12 CHAPTER 2 LITERATURE REVIEW 2.1 SUBSTRATE INTEGRATED WAVEGUIDE SIW technology has received substantial attention due to its ease of integration with other planar and waveguide structures. Other names of SIW are laminated waveguide [44] and post-wall waveguide [45]. SIW technology was for the first time introduced in 1994 though noticed in the year 2001 [46]. Planar circuit topologies have been used in microwave and MmW integrated circuits and systems. Technology like microstrip lines, slot lines, coplanar waveguide (CPW) etc. are example of some of the technologies allowing planar designs. However, they are prone to high conductor losses. While designs utilizing traditional waveguide technology provide the low loss and coupling free characteristics, they are also bulky and expensive [47]. SIW inherits the qualities from traditional rectangular waveguide (RWG) such as low radiation loss, acceptable Q factor and the capability to handle high power along with the added advantage of low cost, low profile and capability of easy integration with planar structures [48]. Hence, efficient technologies like SIW are becoming popular for the design of microwave and MmW circuits as it provides efficient way of designing microwave circuits facilitating easy integration, low radiation loss and low cost of fabrication utilizing Printed Circuit Board (PCB) [47]. SIW structures can also be fabricated with Low-Temperature Co-fired Ceramic (LTCC) technology [49]. Though SIW and RWG have electrical similarities they also have some differences. Firstly, SIW is a periodic guided wave structure and it can also result in electromagnetic band-stop properties. Secondly, there might be some leakage through the space between via holes [50]. Therefore, SIW is designed with design equations derived by some eminent researchers of past [47].
13 2.2 ANTENNAS Antennas are vital part of any wireless communication systems. Proper antenna design is important to the successful implementation of wireless networks as antennas can improve the performance of wireless communication. Due to the small wavelength MmW antennas have small size and narrow beamwidth [51]. Therefore, high gain can be achieved with antennas having relatively small form factor. There are various forms of MmW antennas that have been designed to meet specific requirements such as horn antennas, tapered slot antennas, lens antennas, leaky wave antennas, slot antennas, dielectric rod antennas, microstrip antennas etc. [52-106]. In [107], Anthony et al. have proposed an Air Filled SIW (AFSIW) ALTSA which is made of multilayered PCB process. The impedance bandwidth covers 26-40 GHz. The proposed antenna has a gain of 11.7 dbi at 35.5 GHz. It has 3 db beamwidth of 39 in the xy plane. The antenna has simulated radiation efficiency of 99.4 %. In the paper, the authors have also compared the antenna with only SIW instead of AFSIW and have shown that the efficiency and gain has improved by using AFSIW in the antenna design. However, since the antenna design consists of multilayered PCB it is not as fit for mass production as the single layer SIW based design which can be fabricated with single layer PCB process. Guntupalli et al. have designed a 45 linearly polarized high gain antenna array for 60 GHz radio in [108]. The design consists of a SIW fed dielectric rod antenna. The feeding structure of the dielectric rod antenna also consists of a miniature ALTSA with corrugation. The antenna array is constructed with 1:16 SIW power divider which feed the 16 antennas. The antennas are connected to the power divider vertically. The average peak gain of the 4x4 45 linearly polarized ALTSA array is 17.5 dbi over the frequency range of 57-64 GHz.
14 Ghassemi et al. have designed a high gain planar antenna array for W and E band using SIW technology in [109]. The antenna is an ALTSA fed by SIW horn structure. Further, rectangular dielectric loading has been added on top of the ALTSA to narrow the beamwidth and gain increment. Gain of single element is 14 0.5 db. The antenna has efficiency of 84.23 % at 80GHz. Further, the measured gain of the 1x4 ALTSA array is 19 1 db. In [110], Taringou et al. have designed ALTSA with corrugation. CPW feed based on SIW is used as feed. The antennas are designed for 21-31GHz, 41-61GHz, 90-120GHz frequency ranges. However, only 21-31 GHz range ALTSA is fabricated and its measured and simulated results are compared. The simulated and measured results are found to be in good agreement except the cross polarization level which is found to be slightly higher than simulated. In [111], Natarajan et al. have developed anti-podal Vivaldi antenna with dualmode operation. The antenna operates in the ultra-wideband (3.1-10.6 GHz), GSM 1800 and WLAN. Switches are positioned for the wideband operation, along the tapered profile for bridging the slot line & operating as wide-band tapered slot antenna (TSA). The antenna displays narrow-band mode operation when switches S1 & S2 are OFF. Gain is 2.4 db at 1.8GHz and 5.5 db at 5.2GHz. It's noticed that at higher frequencies there is wide rejection making it suitable for operation in narrow-band. Similarly, antenna functions in wide-band mode when switches are in ON position. It has a gain of more than 6 dbi from 4 to 10 GHz. The antenna has 9.7GHz impedance bandwidth when operating in wide-band mode. The impedance bandwidth is 800 MHz and 280 MHz for the narrowband mode with the reference taken as -10 db. Symmetric radiation pattern is maintained by the antenna in the principal planes. In [112], Liu et al. have designed a Vivaldi antenna using tapered slot edge with resonant cavity structure. This modified design shows a great improvement in directivity and gain for the lower frequencies. The lower-end of the S11 < 10 db
15 limitation of the modified Vivaldi antenna is extended to 0.5 GHz from the 1.2 GHz as seen in conventional Vivaldi antenna. Further, with the modified design a 14.6% increase in impedance bandwidth is noted and 19.5% size reduction as compared to conventional Vivaldi antenna. However, for higher frequency it is seen to reduce the gain. In [113], Puskely et al. have designed a novel high gain Vivaldi antenna which operates in Ka band. The antenna is fed by SIW. The antenna has a high gain and low cross polarization. The measured gain of the fabricated antenna is greater than 10.5 dbi and has an overall good performance in the Ka band. The impedance matching has been improved by using the dielectric loading, corrugation and the printed metallic strips. The maximum measured gain of the antenna is reported to be 13.2 dbi at 34 GHz, and similarly, the minimum gain of the antenna is reported to be 10.4 dbi at 25 GHz. In [114], Hood et al. have designed a compact anti-podal Vivaldi antenna targeting UWB application. Antenna impedance bandwidth covers 3.1-10.6 GHz frequency range. Antenna displays low cross polarization level with decent gain. Substrates Rogers/RO3006 & FR4 is used in design & Radiation pattern, return-loss and gain have been presented. In [115], Lin. S. et al. have developed a compact Vivaldi antenna array on a thick substrate. The antenna array utilizes a compact SIW divider to lower the insertion loss of the feed structure. A novel grounded CPW feed has been used for a wideband transition to the SIW with good input match. In [116], Gong et al. have proposed a SIW based H-plane horn antenna which has an enhanced front-to-back ratio & a decreased sidelobe level (SLL). Using metallic rectangular patches & dielectric-loading which are joined to the horn antenna aperture the overall performance of the horn antenna is improved. It is reported that the gain is increased, SLL is decreased, E-plane beamwidth is decreased and the backward radiation
16 is decreased. The antenna operates at 22.7 GHz and the gain of the horn antenna is reported to be 10.1 dbi. In [117], Wang et al. have designed a dielectric loaded SIW H-plane sectoral horn antenna. Single substrate has been used for designing the SIW horn and the dielectric-loading making the fabrication process low cost and easy. Two different shapes were used for the dielectric loading structure, rectangular and elliptical, which are fabricated and the results measured for the single element antenna. The antenna with rectangle shaped dielectric loading provided the highest gain but the overall performance of the antenna with elliptical dielectric loading is found to be better. The simulated and measured results are shown to be in good agreement. Further, the authors designed the one-dimensional monopulse antenna array using antennas with elliptical shaped dielectric loading structure and achieved a high gain. The gain of 1x8 dielectric loaded monopulse antenna array is observed to be 15.65 dbi. Further, the isolation and return loss are found to be around -20 db. In [118], Iigusa et al. have designed SIW H-plane sectoral horn-antenna. The gain of antenna is increased by connecting several tapered slot antennas to the aperture of the H-plane SIW horn antenna. Further, dielectric loading is applied to the aperture of each tapered slot antenna to further enhance the gain. The antenna has the gain of more than 16 dbi in the 57-66 GHz band. In [119], Abedian et al. have developed a wideband circularly polarised dielectric resonator antenna. To realize a wideband dielectric resonator antenna the vertical coaxial feed that is supported by a small substrate is used to excite the rectangular dielectric resonator. The circular polarization is realized by utilizing the configuration of the feed which excite the orthogonal modes inside the dielectric resonator antenna. Then the corner of the rectangular dielectric resonator is removed at 45 and a floating parasitic strip is added to achieve the dual band circular polarized operation. The antenna has the impedance bandwidth of 59.8%. (6.57-12.18 GHz). The antenna has a dual 3 db axial
17 ratio bandwidths of 10.6% from 8.31 9.24 GHz and 13.5% from 10.18 11.66 GHz. In the lower band the peak gain varies from 4.47 to 4.86 dbic and in the upper band the peak gain varies from 4.33 to 4.91 dbic. In [120], Kazemi et al. have numerically investigated the dielectric rod antennas of circular cross-sections. Comparison of different structures of finite length rods as the function of various physical parameters like rod's diameter, length, dielectricconstant, multilayer & the corrugation effect have been performed. It has been shown that it is possible to extend the operating bandwidth of the antennas utilizing a core having high dielectric constant & cladding layer which has lower dielectric constant or it can also be extended by a material with high dielectric constant. Further, comparison of results from both simulation and measurement of different types of rod antennas is performed & it's noticed that they agree well with each-other. Pazin, et al. have presented a compact end fire 60 GHz TSA in [121]. It is printed on a liquid crystal polymer (LCP) substrate having low-permitivity. The antenna consists of a wideband collinear microstrip to slot transition. The proposed transition is smaller in size than other transition. One main advantage of the antenna is its easy integration with RF module for future WPAN applications. From the simulation it is seen that the antenna has impedance bandwidth from 53.3 to 69.6 GHz. The antenna gain is between 6.8 & 9.9dB. In [122], Yang et al. have proposed a new type of SIW cavity backed patch antenna array for MmW appplications. The antenna consists of a rectangular patch and a backed SIW cavity. The antenna impedance bandwidth is larger than 15 % and has gain of 6.5 dbi. Similarly, for the 4 x 4 antenna array the impedance bandwidth is 8.7 % and gain is 17.8 dbi.
18 In [123], Ferreira et al. have presented a small-footprint printed ring slot antenna with circular polarization. The antenna radiates above the open-cavity which is loaded with an artificial magnetic conducting reflector. The feed network consists of two T-shaped capacitive feed structures which are integrated to a miniature hybrid branch line coupler. Peak gain of the antenna is approximately 6.8 dbic at 2.4 GHz. The antenna also has a good front to back ratio and a low cross polarization. In [124], Hong et al. have proposed a SIW cavity-backed circular ring slot antenna made of textile material and targeted for wireless body area network applications. The antenna has a bottom ground and a top patch with a circular ring slot. They are connected by shorting vias. The antenna contains a SIW cavity-feed structure. All of the components of the antenna are made using textiles. The measured 10-dB impedance bandwidth of the antenna covers the 5.8 GHz Industrial, Scientific, and Medical Band. The measured peak gain of the antenna is 3.12 dbi. The efficiency of the antenna is 37.7%. In [125], Genovesi et al. have presented a compact wearable antenna which is printed on a paper. The antenna consists of a non-resonant coplanar monopole antenna which has been placed on a miniaturized artificial magnetic conductor. The fabrication of the antenna is done through the desktop inkjet printer which consists of conductive nano ink. The -10 db impedance bandwidth spans almost from 750 MHz to a little more than 1 GHz. The antenna design is also compared with the designed antenna on perfect electric conductor and it is found that the antenna has better performance when designed on a miniaturized artificial magnetic conductor. In [126], Basit et al. have designed wide-band slot antenna consisting of parasitic directors offering endfire radiation with CPW feed. The antenna design consists of several slots having different dimension which are etched on ground-plane of substrate. In the design two slots connected directly to the CPW feed. The remaining slots radiate because of parasitic coupling. The antenna can operate in the frequency range 12-18GHz with a peak gain of 10 dbi.
19 In [127], Yu et al. have designed a packaged ultra-broadband terminal antenna. In the design, dual-dipole-element pair which are connected using metallic vias has been adopted as the terminal antenna with a lower radiation pattern ripple. To reduce the mutual interference between the antenna and the inner circuit and to stabilize the antenna bore sight gain versus the operating frequency, a SIW open cavity has been used. The return loss is higher than 10 db from 36-50GHz & higher than 15 db from 38-46.5GHz & 47.5-48.5GHz. The antenna has a peak gain of 3.3 dbi at 40 GHz. In [128], Zhang et al. have developed a compact patch antenna which is fed by microstrip line with improved bandwidth & suppressed harmonic. This is achieved by using the λ/4 microstrip line resonators which are introduced & coupled in proximity of the rectangular patch. The antenna has a low profile property with thin substrate. Compared to the inset fed rectangular patch this antenna has 2.7 times more bandwidth. The antenna operates at 4.9 GHz and the peak gain is 7.3 db. In [129], Li et al. have designed a compact triple-band printed monopole antenna for WLAN/WiMAX applications. The antenna design mainly consists of a fork shaped strip & defected ground plane. The fork shaped strip has been imprinted on a modified rectangular ring. The antenna operates in the frequency bands 2.41 2.63, 3.39 3.70, and 4.96 6.32 GHz. The antenna has peak gain of -0.10 0.28, 0.24 1.42, and 2.67 4.76 db in 2.4 2.7, 3.4 3.7, and 5.0 6.0 GHz, respectively. 2.3 BEAMFORMING NETWORKS AND MULTIBEAM ANTENNAS Beamforming systems play important role in 60 GHz wireless communication due to the atmospheric attenuation and signal blockage faced by the 60 GHz link. Therefore, the multbeam antenna systems are important for successful implementation of 60 GHz wireless network. Numerous research work regarding multibeam antennas have been presented in various literatures [130-141].
20 In [137], Cheng et al. have designed a SIW multi-beam antenna using the principle of parabolic reflector. By positioning the point source feed in the focus of paraboloid structure made of SIW, a spherical wave is produced and its conversion to plane wave occurs upon reflection while it travels toward the parabola axis direction. Slotted SIW antenna is integrated to the BFN. The reflection coefficient and the isolations are below -10 db for the designed band. The multibeam antenna has been designed for 37.5 GHz. The radiated beam directions are -30, -21, -13, -5, 5, 14 and 23. The antenna has a peak gain of 19.1 dbi. In [140], Cheng et al. have developed a SIW based multibeam antenna based on eight port hybrid. The design uses four 90 hybrid couplers which are connected together in a symmetric arrangement. When port 1 is excited, the reflection coefficient and the mutual couplings with other ports are below -20 db at 30 GHz. The beam is directed towards 15 when port 1 is excited and similarly the beam is directed towards 47 when port 2 is excited at 30 GHz. The gain of the antenna is 12.2 dbi when port 1 is excited and the gain is 13 dbi when port 2 is excited at 30 GHz. An inexpensive switched-beam patch antenna is proposed in [142] by Tseng et al. where a 4 x 4 planar butler matrix constructed using microstrip technology is used as the BFN. The antenna array and the BFN are integrated on the same substrate. For evaluating the designed switched-beam antenna only port 1 & 2 are excited as it's a symmetrical structure. The switched beam antenna has a gain of 8.9 dbi when port 1 is excited and it provides a gain of 7.7 dbi when port 2 is excited at 62 GHz. The main beam points at 14 when port 1 is excited & while exciting port 2 it points towards 40. The return loss is greater than 10dB over 55-65GHz which is the total measurement bandwidth when port 1 is excited. return-loss is better than 9.6dB from 59.7 to 65GHz when port 2 is excited. In [143], Tekkouk et al. have proposed a switched beam antenna utilizing the ridged waveguide technology. The switched beam antenna consists of slot antenna array
21 and bulter matrix network along with the side-lobe suppression circuit. The novel design has SLL control circuit which is made of 90 couplers with different coupling factors & crossovers. The dual layer antenna has been assembled utilizing diffusion bonding technology. Field of view of the antenna is 43 and has a SLL lower than -17.5 db. Further, the isolation between the input ports at designed frequency of 61.5GHz is better than 25dB. Impedance bandwidth is greater than 6.5%. When port 1 is excited the switched beam antenna has a gain of 26.25 dbi and the gain is 25.24 dbi when port 2 is excited. The first BFN based on SIW design was proposed in the year 2002 by Yamamoto et al. in [144]. The design incorporated slot antenna array and 4 x 4 SIW butler matrix network. The proposed multibeam antenna system provided four beams covering 90 sector in horizontal plane with a peak gain of 21.3 dbi in the 26 GHz band. Chen et al. have proposed a 4 x 8 optimized SIW butler matrix structure in [145]. The switched beam antenna consists of slot antenna arrays and an optimized butler matrix network with 4 input ports and 8 output ports. The length of the multibeam antenna is 329 mm and is designed in the Ku band. The return loss is observed to be better than 14 db from 15.6 16.6 GHz. The main beam is directed towards 45 when port 2 & 3 is excited. Similarly, it switches to 15 while exciting port 1 & 4. SLL is less than -21.5 db while exciting port 1 & 4 and the side-lobe is less than -14.5 db while exciting port 2 & 3. In [146], Guntupalli et al. have designed switched beam antenna using SIW butler matrix and dieletric rod antenna consisting of miniature ALTSA fed by SIW. So, basically the radiating part consists of miniature ALTSA which is used for excitation of the dielectric rod antenna in front of it. BFN or the BM design is 4x4 BM designed with single layer SIW technology. The BFN has four input ports and four output ports. Four antennas are integrated to the four output ports of the BFN. The beam directions corresponding to each input port are 46, 12, +12 and
22 +47 for port 1-4 respectively. Similarly, antenna has gain of 14.5 dbi, 12.2 dbi, 12.3 dbi & 14.5 dbi for port 1-4 respectively. In [147], Yang et al. have presented a multibeam slot array using SIW technology which operates at ~ 30GHz focusing on future mobile terminal application for 5G. In multibeam slot array design, BM has been used as BFN. The BM contains crossovers, phase-shifters (135 & 0 ) & couplers. 4x4 butler matrix has been used as BFN and slotted SIW antenna array has been used as the radiating part. The -10 db impedance bandwidth of the slot array is 28-32 GHz. The multibeam antenna gain for each port at 30GHz is 10.8, 12.1, 12, and 11 db. Main beam points toward +13 & -13 during excitation of port 2 & 3 respectively. Main beam points toward +51 & -51 during excitation of port 4 & 1 respectively 2.4 PROPAGATION MEASUREMENT Because of the propagation mechanisms in the 60 GHz band, the 60 GHz communication link experiences attenuation due to atmospheric absorptions. However, this high attenuation is more of an advantage when dealing with the security issues. Therefore, the 60 GHz band has an inherent robust physical security due to the atmospheric attenuation. This also allows less interference between 60 GHz links located in close vicinities and in-turn provides higher frequency reuse for WLAN/WPAN cells in indoor environment. In [148], Hwang et al. have investigated and revealed the true potential of indoor Super Wi-Fi. The signal propagation characteristics of Super Wi-Fi have been experimentally compared with Wi-Fi in the same indoor environment. The wall and floor attenuation factors and Pth-Loss distribution at 770MHz, 2.401 GHz, and 5.540 GHz have been measured. The downlink capacity of Wi-Fi and Super Wi-Fi has been predicted. It has been found that TV White Spaces (TVWS) signals can penetrate up to two floors
23 above and below. However, it has been noted that Wi-Fi signals experience significant Pth-Loss even through a single floor. In [149], MacCartney et al. have performed propagation measurements in 28GHz & 73GHz bands in an office environment. Sliding correlator channel sounder systems have been used in the propagation measurement campaign. The measurements done in the indoor office environment gives insight to large scale Pth-Loss & temporal statistics. The indoor environment where measurement is performed is a closed-plan inbuilding scenario which consists of Line of Sight (LOS) and Non-Line of Sight (NLOS) corridor, a hallway, a cubicle-farm & adjacent room communication links. In this paper, the researchers have given a new large scale Pth-Loss models which are more physically based & simple in comparison to indoor models from 3GPP & International Telecommunication Union (ITU). In [150], Radi et al. have studied indoor propagation issues in indoor environment at 17 & 60GHz. In the paper, estimation of the coverage and frequency reuse capabilities of these bands is done with the aid of dual narrowband sounder. Several propagation models for indoor propagation like the free space loss, wall/floor attenuation model and atmospheric absorption model have also been discussed at 17 and 60 GHz. In [151], Yang has provided a detailed analysis on the indoor propagation and channel modeling. Further, the effect of antenna radiation patterns have been discussed along with the design of low cost radios at 60 GHz. Yang has used free space model, logdistance model and channel impulse response models in his study of the radio propagation. He has also characterized the 60 GHz wave propagation utilizing the channel measurements and the ray-tracing simulations with both the narrow beam and omnidirectional configurations. LOS and NLOS scenarios have been considered for the measurements. From the measurement study Yang reveals that directional antennas with narrow beam can boost received power as compared to the omnidirectional antennas.
24 In [152], Jung et al. have done a Pth-Loss measurement in indoor environment in-order to analyze the characteristics of indoor MmW channel and also studied the influence of geometry in this phenomenon mainly targeting NLOS environment where severe attenuations can be observed due to the partition, floors, furnitures and walls etc. Jung et al. have proposed the pathloss model using the statistical method based on measurement. The proposed model comprises of three parts (1) Free space Pth-Loss (2) Attenuation factor (3) Excess loss. Omnidirectional and horn antennas have been used for the measurement campaign. In [153], Moratitis et al. have performed a measurement campaign in indoor environment using horn antennas at 60 GHz. They have presented Pth-Loss measurements for both LOS & NLOS cases. They have also extracted the fading statistics in stationary environment and done detailed studies of human movement on temporal fading envelope. In [154], Maltsev et al. have presented empirical study of WLAN in an office environment in 60GHz band. They have used highly directional mechanically steerable horn antennas for measurement. Measurements have been performed in cubical environment and conference room. They have presented experimental results which demonstrate effect of polarization on propagation channel characteristics. Sulyman et al. have done propagation studies targeting 5G-Cellular systems in 28GHz, 60GHz & 73GHz bands & compared the measurements results with various MmW Pth-Loss models in LOS & NLOS cases. 60GHz measurements were carried out in courtyard and in-vehicle environment [155]. In India also research works regarding propagation Pth-Loss measurement at 60 GHz have been conducted. In [156], Shrivastava et al. have used horn antenna and ALTSA for propagation studies in narrow indoor corridor environment. Similarly, Ramesh et al. have also performed propagation studies in 60 GHz indoor environment in a narrow
25 hallway using elliptical tapered slot antenna [157]. Kumar et al. have performed pathloss measurements in narrow hallway and class room using horn antennas at 60 GHz [158].