77-GHz Integrated Antenna with Plano-Convex Lens: Design and Measurement Siew Bee Yeap 1 , Xianming Qing 1 , and Zhi Ning Chen 1,2 1 RF, Antenna and Optical Department, Institute for Infocomm Research, A*STAR, Singapore {sbyeap, qingxm, chenzn}@i2r.a-star.edu.sg 2 Electrical and Computer Engineering Department, National University of Singapore, Singapore [email protected]Abstract— A 77-GHz four-beam plano-convex lens antenna with SIW slot feed for automotive radar is presented. The primary feed consists of four substrate integrated waveguide (SIW) slots which are designed with complete routing and SIW to grounded co-planar waveguide (GCPW) transition. The transition is designed for the integration with a 3D embedded wafer level ball grid array (eWLB) module as well as for on- wafer probing measurements, respectively. The antenna prototype at 77 GHz achieves the gain of 24 dBi and a combined beam coverage of ±12 o . The simulated and measured results agree quite well Index Terms—77GHz, automotive radar, multiple bean antenna, SIW slot antenna, lens. I. INTRODUCTION The automotive radar with its autonomous cruise control (ACC) and collision warning have been introduced since the late nineties [1][2]. The commercialization however mostly applies to high- and middle-class range cars, providing safety functions like pre-crash warning, collision mitigation as well as the ACC function. Today, automotive radars demand a highly integrated radar package, compatible with standard Surface Mount Device (SMD) technology to meet low cost requirements [3]. Embedded wafer level ball grid array (eWLB) [4] is a promising packaging technology allowing for higher ball counts which increase the package size beyond the chip area. This technology allows for 3D Package-on-Package (PoP) integration, which is increasingly becoming main-stream due to its flexibility [5]. The antenna suitable for package integration must be light in weight and small in size. The automotive radar however requires high gain antennas with multiple-beams for wider field of view, improved range and angular resolution. Antenna arrays are not suitable due to its large size and heavy weight to be assembled on the module. The size of the antenna array is expected to be much larger than the transceiver package. As such, free space beam forming is a technique to avoid feed networks and the loss associated with it in antenna arrays. Substrate lens is a suitable candidate for high gain and close integration with primary feeds [6][7]. In this paper, four primary feeds consists of substrate integrated waveguide (SIW) slot [8], is designed with complete routing and transition from SIW to grounded co- planar waveguide (GCPW) for assembly with an eWLB module as well as for on-wafer probing measurements of the antenna performance. The high gain is achieved with a plano- convex lens. II. 77-GHZ FOUR-BEAM PLANO-CONVEX LENS ANTENNA A. 77-GHz SIW slot primary feed The SIW slot is selected as the primary feed because it can be designed on single-layer PCB and assembled to chip module via GCPW transition and solder bumps. A four-port SIW slot primary feed operating at 77 GHz as shown in Fig. 1 is designed using RO4003C with substrate parameters of r = 3.38, tan= 0.0027 and a thickness of 0.203 mm. The SIW is with width, W SIW , of 1.4mm; slot length, L s , and width, W s , of 1.65 mm and 0.15 mm, respectively. The SIW slots are placed apart with G 1 = 3 mm and G 2 = 3.2 mm. For on-chip integration, SIW to GCPW transitions are designed, with the GCPW rerouted to smaller separation, g 1 = 1.6925 mm and g 2 = 1.325 mm. The SIW to GCPW transition is with gap, g gcpw1 , of 0.16mm and widths, w gcpw , and w gcpw1 , of 0.7 mm and 0.3 mm, respectively. The bottom layer of the antenna is covered with a layer of solder mask for integration with eWLB package. The solder bumps in the eWLB will be connected to the openings if the solder mask, circling the back of the PCB, while the opening on the GCPW pad is for the ground-signal- ground connection as shown in Fig. 1 (d). The overall dimensions are: width W a = 12 mm and length L a = 38.15 mm. For return loss and radiation pattern measurements, the GCPW is further reduced in size near the edge to accommodate W-band probes with pitch of 150 m where g gcpw2 = 0.05 mm and w gcpw2 = 0.15 mm. For pattern measuring purposes, the GCPW are extended longer to allow probing and to minimize any interference of the probes, with L ext = 28mm. Fig. 2 shows the four-port SIW slot primary feed for |S 11 |, gain patterns measurement as well as the GCPW transition for on-wafer probe measurement, respectively.
Transcript
77-GHz Integrated Antenna with Plano-Convex Lens: Design and Measurement
Siew Bee Yeap1, Xianming Qing1, and Zhi Ning Chen1,2
1 RF, Antenna and Optical Department, Institute for Infocomm Research, A*STAR, Singapore {sbyeap, qingxm, chenzn}@i2r.a-star.edu.sg
2 Electrical and Computer Engineering Department, National University of Singapore, Singapore [email protected]
Abstract— A 77-GHz four-beam plano-convex lens antenna with SIW slot feed for automotive radar is presented. The primary feed consists of four substrate integrated waveguide (SIW) slots which are designed with complete routing and SIW to grounded co-planar waveguide (GCPW) transition. The transition is designed for the integration with a 3D embedded wafer level ball grid array (eWLB) module as well as for on-wafer probing measurements, respectively. The antenna prototype at 77 GHz achieves the gain of 24 dBi and a combined beam coverage of ±12o. The simulated and measured results agree quite well
The automotive radar with its autonomous cruise control (ACC) and collision warning have been introduced since the late nineties [1][2]. The commercialization however mostly applies to high- and middle-class range cars, providing safety functions like pre-crash warning, collision mitigation as well as the ACC function. Today, automotive radars demand a highly integrated radar package, compatible with standard Surface Mount Device (SMD) technology to meet low cost requirements [3]. Embedded wafer level ball grid array (eWLB) [4] is a promising packaging technology allowing for higher ball counts which increase the package size beyond the chip area. This technology allows for 3D Package-on-Package (PoP) integration, which is increasingly becoming main-stream due to its flexibility [5]. The antenna suitable for package integration must be light in weight and small in size. The automotive radar however requires high gain antennas with multiple-beams for wider field of view, improved range and angular resolution. Antenna arrays are not suitable due to its large size and heavy weight to be assembled on the module. The size of the antenna array is expected to be much larger than the transceiver package. As such, free space beam forming is a technique to avoid feed networks and the loss associated with it in antenna arrays. Substrate lens is a suitable candidate for high gain and close integration with primary feeds [6][7].
In this paper, four primary feeds consists of substrate integrated waveguide (SIW) slot [8], is designed with complete routing and transition from SIW to grounded co-
planar waveguide (GCPW) for assembly with an eWLB module as well as for on-wafer probing measurements of the antenna performance. The high gain is achieved with a plano-convex lens.
II. 77-GHZ FOUR-BEAM PLANO-CONVEX LENS ANTENNA
A. 77-GHz SIW slot primary feed
The SIW slot is selected as the primary feed because it can be designed on single-layer PCB and assembled to chip module via GCPW transition and solder bumps. A four-port SIW slot primary feed operating at 77 GHz as shown in Fig. 1 is designed using RO4003C with substrate parameters of r = 3.38, tan= 0.0027 and a thickness of 0.203 mm. The SIW is with width, WSIW, of 1.4mm; slot length, Ls, and width, Ws, of 1.65 mm and 0.15 mm, respectively. The SIW slots are placed apart with G1 = 3 mm and G2 = 3.2 mm. For on-chip integration, SIW to GCPW transitions are designed, with the GCPW rerouted to smaller separation, g1 = 1.6925 mm and g2 = 1.325 mm. The SIW to GCPW transition is with gap, ggcpw1, of 0.16mm and widths, wgcpw, and wgcpw1, of 0.7 mm and 0.3 mm, respectively. The bottom layer of the antenna is covered with a layer of solder mask for integration with eWLB package. The solder bumps in the eWLB will be connected to the openings if the solder mask, circling the back of the PCB, while the opening on the GCPW pad is for the ground-signal-ground connection as shown in Fig. 1 (d). The overall dimensions are: width Wa = 12 mm and length La = 38.15 mm. For return loss and radiation pattern measurements, the GCPW is further reduced in size near the edge to accommodate W-band probes with pitch of 150 m where ggcpw2 = 0.05 mm and wgcpw2 = 0.15 mm. For pattern measuring purposes, the GCPW are extended longer to allow probing and to minimize any interference of the probes, with Lext = 28mm.
Fig. 2 shows the four-port SIW slot primary feed for |S11|, gain patterns measurement as well as the GCPW transition for on-wafer probe measurement, respectively.
Fig. 1 Four-port SIW slot for on-chip integration (a) Top view, (b) Bottom view, and (c) SIW to GCPW transitions, (d) Screen with holes for solder balls integration.
measurement, and (c) SIW-GCPW transition for probing
Fig. 3 Dimension of the plano-convex lens at 77 GHz
(b)
(c)
(d)
G1 G2 G1
Ws
Ls
WSI
via
(a)
Wa
La
g1 g2 g1
wgcpw
wgap
ggcpw1 wgcpw
wgcpw1
ggcpw1 ggcpw1
Lext
(b)
(c)
wgcpw1
ggcpw1
ggcpw2 wgcpw2
(a)
hRex
DRex
B. Plano-convex Lens
The plano-convex lens has been studied [6][7] and the design is mentioned here briefly. The material chosen is Rexolite with r = 2.53 and tan= 0.0013 as it is a low-loss material and suitable for applications at millimeter-waves. The plano-convex lens designed at 77 GHz is shown in Fig. 3 with the lens dimension for height hRex = 19 mm and diameter DRex = 48 mm. The focus is Lf = 20.5 mm beneath the lens.
III. MEASUREMENTS RESULTS
The SIW slot designs for |S11| and gain measurements were
fabricated as shown in Fig. 4. The four-port SIW slot is labelled as P1 starting from the left-most SIW slot and correspondingly P2, P3 and P4, as shown in Fig. 4 (a). Fig. 5 shows results for P1. The |S11| was measured for each port and results agree quite well with simulation, with frequency shift within 1%. All studies based on simulation were carried out using CST Microwave Studio [9].
Fig. 4 Fabricated SIW slot primary feed for (a) S11 measurements, and (b)
gain pattern measurements at 77 GHz
For the radiation pattern measurement, special fixture was
designed to hold the SIW slot and align the plano-convex lens. Fig. 6 shows the SIW slot placed into a fitted shallow cavity and the lenses held by four poles, respectively.
The measurement was conducted using a Cascade Microtech Summit 11000 probe station, Agilent E8361A vector network analyzer and 75-110GHz OML extender module. The gain patterns were measured in an anechoic-chamber as shown in Fig 7. As for the gain measurement, the calibrations were performed with two standard gain horn antennas. The receiving standard horn was then replaced by the SIW slot antennas and lens. All the losses were considered
Fig. 5 Simulated and measured (a) |S11|, (b) |S22|, (c) |S33|, and (d) |S44|
Fig. 6 Fixture for SIW slot and plano-convex lens alignment
in the measurements i.e. connector loss and probe loss etc. For pattern measurement, the lens antenna, together with the feeding probe, was fixed on the probe station while the horn antenna was rotated. Only the E-plane of the four-port lens antenna was measured to demonstrate the multiple beam characteristic.
Fig. 8 shows the measured E-plane co-polar radiation
patterns of the four-port lens antenna. The measured results agree quite well with simulated. The slightly higher side lobe levels and some discrepancy may attributed to PCB fabrication tolerances of the SIW slot, the alignment of the SIW slot to the lens or the lens to the rotating horn.
Fig. 7 77-GHz on-wafer setup for gain/pattern measurement
IV. CONCLUSIONS
A 77-GHz four-beam plano-convex lens antenna with SIW
slot primary feed has been presented. The SIW slot has been designed to show compatibility with on-chip integration through an SIW to GCPW transition. The plano-convex lens has been designed with low-loss Rexolite material. The simulated gain patterns have been validated through measurements. The plano-convex lens antenna has shown the gain of 24 dBi with a beam-span of ±12o.
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[6] S. K. Ryu, D. M. Yeo, Y. H. Kim, “ Approximated synthesis design of plano-convex teflon lens”, Asia-Pacific Microwave Conf., vol. 3, pp. 1056-1059, 2001.
Fig. 8 Simulated and measured radiation patterns of the plano-convex lens with four primary feeds at 77-GHz, (a) ±90o span of the four antennas, respectively, and (b) ±20o span
[7] T. Binzer, M. Klar, and V. Gross,”Development of 77-GHz radar lens antennas for automotive applications based on given requirements”, 2nd International ITG Conference on Antennas (INICA), pp. 205 – 209, 2007.
[8] S. Cheng, H. Yousef, and H. Kratz, “79-GHz slot antennas based on substrate integrated waveguides in a flexible printed circuit board”, IEEE Trans. on Antennas & Propag., vol. 57, no. 1, pp.64-71, January 2009.
