QPSK Modulation and Demodulation System Using SIW Interconnect

In this paper, design and fabrication of a substrate integrated waveguide (SIW) with 1428 GHz bandwidth is implemented. The SIW-based system with Quadrature Phase Shift Keying (QPSK) modulation and demodulation technique is designed and implemented. The measurement results show that the proposed system has up to 8 Gbps transmission data rate, which doubles the transmission rate compared with traditional mixing system. The demonstrated system is verified to be an effective interconnect system for ultra high speed transmission. Introduction A substrate integrated waveguide (SIW), presenting a planar and integrated form with metalized hole arrays instead of metallic sidewalls of the rectangle waveguide, has been widely used for the design of a new class of millimeter-wave components [1]. Due to easy fabrication process and a relatively low cost of production [2]-[3], SIW interconnects are often employed as high speed data transfer physical channels in the field of high frequency communication system. With the highpass characteristics of SIW, baseband signals must be modulated before entering the SIW interconnect and demodulated after extracting from the same interconnect channel to satisfy high speed data transmission. A waveguide system yielding 5 Gbps data transmission capacity is designed and validated by using mixing technique experimentally where excellent signal integrity characteristics are obtained [4]. However, traditional mixing, whose channel bandwidth usage is not very efficient due to its double sideband modulation, is no longer prevalent for high speed and large bandwidth signal transmission. To further increase the channel capacity, Quadrature Phase Shift Keying (QPSK) and 16 Quadrature Amplitude Modulation (16QAM) can be employed. In this paper, an experimental prototype of SIW covering wide bandwidth is presented. Based on QPSK scheme, data communication utilizing SIW interconnect in high-speed signaling applications is addressed. At last experimental platform is established and verified for the proposed communication system. System Implementation Design and Fabrication of SIW. The center frequency of SIW is 21 GHz with 14 GHz cut-off frequency, thus the usable bandwidth spans from 14 GHz up to about 28 GHz, i.e. about 14 GHz. As we know, microstrip line is widely used in the traditional coplanar integrated circuits whose characteristic impedance is set to 50 Ω in common practice. In order to realize the integration between microstrip line and SIW, an efficient taper transition structure with good impedance matching is designed and optimized here. The detailed dimensions and design parameters of the SIW structure are summarized in Table 1. According to these design rules, the final SIW structure is shown in Fig. 1 (a). 2nd International Conference on Electrical, Computer Engineering and Electronics (ICECEE 2015) © 2015. The authors Published by Atlantis Press 1169 table 1. dimensions of siw, microstrip line and tapered transition (unit: mm) / SIW Microstrip Tapered transition Via spacing distance Width 7.016 1 3.776 0.8 Length 36 3.7 6.4 Via diameter Height 0.035 0.035 0.035 0.4 Fullwave simulations are employed to illustrate the performance of SIW with a Rogers 5880 substrate and the results are shown in Fig. 1 (b). It can be seen that the return loss is better than 15 dB while the insertion loss is less than 0.5 dB in the entire designed bandwidth except for the cutoff frequency nearby. Since the microstrip line in Fig. 1 (a) lies in the middle of substrate, odd modes will be activated on the one side of SIW rather than even modes due to their heterodromous distributed electric field in transverse section. Furthermore, there is no apparent coupling between the dominant mode TE10 and other higher order modes in the wide bandwidth to support lager data rate transmission in SIW. To validate the performance of designed SIW, two SIW prototypes with different test fixtures composed by metallic Cu and Al are fabricated for comparison as shown in Fig. 2. SIW Tapered transition substrate