Proceedings of the 37th European Microwave Conference
Active Integrated Antenna with Image Reject Mixer
M.K.A. Rahim#1, W.K. Chong#2, T. Masri#3
#
Wireless Communication Center (WCC),
Faculty of Electrical Engineering,
Universiti Teknologi Malaysia
81310 UTM Skudai
Johor, Malaysia
[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 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.
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. 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
filter.
Figure 1 shows the architecture of active integrated antenna
with image reject mixer.
Let the RF input signal to mixer A is expressed as
I. INTRODUCTION
RFA = cos fRF + cosfIM
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
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
978-2-87487-001-9 © 2007 EuMA
(1)
While the RF input signal to mixer B is expressed as
RFB = cos (fRF+1800) + cos (fIM + 1800)
(2)
where
fRF represent the desired frequency
fIM represent the image frequency
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)
(3)
(4)
The RFB mixed with LO signal (cos(fLO)) through mixer B
and passing through LPF are
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cos (fRF + 1800).cos (fLO + 900)
= 0.5cos(fLO-fRF - 900)
(5)
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
suppressed at the other one. The case is vice versa when 2.4
GHz is detected. The design of AIA with IRM is such that
when 2.4 GHz is received, it’s IF frequency only appears at
IFA output port. When 2.3 GHz is detected the IF frequency
will only appear at IFB. Fig. 2 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.
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)
IFA
(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)
IFB
(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. 2 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 signals is illustrated as shown in Fig. 3 (a) and (b).
m14
freq=50.00MHz
dBm(IFA)=-46.598
m15
freq=50.00MHz
dBm(IFB)=-27.718
0
0
-40
-60
-80
-40
-60
-80
-100
-100
10
Fig. 1
m15
-20
m14
dBm(IFB)
dBm(IFA)
-20
AIA with IRM architecture
30
50
70
90
100
10
freq, MHz
(a)
30
50
70
90
100
freq, MHz
(b)
II. SIMULATION AND MEASUREMENT RESULT
Fig. 3
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
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
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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. 4 shows the
received signal at IFA and IFB when 2.4 GHz is received
m18
freq= 50.00MHz
dBm(IFB)=-53.071
m17
freq=50.00MHz
dBm(IFA)=-26.209
0
0
m17
-20
dBm(IFB)
dBm(IFA)
-20
-40
-60
-40
100
90
70
50
100
Fig. 4.
90
70
50
30
10
(a)
30
-80
-100
10
-80
-100
freq, MHz
m18
-60
freq, MHz
(b)
2.4 GHz signal is received. (a) At branch A, IFA. (b) At branch B,
IFB.
(a)
The fabricated AIA with IRM is shown in Fig. 5. in which the
signals of concerned are IFA and IFB. For the case when 2.3
GHz is received, IF is suppressed to around -70 dBm at port
IFA while exist significantly at port IFB at about magnitude of
-50 dBm. From the difference between the magnitudes of IF
signal at port IFA and IFB, an isolation of about 20 dB is
observed.
(b)
Fig. 6
Fig. 5
Fabricated of AIA with IRM
Fig. 6 shows the IF signals at IFA and IFB ports when 2.3 GHz
is received. It shows that the there is more than 20 dB
suppression between the two ports.
2.3 GHz signal is received. (a) At branch A, IFA. (b) At branch B,
IFB.
When 2.4 GHz is received, the IF signal is suppressed to
about -70 dBm at port IFB but unsuppressed at port IFA. At
port IFA, the IF signal still exist significantly at the magnitude
of approximately -50 dBm. As observed, there is an isolation
of about 20 dB between the signal at port IFA and IFB. The IF
at IFA and IFB ports when 2.4 GHz signal received is
illustrated in Fig. 7. It shows that the isolation between the
two is 20 dB. The signal receide at port IFB has been
suppressed to -73 dBm. While the signal received at IFA is -53
dBm
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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.
REFERENCES
[1]
[2]
[3]
(a)
[4]
[5]
J. Lin and T. Itoh, Active Integrated Antennas,
IEEE
Transactions on Microwave Theory and Techniques, Vol. 42,
No. 12, pp. 2186-2194, December 1994
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.
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
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.
W. Ismail, P Gradner, Low Noise integrated active antenna as
image reject mixer, 6th IEEE High Frequency Postgraduate
Student Colloquium, 9- 10th Sept 2001.
(b)
Fig. 7.
2.4 GHz received is received. (a) At branch A, IFA. (b) At branch B,
IFB.
III. CONCLUSION
The theory and operation of conventional IRM architecture
and architecture of this project has been discussed.
Comparatively, the phase manipulation approach of this
project differs from that of the conventional IRM architecture
and it is proven that the proposed architecture of this project
can perform the image rejection process. The fabricated AIA
with IRM can attain an isolation of approximately 20 dB
between the image and desired frequency with 7 dBm LO
drive at 2.35 GHz. Prediction through simulation also
indicates an isolation of around 20 dB between the image and
desired frequency. In this work, by integrating IRM with
antenna, size reduction is attained by two means; the removal
of space consuming external image-reject filter and
incorporation of IRM directly into active integrated antenna.
Besides, losses are reduced by the elimination of external
transmission line which inflicts losses.
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