ACTIVE INTEGRATED ANTENNA WITH LOW NOISE AMPLIFIER DESIGN AT 5 GHz T.Peter", M.K. A. Rahim J. Ding, T.Masri" ,
# Wireless Communication Centre Faculty of Electrical Engineering Universiti Teknologi Malaysia (UTM) 81310, Skudai, Johor Bahru
Email:
[email protected],
[email protected],
[email protected],
[email protected]
Keywords: Active Integrated Antenna, Low Noise Amplifier, micostrip antenna, proximity coupled feed,
Abstract An Active Integrated Antenna with Low Noise Amplifier (ALNA) at 5 GHz has been design and fabricated for wireless communications. The design achieved a low noise figure by directly integrating a low noise amplifier to a dual layered microstrip close proximity coupled patch antenna at 5 GHz. Measured results show a noise figure (NF) of 1.22 dB, an excellent return loss of greater than 12 dB and good impedance matching which resulted in a bandwidth of about 10% for the active device. This paper presents the methodology, simulations and experimental works carried out in accomplishing the above objective. LINC2 and Microwave Office software were used to simulate and to obtain the
optimum design and results.
1 Introduction The recent migration and upsurge in the demand for portable wireless communication products for the 5 GHz WLAN applications has caused much research interest in Active Integrated Antenna (AIA) technology where the passive antenna is integrated with an active device in the front-end of RF systems. In this project a close proximity coupled microstrip antenna is directly integrated with a Low Noise Amplifier (LNA) to produce an AIA system with low noise characteristic. Even though this technology has provided a lot of attraction and avenue, there are still many technical hurdles, like the availability of inexpensive good quality dielectric substrates (materials with tight dielectric tolerance, loss tangent, and good mechanical properties) and antenna miniaturization, that need to be overcome before a low noise receive antenna can be realized at 5 GHz. The closest work attempted in this respect is for the frequency range of 1.8-2.0 GHz [1] where the LNA gain of 2.73 dB, NF of 0.77 dB,
input return loss of -14.14 dB, and output return loss of -15.8 dB at a design frequency of 1.8388 GHz was demonstrated. A modified feed line approach of high E, (>5) on a thin substrate (h-10
1CXi Artenn]
-20
Figure 8: Return loss measurement on HP Network Analyzer The plots of the radiation patterns for the antenna are shown Figure 9. The radiation pattern of the antenna is in 312/directional pattern. The radiation patterns show a good isolation of approximately 20-25 dBm between the co and cross polarization in both the E and H planes. The HPBW is about 1050 in both planes. in
|30
___________40___________________________
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4
e
6
Frequencay (GHz)
Figure 7: Return loss of antenna at feed point impedance of 50 Q
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15 10 5
116dB
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0 -5
5GH
-10
LNA5G-
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-20
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-30 4
(a) E Plane
4.5
6
5.5
Frequency(Gz
Figure 12: Final LNA after insertion of source inductance
(b) H Plane
Figure 9: Radiation pattern- Co and Cross polarization of the passive antenna
3.2 Low Noise Amplifier Results
Stability check for the final LNA circuit showed that the circuit had become unstable and started to oscillate. This could be due to external feedback and excess gain outside the band of operation. The Rollet Stability Factor (K-Factor) started to dip below 1 from 4.9 GHz to around 6.7 GHz as shown in Figure 10. Stability F _
Figure 13 below shows the final LNA unconditionally stable after insertion of the 6 Q resistor. The stability factor, KI and B 1 are shown to be above 1 and 0 respectively throughout the frequency range from 2 GHz to 8 GHz thus satisfying the conditions for unconditional stability. st-ltaity
3
K()I E
2
1
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7~~~~~~~~~~ .,~~~~~~~~~~~~
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KO 5GHiz LNA
2
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Figure 13: Final LNA unconditionally stable with 6 Q stability resistor -1
2
4
6 Frequency (GHz)
Figure
10:
Final LNA circuit unstable from 4.7 GHz to 6.7 GHz
Figures 11I
& 12 show the simulation results before and after
insertion of source inductance. The NF improved from 1.102 dB. to 1.098 dB but the gain dropped by 0.19 dB and the input return loss deteriorated slightly by 0.82 dB. However, the output return loss improved by -10.38 dB. I~~~~~~~~~~~
15 10
5
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Table 2 shows the noise figure of the LNA before and after tweaking the amplifier. Better results were obtained after tweaking the input and output matching network stub lengths of the LNA. The tweaking was done by using strips of copper foil to vary the length of the stubs until desired results were obtained. The tweaking approach is done to move Fin close to Fopt to obtain the best match noise figure as shown in Figure 14. Table 2: S-parameter and noise figure measurement of the LNA.
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Figure 11: Final LNA before insertion of source inductance
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Figure 15: The simulated results of the ALNA STAPT -01-W 900 008 GHz
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Figure 14: Movement of Fin SI, toward simulated F,ut location The NF obtained was 1.97 dB from the existing Avago's LNA compared to the NF of the tweaked prototype which was at 1.37 dB. Their LNA's NF should have been 1.2 dB as per Avago's Application Note: 1285. The high reading could have due to soldering defects. The NF of the prototype should be around 1.22 dB after discounting 0.15 dB noise figure contribution from the connectors. The LNA's S1I was 4.47 dB lower than the simulated S1I of -11.25 dB and the gain was 3.55 dB lower than the simulated gain of 11.67 dB. One reason for the poor performance of the LNA could be because the LNA was fabricated from the integrated LNA portion of the LNA. The LNA's input and output matching had been optimized to give the best return loss for the ALNA. As such by dissecting the LNA portion of the board from the ALNA and using it as a discrete LNA may not give the desired results. The LNA may have performed better had it been One separately designed, optimized and fabricated. consolation is that the noise figure of 1.22 dB obtained for the LNA after deduction of 0.15 dB for the connector losses, is close to that of the desired noise figure goal for the ALNA; lower the noise figure of the LNA the better would be the expected noise figure performance of the ALNA. 3.3 Active Integrated Antenna
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S
.
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,10
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45
6
Figure 16: Simulated results of the LNA without CPPA ........
is
10
De(r{1 1y)1
ALNA
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-30 4
Figure 17: Simulated return loss and VSWR of the ALNA
The simulation results of ALNA are shown in Figure 15, The return loss of the ALNA before tweaking was not so Figure 16 and Figure 17. The results indicate that the good; it registered a SI, of -6.3 dB. Better results were ALNA's NF is dependent on the performance of the LNA. obtained after tweaking at both the input and output matching This can be seen by the simulated results of the LNA without circuits of the LNA portion of the ALNA. The output the antenna being integrated in Figure 16. This is justified by matching stub especially, was lengthened by soldering a the fact that the noise figure would not be the same if the rectangular strip of copper foil to extend it by a length of 10 LNA is connected to the CPPA using a 50 Q connector [2] mm and tweaked by slowly cutting it down to a length of 9.4 which is the aim of this research i.e to integrate the CPPA to mm. The SI, peak of-18 dB at 4.7 GHz as shown in Figure the LNA to reduce the noise figure. The overall return loss 18 (a) gradually moved towards the 5 GHz frequency point to and VSWR of the ALNA in simulation are -19.61 dB and register value of about -12.75 dB as in Figure 18(b). Figure 1.234 respectively. 18(a),(b), (c) and (d) show the improvement of the SI, reading as the tweaking is carried out.
(a)
soldering proficiency to some extent affect the outcome of the actual performance of the ALNA. The aim of this research was to design an ALNA for WLAN applications at 5 GHz with a NF lesser than 1.2 dB, a return loss greater than -12 dB, a bandwidth greater than 10 %, and a gain greater than 10 dB has been achieved. The measured results were a gain of 8.12 dB and a noise figure of 1.22 dB for the LNA after excluding losses 0.15 dB for the connectors, a return loss of 12.75 dB and a bandwidth of 10 % for the ALNA. Although the actual gain and noise figure of the ALNA were not measurable, going by the results obtained in Table 2 for the gain and NF of the LNA after tweaking, the gain for the ALNA is expected to be above 8 dB and close to the desired gain of 10 dB whilst the noise figure around 1.2 dB.
(b)
Acknowledgements The authors would like to thanks the 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 this paper presentation. (d)
(c)
References
Figure 18; Return Loss graphs of the ALNA before and after tweaking/tuning process The antenna
was
also connected using
a
50
Q
[1]
SMA plug
connector to Avago's 5 GHz LNA board and tested. The return loss obtained was summarized and tabled together with the results for the SI1 obtained for the ALNA prototype before
[2]
and after tweaking in Table 3.
Table 3: The finalized S-parameter measurement of the Active Integrated Antenna with LNA
[3] [4] [5]
-19-61
1.23
1.00
-6.3
3.0
25.12
-12.7
1.6
5.33
-12.05
1.67
10.00
4 Conclusion The use of a two-layered substrate design with different dielectrics for the close proximity antenna had greatly improved the performance of the antenna. As for the LNA, it has been demonstrated that a modified design approach incorporating both stability resistor and inductive feedback can help to achieve unconditional stability. Fabrication and
[6]
[7]
S. Vajha and P. Shastry, "A Novel Proximity Coupled Patch Antenna for Active Circuit Integration," Antennas and Propagation Society International Symposium, 2001, IEEE, Vol. 4, pp 772-775, 8-13 July 2001 A. Parfitt and L. Milner, "The Design of Active Receiving Antennas for Broadband Low-Noise Operation," 27th General Assembly of the International Union of Radio Science, (URSI),17-24 August 2002. D.M. Pozar, "Microstrip Antennas," Invited Paper, Proceedings of The IEEE, Vol. 80, No. 1, pp. 79-81, January 1992. C.A. Balanis, "Antenna Theory, Analysis and Design," John Wiley & Sons Inc., 2nd Edition, 1997. G. Splitt and M. Davidovitz, "Guidelines for Design of Electromagnetically Coupled Microstrip Patch antennas on two layer substrates," IEEE Transactions on Antennas and Propagation, Vol. 38, No. 7, pp. 11361140, July 1990. Data Sheet, "Agilent ATF-55143 Low Noise Enhancement-mode Pseudomorphic HEMT in a Surface-mount Plastic Package," Agilent Technologies Inc., 2003. D.D. Henkes (1998). "LNA Design Uses Series Feedback to Achieve Simultaneous Low Input VSWR and Low Noise," Applied Microwave & Wireless, October 1998, p. 26.
