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时间：2022-05-03

1THE UNIVERSITY OF QUEENSLAND

School of Information Technology

& Electrical Engineering

COMS4104/7104

Microwave Subsystems and Antennas

Practical 2

Hybrid Circuits:

Microstrip Phase Shifters with PIN Diodes

2 The PIN diode is a very popular choice to build series and

parallel switches.

The equivalent RF circuits for the ON and OFF states (when

the diode is forward or reverse biased) are shown below.

ON state OFF state

The values of the equivalent circuit parameters depend on

the choice of a particular diode, which can be in a chip or

packaged form. Also, they are governed by bias voltages.

Application of PIN diodes in Digital

Phase Shifters

3Exercise #1

Using ADS, study the performance (return and insertion losses)

of a PIN diode operating as a switch in both a series and a shunt

configuration with a 50 Ω microstrip transmission line over the

frequency band from 4.5 GHz to 5.5 GHz, using the following

values:

(a) Li = 0.5nH, Rf = 1Ω

Cj = 1pF, Rr = 5Ω

(b) Repeat your calculations using:

Li = 0.05nH, Rf = 0.5Ω

Cj = 0.1pF, Rr = 5Ω

Calculate insertion loss (IR) and return loss (RL) for both (a) and (b); the

equations of IR and RL are available in the lecture's notes (Module #4).

Hint: Using the same ADS schematic, use ports 1 & 2 to test the

operation of the diode in the ON state, and ports 3 & 4 to test the

operation of the diode in the OFF state, so that you can plot S11,

S21 and S33, S43 for the two states in the same figure.

4 A 3dB branch-line coupler can be used to build a reflection

digital phase shifter with a phase shift between 0 and 180

degrees. The concept is presented in the figure below:

As shown, the circuit uses a 3dB coupler, series switches

(S1 and S2) and sections of open-circuited transmission line

of electrical length . The switches make an O/C or S/C

to obtain the two states of the binary phase shifter.

Reflection Digital Phase Shifter

5Exercise #2

Using Linecalc and ADS, design a 3dB branch-line coupler

operating at 5 GHz using microstrip transmission lines on a

substrate with parameters of h = 1.27 mm and r = 10.2. The

reference impedance is Z0 = 50 Ω.

(Other Linecalc parameters: Mur = μr = 1, Hu = 3.9e+34 mil, T = 0, Cond =

5.8e7, TanD = tanδ = 0, Rough = 0, DielectricLossModel = 0, FreqForEpsrTanD

= 1e9, LowFreqForTanD = 1e3, HighFreqForTanD = 1e12)

Investigate its performance by plotting all its S-parameters over a

frequency range from 4.5 GHz to 5.5 GHz.

Using this branch-line coupler, design a reflection phase shifter

with a phase shift of 90º, assuming ideal performance for the

switches and the two sections of connected TLs.

(a) Plot the transmission coefficient S21 for the phase shifter for

the two states of the switches.

(b) Repeat (a) assuming that the switches use PIN diodes from

Exercise #1 (b).

Comment on the results obtained. How does the non-ideality of

the PIN diode affect the performance of the phase shifter?

Tune the parameters of connected TLs to reduce the effect of

the non-ideality of the PIN diode.

6 This design is useful for small amounts of phase shift of 45º or

less. The basic principle of operation of this phase shifter can be

understood by considering the circuit with a shunt susceptance

jB shown in Fig. (a) below.

Note that the susceptance B can be implemented using a short-

circuited stub whose input impedance is given by Zin = jZstan s,

where the characteristic impedance of the stub is Zs = zsZ0 ands is its electrical length.

The normalised value of B is b, given by b = BZ0.

Loaded-Line Phase Shifter

2

1

1 (1 )

1 (1 ) 2

2 21 2

2 2

tan ( / 2)

jb jb

jb jb

T jb

jb jb

b

7 The reflection from the shunt susceptance can be reduced by

introducing an equal shunt susceptance separated by a quarter

wavelength transmission line (Fig. (b)). The entire practical

realisation of the loaded phase shifter with PIN diodes and short-

circuited stubs is shown in Fig. (c).

For the circuit of Fig. (b):

For = 90°, and two susceptance states, B1 and B2:

For further details see: S. K. Koul and B. Bhat, Microwave and Millimeter Wave Phase Shifters,

pp. 463-473, Artech House.

Loaded-Line Phase Shifter

21 21

2 2

0 0 0

2

2(cos sin ) & 2(sin cos ) sin

S S

E jF

E BZ F Z B B Z

1 2 1 2 1 22 1

0 0 0

0 0 0

tan 2 & tan 2 tan 2

2 2 2

B BBY Y Y

Y Y Y

A narrowband, perfectly matched, loaded line phase shifter can be

designed by setting b2 = B2Z0 = 0 and by making b1 = B1Z0 equal to a

positive number. The latter can be achieved by using a short-circuited

λ/8 stub.

To make S11 = 0, the following condition for the electrical length has to

be fulfilled: tan = 2/b1.

The differential phase shift is: ∆= π– 2 tan-1(2/b1)

Hence, in terms of the desired phase shift:

b1= 2 tan [∆Φ/2], Z1=Z0/b1

θ= 0.5 (π+ ∆Φ)

Note that this value of θ will be close to 90º, but will not be exactly equal to

it, due to the loading effect of the shunt susceptances.

In state 1: B=B1, the diodes are forward biased.

In state 2: B=B2, the diodes are reverse biased.

8

Loaded-Line Phase Shifter

9Exercise #3

Using ADS and the equations shown on page 8, design a

Δ Φ= 22.5º loaded-line phase shifter using λ/8 short-circuited stubs, that is

perfectly matched at its two ports at a frequency of 5 GHz. The main line is

to be implemented using a Z0 = 50 Ω microstrip transmission line on a

substrate with parameters of h = 1.27 mm and εr = 10.2.

(Other Linecalc parameters: Mur = μr = 1, Hu = 3.9e+34 mil, T = 0, Cond = 5.8e7,

TanD = tanδ = 0, Rough = 0, DielectricLossModel = 0, FreqForEpsrTanD = 1e9,

LowFreqForTanD = 1e3, HighFreqForTanD = 1e12)

Investigate its performance by plotting all its S-parameters over a

frequency range from 4.5 GHz to 5.5 GHz in the two states.

(a) Plot the transmission coefficient S21 for the phase shifter for

the two states of the switches.

(b) Repeat (a) assuming that the switches use PIN diodes from

Exercise #1 (b).

Comment on the results obtained. How does the non-ideality of

the PIN diode affect the performance of the phase shifter?

10

Submission Instructions

1. The lab report must be typewritten.

2. Include your name and student number on the report.

3. There is a 10-page limit for the report.

4. Include ADS schematics and S-parameter plots, sample

calculations and final numerical results.

5. Include discussion and conclusion sections.

School of Information Technology

& Electrical Engineering

COMS4104/7104

Microwave Subsystems and Antennas

Practical 2

Hybrid Circuits:

Microstrip Phase Shifters with PIN Diodes

2 The PIN diode is a very popular choice to build series and

parallel switches.

The equivalent RF circuits for the ON and OFF states (when

the diode is forward or reverse biased) are shown below.

ON state OFF state

The values of the equivalent circuit parameters depend on

the choice of a particular diode, which can be in a chip or

packaged form. Also, they are governed by bias voltages.

Application of PIN diodes in Digital

Phase Shifters

3Exercise #1

Using ADS, study the performance (return and insertion losses)

of a PIN diode operating as a switch in both a series and a shunt

configuration with a 50 Ω microstrip transmission line over the

frequency band from 4.5 GHz to 5.5 GHz, using the following

values:

(a) Li = 0.5nH, Rf = 1Ω

Cj = 1pF, Rr = 5Ω

(b) Repeat your calculations using:

Li = 0.05nH, Rf = 0.5Ω

Cj = 0.1pF, Rr = 5Ω

Calculate insertion loss (IR) and return loss (RL) for both (a) and (b); the

equations of IR and RL are available in the lecture's notes (Module #4).

Hint: Using the same ADS schematic, use ports 1 & 2 to test the

operation of the diode in the ON state, and ports 3 & 4 to test the

operation of the diode in the OFF state, so that you can plot S11,

S21 and S33, S43 for the two states in the same figure.

4 A 3dB branch-line coupler can be used to build a reflection

digital phase shifter with a phase shift between 0 and 180

degrees. The concept is presented in the figure below:

As shown, the circuit uses a 3dB coupler, series switches

(S1 and S2) and sections of open-circuited transmission line

of electrical length . The switches make an O/C or S/C

to obtain the two states of the binary phase shifter.

Reflection Digital Phase Shifter

5Exercise #2

Using Linecalc and ADS, design a 3dB branch-line coupler

operating at 5 GHz using microstrip transmission lines on a

substrate with parameters of h = 1.27 mm and r = 10.2. The

reference impedance is Z0 = 50 Ω.

(Other Linecalc parameters: Mur = μr = 1, Hu = 3.9e+34 mil, T = 0, Cond =

5.8e7, TanD = tanδ = 0, Rough = 0, DielectricLossModel = 0, FreqForEpsrTanD

= 1e9, LowFreqForTanD = 1e3, HighFreqForTanD = 1e12)

Investigate its performance by plotting all its S-parameters over a

frequency range from 4.5 GHz to 5.5 GHz.

Using this branch-line coupler, design a reflection phase shifter

with a phase shift of 90º, assuming ideal performance for the

switches and the two sections of connected TLs.

(a) Plot the transmission coefficient S21 for the phase shifter for

the two states of the switches.

(b) Repeat (a) assuming that the switches use PIN diodes from

Exercise #1 (b).

Comment on the results obtained. How does the non-ideality of

the PIN diode affect the performance of the phase shifter?

Tune the parameters of connected TLs to reduce the effect of

the non-ideality of the PIN diode.

6 This design is useful for small amounts of phase shift of 45º or

less. The basic principle of operation of this phase shifter can be

understood by considering the circuit with a shunt susceptance

jB shown in Fig. (a) below.

Note that the susceptance B can be implemented using a short-

circuited stub whose input impedance is given by Zin = jZstan s,

where the characteristic impedance of the stub is Zs = zsZ0 ands is its electrical length.

The normalised value of B is b, given by b = BZ0.

Loaded-Line Phase Shifter

2

1

1 (1 )

1 (1 ) 2

2 21 2

2 2

tan ( / 2)

jb jb

jb jb

T jb

jb jb

b

7 The reflection from the shunt susceptance can be reduced by

introducing an equal shunt susceptance separated by a quarter

wavelength transmission line (Fig. (b)). The entire practical

realisation of the loaded phase shifter with PIN diodes and short-

circuited stubs is shown in Fig. (c).

For the circuit of Fig. (b):

For = 90°, and two susceptance states, B1 and B2:

For further details see: S. K. Koul and B. Bhat, Microwave and Millimeter Wave Phase Shifters,

pp. 463-473, Artech House.

Loaded-Line Phase Shifter

21 21

2 2

0 0 0

2

2(cos sin ) & 2(sin cos ) sin

S S

E jF

E BZ F Z B B Z

1 2 1 2 1 22 1

0 0 0

0 0 0

tan 2 & tan 2 tan 2

2 2 2

B BBY Y Y

Y Y Y

A narrowband, perfectly matched, loaded line phase shifter can be

designed by setting b2 = B2Z0 = 0 and by making b1 = B1Z0 equal to a

positive number. The latter can be achieved by using a short-circuited

λ/8 stub.

To make S11 = 0, the following condition for the electrical length has to

be fulfilled: tan = 2/b1.

The differential phase shift is: ∆= π– 2 tan-1(2/b1)

Hence, in terms of the desired phase shift:

b1= 2 tan [∆Φ/2], Z1=Z0/b1

θ= 0.5 (π+ ∆Φ)

Note that this value of θ will be close to 90º, but will not be exactly equal to

it, due to the loading effect of the shunt susceptances.

In state 1: B=B1, the diodes are forward biased.

In state 2: B=B2, the diodes are reverse biased.

8

Loaded-Line Phase Shifter

9Exercise #3

Using ADS and the equations shown on page 8, design a

Δ Φ= 22.5º loaded-line phase shifter using λ/8 short-circuited stubs, that is

perfectly matched at its two ports at a frequency of 5 GHz. The main line is

to be implemented using a Z0 = 50 Ω microstrip transmission line on a

substrate with parameters of h = 1.27 mm and εr = 10.2.

(Other Linecalc parameters: Mur = μr = 1, Hu = 3.9e+34 mil, T = 0, Cond = 5.8e7,

TanD = tanδ = 0, Rough = 0, DielectricLossModel = 0, FreqForEpsrTanD = 1e9,

LowFreqForTanD = 1e3, HighFreqForTanD = 1e12)

Investigate its performance by plotting all its S-parameters over a

frequency range from 4.5 GHz to 5.5 GHz in the two states.

(a) Plot the transmission coefficient S21 for the phase shifter for

the two states of the switches.

(b) Repeat (a) assuming that the switches use PIN diodes from

Exercise #1 (b).

Comment on the results obtained. How does the non-ideality of

the PIN diode affect the performance of the phase shifter?

10

Submission Instructions

1. The lab report must be typewritten.

2. Include your name and student number on the report.

3. There is a 10-page limit for the report.

4. Include ADS schematics and S-parameter plots, sample

calculations and final numerical results.

5. Include discussion and conclusion sections.