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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 ands 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.


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