SIW Based Multilayer Transition and Power Divider in LTCC. Technology. Hattan Abuzaid1, Ali Doghri2, Ke Wu2, and Atif Shamim1. 1IMPACT Lab, Electrical ...
SIW Based Multilayer Transition and Power Divider in LTCC Technology Hattan Abuzaid1, Ali Doghri2, Ke Wu2, and Atif Shamim1 1
IMPACT Lab, Electrical Engineering Program, King Abdullah University of Science and Technology, Thuwal 23955-6900, Kingdom of Saudi Arabia
Poly-Grames Research Center, Département of génie électrique, Ecole Polytechnique de Montreal, C. P. 6079, Succ. Centre-ville, Montréal, QC, Canada H3C 3A7
2
Abstract — A multilayer transition and balanced power divider are presented for millimeter-wave system-on-package (SoP). These two components operate at Ka-band and exploit the substrate integrate waveguide (SIW) technology with its shielding characteristics and the Low-temperature co-fired ceramics (LTCC) technology for its high density integration. A coupling slot has been used to perform vertical integration, which can be easily optimized through its length. The measured input return loss within the bandwidth of interest (32 GHz – 38 GHz) is less than -15 dB and -18 dB for the multilayer transition and the power divider, respectively. The lateral dimensions of a multilayer system, such as a feed network of an array, can be greatly reduced by employing these 3D slot-coupled components. Index Terms — Substrate integrated waveguide (SIW), power divider, low temperature co-fired ceramic (LTCC), multilayer transition.
I. INTRODUCTION Low temperature co-fired ceramic (LTCC) technology is prevalent as a platform for microwave components such as filters, antennas, and couplers. It features the ability to make structures with a large number of layers, enabling reduction of the module’s footprint through vertical integration. Compared to its multilayered printed circuit board (PCB) counterpart, LTCC technology offers easier implementation of blind vias, buried vias, and air cavities as well as precise layer alignment. This makes it a better candidate for system-on-package (SoP) solutions [1]. Typical planar transmission lines such as microstrip, stripline, or coplanar waveguide are prone to significant crosstalk when incorporated in a multilayered structure, in addition, these transmission media suffer large losses at millimeterwaves (MMW). On the other hand, electromagnetically shielded guides, such as the substrate integrated waveguide (SIW) [2], are characterized by excellent isolation and low loss at MMW bands. Because of its suitability for high frequencies and its planar integrated nature, researchers have developed a multitude of components using SIW. Utilizing vertical integration in LTCC requires efficient layer-to-layer transition and schemes that use this transition to realize desired functions such as power splitting. In [3], a compact Ka-band SIW power divider was made using a coupling slot transition between the different layers, however,
its bandwidth was relatively narrow. A 60 GHz SIW fed cavity array antenna on LTCC was reported in [4], and a crossed, broadwall coupler was employed to transmit power vertically along the structure. Even though the transition in [4] is broadband, there are several parameters involved in its design, which makes it fairly complex to optimize. In this paper, an efficient, wideband, and simple Ka-band multilayer transition is made on LTCC using SIW technology. Afterwards, this transition is used as a key component to form a multilayer, balanced, 2-way power divider. Section II handles the theoretical representation of the structure, and Sections III and IV describe the design parameters and simulation model of the multilayer transition and the 3-dB power divider, respectively, along with a discussion on measured results conformity with simulation results. II. FOLDED SIW CONCEPT The folded SIW was first presented for miniaturization purposes [5]. It is formed by partially inserting a metallic sheet inside a waveguide along its broadwall. The electric field of the TE10 mode will then conform to the folded structure and rotate its orientation accordingly. At frequencies where the full width of the folded structure satisfies the cut-off frequency requirement, the structure exhibits interesting characteristics; the maximum value of the electric field occurs at the small gap between the end of the inserted plate and the narrow wall of the structure, thereby resembling the distribution magnitude found in the conventional waveguide (i.e. maximum field value occurring at the width’s center). However, when considering the vicinities above and below the inserted plate to be separate waveguides of full width, at such a frequency this structure forms a multilayer transition through a coupling slot in the common broadwall.
Fig. 1.
Geometry of a) SIW and b) Folded SIW.
III. MULTILAYER TRANSITION Fig. 2 shows the model of the multilayerr transition; two waveguides lying on different layers are connnected through a longitudinal slot, and the slot is positioned at the extreme side of the broadwall. The upper waveguidde is gradually terminated as the slot opens, whereas, the llower waveguide gradually opens to eventually reach full w width as the slot terminates. The optimization of this structuure is fairly easy with one parameter to choose, namely, the length of the slot Ls. A microstrip-to-SIW transition is added on both sides to provide testing accessibility. Using Ansys H HFSS v14.0, the multilayer transition was optimized for perfoormance from 32 GHz to 38 GHz, and its geometrical dimensiions are listed in Fig. 2.
measured S-parameters of the mulltilayer transition are listed and compared in figures 4 and 5, and general agreement is observed between them.
Fig. 4. Measured and simulated reeturn loss of the proposed multilayer transition.
Fig. 2. Geometry of the multilayer transition: Ls = 9.16mm, Ws =0.105mm, Wt = 2mm and Wsiw= 2.39mm,, P=0.375mm and d=0.1363mm.
The fired layer thickness used in the model is 0.112 mm, and the substrate material is DuPont 9K7 with a ddielectric constant of 7.1 and a loss tangent of 0.001. Although two layers are needed to realize the structure theoreticcally, the used fabrication process mandates the minimum nnumber of layers to be six, thus, four extra layers are addded beneath the structure to successfully fabricate it. Thhe electric field magnitude inside the structure, represented in cross sections, is shown in Fig. 3a. The image of the fabriicated multilayer transition is depicted in Fig. 3b.
Fig. 5. Measured and simulated inssertion loss of the proposed multilayer transition.
IV. MULTILAYER BALANCED D POWER DIVIDER
a)
b)
Fig. 3. a) Multilayer transition E-field magnnitude distribution simulated at 35GHz for different cross-sections, and b) Fabricated multilayer transition.
The prototype was measured using a V Vector Network Analyser (VNA) and a Thru Reflect Line (TR RL) calibration to de-embed connector and transition effects.. Simulated and
Fig. 6 depicts the structure of the 3-dB power divider. A slot is opened between two layers as discussed previously, then, a Y-shaped branch is gradually openeed in the lower layer until it splits into two separate waveguidess where the slot terminates. The same slot dimensions of the mu ultilayer transition are used. The electric field magnitude pllot into the two layers is shown in Fig. 7a. The image of the fabricated balanced power divider is featured in Fig. 7b. Simulated and measured S-param meters of the power divider are listed and compared in figures 8 and 9.
Fig. 6. Geometry of the multilayer power divider: Ls = 9.16mm, Ws =0.105mm, Wt = 2mm and Wsiw= 2.39mm.
A good agreement is seen in Fig. 8. There are some discrepancies between the results in Fig. 9, however, the module still performs well within the targeted bandwidth. This disagreement could be attributed to the reduction of the postfire shrinkage percentage of the LTCC module, which resulted in different structure dimensions. In addition, the dielectric constant and loss tangent used in simulations were acquired using measurements at 10 GHz, and these parameters could vary at 35 GHz, resulting in further disagreement. The phase shift between the two output ports is 1820 ± 0.70. Port3 (Layer2) Port2 (Layer2)
Port1 (Layer1)
a)
b)
Fig. 7. a) Power divider E-field magnitude distribution simulated at 35GHz, and b) Fabricated multilayer balanced power divider.
Fig. 8. Measured and simulated return loss of the proposed multilayer power divider.
Fig. 9. Measured and simulated transmission coefficients of the proposed multilayer power divider.
V. CONCLUSION In this paper a multilayer transition and multilayer power divider were created based on Substrate Integrated Waveguide (SIW) and Low Temperature Co-fired Ceramic (LTCC) technologies. The measured input return loss within the bandwidth of interest 32 GHz to 38 GHz is less than -15 dB and -18 dB for the multilayer transition and the power divider, respectively. Compared to previous work, the modules exhibited wide bandwidth characteristics and design simplicity. The proposed components could be used to make 3D system-on-package structures with a greatly reduced footprint. REFERENCES [1] Sangsub Song; Youngmin Kim; Jimin Maeng; Heeseok Lee; Youngwoo Kwon; Kwang-Seok Seo; , "A Millimeter-Wave System-on-Package Technology Using a Thin-Film Substrate With a Flip-Chip Interconnection,"Advanced Packaging, IEEE Transactions on , vol.32, no.1, pp.101-108, Feb. 2009. [2] Deslandes, D.; Wu, K.; "Integrated microstrip and rectangular waveguide in planar form," Microwave and Wireless Components Letters, IEEE , vol.11, no.2, pp.68-70, Feb. 2001. [3] Zhongshan Xie; Bing Liu; Yongjiu Zhao; Bo Tian; Shengli Jia; , "A novel Ka band multi-layer SIW power divider," Cross Strait Quad-Regional Radio Science and Wireless Technology Conference (CSQRWC), 2011 , vol.1, no., pp.634-636, 26-30 July 2011. [4] Junfeng Xu; Zhi Ning Chen; Xianming Qing; Wei Hong; "Bandwidth Enhancement for a 60 GHz Substrate Integrated Waveguide Fed Cavity Array Antenna on LTCC," Antennas and Propagation, IEEE Transactions on , vol.59, no.3, pp.826-832, March 2011. [5] G. L. Chen, T. L. Owens, and J. H. Whealton, "Theoretical study of the folded waveguide," Plasma Science, IEEE Transactions on, vol. 16, pp. 305-311, 1988.
