Download Design AND development of voltage controlled RF variable

DESIGN AND DEVELOPMENT OF VOLTAGE CONTROLLED RF
VARIABLE PHASE SHIFTERS BY REFLECTION TYPE TECHNIQUE
Subhasish Basak1, Ananjan Basu2, S.K. Koul2
1
VECC, 1/AF Bidhannagar, Kolkata-700064
2
IIT Delhi, New Delhi -110016
Abstract
This paper presents the design and development of
compact voltage controlled RF analog variable phase
shifter at a design frequency of 1.3GHz (and 10%
bandwidth) using reflection type technique with proper
varactor diode based reflective circuit placed at through
and coupled ports of a 3dB hybrid. The principle of
operation is that the input RF signal at input port of
hybrid is split into two components at the through and
coupled ports which then undergoes a reflection with a
phase shift depending upon control (bias) voltage and
finally combines at the isolated port to give the proper
phase shifted RF output signal. The complete circuit was
modeled, simulated and optimized in ADS / Momentum
and finally fabricated on microstrip. The design
methodology, simulated and measured
results are
presented. We obtained greater than (full) 0-360˚ phase
shift range using this technique with average insertion
loss of about 5 dB and return loss ≤ 17 dB for a voltage
range of 0-12V. The phase shifter is a vital control
device used in phase feedback control of the RF cavity
voltage in particle accelerators.
REFLECTION TYPE PHASE SHIFTER
The reflection-type phase shifter (RTPS) using
hybrid and varactor diode based reflection circuits/
loads has become popular choice for design of analog
phase shifters because of its the excellent input and
output matches and simpler construction. The hyperabrupt
varactor diodes are specially suited for realising the
reflective circuits since the hyperabrupt active layer of
the varactor diode can be controlled to achieve a
capacitance versus voltage characteristic that offers the
potential of large phase shifts with
voltage. The
hyperabrupt varactor diode used in this phase shifter is
the Skyworks make SMV1232. The basic design
schematic of RTPS is shown in Fig.1
INTRODUCTION
A variable phase shifter is a RF two port device with
a control voltage input in which the phase of the RF
output signal is changed in a controlled manner by
varying the control voltage. Phase shifters are required
for numerous applications, such as in radar, wireless
communication receivers, adaptive antenna combining,
measurement, and feed-forward systems and so on. These
are also vital devices in the phase feedback control of the
RF cavity in particle accelerators so as to regulate phase
of the RF voltage at a given fixed value for proper beam
acceleration and also to control/maintain the cavity to
cavity phase relations in a chain of RF cavities. Phase
shifters can be of analog type or digital type or a
combination of both. Analog phase shifter permit
continuous variation of phase shift whereas digital phase
shifters allow phase shift only in discrete steps . A digital
phase shifter consists of a cascade of several phase bits
with phase shift incremented in binary steps. The analog
phase shifters has
the
advantages of providing
continuous i.e., infinite resolution and having compact
sizes compared to digital ones. The two main types of
analog phase shifter are the vector modulator based phase
shifters and the reflection type phase shifters.
[email protected]
Figure 1: RTPS design schematic.
This work present the design and development of
complete 0-360° variable reflection type phase shifter at
a design frequency of 1.3 GHz realized using 3-dB hybrid
and varactor diode based reflective circuits on microstrip.
The design principle can easily be adapted to other design
frequencies. For obtaining substantially increased phase
shift range the reflective load was chosen to comprise
of series resonated varactor diode and shunted with
proper resistor for minimizing insertion loss variations
and placed at both ends of a quarter wavelength
transformer. The RF input signal at input port of hybrid
is split into two components at the through and coupled
ports which then undergoes a reflection from the
reflective circuit/load with a phase shift depending upon
control (bias) voltage and finally combines at the isolated
port to give the proper phase shifted RF output signal.
SIMULATION
The phase shifter was designed and simulated using
the Advanced Design System (ADS) software. The 3dB
hybrid was designed for the on microstrip using standard
method and simulated in ADS at the design frequency.
The varactor diode and the the other components was
accurately modelled using the given manufacturer
equivalent model/ parameters and then the entire circuit
was simulated in ADS software for a microstrip
realisation. The inductance and the resistance were
optimised using the ADS software. A DC blocking
capacitor is used between the hybrid and the reflective
circuits. The simulation results in Fig.2 shows phase
shift versus a voltage range of 0-10 V which shows that
greater than 0-360˚ phase shift
can be obtained.
200
Figure 4: Fabricated phase shifter.
phase(S(2,1))
100
0
600
550
-100
500
450
0
2
4
6
8
Phase Shift (deg)
-200
10
SP.x
400
350
300
250
200
Figure 2 : Phase shift versus voltage.
150
100
The simulation results showing the Insertion loss
versus voltage and Return loss versus voltage is shown
in Fig. 3.
50
0
0
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Voltage (V)
Figure 5: Measured phase shift versus voltage.
-2
dB(S(1,1))
dB(S(2,1))
-3
-4
-5
-6
-7
-8
-9
-10
0
1
2
3
4
5
SP.x
6
7
8
9
10
2
0
-2
-4
-6
-8
-10
-12
-14
-16
-18
-20
-22
-24
-26
-28
-30
-32
-34
0
-1
-2
-3
S21 (dB)
0
-1
-4
-5
-6
0
1
2
3
4
5
6
7
8
9
10
-7
SP.x
-8
-9
-10
0
Figure 3 : (a) Insertion loss versus voltage and
(b) Return loss versus voltage
FABRICATION & MEASUREMENTS
The phase shifter layout was developed using the
ADS software and it was then fabricated by the MIC
technology using photolithographic fabrication process on
soft substrate of dielectric constant = 3.2 and thickness
= 30 mil. The photograph of the fabricated phase shifter
is shown in Fig. 4. The measured phase shift versus
voltage and the measured insertion loss versus voltage
are shown in Fig.5 and Fig.6 respectively.
1
2
3
4
5
6
7
8
9
10
11
12
13
14
Voltage (V)
Figure 6: Measured insertion loss versus voltage.
The measured results shows that we obtained greater
than 0-360° variable phase shift for a voltage span of 012 V with average insertion loss of about 5dB and return
loss better than 17dB. The measured results are in good
agreement with the simulation results and thus the phase
shifter has been successfully demonstrated.
REFERENCES
Shiban Koul and Bharathi Bhat , “Microwave
and Millimeter Wave Phase Shifters” Vol 2 ISBN 089006-585-3, Norwood: Artech House, June 2000.
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