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

69

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

70

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.

71

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

72

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.

73

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.

74

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.

75

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

76

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

77

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

78

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

79

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

80

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

81

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.

82

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

83

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

84

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

85

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

86

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).

87

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

88

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.