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A multibeam antenna using quasi-optical antenna-mixers
Int. J. Electron. Commun. (AEÜ) 62 (2008) 450 – 454 www.elsevier.de/aeue
A multibeam antenna using quasi-optical antenna-mixers Suwan Janina,∗ , Keattisak Sripimanwatb , Chuwong Phongcharoenpanicha , Monai Krairiksha a Faculty of Engineering and Research Center for Communications and Information Technology, King Mongkut’s Institute of Technology
Ladkrabang, Bangkok 10520, Thailand b National Electronics and Computer Technology Center, 112 Thailand Science Park, Phahon Yothin Road, Klong 1, Klong Luang,
Pathumthani 12120, Thailand Received 4 January 2007; accepted 11 July 2007
Abstract A multibeam antenna could be designed without using a complicated feeding system by using quasi-optical antennamixers. Accurate beam directions could be obtained when practical antenna patterns was taken into account in the design. The effectiveness of a three-beam antenna is demonstrated at K-band showing accurate beam directions which is very useful in modern wireless communications. 䉷 2007 Elsevier GmbH. All rights reserved. Keywords: Quasi-optical; Antenna-mixer; Multibeam antenna
1. Introduction A quasi-optical antenna-mixer, which mixes radio frequency (RF) and local oscillator (LO) signals to obtain an intermediate frequency (IF) at the antenna, was proposed to resolve transmission loss at high frequencies [1–6]. This antenna could scan the mainbeam by controlling the LO’s incoming incident angle [7,8]. However, the work in [7] provides a single beam that cannot fulfill the requirement of the system like multiple input multiple output (MIMO) system [9,10] and angle diversity [11] systems. These systems need an antenna that provides multiple beams simultaneously. In order to produce a multibeam antenna without a complicated feeding system, this letter proposes the use of quasi-optical antenna-mixers. Multiple LO transmitters at different frequencies are used to provide multibeam at different IF frequencies. By taking element patterns into account, ∗ Corresponding author.
E-mail addresses: [email protected] (S. Janin), [email protected] (K. Sripimanwat), [email protected] (C. Phongcharoenpanich), [email protected] (M. Krairiksh). 1434-8411/$ - see front matter 䉷 2007 Elsevier GmbH. All rights reserved. doi:10.1016/j.aeue.2007.07.004
accurate beam directions can be accomplished. This kind of multibeam antenna is useful for modern wireless communications.
2. Principle of a multibeam antenna using quasi-optical antenna-mixers Our multibeam antenna was designed based on the principle of quasi-optical antenna mixers. By using the technique in [7], the mainbeam of the antenna could scan by changing the LO direction and the LO frequency without using phase shifters. In this letter, this technique is used to demonstrate a multibeam application which was achieved by using three LO transmitting signals instead of one LO signal. Fig. 1 shows the proposed multibeam antenna. The configuration of the multibeam antenna with quasi-optical hybrid ring antenna-mixers is shown in Fig. 1(a). Fig. 1(b) shows the top view of mixer circuits and the cross-section of quasi-optical antenna-mixer element. The direction of the RF-receiving beam at the lower side of the antenna is defined by the direction of the LO-transmitting antenna at the
S. Janin et al. / Int. J. Electron. Commun. (AEÜ) 62 (2008) 450 – 454
f2
f1
451
fM
LO1
LO2
LOM
x z
Quasi-optical antenna-mixer
dL
Σ
1
2
BPF1
IF1
BPF2
N
IF2
dR Biasing circuits
Beam 1
Beam 2
IFM
Beam M
s1
s2
Gnd. HSCH-9101
BPFM
Multibeam footprint
Gnd.
RF receiving antenna Gnd. Gnd.
dR HSCH-9101
dL LO receiving antenna +VCC
+VCC
+VC C
+VCC
IF output LO receiving patch
RO3003
antenna LO coupling slot
foam Mixer and the feeding side
TLC-27 foam
RF coupling slot RO3003 RF receiving patch antnna
Fig. 1. Configuration of: (a) A multibeam antenna using quasi-optical antenna-mixers; (b) Top view of mixer circuits and the cross-section of quasi-optical antenna-mixer.
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S. Janin et al. / Int. J. Electron. Commun. (AEÜ) 62 (2008) 450 – 454
3. Experimental results
30 R : RF receiving direction (degrees)
Isotropic element
To demonstrate the multibeam operation, a 4 × 1 quasioptical hybrid ring antenna-mixer was fabricated as shown in Fig. 3. Fig. 3(a) shows hybrid ring mixers on feeding side and Fig. 3(b) shows the mixer circuit using HSCH9101 Schottky diodes. Fig. 3(c) shows an experimental setup for multibeam operation. The distance between antenna elements was 0.9 at 18.8 GHz. It was limited by the hybrid
20 10 0 –10
Patch element
fL fL fL fL fL fL
–20 –30 –30
–20
–10
0
10
= 17 GHz = 17.5 GHz = 18 GHz = 17 GHz = 17.5 GHz = 18 GHz
20
0.23 mm 30
L : LO transmitting direction (degrees)
Fig. 2. Relation of mainbeam direction to LO direction.
upper side, and the multibeam operation were realized at different LO frequencies with different resultant intermediate frequencies. For a linear array of N elements, radiation pattern of the down converted intermediate frequency (IF) signal on XZ plane including radiation patterns of patch antennas is IF = 0.5 cos(R − L )t × AR ()AL () N × [ej(i−1)(kR dR cos R −kL dL cos L ) ],
76 mm
HSCH-9101
(1)
i=1
where AR () and AL () are H-plane radiation patterns of the microstrip patch antennas of the RF-and LO-receiving antennas, respectively [12]. N is the number of elements, kR is the wave number of the RF signal, kL is the wave number of the LO signal, dR is the separation between elements of RF receiving patch antennas, and dL is the separation between elements of LO receiving patch antennas. dR and dL are generally different, but they can be same in practice. The directions of RF and LO signals are depicted by R and L , respectively. Fig. 2 shows relation of mainbeam directions to LO directions for RF of 18.8 GHz when isotropic sources and patch antennas are used. It is noted that the relation fluctuates instead of linear relationship when the patch antennas are used instead of the isotropic sources. This is due to the pattern multiplication of array factor with patch radiation patterns. For instance, when the mainbeam direction of array factor is at −20 ◦ , the H-plane patch radiation pattern has maximum at 0◦ . Therefore, the mainbeam results from pattern multiplication will be at −18◦ . The beam direction, normally depending on the direction of the LOtransmitting antenna and LO frequency (fL ), is limited by non-isotropic radiation patterns, the distance between antenna elements and the difference between RF and LO frequencies. However, Fig. 2 shows that LO direction produces more pronounced effect on mainbeam direction than LO frequency. Therefore, it is important to carefully specify the LO direction.
HSCH-9101
RF transmitting antenna
4x1 Quasi-optical antennamixers
Microwave absorber LO1 4x1 Wilkinson power combiner
LO2
LO3 LO feeding antennas
Biasing circuit
Fig. 3. Photographs of the fabricated multibeam antenna (a) Hybrid ring mixers on feeding side; (b) Mixer circuit; (c) Experimental setup for multibeam operation.
S. Janin et al. / Int. J. Electron. Commun. (AEÜ) 62 (2008) 450 – 454 z
Simulation 1.8 GHz (-23.8 degrees) Measurement 1.8 GHz (-23.8 degrees)
0
x 30
-30
-60
60
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90
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-10
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LO1 (17 GHz) -30 degrees Simulation 1.3 GHz (0 degrees) Measurement 1.3 GHz (0 degrees)
z 0
x
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-30
-60
60
-90
90
-20
-10
4. Conclusion z
A multibeam antenna using quasi-optical antenna-mixers is presented in this letter. The accurate RF-receiving mainbeam direction could be obtained when the patch antenna element patterns are taken into account. The result shows three receiving mainbeams which can be used in multibeam operation.
0
x
30
-30
-60
60
-90
90
-20
-10
0 [dB]
0 30
-30
Acknowledgements This work was supported by the Thailand Graduate Institute of Science Technology under Grant number TG-B-1144-22-717D and the Thailand Research Fund under Grant number RTA-4880002.
LO3 (18 GHz) +30 degrees
Side lobes
ring coupler dimension. Each LO signal was produced by using a tilted active patch antenna placed at three positions. The three active patch antennas were placed at −30◦ , 0◦ and +30◦ off broadside to feed LO signals at 17 GHz (LO1), 17.5 GHz (LO2) and 18 GHz (LO3) for multibeam demonstration. The IF power of each element was calibrated by adjusting biasing current to obtain uniform amplitude excitation. The radiation patterns are shown in Fig. 4, which demonstrate three beam operations at the same time. The results were measured at 1.8 GHz (Beam 1), 1.3 GHz (Beam 2) and 0.8 GHz (Beam 3) as shown in Fig. 4(a), (b) and (c), respectively. The measured mainbeam directions agree well with the calculated patterns. However, the side lobe levels were different because calculation in Eq. (1) neglected mutual coupling effect and non-uniform LO amplitude excitation due to the fabrication process. Grating lobes took place due to wide separation of antenna elements. To illustrate effect of dR on side-lobe level, Fig. 4(d) shows simulated patterns of the proposed antenna with dR = 0.5, 0.7 and 0.9. The corresponding side lobes are −13, −7 and −3 dB down from the main lobe, respectively. It is clear that side lobe could be reduced further by reducing separation between antenna elements. It can be improved by reducing hybrid ring size.
0 [dB]
LO2 (17.5 GHz) 0 degrees Simulation 0.8 GHz (+26.3 degrees) Measurement 0.8 GHz (+26.3 degrees)
453
z x
References -60
60
90
-90
dR= 0.5 λ dR= 0.7 λ dR= 0.9 λ 0
-20
-40
[dB]
fL (17.5 GHz) +30 degrees
Fig. 4. Multibeam radiation patterns: (a) Beam 1 at −23.8 degrees; (b) Beam 2 at 0 degrees; (c) Beam 3 at +26.3 degrees; (d) simulated patterns at different dR .
[1] Stephan KD, Camilleri N, Itoh T. A quasi-optical polarizationduplexed balance mixer for millimeter-wave applications. IEEE Trans Microw Theory Tech 1983;31:164–70. [2] Hwang VD, Uwano T, Itoh TT. Quasi-optical integrated antenna and receiver front end. IEEE Trans Microw Theory Tech 1988;1:80–5. [3] Masarweh SK, Sherer TN, Yngvesson KS, Gingras RL, Drubin C, Cardiasmenos AG, et al. Modeling of a monolithic slot ring quasi-optical mixer. IEEE Trans Microw Theory Tech 1994;42:1602–9.
454
S. Janin et al. / Int. J. Electron. Commun. (AEÜ) 62 (2008) 450 – 454
[4] Tong C-Y, Blundell R. A self-diplexing quasi-optical magic slot balanced mixer. IEEE Trans Microw Theory Tech 1994;3:383–8. [5] Robertson SV, Katehi LPB. A planar quasi-optical mixer using a folded-slot antenna. IEEE Trans Microw Theory Tech 1995;43:896–8. [6] Neculoiu D, Bartolucci G, Konstantinidis G, Marcelli R, Petrini I, Dragoman M, et al. A micromachined 38 GHz schottky-diode uniplanar monolithic integrated quasi-optical mixer. IEEE Radio Frequency Integrated Circuits (RFIC) Symposium 2004; 531–4. [7] Nishimura T, Ishii N, Itoh K. Beam scan using the quasioptical antenna mixer array. IEEE Trans Antennas Propag. 1999;47:1160–6. [8] Saito H, Nishimura T, Yamamoto M, Itoh K. Quasi-optical antenna-mixer array composed of a magnetic loop antenna
[9]
[10]
[11]
[12]
operated at 10 GHz band. Electronics and Communications in Japan 2004;87:45–53. Paulraj AJ, Gore DA, Nabar RU, Bolcskei H. An overview of MIMO communications – A key to gigabit wireless. Proc IEEE 2004;92:198–218. Foshini G, Gans M. On limits of wireless communications in a fading environment when using multiple antennas. Wireless Personal Communications 1998;6:311–35. Perini PL, Holloway CL. Angle and space diversity comparisons in different mobile radio environments. IEEE Trans Antennas Propag 1998;46:764–75. Balanis CA. Antenna theory analysis and design. Canada: Wiley; 1997.
A multibeam antenna using quasi-optical antenna-mixers Suwan Janina,∗ , Keattisak Sripimanwatb , Chuwong Phongcharoenpanicha , Monai Krairiksha a Faculty of Engineering and Research Center for Communications and Information Technology, King Mongkut’s Institute of Technology
Ladkrabang, Bangkok 10520, Thailand b National Electronics and Computer Technology Center, 112 Thailand Science Park, Phahon Yothin Road, Klong 1, Klong Luang,
Pathumthani 12120, Thailand Received 4 January 2007; accepted 11 July 2007
Abstract A multibeam antenna could be designed without using a complicated feeding system by using quasi-optical antennamixers. Accurate beam directions could be obtained when practical antenna patterns was taken into account in the design. The effectiveness of a three-beam antenna is demonstrated at K-band showing accurate beam directions which is very useful in modern wireless communications. 䉷 2007 Elsevier GmbH. All rights reserved. Keywords: Quasi-optical; Antenna-mixer; Multibeam antenna
1. Introduction A quasi-optical antenna-mixer, which mixes radio frequency (RF) and local oscillator (LO) signals to obtain an intermediate frequency (IF) at the antenna, was proposed to resolve transmission loss at high frequencies [1–6]. This antenna could scan the mainbeam by controlling the LO’s incoming incident angle [7,8]. However, the work in [7] provides a single beam that cannot fulfill the requirement of the system like multiple input multiple output (MIMO) system [9,10] and angle diversity [11] systems. These systems need an antenna that provides multiple beams simultaneously. In order to produce a multibeam antenna without a complicated feeding system, this letter proposes the use of quasi-optical antenna-mixers. Multiple LO transmitters at different frequencies are used to provide multibeam at different IF frequencies. By taking element patterns into account, ∗ Corresponding author.
E-mail addresses: [email protected] (S. Janin), [email protected] (K. Sripimanwat), [email protected] (C. Phongcharoenpanich), [email protected] (M. Krairiksh). 1434-8411/$ - see front matter 䉷 2007 Elsevier GmbH. All rights reserved. doi:10.1016/j.aeue.2007.07.004
accurate beam directions can be accomplished. This kind of multibeam antenna is useful for modern wireless communications.
2. Principle of a multibeam antenna using quasi-optical antenna-mixers Our multibeam antenna was designed based on the principle of quasi-optical antenna mixers. By using the technique in [7], the mainbeam of the antenna could scan by changing the LO direction and the LO frequency without using phase shifters. In this letter, this technique is used to demonstrate a multibeam application which was achieved by using three LO transmitting signals instead of one LO signal. Fig. 1 shows the proposed multibeam antenna. The configuration of the multibeam antenna with quasi-optical hybrid ring antenna-mixers is shown in Fig. 1(a). Fig. 1(b) shows the top view of mixer circuits and the cross-section of quasi-optical antenna-mixer element. The direction of the RF-receiving beam at the lower side of the antenna is defined by the direction of the LO-transmitting antenna at the
S. Janin et al. / Int. J. Electron. Commun. (AEÜ) 62 (2008) 450 – 454
f2
f1
451
fM
LO1
LO2
LOM
x z
Quasi-optical antenna-mixer
dL
Σ
1
2
BPF1
IF1
BPF2
N
IF2
dR Biasing circuits
Beam 1
Beam 2
IFM
Beam M
s1
s2
Gnd. HSCH-9101
BPFM
Multibeam footprint
Gnd.
RF receiving antenna Gnd. Gnd.
dR HSCH-9101
dL LO receiving antenna +VCC
+VCC
+VC C
+VCC
IF output LO receiving patch
RO3003
antenna LO coupling slot
foam Mixer and the feeding side
TLC-27 foam
RF coupling slot RO3003 RF receiving patch antnna
Fig. 1. Configuration of: (a) A multibeam antenna using quasi-optical antenna-mixers; (b) Top view of mixer circuits and the cross-section of quasi-optical antenna-mixer.
452
S. Janin et al. / Int. J. Electron. Commun. (AEÜ) 62 (2008) 450 – 454
3. Experimental results
30 R : RF receiving direction (degrees)
Isotropic element
To demonstrate the multibeam operation, a 4 × 1 quasioptical hybrid ring antenna-mixer was fabricated as shown in Fig. 3. Fig. 3(a) shows hybrid ring mixers on feeding side and Fig. 3(b) shows the mixer circuit using HSCH9101 Schottky diodes. Fig. 3(c) shows an experimental setup for multibeam operation. The distance between antenna elements was 0.9 at 18.8 GHz. It was limited by the hybrid
20 10 0 –10
Patch element
fL fL fL fL fL fL
–20 –30 –30
–20
–10
0
10
= 17 GHz = 17.5 GHz = 18 GHz = 17 GHz = 17.5 GHz = 18 GHz
20
0.23 mm 30
L : LO transmitting direction (degrees)
Fig. 2. Relation of mainbeam direction to LO direction.
upper side, and the multibeam operation were realized at different LO frequencies with different resultant intermediate frequencies. For a linear array of N elements, radiation pattern of the down converted intermediate frequency (IF) signal on XZ plane including radiation patterns of patch antennas is IF = 0.5 cos(R − L )t × AR ()AL () N × [ej(i−1)(kR dR cos R −kL dL cos L ) ],
76 mm
HSCH-9101
(1)
i=1
where AR () and AL () are H-plane radiation patterns of the microstrip patch antennas of the RF-and LO-receiving antennas, respectively [12]. N is the number of elements, kR is the wave number of the RF signal, kL is the wave number of the LO signal, dR is the separation between elements of RF receiving patch antennas, and dL is the separation between elements of LO receiving patch antennas. dR and dL are generally different, but they can be same in practice. The directions of RF and LO signals are depicted by R and L , respectively. Fig. 2 shows relation of mainbeam directions to LO directions for RF of 18.8 GHz when isotropic sources and patch antennas are used. It is noted that the relation fluctuates instead of linear relationship when the patch antennas are used instead of the isotropic sources. This is due to the pattern multiplication of array factor with patch radiation patterns. For instance, when the mainbeam direction of array factor is at −20 ◦ , the H-plane patch radiation pattern has maximum at 0◦ . Therefore, the mainbeam results from pattern multiplication will be at −18◦ . The beam direction, normally depending on the direction of the LOtransmitting antenna and LO frequency (fL ), is limited by non-isotropic radiation patterns, the distance between antenna elements and the difference between RF and LO frequencies. However, Fig. 2 shows that LO direction produces more pronounced effect on mainbeam direction than LO frequency. Therefore, it is important to carefully specify the LO direction.
HSCH-9101
RF transmitting antenna
4x1 Quasi-optical antennamixers
Microwave absorber LO1 4x1 Wilkinson power combiner
LO2
LO3 LO feeding antennas
Biasing circuit
Fig. 3. Photographs of the fabricated multibeam antenna (a) Hybrid ring mixers on feeding side; (b) Mixer circuit; (c) Experimental setup for multibeam operation.
S. Janin et al. / Int. J. Electron. Commun. (AEÜ) 62 (2008) 450 – 454 z
Simulation 1.8 GHz (-23.8 degrees) Measurement 1.8 GHz (-23.8 degrees)
0
x 30
-30
-60
60
-90
90
-20
-10
0 [dB]
LO1 (17 GHz) -30 degrees Simulation 1.3 GHz (0 degrees) Measurement 1.3 GHz (0 degrees)
z 0
x
30
-30
-60
60
-90
90
-20
-10
4. Conclusion z
A multibeam antenna using quasi-optical antenna-mixers is presented in this letter. The accurate RF-receiving mainbeam direction could be obtained when the patch antenna element patterns are taken into account. The result shows three receiving mainbeams which can be used in multibeam operation.
0
x
30
-30
-60
60
-90
90
-20
-10
0 [dB]
0 30
-30
Acknowledgements This work was supported by the Thailand Graduate Institute of Science Technology under Grant number TG-B-1144-22-717D and the Thailand Research Fund under Grant number RTA-4880002.
LO3 (18 GHz) +30 degrees
Side lobes
ring coupler dimension. Each LO signal was produced by using a tilted active patch antenna placed at three positions. The three active patch antennas were placed at −30◦ , 0◦ and +30◦ off broadside to feed LO signals at 17 GHz (LO1), 17.5 GHz (LO2) and 18 GHz (LO3) for multibeam demonstration. The IF power of each element was calibrated by adjusting biasing current to obtain uniform amplitude excitation. The radiation patterns are shown in Fig. 4, which demonstrate three beam operations at the same time. The results were measured at 1.8 GHz (Beam 1), 1.3 GHz (Beam 2) and 0.8 GHz (Beam 3) as shown in Fig. 4(a), (b) and (c), respectively. The measured mainbeam directions agree well with the calculated patterns. However, the side lobe levels were different because calculation in Eq. (1) neglected mutual coupling effect and non-uniform LO amplitude excitation due to the fabrication process. Grating lobes took place due to wide separation of antenna elements. To illustrate effect of dR on side-lobe level, Fig. 4(d) shows simulated patterns of the proposed antenna with dR = 0.5, 0.7 and 0.9. The corresponding side lobes are −13, −7 and −3 dB down from the main lobe, respectively. It is clear that side lobe could be reduced further by reducing separation between antenna elements. It can be improved by reducing hybrid ring size.
0 [dB]
LO2 (17.5 GHz) 0 degrees Simulation 0.8 GHz (+26.3 degrees) Measurement 0.8 GHz (+26.3 degrees)
453
z x
References -60
60
90
-90
dR= 0.5 λ dR= 0.7 λ dR= 0.9 λ 0
-20
-40
[dB]
fL (17.5 GHz) +30 degrees
Fig. 4. Multibeam radiation patterns: (a) Beam 1 at −23.8 degrees; (b) Beam 2 at 0 degrees; (c) Beam 3 at +26.3 degrees; (d) simulated patterns at different dR .
[1] Stephan KD, Camilleri N, Itoh T. A quasi-optical polarizationduplexed balance mixer for millimeter-wave applications. IEEE Trans Microw Theory Tech 1983;31:164–70. [2] Hwang VD, Uwano T, Itoh TT. Quasi-optical integrated antenna and receiver front end. IEEE Trans Microw Theory Tech 1988;1:80–5. [3] Masarweh SK, Sherer TN, Yngvesson KS, Gingras RL, Drubin C, Cardiasmenos AG, et al. Modeling of a monolithic slot ring quasi-optical mixer. IEEE Trans Microw Theory Tech 1994;42:1602–9.
454
S. Janin et al. / Int. J. Electron. Commun. (AEÜ) 62 (2008) 450 – 454
[4] Tong C-Y, Blundell R. A self-diplexing quasi-optical magic slot balanced mixer. IEEE Trans Microw Theory Tech 1994;3:383–8. [5] Robertson SV, Katehi LPB. A planar quasi-optical mixer using a folded-slot antenna. IEEE Trans Microw Theory Tech 1995;43:896–8. [6] Neculoiu D, Bartolucci G, Konstantinidis G, Marcelli R, Petrini I, Dragoman M, et al. A micromachined 38 GHz schottky-diode uniplanar monolithic integrated quasi-optical mixer. IEEE Radio Frequency Integrated Circuits (RFIC) Symposium 2004; 531–4. [7] Nishimura T, Ishii N, Itoh K. Beam scan using the quasioptical antenna mixer array. IEEE Trans Antennas Propag. 1999;47:1160–6. [8] Saito H, Nishimura T, Yamamoto M, Itoh K. Quasi-optical antenna-mixer array composed of a magnetic loop antenna
[9]
[10]
[11]
[12]
operated at 10 GHz band. Electronics and Communications in Japan 2004;87:45–53. Paulraj AJ, Gore DA, Nabar RU, Bolcskei H. An overview of MIMO communications – A key to gigabit wireless. Proc IEEE 2004;92:198–218. Foshini G, Gans M. On limits of wireless communications in a fading environment when using multiple antennas. Wireless Personal Communications 1998;6:311–35. Perini PL, Holloway CL. Angle and space diversity comparisons in different mobile radio environments. IEEE Trans Antennas Propag 1998;46:764–75. Balanis CA. Antenna theory analysis and design. Canada: Wiley; 1997.