Proceedings of the Asia-Pacific Microwave Conference 2016
Dual-Band Dual-Polarized Resonant Patch Antenna Excited Through Isolated Ports Anindya Ghosh(1), Mrinal Kanti Mandal(2), Arijit De(3), Ajay Chakrabarty(4), and Binay Kumar Sarkar(5) Advanced Technology and Development Centre (1) Department of Electronics and Electrical Communication Engineering (2) (3) (4) (5) Indian Institute of Technology Kharagpur, India, 721302. (1)
[email protected], (2)
[email protected] Abstract-A high gain shared aperture dual-band dualpolarized (DBDP) patch antenna is proposed in this work. Dual polarization is obtained by exciting the antenna in two orthogonal directions using two separate ports. Higher order resonant mode is used to obtain higher gain. The antenna transmits and receives in L and S bands simultaneously with good isolation between the ports. Improved isolation is obtained by using an L-shaped slot and non-shorting pins on and below the radiating patch, respectively. A prototype element is fabricated. Isolation between the ports is 21 dB at 1.48 GHz and 39.25 dB at 2.59GHz. The measured gains in the broadside directions are 6.2 dB and 5.5 dB at the respective frequencies. Index Terms—Antenna, microstrip patch.
I.
I
dual-band,
dual-polarization,
INTRODUCTION
N remote
sensing and satellite communication transceivers systems, dual-band dual-polarized (DBDP) patch antennas are widely used as a cost effective solution to reduce interference between the transmitting and receiving frequencies. Instead of using two different antennas or antenna array elements, a single antenna operating at both the frequencies would be beneficial as it would reduce the weight and the dimension of the system [1]. Also in multi-band communication systems, circulators are the source of passive intermodulation distortion (PID) which produces significant interference and degrades the system performances. Although it can be avoided by using low magnetization and high impedance ferrite material but low magnetization can only be achieved within limited frequency band [2]. Particularly in synthetic aperture radar applications, performance of systems is decided by the sensitivity of backscattered wave polarization and operating frequency. The L band radar system is more sensitive to different variation of size of vegetation as compare to other frequency bands [3]. Accuracy for detecting forest and shrub land at L band is much higher than S and C band. On the other hand, VV (vertical polarization for transmission and vertical polarization for reception) polarization is more effective to detect back scattering coming from forest land than the HH (horizontal polarization for transmission and horizontal polarization for reception) polarization at L band. Therefore the L-band in VV polarization and S-band in HH polarization is suitable for synthetic aperture radar applications. A dual port dual-polarized patch antenna is reported in [4], where electromagnetically coupled ports are used for shared aperture
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excitation. Whereas in [5], proximity coupled feed with mushroom type resonators underneath the transmission line of two ports is used for high isolation between the ports. In [6], the excitation of dual frequency is done by two coaxial feed ports where the frequency ratio of two bands is close to unity. Inset feed techniques for dual port dual -polarized patch antenna is proposed in [7]. However, the frequencies of operation are limited to less than 1.5. In this work, a slot loaded dual-band microstrip patch antenna is presented for L and S band satellite applications. Separate port is used for each frequency of operation. Isolation between these two ports is improved by using localized periodic metallic posts. II. DESIGN OF THE PROPOSED ANTENNA A. Antenna design Firstly, as shown in Fig. 1(a), a probe fed rectangular patch antenna is designed for the lower frequency = 1.63 GHz and the higher frequency = 2.62 GHz. The resonant frequency depends on length W2 and excited by port P1 whereas depends on the length L2 which is excited by port P2 .The resonance frequencies and antenna geometry are related as [8] ( ⁄ ) + ( ⁄ ) , (1) = is resonant frequency of the excited mode , where and are the effective length and width of rectangular patch, respectively, is the velocity of light in free space and is the effective dielectric constant. TM30 mode is chosen to achieve higher gain requirement for the given application. Therefore, the preliminary design geometry as obtained in a 3.048 mm thick Roger RO6002 substrate with dielectric constant 2.94 and loss tangent 0.0012 are = 100 mm, = 50 mm, = 152 mm, = 99 mm. Next the probe positions are optimized for good port isolation. However, the unwanted TM11 mode excited by port P2 in x-direction is close to the TM01 mode excited by port p1 which limits the port isolation. Similar problem arises because of the next undesired higher order mode TM03 excited by port P1. Fig. 1(b) shows the simulated input matching for the ports at P1 (11 mm, 42.2 mm) and P2(61.2 mm, 30.2 mm). It is observed from the radiation patterns shown in Fig. 1(c) that the undesired resonant modes cause additional problem of high crosspolarization. The Ansoft’s HFSS-15 has been used for all full wave simulations. To solve the problem, as shown in Fig. 2, an
L-shaped slot is introduced to suppress the undesired TM11, and TM03 modes. The slot perturbs the surface current distribution. It is observed from the parametric variations of the L-shaped slots in Fig.3 that increasing ′ shifts the desired mode to lower frequency. Input matching for the undesired mode degrades but improves for desired TM30 mode. For the port positions mentioned above, ′ = 29mm, ′ = 24mm, ′ = 3.5mm, ′ = 1.5 mm provide optimum result. The resonant frequency shifted to 1.48 GHz for port 1 and 2.59 GHz for port 2 due to the L slot. The radiating frequencies can be recovered by tuning W2 and L2. However, looking at the present requirement, the frequencies are kept unchanged. It is observed that maximum isolation that can be achieved between the ports are 15 dB and 16.7 dB at and , respectively.
(a)
(b) Fig.3.Variation in length of ′ and changes in return loss at (a) port-1, and (b) port-2.
(b)
Fig. 4.Proposed antenna geometry from (a) top and (b) side view with nonshorting cylindrical post.
(c) (d) Fig.1. (a) Initial antenna geometry, top and side view , (b) simulated |S|parameter and simulated radiation patterns for (c) vertical polarization at 1.63GHz, and (d) horizontal polarization at 2.62GHz.
Fig.2.Proposed antenna geometry. The slot on top patch is shown by black region.
B. Isolation Improvement Next, as shown in Fig. 4, isolation is further improved by introducing eight non-shorting metallic posts [9] of height h = 1.4 mm and radius r = 3mm. They are attached to the ground plane of the antenna (p3 = 26 mm, p4 = 53.5 mm). The post positions are chosen so that their effect on f10 and f03 is minimum while provides maximum isolation between the ports. As seen in Table I and II, the isolation between two ports depends on a) number of arrays of metallic posts, b) height of metallic posts and c) radius of metallic posts. Effect of metal post on the resonance frequencies is insignificant. However, the input matching levels changes. Therefore, the port positions are to be re-tuned.
TABLE I VARIATION OF RADIUS AND ISOLATION FOR DOUBLE ARRAY POST
Radius of post (r in mm) 1 1.5 2 2.5 3 3.5 4
Isolation (dB) (GHz) (GHz) 19.49 18.872 19.296 19.314 19.322 22.963 19.047 26.119 20.005 35.97 18.849 32.417 18.863 28.195
(a)
TABLE II NUMBER OF ARRAYS AND ISOLATION
Number of array of post One Two Without array
Isolation (dB) (GHz) (GHz) 18.74 9.92 20.005 35.97 13.88 16.56
TABLE III VARIATION OF HEIGHT AND ISOLATION
Height of post (h in mm) 1 1.2 1.4 1.6 1.8 2
Isolation (dB) (GHz) (GHz) 18.371 21.962 18.442 25.093 20.005 35.97 17.747 31.141 16.892 26.743 15.981 22.362
(b) Fig.6.Comparison of (a) return loss and (b) isolation between two ports.
III. FABRICATION AND MEASUREMENT RESULT The fabricated antenna is shown in Fig. 5. The final dimensions of the antenna as obtained in a 3.048 mm thick = 50mm, = 152 Roger RO6002 substrate are = 100 mm, mm, = 99 mm and the slot dimensions are ′ = 29 mm, ′ = 24mm, ′ = 3.5mm, ′ = 1.5 mm. Therefore the size of the ground plane is 100mm X 152mm. Fig. 6 shows the measured and simulated |S|-parameters of the antenna. The port isolation has been improved to 20.8 dB at 1.48 GHz and 39.25 dB at 2.59 GHz. The measured return losses are more than 15 dB at these two frequencies. Fig.7 and Fig.8 show the measured and simulated radiation patterns of the antenna at 1.48 GHz and 2.59 GHz, respectively. Measured broadside gains of the antennas are 6.2 dB and 5.5 dB, respectively. It is observed that the crosspol levels are 28 dB and 29.6 dB below the co-pol level in the main lobe direction at 1.48 GHz and 2.59 GHz, respectively.
(a) (b) Fig.5.Dual band dual port patch antenna (a) top view (b) bottom view.
Fig.7. Measured and simulated normalized radiation patterns at 1.48 GHz for vertical polarization.
TABLE IV COMPARISON WITH EXISTING WORKS References
Feed Configurations
Layer
Radiating Patch
Isolation
Gain at ( f1& f2)
Frequency Ratio
[1]
Both proximity coupled
Two
One
> 25 dB
Gain (not given) 1.21 GHz, 1.71 GHz
1.41
[4]
T-line, CPW
Two
One
> 31dB
4.23 dB & 1.61dB at 2 GHz & 2.78 GHz
1.39
[5]
Both proximity coupled
Three
One
40 dB
7.3 dB ,8.2 dB at 2 GHz, 2.45 GHz
1.16
[6]
Both coaxial
Two
Two
23 dB
Gain (not given) 1.26 GHz, 1.41 GHz
1.119
[7]
Both inset feeds
One
One
22dB & 62 dB
4.66 dB, 4.83 dB at 2 GHz & 2.5 GHz
1.25
This work
Both coaxial feeds
One
One
20.8dB & 39.25 dB
6.2dB,5.5dB at 1.48 GHz & 2.59 GHz
1.756
& 55 dB
comparison with other existing works is shown in Table-IV. The proposed design provides higher frequency ratio, improved isolation and higher gain with single radiating element for both the frequencies. ACKNOWLEDGMENT Authors are thankful to SAMEER Kolkata for their instrumental supports and also acknowledge SAC, ISRO, for their financial supports. REFERENCES [1]
[2] [3]
[4] [5] [6] [7] Fig.8. Measured and simulated normalized radiation patterns at 2.59 GHz for horizontal polarization.
IV. CONCLUSION
[8]
A single layer dual-port and dual-polarized antenna is proposed which can operate simultaneously at two different frequencies. The proposed antenna can be used for simultaneous operation at L and S band. The antenna can be used for both VV and HH polarization, respectively, at the lower and higher frequencies using additional circulators. A
[9]
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