5 GHz Voltage Controlled Oscillations for Frequency Agile RADAR

International Journal of Engineering and Advanced Technology (IJEAT)
ISSN: 2249 – 8958, Volume-4, Issue-1, October 2014
5 GHz Voltage Controlled Oscillations for
Frequency Agile RADAR, with Initial Frequency
Tuning Capacitor
Zar Khitab, Farooq Ahmed Bhatti
This is demonstrated in fig. 1. The parameters of concern are
post tuning drift in frequency, settling time and frequency
overshoot. These parameters changes and these changes
depend on switching period of VCO. Very high Quality
factor Q impedance matching networks are characteristics for
negative resistance design [4]. [7] Compares several recently
developed oscillators. This Paper presents voltage controlled
oscillator at 5GHz, 300 MHz bandwidth, and up to 50 kHz
wide pulse repetition frequency, for pulse to pulse frequency
agile radar. Negative-resistance method with initial
frequency tuning capacitor is used in design. This Oscillator
is proposed for pulse to pulse frequency agile radar at 5GHz
frequency, 300 MHz bandwidth, and up to 50 kHz wide pulse
repetition frequency. Wide band frequency diversity
waveforms are required on radar transmitter to achieve
adequate sensitivity at receiving side [5]. The receive
sensitivity is directly proportional to receiver BW
(bandwidth). Receive sensitivity is also inversely related to
the product of PW (pulse width) and peak power.
Abstract—This Paper presents voltage controlled oscillator
at 5GHz, 300 MHz bandwidth, and up to 50 kHz wide pulse
repetition frequency, for pulse to pulse frequency agile
radar. Negative-resistance method with initial frequency
tuning capacitor is used in design. The frequency tuning is
based on resonant capacitance for varying controlled
voltage. The oscillator peak out power is 7.7 dBm,
minimum output power in 300 MHz range is 6.997 dBm.
First harmonic have power -7.793 dBm. Peak voltage
deviation of 12249mV occurs for 34.025 MHz band. The
proposed oscillator satisfies standard requirements to
generate oscillation frequency for wide band radar systems.
Suppressed harmonics and lesser variation in output power
throughout 300MHz chip enhances the receive sensitivity
of RADAR.
Index Terms—, frequency agile radar, Harmonics, output power
variation, Voltage Controlled Oscillator.
I. INTRODUCTION
Voltage controlled oscillator (VCO) plays an important role
in communication systems, phase locked loops and
especially in radars. The demand of high data rate, more
channels in a unit bandwidth higher oscillator frequency
lower power requirement and phase immunity makes
oscillator design critical. Systems overall performance is
limited by controlling parameters of VCO. Good VCO design
is trade-offs among the several design parameters like power
consumption, phase noise, and size on chip [7]. Good
oscillator design heavily depends on LC components used in
circuit for radiofrequency based systems [2]. The effect of
these matching circuit components are investigated in a [3]
and references therein. Parameters in design process of
oscillators are frequency, power, phase noise, DC current
requirement, residual FM, tuning sensitivity, harmonic
powers and frequency push pulls [1]. VCO output frequency
in respect to tuning voltage can further derivate tuning
sensitivity as initial point to decide for the quality design.
This can also be affected by power supply (also called as
frequency pushing). Output RF signal power also depends on
frequency and power supply power [1] [7] [8]. Post tuning
drift calculations shows how much time the VCO will take to
stabilize on frequency f2 after initial frequency f1 by changing
voltage.
Fig. 1. Post Frequency Tuning Drift of VCO [1]
The oscillator achieves temperature and supply voltage
independent tunable at 5GHz. The proposed oscillator
satisfies standard requirements to generate oscillation
frequency. The initial frequency tuning is achieved by
resonant capacitor. Capacitor mismatch effects are not
discussed here and the reader may find them in [3]. With
capacitor mismatch [3], the amplitude of oscillation
frequency decreases. [3] Also quotes the decrease in locking
frequency with increase in percent capacitor mismatch [6].
Manuscript Received on October 2014.
Zar Khitab, Electrical Engg., Military College of Signals, NUST,
Rawalpindi, Pakistan.
Farooq Ahmed Bhatti, Electrical Engg, Military College of Signals,
NUST, Rawalpindi, Pakistan.
19
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5 GHz Voltage Controlled Oscillations for Frequency Agile RADAR, with Initial Frequency Tuning Capacitor
II. VCO CIRCUIT
A. Equations
Most Microwave Oscillators are negative resistance. From
[4] port impedance must have negative real part and positive
feedback should give reflection co-efficient Ƭa> 1, for the
active device. For stable oscillations S11 < 0, for resonating
port of circuit Fig.3 (a) below shows that S11 magnitude is less
than 1, which makes Ƭres< 1 and equation (2) satisfied.
Further
Ƭa Ƭres = 1
Ra + Rres = 0
(2)
Xa + Xres = 0
t
min(ICC_dc )
mean(ICC_dc )
-10.37 m
max(ICC_dc )
-10.34 m
-10.07 m
Table. 1 Collector Current
For oscillation to be get started [4].
Ƭa Ƭres > 1
Ra + Rres < 0
Xa + Xres = 0
(3)
Fig. 2 (a) Block Diagram of Neg-Resistance VCO
The resonant circuit inductance is adjusted to constant value
as per equation.
Vout
R
L=1/(ωo2C)
(4)
Considering the damping factor in Fig. 1.,ωo is adjusted as[1].
ωo = HarmonicBalance
HB1
Freq[1]=5 GHz
Order[1]=5
StatusLevel=3
OscMode=yes
OscPortName="OscTickler"
IgnoreOscErrors=
SweepVar="Vtune"
Start=1
Stop=10
Step=0.25
(5)
Where
= √1 −ζ
(6)
ζisdampingfactorasshowninFig. 1. [1]
ζ = |
#$ %
|
& ' ()' %
(7)
Var
Eqn
And
*=
+,-. +,/$
+,-.
R3
R=50
C Ohm
C2
C=1000 pF
HARMONIC BALANCE
(8)
VAR
VAR1
Rbias = 50
Vtune = 10
MTEE_ADS
Tee2
Subst="MSub1"
W1=25.0 mil
W2=25.0 mil
W3=25.0 mil
MSub
MSUB
MSub1
H=10.0 mil
Er=9.6
Mur=1
Cond=1.0E+50
Hu=3.9e+034 mil
T=0 mil
TanD=0
Rough=0 mil
R
R4
R=Rbias
L
R2
L=100 nH
R=681-Rbias
MLIN
TL4
Subst="MSub1"
W=25.0
mil
pb_hp_AT41411_19921101
Q2
L=9.68
mm
V_DC
SRC3
Vdc=10 V
Vres
The Quality factor Q is
Q=0 *freq*(delay (2,1))
C
OscPortC1
C=1 pF
OscTickler
V=
Z=1.1 Ohm
NumOctaves=2
Steps=10
FundIndex=1
MaxLoopGainStep=
(9)
Using graph in Fig.3 (b)
L
L1
L=100 pH
R=
The settling time for VCO at given frequency can indicate
for short and long term tuning drift. The time domain analysis
model for settling time is presented in [4].
MTEE_ADS
Tee3
Subst="MSub1"
W1=25.0 mil
W2=25.0 mil
W3=25.0 mil
L
R1
L=0.4 nH
R=422
V_DC
SRC1
Vdc=Vtune
B. Circuit Diagram
The frequency tune based on initial resonant capacitance with
varactor diode’s biasing VCO is shown in Fig. 2. The
Oscillator is designed for pulse to pulse frequency agile radar
at 5GHz frequency. Specifications for substrate and other
components as expressed in Fig.2 are based on equations
presented in section II-A. The matching networks are
designed using smith chart tool available in ADS. Collector
current rating is given in table 1. The difference in maximum
collector current and minimum collector current is only
0.3mA.
MLIN
TL2
Subst="MSub1"
W=25.0 mil
L=9.68 mm
ap_dio_MV1404_19930601
D1
V_DC
SRC2
Vdc=-5 V
L
L2
L=10 pH
R=
Fig. 2 (b) Proposed VCO Schematics with Description
III. SIMULATIONS
Simulations for varactor diode’s bias voltage and VCO
tuning characteristic are performed. Simulation results of
resonance network for the oscillator in terms of S11 are shown
in Fig.3. Since real S11 is less than 1, making Ƭres<1. It is
obvious that real S11 is not equal to zero in 300MHz band. To
calculate Q factor Fig.4 is used. Using equation (9) and Fig.4.
Quality factor for the circuit.
Q =3.1416 * 5*109*8.200*10-10 = 13.2
20
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1.0
20
0.5
0
dBm(Vout)
real(S(1,1))
International Journal of Engineering and Advanced Technology (IJEAT)
ISSN: 2249 – 8958, Volume-4, Issue-1, October 2014
0.0
-20
-40
-0.5
-60
-1.0
1
2
3
4
5
6
7
8
9
0
10
5
10
freq, GHz
15
20
25
30
freq, GHz
Fig. 3 S11 Magnitude Against Resonance Frequency
Fig. 5 (b) VCO Output Power vs Harmonics
Different parts of target scatter different amount of power
from incoming wave. Uniform power throughout radar’s
transmitted band can make detection more accurate.
m1
freq= 5.000GHz
delay(2,1)=8.200E-10
1.0E-9
m1
delay(2,1)
8.0E-10
m1
m2
indep(m1)= 4.849
indep(m2)= 5.150
PowerFlatness =7.127 PowerFlatness =6.997
6.0E-10
m3
indep(m3)= 4.998
PowerFlatness =7.700
4.0E-10
7.8
m3
2.0E-10
7.6
1
2
3
4
5
6
7
8
9
Pout, dB m
0.0
10
freq, GHz
7.4
m1
7.2
m2
7.0
Fig. 4 Delay (2,1) vs Frequency
6.8
4.80
Results for output power at the fundamental frequency, two
harmonics, harmonics power and their frequency and power
flatness against fundamental frequency are shown in Fig.5
(a), Fig.5 (b) and Fig 5. (c) respectively. This figure indicates
that harmonics are very weak. First harmonic have 15.6 dB
lesser power then fundamental frequency. While second
harmonic have 23 dB lesser power in comparison to
fundamental frequency.
4.90
4.95
5.00
5.05
5.10
5.15
Freq, GHz
Fig. 5 (c) Power Flatness vs Frequency of Oscillation
Further tuning characteristic of VCO, tuning linearity
deviation, and KVCO (MHz/V) are investigated in Fig. 6 (a)
and Fig. 6 (b). Fig. 7. Show the time domain analysis for the
device. The graph show the response time for the device as
frequency is swept across 300MHz. This also shows the time
the device will take to settle on frequencies it generates.
m1
m2
m3
indep(m1)=4.998 indep(m2)=4.998 indep(m3)=4.998
VOUT_fund =7.700 VOUT_2nd =-7.973 VOUT_3rd =-15.388
m1
10
0
m2
-10
m3
5.2
-20
-30
4.80
4.85
4.90
4.95
5.00
5.05
5.10
O u tp u t F re q , G H z
Power, dBm
4.85
5.15
Freq, GHz
Fig. 5 (a) VCO Output Power & Harmonics vs. Tuning
Voltage
Fig. 5 (c) shows that the variation in power when
fundamental frequency is swept across 300 MHz bandwidth.
At frequency 4.85GHz the output power is 7.12 dBm, at 5.15
GHz the output power is 6.997 dBm, while at centre
frequency (5 GHz) the output power is 7.7 dBm. This shows
flat and smooth response of oscillator for power. This is
important in radar applications because radar sensitivity and
target cross section depends on back wave’s received power.
5.1
5.0
4.9
4.8
1
2
3
4
5
6
7
8
9
Tuning Voltage, volts
Fig. 6 (a) VCO Tuning Characteristic
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5 GHz Voltage Controlled Oscillations for Frequency Agile RADAR, with Initial Frequency Tuning Capacitor
KVCO_MHz
[5] Bharadwaj, kumar vijay mishra and v. chandrasekar,
“waveform considerations for dual-polarization doppler
weather radar with solid-state transmitters”, 2009 IEEE.
Peak_dev
34.025
1224.905
[6]
deviation_MHz
1500
1000
[7]
500
0
-500
1
2
3
4
5
6
7
8
9
[8]
10
Vtune
S.Y Lee, S. Amakawa, N. Ishihara, K. Masu, “Low-Phase-Noise
Wide-Frequency-Range Differential Ring-VCO with Non-Integral
Subharmonic Locking in 0.18 µm CMOS.” Proceedings of the 40th
European Microwave Conference. 2010 EuMA.
M. R. Basar, F. Malek, Khairudi M. Juni, M. I. M. Saleh, M. Shaharom
Idris. “A Low Power 2.4-GHz Current Reuse VCO for Low Power
Miniaturized Transceiver System.” 2012 IEEE International
Conference on Electronics Design, Systems and Applications
(ICEDSA)
S. L. Jang, S. S. Lin, C. W. Chang, and S. H. Hsu, “Quadrature VCO
Formed with Two Colpitts VCO Coupled via an LC-Ring Resonator,”
Progress In Electromagnetics Research C, vol. 24, pp. 185-196, 2011.
Fig. 6 (b) Deviation from Linear Tuning, MHz
VOUTwaveform , V
1.0
Vtune=9.500
Vtune=9.250
Vtune=9.750
Vtune=10.000
Vtune=9.000
Vtune=8.750
Vtune=8.500
Vtune=6.000
Vtune=5.750
Vtune=5.500
Vtune=5.250
Vtune=6.250
Vtune=5.000
Vtune=4.750
Vtune=6.500
Vtune=4.500
Vtune=4.250
Vtune=4.000
Vtune=8.250
Vtune=6.750
Vtune=3.750
Vtune=3.500
Vtune=3.250
Vtune=3.000
Vtune=2.750
Vtune=2.500
Vtune=2.250
Vtune=2.000
Vtune=1.750
Vtune=1.500
Vtune=8.000
Vtune=7.000
Vtune=1.250
Vtune=1.000
Vtune=7.750
Vtune=7.250
Vtune=7.500
0.5
0.0
-0.5
-1.0
0
50
100 150 200 250 300 350 400 450
time, psec
Fig. 7 Time Domain Analysis of Output Signal
IV. RESULTS
The oscillator shows good flat output power response
throughout 300MHz bandwidth. The oscillator peak out
power is 7.7 dBm, minimum output power in 300 MHz range
is 6.997 dBm. First harmonic have power -7.793 dBm. While
second harmonic power is -15.388 dBm. Such low value of
harmonics power can easily be ignored in wireless
communication environment. Highest tuning deviation of
12249mV occurs for 34.025 MHz band.
V. CONCLUSION
This paper investigates oscillation frequency and tuning
range VCO at 5GHz. The device design agrees with standard
specification and provides large band width for transmitted
signal. Uniform power throughout 300MHz transmitted band
makes the device suitable for wide band radars. The settling
provides enough time for the system to generate pulses with
pulse repetition frequency up to 50 KHz. The device tuning
voltage is almost independent of supply power. The
difference in maximum collector current and minimum
collector current is only 0.3mA.
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[1]
[2]
[3]
[4]
Branislav LOJKO, Peter FUCH., “A Contribution to the VCO
modeling and simulation.” 2009 IEEE.
Craninckx, J. and Steyaert, M., “Low-noise voltage controlled
oscillators using enhanced LC-tanks,” IEEE Transactions on Circuits
and Systems II: Analog and Digital Signal Processing. vol.42, no.12,
pp.794-804. 1995
Antonio Buonomo, Alessandro Lo Schiavo. “The Effect of Parameter
Mismatches in RF VCO.” 2008 IEEE.
Wang Xiantaiy, Shen Huajun, Jin Zhi, Chen Yanhu, and Liu Xinyu, “A
6 GHz high power and low phase noise VCO using an InGaP/GaAs
HBT,” Vol.30, No.2 Journal of Semiconductors, 2008 IEEE.
22
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