TRANSITIONS FOR SUBSTRATE INTEGRATED WAVEGUIDES (SIWs) AND SIW-BASED ANTENNAS

Abstract

The transmission lines (TLs) have been used in designing radio frequency (RF), microwave, mm-wave, and THz applications such as filters, antennas, and as parts of other active/passive circuits. The wide use of planar TLs is due to their low cost, easy availability, and simple fabrication procedure. However, the limited conductivity of the metal traces and substrate dielectric losses prevent them from achieving low insertion losses (IL) and return losses (RL), and wide bandwidth, especially as frequency increases into mm-wave and THz regions. Three-dimensional (3D) waveguides often exhibit superior performance to that of planar TLs, yet their fabrication cost is significantly higher than that of planar TLs. The concept of substrate integrated waveguide (SIW) was first proposed in 1998 and realized in 2001 to produce a structure that offers superior performance than planar TLs at a much lower cost than 3D waveguides. As planar TLs such as microstrip lines (MLs) and coplanar waveguides (CPWs) are widely used for 2D circuit implementations, low-loss broadband transitions from these TLs to SIW are required for the construction of entire systems. Furthermore, the SIW-based antennas are also gaining attention over traditional 3D antennas because of their 2D nature, making it easy to integrate with other 2D RF components. The present thesis deals with the design and analysis of transitions between other widely used planar transmission lines and SIWs; design and analysis of some novel SIW-based antennas for some specific applications. On the transition side, our focus is to make the transition broadband, with minimum loss at mm-wave frequencies. On the antenna side, the focus is to make circularly polarized SIW novel design-based antennas for specific applications. Chapter 1 introduce the SIW concept and its requirement in the current scenario, like SIW-based transitions and antennas. The advantages, drawbacks, and working principles of SIW are also discussed. In addition, this thesis’s motivation and problem statement research objective is presented. Moreover, the outline of the complete thesis is also discussed at the end of this chapter. A comprehensive review of the various transitions available for SIW and the SIWbased planar antenna is presented in Chapter 2. A new broadband low-loss transition from conductor-backed CPW to SIW is presented in Chapter 3. The proposed approach develops to improve transition characteristics from CB-CPW with the substrate-integrated coaxial line to SIW for the C-band application. In addition to this, a broadband coaxial line-to-SIW transition using the aperture-coupling method is designed and analyzed in this chapter. Laboratory prototypes of all the transitions were made and experimentally measured for cross-verification of the simulation results. The performance of the proposed transitions was compared with their counterparts to find the superiority of our proposed transitions. The concept of corrugated-via-wall technique (CVWSIW) is introduced in Chapter-4 in order to reduce the overall loss of traditional SIW. After introducing the CVWSIW concept, transitions from other transmission lines like microstrip line/conductor backed- CPW/coaxial line to this newly introduce CVWSIW are designed and its electromagnetic property is analysed. All the transitions have been designed, fabricated, and experimentally measured to cross-check the simulation results. The performance of proposed transitions is compared with their counterparts. To cater to the need for modern communication systems, antenna engineers have made continuous efforts to provide antennas with improved performance in terms of impedance bandwidth, gain, efficiency, and reduced harmonics. Getting these characteristics in a planar microstrip antenna, the preferred structure in the planar antenna category, is challenging. The substrate-integrated waveguides have higher power handling capability and lower loss than the microstrip while compact and lighter than the conventional waveguides. Additionally, the most significant leveraging of SIW-based planar antenna is the integration of the active and passive components in the same substrate, which is one of the better options for planar integration. Moreover, circularly polarized (CP) antennas have received extensive attention in modern wireless communication since they can suppress multipath reflection, avoid polarization mismatch, and support a flexible alignment for the receiving and transmitting antennas. Furthermore, if the antenna is specifically designed for strategic applications, another essential requirement is to keep the cross-polarization level well below the co-polarization level. A dual-band circularly polarized (CP) SIW cavity slot antenna with an asymmetric aperture is designed in Chapter 5 with the aim of designing a multi-band antenna with a small frequency ratio. Over and above that, applying reconfigurability to SIW-based antennas is a challenge compared to other planar antenna structures. An effort has been made in this thesis to apply mechanical reconfigurability to make a SIW-based antenna frequency reconfigurable in Chapter 6. The conclusions of the complete work are drawn in chapter 7. In addition, the scope to extend this work further in the future is also included.