(a). As seen from figures, it can be
noted that there is reduction in the size of the KOCH based phase shifter as
compared to conventional reflection type phase shifter.
2.40 2.41 2.42 2.43 2.44 2.45 2.46 2.47 2.48 2.49 2.50-135
-90
-45
0
Ph
ase
sh
ift
(deg)
Frequency (G Hz)
S im ulation
M easurem ent
Figure 3.18(a) Comparison of simulated and measured phase shift
performances 90 KOCH type phase shifter
Figure 3.18(b) Comparison of the size of 90 conventional and KOCH
reflective type phase shifters
96
2.40 2.41 2.42 2.43 2.44 2.45 2.46 2.47 2.48 2.49 2.50
-180
-90
0
Ph
ase
sh
ift
(deg
)
Frequency (GHz)
Simulation
Measurement
Figure 3.19(a) Comparison of simulated and measured phase shift of
180 KOCH type phase shifter
Figure 3.19(b) Comparison of the size of 180 conventional and KOCH
reflective type phase shifters.
97
2.40 2.41 2.42 2.43 2.44 2.45 2.46 2.47 2.48 2.49 2.50
-360
-270
-180
-90
0
Ph
as
e s
hif
t (d
eg
)
Frequency (GHz)
Measurement
Simulation
Figure 3.20(a) Comparison of simulated and measured phase shift of
270 KOCH reflective type phase shifter
Figure 3.20(b) Comparison of the size of 270 conventional and KOCH
reflective type phase shifters.
98
3.7 CONCLUSION
In this chapter the issue of miniaturization of reflective type phase
shifter has been addressed using the concept of fractal geometry. To start with
a 90° KOCH fractal based reflective line phase shifter is designed and
developed. The simulation results at 2.45GHz show an insertion loss of -
1.3dB, return loss of -21.2dB and a phase error of -0.03°.The measured results
at 2.45GHz show an insertion loss of -2.36dB, return loss of -12.45 dB and a
phase error -1.34°.
Next a the 180° KOCH fractal based reflective type phase shifter
is designed and developed. The simulation results at 2.45GHz show an
insertion loss of -1.36 dB, return loss of -19.79dB and phase error of 0.2°. The
measured results show an insertion loss of -2.97 dB , return loss of -13.92dB
and a phase error of -2.6°.
Then a 270° KOCH fractal based reflective type phase shifter is
designed and developed. The simulation results at 2.45GHz show an
insertion loss of -2.03 dB, return loss of -24.79dB and phase error of -1.76°.
The measured results show an insertion loss of -3.28 dB , return loss of -
14.56dB and a phase error of -0.56°.
The deviation in insertion loss and phase error between simulation
and measurement may be due to loss tangent variation of dielectric material
used. The variation in return loss may be due to discontinuities arising out of
the manufacturing processes.
However the RF performance of the 90°,180° and 270° bits KOCH
reflective type phase shifters are found to be suitable for the WLAN
applications.
99
By applying Koch fractal technique, a size reduction of 32.6% is
achieved in 90° and 180° reflective type phase shifters whereas a size
reduction of 35% is obtained in 270° reflective type phase shifter. It is
observed that the size reduction (miniaturization)has been achieved without
sacrificing the RF performance KOCH fractal based reflective type phase
shifter.