SIMULTENOUS TRANSMIT AND RECEIVE CIRCULAR POLARIZED ACTIVE INTEGRATED ANTENNA M. K. A. Rahim, Q. X. Feng, T. Masri, M. N. A Karim Faculty of Electrical Engineering, Universiti Teknologi Malaysia (UTM) 81300 UTM Skudai, Johor, Malaysia
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the other is the gate voltage (Vgs), which is negative. When Vgs is fixed at a certain value, the current (Ids) from drain to source varies while tuning Vds and when Vds is fixed at certain values, Ids also varies, while tuning Vgs. After integrating all of Abstract the components such as antenna, coupler, amplifier and the This paper discusses the design and implementation of an power divider altogether, the antenna is measured and tested active transmit-receive antenna, integrating an active devices for both transmit and receive functions. onto a printed antenna to improve its performance and combine functions within the antenna itself. It includes a circular polarized microstrip patch antenna, two amplifiers, a 2. Design considerations power divider and a rat race coupler to isolate transmit and receive paths. The beamwidth of the antenna is in the range of 2.1 Circular Polarized Microstrip Antenna Design 600 to 700 for H plane. The radiation pattern for E plane is smaller compared to the H plane. The comparison between the The design of this Active Integrated Antenna (AIA) starts passive and the active integrated antenna shows that the active with designing a square patch linear polarized antenna. After integrated antenna has 3 dB extra gain compared to the matching it at 2.4 GHz, it is then converted into a circular passive antenna, for both transmit and receive. The isolation polarized antenna. This square patch dimensions are between transmit and receive is between 20 to 25 dB. This calculated by [9]: active antenna has potential uses in WLAN communication applications. c (1) w 2f cr Keywords: Active Integrated Antenna, Circular Polarization, microstrip antenna,
1. Introduction An active antenna with simultaneous transmit and receive function is of increasing interest, as system designers require more complex functions to be implemented in reduced space. This paper discusses the integration of active antennas by combining both transmit and receive functions into one single antenna. Four main components in the design are circular polarized microstrip patch antenna, rat race coupler, power divider and amplifiers. Each individual component was designed using Agilent ADS software before the components were fabricated. The circular polarized antenna resonates at 2.4 GHz. Two MESFET amplifiers have been used to transmit and receive the channel separately. The rat race coupler isolates the two channels and a Tee junction power divider connects the two channels to the input and output port. The channels operate at the same frequency. The antenna polarization is confirmed as a circular polarized, as can be seen in the radiation pattern from the measured and simulated results. The amplifier biasing circuit is supplied by two power sources; one is the drain voltage (Vds) which is positive and
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f= 2.4 GHz, the square circular polarised (CP) antenna dimensions are found to be: W=L=28.87mm. For optimization purposes, the width and the length are computed from 28.00mm to 30.00mm and simulated using Agilent ADS software. The square patch is then cut (truncated) on one corner to obtain the circular polarization characteristic. The width is 3mm. In order to get a good return loss and wide bandwidth, a quarter wave transformer is added between the patch and a 50 ohm transmission line, to match them. This circular polarized antenna design configuration is shown in
figure l(a), and the simulated and measured results of the return loss (SII) and radiation patterns are shown in figure 5.
(a)
(b)
Figure 1: (a) Circular patch antenna optimized configuration; W= 30mm, L = 28.5mm; Bandwidth: 135 MHz; W2=1.5mm, L2= 17mm. (b) The Rat Race configuration
2.4 TEE junction power divider
The purpose of this T-junction power divider (Figure 2(b)) is to connect transmit channel and receive channel to the input & output port. According to equation Z = 12Z, Z=70.71 ohm, and using this number in the 'Line Calculator' tool of ADS, the width (W4) of the quarter wave transformer is computed as 1.5 mm and its length is 17.24 mm. After optimization process, the final results produced W4 =1.51 mm, L7= 14.52 mm, L8 8.43 mm, Lg= 17.56 m.
3. Active Integrated Antenna (AIA) After all the individual parts of this antenna has been designed, they were combined (Figure 3) and simulated to analyse the isolation of the transmit channel and receive channel.
Rat Race coupler Design
2.2
The purpose of this rat-race coupler (Figure l(b)) is to connect the antenna with transmit and receive channels/paths and at the same time isolate these two channels. From equation ZR = 12Zo, ZR=70.71 ohm, the width of the ring can be calculated. In order to match this coupler with the whole antenna circuit, the length of three of its transmission lines that is connected to the ports, should be tunned (varied) for optimization. Final optimized results: W3 = 1.53 mm, L3= 52.26 mm L4= 31.18 mm, L5= 20mm, L6= 25.85 mm, Ring radius = 16.98 mm. 2.3 Amplifier Biasing Design Two MESFET transistors (ATF-21186) are used in transmit channel and receive channel respectively to act as the amplifier in this design, and the radial stub is used to bias this amplifier. From figure 2(a), the radial stub angle is 700. The transmission lines between the radial stub ends to the main circuit are both quarter wave length where the width is 0.7 mm, and the length of the quarter wave transmission line is 17.96 mm.
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Figure 3: Schematic configuration of the coupler and the amplifier for isolation analysis purposes. This whole AIA antenna is then fabricated onto an FR4 board as shown in figure 4, and the antenna radiation patterns were measured and plotted as shown in figure 6. The results comparison between active and passive antenna gain is shown in figure 7. From the graph, the active and passive antenna gain is lower compared to a monopole antenna, but the active antenna gain is about 3dB higher than passive antenna, at 2.4GHz.
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Figure 2: (a) The Amplifier biasing configuration. (b) The Figure 4: AIA antenna fabricated onto a FR4 board. TEE junction power divider configuration
4. Result and Discussion Four main components in the design are circular polarized microstrip patch antenna, rat race coupler, power divider and amplifiers. Each of them was designed separately before being combined as one to produce the AIA. The optimization and the analysis have also been carried out. The circular polarized antenna resonates at 2.4 GHz. Two MESFET amplifiers biasing circuit have been designed successfully to transmit and receive the channel separately. The rat race coupler isolates the two channels and a Tee junction power divider connects the two channels to the input and output port. The channels operate at the same frequency. The simulation and measurement results of the microstrip patch antenna for SI, has an adequate bandwidth of about 10% at a reference level lower than -10 dB at frequency of 2.4 GHz. The antenna polarization is confirmed as a circular polarized, as can be seen in the radiation pattern from the measured and simulated results in figure 6. The beamwidth of the antenna is in the range of 600 to 700 for H plane. The radiation pattern for E plane is smaller compared to the H plane.
REFERENCES [1] [2] [3]
[4]
[5]
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[8]
[9]
M.J. Cryan and P.S. Hall, 'Integrated Active Antenna with Full Duplex Operation', IEEE Transactions on Microwave Theory and Techniques, vol 45, No 10 Oct 1997 K Kurokawa, 'Active Intggrated antenna Technique', Proc IEEELow Frequency Plasmons for Thin-Wire Structure, J. Phys. Condens. Matter 10 4785 - 4809, 20 March 1998 Jiunn-Nan Hwang, and Fu-Chiarng Chen, Study of SAR Reduction with Split Ring Resonators, IEEE, 2005 Hu Jun, Yan Chun-sheng, Lin Qing-chun, New Patch Antenna with MTM Cover, J Zhejiang University SCIENCE A 7(1), 89-94, 2006 Shah Nawaz Burokur, Mohamed Latrach and Sergre Toutain, Theoritical Investigation of a Circular Patch Antenna in the Presence of a Left-Handed Mematerial, IEEE Antennas and Wireless Propagation Letters, Vol. 4, 2005 I. Gil, J. Bonache, J.Garcia-Garcia, F. Falcone, F. Martin, Metamaterials in Microstrip Technology for Filter Applications, IEEE, 2005 Qun Wu, Fan Yi-Meng, Ming-Feng Wu, Jian Wu, Le-Wei Li, Design of Planar LHM with Broad Bandwidth and Miniaturized Cell, IEEE, 2006 Richard R. Ziolkowski, Double Negative Metamaterial Design, Experiments and Applications, IEEE Transactions on Microwave Theory and Techniques, Vol.5 1, No. 7, July 2003 C.A Balanis,"Antenna theory analysis and design" John Wiley & Son Inc. Publication 2005
After integrating all of the components such as antenna, coupler, amplifier and divider together, the antenna is measured and implemented for both transmit and receive. The comparison between the passive and the active integrated antenna shows that the active integrated antenna has 3 dB extra gain compared to the passive antenna, for both transmit and receive. The isolation between transmit and receive is between 20 to 25 dB as shown in figure 8(a) and in figure 8(b), the gain is about 3.416 dB. This active antenna has potential uses in WLAN communication applications.
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5. Conclusion The goal of this project is to design and produce an AIA that comprises of a circularly polarized microstrip antenna (Passive and active), a rat-race coupler, an amplifier's biasing circuit and a T-junction power divider and to integrate these designs to come out with a final prototype. The active integrated antenna with transmit and receive function has been designed, fabricated and measured. The integration of the active devices onto the passive antenna can improve its gain. Simultaneous transmit and receive functions has been proven and can be integrated onto one single module. Although the simulation gives good results, the measurement results are not good enough. The main problem is that the active part is not stable and matching well with the passive part. In the future work, these problems should be solved.
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(b) Figure 6: Antenna radiation pattern measurement results (a) TX and (b) RX.
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Figure 8: (a) TX and RX isolation and (b) TX and RX gain comparison.
