Realization of three dimensional printed antennas with its geometrical configuration and applications
The next generation mobile technology is been developed in most of the nations addressing the need for higher data rate. The researchers first outlined the current implementation in most countries for upcoming 5G standardization. 5G wireless technology is a major improvement to the current technology, which is expected to increase the overall system capacity by hundreds of times, and increase the overall system throughput with higher spectrum and energy efficiency, while minimizing system delay. In order to meet the 5G communication high transmission rate, intelligent beam shaping, beam energy gathering, and other functions, the design difficulty of 5G antennas will inevitably be upgraded. To expand coverage and ensure signal stability, 5G antennas should have good environmental adaptability with higher gain values. These would be smaller and lighter. The traditional 5G base station parts are mainly processed by Computer Numerical Control (CNC) processing technology, which has relative advantages in product precision, surface cleanliness, flatness, product structure integrity, and strength. But there is also a problem of heavy weight in 5G antenna products processed by CNC. Facing the trend of miniaturization of 5G antennas, CNC processing technology seems challenging. The advantages in weight control and time cost, 3D printing technology is gradually emerging in the field of 5G antenna productions. Along with speed and affordability, 3D printing also allows the researchers to develop complex shapes in cost effective ways. 3D printing is often a catalyst for more significant innovation in creating parts like antennas, encouraging new concepts and expansion of traditional applications as researchers bring forth new projects featuring antennas in diverse field of microwave and satellite communication. The thesis starts with presentation of its objectives, problems and solution approach of antenna prototypes and brief overview of simulated and measured results described in various sections detailed in Chapter 1. The literature reviews for several types of studied Resonant Cavity Antennas (RCA) are analyzed in Chapter 2. Moreover, different types of 3D printing materials that are used in the fabrication of our proposed antenna prototypes as such resin, Vero CMYK materials are discussed in this chapter, which also details the analysis performed for unit cell designs. We have considered cubes, cuboids, cylinders for maintaining the required database of transmission coefficient magnitude and phase values. These databases are used for generation of uniform phase distribution, beam deviation phenomenon detailed in further chapters. The interesting concept of this thesis begins with studies carried out for relative placement of unit cells either in rectangular or circular patterns. The rectangular pattern seems to have more beneficial aspects in terms of increased gain values, aperture efficiency and bandwidth aperture efficiency product (BAEP). In our case, the gain value is increased from 21.98 to 24.09 dBi whereas aperture efficiency and BAEP risen from 34.24 to 55.78% and 55.024 to 109.33%2 respectively. For this, we have considered two-layer of cubes arrangement, which are placed in defined aperture position. Additionally, variable height of unit cells are presented to study partially reflecting 3D printable surface design with minimum phase values considering cubes arrangement from single to five layers. The Resonant Cacity Antenna (RCA)’s aperture efficiency is improved to 39% with half power directivity bandwidth extending from 11.6 to 12.3 GHz and improvement of gain to 18.9 dB. However, this proposed 3D printable design depicts a structure with greater height extending to 30 mm, due to which we have been able to design Block Expansion Structures (BES) which is of 105 mm× 105 mm× 15 mm. This structure can show aperture efficiency of 47% and measured broadside directivity of 20.15 dBi and more uniform aperture phase distribution to about 77◦ at quarter wavelength above the BES top surface. These are detailed in Chapter 3. Moving on with the approach to enhance bandwidth of feed source, we can design a wide band 3D printed prototype as detailed in Chapter 4. Horn antenna is used for directional transmission and reception of electromagnetic (EM) waves. It is an example of an aperture antenna where the electromagnetic field passes through the aperture of the antenna. This is used as a feed source where the proposed wide band structure shows the overall increment of directivity from 18 to 24 dBi over the Ku-band frequency range from 10 to 18 GHz, and the aperture efficiency are observed to improve from 35% to 72%, and side lobe level of -16 to -40 dB. Interestingly, the application of 3D printable structures, which signifies the beam tilting phenomenon and methods to improve the characteristics features of feed source is detailed in Chapter 5. This chapter details the beam steering phenomenon with the use of Beam Deviation Surface (BDS) and Conical Rotating Surface (CRS). The proposed BDS layer is able to deviate radiated beam for fixed elevation angle of 22.5◦ whereas CRS prototype shows the conical rotation of tilted beam from 180◦ down to 0◦ in the interval of 30◦. Here, the side lobe level is as low as -8 dB, and the voltage standing wave ratio (VSWR) is below 2 and S11 values are less than -10 dB over the operating frequency range from 10 to 15 GHz. Additionally, five layer of the designed structure above the feed horn source can maintain more uniform wave fronts at a quarter wavelength above the top surface of the proposed prototype. In the case of larger aperture of feed horn source, the consistent phase is of 19.68◦ is noted after the placement of proposed five layer structure above the feed source as observed in the operating frequency of 12 GHz. This has improved directivity and gains by 2 dB over the operating frequency range. In addition, for small aperture feed horn source, the proposed prototype shows uniform phase variation of 20.47◦ as noted in quarter wavelength distance above the top surface of the proposed prototype where the improvement of 3 dBi in directivity and gain of feed source is observed. The story of thesis now turns to the approach to propose the miniaturized wide band structures, which signifies the light weight and economical solutions against the other structures in the literature are detailed in Chapter 6. Firstly, the design is proposed with diverse materials along the vertical direction where 40% of directivity-bandwidth and improvement of 15 dBi in broadside directivity are noted over the operating frequency range from 10 to 15 GHz. Secondly, we have proposed wide band prototype with multiple cuboids utilizing single material, which is 60 mm × 60 mm × 12.83 mm, at an operating frequency of 12 GHz. The maximum directivity is 17.5 dBi over reflection coefficient bandwidth of 50% from 10 GHz to 15 GHz. Adding to the approach for steering the radiated beam direction, we have proposed the placement of cylindrical units in defined aperture positions considering the flat lens concept as detailed in Chapter 7, where the beam steering is observed for relative rotation angles of WR-75 waveguide in 0◦, 30◦, 45◦, 75◦ and 90◦ degrees. Chapter 7 signifies the beam steering phenomenon as obtained from 3D printed structures adjusted between the two parallel plates whose performance is compared against the other structures in literature. Finally, this thesis concludes with remarkable points for future activities that could be further performed to enhance the applicability of 3D printing technologies for developing antenna prototypes.