Proceedings of the 2007 IEEE International Conference on Telecommunications and
Malaysia International Conference on Communications, 14-17 May 2007, Penang, Malaysia
Simulation of Active Integrated Antenna with
Image Reject Mixer
M.K.A. Rahim, W.K. Chong, T. Masri
Wireless Communication Center (WCC),
Faculty of Electrical Engineering,
Universiti Teknologi Malaysia
Email: [email protected] [email protected] , [email protected]
Abstract - Active integrated antenna with image reject mixer
(AIA with IRM) operating at licenseless frequency of 2.4 GHz
and intermediate frequency (IF) of 50 MHz is proposed. In this
work, IRM is integrated with microstrip patch antenna on the
similar substrate to attain size, weight and cost reduction. The
suitable substrate that serves as the common platform for all
integral components is FR-4 with dielectric constant of 4.7 and
thickness of 1.6mm. This AIA with IRM employs a different
phase manipulation approach from the of the previous research
in which the RF signal from the antenna is initially fed to 1800 rat
race coupler instead of a 900 coupler. Practically, this system is
able to achieve image suppression with an isolation of
approximately 20 dB between image and desired frequency with
7 dBm LO drive at 2.35 GHz. The integral components of AIA
with IRM consist of 2-elements microstrip rectangular patch
antenna, singly balanced schottky diode mixers, low pass filter,
branch-line 900 hybrid coupler, lumped element 900 coupler and
1800 rat race coupler
IF and LO frequency chosen for this work is 50 MHz and 2.35
GHz.
In heterodyne receiver, it is not practical to filter out
the image because the IF frequency is low, and the image is
therefore too close to RF and LO frequencies. To filter out the
image signal high-Q image-reject filter has to be used between
low noise amplifier (LNA) and mixer. The shortcomings of
utilizing external image-reject filter are increased cost,
increased board area, reduced reliability and increased weight
[3]. Besides, double conversion is employed in most of
the superheterodyne receiver for better image suppression at
the expense of increased circuit complexity and cost As such,
one cost effective and practical way of rejecting image signal
is to use IRM which remove the need of external image-reject
filter and one or more stages of up/down conversion [4].
In this work, by integrating IRM with antenna, size reduction
is achieved by two means; the removal of space consuming
external image-reject filter and incorporation of IRM directly
into active integrated antenna. Meanwhile, cost reduction is
achieved by removing the need of using external image-reject
Keyword : active integrated antenna, image reject mixer,
microstrip antenna, down conversion
filter.
I. INTRODUCTION
The terminology “Active Integrated Antenna” indicates
specifically that the passive antenna elements and the active
circuitry are integrated on the same substrate. Due to the
mature technology of microwave integrated circuit (MIC) and
monolithic microwave integrated circuit (MMIC), the active
integrated antenna (AIA) became an area of growing interest
in recent years [1]. Incorporation of active devices
functions directly into active integrated antenna reduces the
size, weight, and cost of many microwave systems [2].
In this work, Image Reject Mixer (IRM) is integrated with
microstrip patch antenna for the purpose of translating radio
frequency (RF) to Intermediate Frequency (IF) and provide
isolation to two possible IF namely Upper Sideband (USB)
and Lower Sideband (LSB) in which USB and LSB is the
desired frequency and image frequency respectively. The
1-4244-1094-0/07/$25.00 ©2007 IEEE.
II. IMAGE REJECT MIXER (IRM) AND ACTIVE
INTEGRATED ANTENNA (AIA) WITH IRM.
The conventional IRM architecture is made of two quadrature
couplers at the RF and IF frequencies, an in phase power
divider and two isolated mixing devices. Normally, in basic
IRM, antenna and IRM are two different entities connected via
external transmission line and connectors. Conventional IRM
architecture is illustrated in Fig. 1.
In this project which is AIA with IRM (eg. Fig. 2), patch
antenna is integrated directly into the IRM structure which
brings upon size reduction and losses by the elimination of
external transmission lines and connectors which is otherwise
needed in the conventional IRM. Besides, AIA with IRM
exploits a different phase manipulation approach than that of
the conventional IRM. RF signal is initially fed into an 1800
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rat race coupler in AIA with IRM instead of a 900 coupler as
in the conventional IRM. And, the LO signal of this system is
directed into a 900 coupler to equally divide the LO signal into
two with a phase shift of 900 whereas in the conventional
IRM, the LO signal is fed into a Wilkinson power divider to
equally divide the signal into two with a phase shift of 00.
= 0.5cos(fLO-fRF-900)
cos(fIM+1800).cos(fLO + 900)
= 0.5cos(fIM-fLO+900)
(6)
Resulting signals from Mixer A and Mixer B which are (3),
(4), (5) and (6) are recombined through 900 IF hybrid coupler
giving the following outputs
IF1 = 0.5 cos (fLO-fRF)+0.5 cos (fIMfLO)+
0.5 cos (fLO-fRF-900+900) + 0.5 cos (fIM- fLO+900+900)
IF1 = cos (fLO-fRF)
(7)
IF2 = 0.5 cos (fLO-fRF-900) + 0.5cos (fIM-fLO+90) + 0.5
cos (fLO - fRF + 900) +0.5 cos (fIM - fLO + 900)
IF2 = cos(fIM–fLO+900)
(8)
which is seen that the desired frequency (fRF ) and the image
frequency (fIM) are downconverted and isolated at different IF
ports through the quadrature phase recombinations. Equation
(7) and equation (8) clearly shows the presence of a 900 phase
shift between the two sidebands.
Fig. 1. Conventional IRM architecture
By manipulating trigonometry identity, how isolation
between the desired frequency, fRF and image frequency, fIM
is achieved through phase cancellation can be proven. With
the assumption of low side injection, the desired frequency in
this case is the upper sidebands (fLO + fIF ) while the image
frequency is the lower sidebands (fLO - fIF). In the following
analysis cos(freq) is used to represent the signals.
Let the RF input signal to mixer A is expressed as
RFA = cos fRF + cosfIM
(1)
While the RF input signal to mixer B is expressed as
RFB = cos (fRF+1800) + cos (fIM + 1800)
(2)
where
Fig. 2. AIA with IRM architecture
fRF represent the desired frequency
fIM represent the image frequency
III. SIMULATION RESULT AND DISCUSSION
After mixing RFA with LO signal (cos(fLO) through mixer A
and low pass filtering, the signals are
cos (fRF).cos (fLO) =0.5cos (fLO-fRF)
cos (fIM).cos (fLO) =0.5cos (fIM-fLO)
Simulation of AIA with IRM was executed in two manners.
One is at 2.3 GHz frequency and another one is at 2.4 GHz.
In this project, 2.4 GHz is the desired frequency while 2.3
GHz is the image frequency. Theoretically, of the two output
ports of AIA with IRM, 2.3 GHz and 2.4 GHz will only
appear individually at one of it when down conversion
process. In other words, when 2.3 GHz is received, its
intermediate frequency (IF) will only appear at one of the
ports while suppressed at the other one. The case is vice versa
when 2.4 GHz is detected. The design of AIA with IRM is
(3)
(4)
The RFB mixed with LO signal (cos(fLO)) through mixer B
and passing through LPF are
cos (fRF + 1800).cos (fLO + 900)
(5)
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such that when 2.4 GHz is received, its IF frequency only
appears at IFA output port. On the other hand, IF frequency
only appears at IFB port when 2.3 GHZ is detected. Fig. 3
shows the circuitry of AIA with IRM which clearly illustrate
the physical structure of the circuitry of AIA with IRM. It
basically consists of two branches which is branch A and
branch B. IFA and IFB output ports is at branch A and branch
B respectively.
m 15
fre q = 5 0 .0 0 M H z
d B m (IF B )= -2 7 .7 1 8
0
m 15
dBm(IFB)
-2 0
-4 0
-6 0
-8 0
-1 0 0
IFA
10
30
50
70
90
100
fre q , M H z
(b)
IFB
Fig. 4. 2.3 GHz signal is received. (a) At branch A, IFA. (b)
At branch B, IFB
In fact, the phenomenon that take place in the whole system
when 2.4 GHz is received is similar to that happens when 2.3
GHz is received. The difference of the case when 2.4 GHz is
received is that IF signal is suppressed at IFB port while
unsuppressed at IFA port. This is a vice versa of that when 2.3
GHz is received. The IF signal is suppressed to -53.071 dBm
at IFB port whereas at IFA port, the IF signal still exists
significantly at magnitude of -26.209 dBm. Similar to the case
when 2.3 GHz is received, there is an isolation of about 20 dB
between the desired and image frequency. Fig. 5 shows the
received signal at IFA and IFB when 2.4 GHz is received
Fig. 3. Circuitry of AIA with IRM
When 2.3 GHz is received, IF is only observed at IFB while
suppressed at IFA. At IFA port, IF is suppressed to -46.498
dBm while still exist significantly at IFB port at magnitude of 27.728 dBm. The difference between the magnitude at IFA and
IFB ports is approximately 20 dB which means there is an
isolation of 20 dB between the desired and image frequency.
The IF signal is as illustrated in Fig. 4.
m 17
freq = 50.00MHz
d B m (IF A)=-26.209
0
m 17
dBm(IFA)
-20
m 14
freq = 50.00MH z
d B m (IF A)=-46.598
-60
-80
0
-100
-20
(a)
-1 00
10
30
50
70
90
1 00
fre q, M Hz
(a)
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100
-80
90
freq, M Hz
-60
70
-40
50
m 14
30
10
dBm(IFA)
-40
Bert C. Handerson, James A. Cook, Image-Reject and SingleSideband Mxers, Watkins-Johnson Company Technical Notes,
Vol. 12 No.3 May/June 1985 pp.1.
[5] W. Ismail, P Gradner, Low Noise integrated active antenna as
image reject mixer, 6th IEEE High Frequency Postgraduate
Student Colloquium, 9- 10th Sept 2001.
[4]
m18
freq= 50.00MHz
dBm(IFB)=-53.071
0
dBm(IFB)
-20
-40
m18
-60
-80
-100
100
90
70
50
30
10
freq, M Hz
(b)
Fig. 5. 2.4 GHz signal is received. (a) At branch A, IFA. (b)
At branch B, IFB.
IV. CONCLUSION
The theory and operation of conventional IRM and the
architecture of this project has been discussed. Comparatively,
the phase manipulation approach of this project differs from
that of the conventional IRM architecture. This is a new
technique and approach in order to obtain this AIA with image
reject mixer. It is proven that the proposed architecture of this
project can perform the image rejection process. Simulation
indicates an isolation of around 20 dB between the image and
desired frequency with 7 dBm LO drive at 2.35 GHz.
ACKNOWLEDGEMENT
The authors thank to Ministry of Science Technology and
Innovation (MOSTI) for supporting the research work,
Research Management Centre (RMC) and Wireless
Communication Centre Universiti Teknologi Malaysia (UTM)
for the support of paper presentation.
C CONCLUSION
REFERENCES
J. Lin and T. Itoh, Active Integrated Antennas,
IEEE
Transactions on Microwave Theory and Techniques, Vol. 42,
No. 12, pp. 2186-2194, December 1994
[2] Robert A. Flynt, Lu Fan, J. A. Navarro and Kai Chang, Low
Cost and Compact Active Integrated Antenna Transceiver for
System Application, IEEE Transactions On Microwave Theory
and Techniques, Vol. 44, No. 10, pp. 1642-1649, October 1996.
[3] P. B. Khannur and S.L. Koh, A 2.45GHz Fully-Differential
CMOS Image-Reject Mixer for Bluetooth Application, IEEE
Radio Frequency Integrated Circuits Symposium, pp. 439-442,
2002
[1]
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