Periodic transmission lines for leaky- wave antenna applications at millimeter wavelengths

Aalto University, P.O. Box 11000, FI-00076 Aalto www.aalto.fi Author Tomas Zvolensky Name of the doctoral dissertation Periodic transmission lines for leaky-wave antenna applications at millimeter wavelengths Publisher School of Electrical Engineering Unit Department of Radio Science and Engineering Series Aalto University publication series DOCTORAL DISSERTATIONS 190/2014 Field of research Periodic transmission lines, leaky-wave antennas Manuscript submitted 7 March 2014 Date of the defence 12 December 2014 Permission to publish granted (date) 21 October 2014 Language English Monograph Article dissertation (summary + original articles) Abstract This thesis focuses on planar leaky-wave antennas based on periodic transmission lines with resonant loads also called metamaterial transmission lines operating at millimeter waves. Planar transmission lines proved to be suitable for metamaterial transmission lines and are here investigated with regard to application as a leaky-wave antenna. Most of them can support backward wave propagation, but the ones with a ground plane provide better directive properties of the final leaky-wave structure.This thesis focuses on planar leaky-wave antennas based on periodic transmission lines with resonant loads also called metamaterial transmission lines operating at millimeter waves. Planar transmission lines proved to be suitable for metamaterial transmission lines and are here investigated with regard to application as a leaky-wave antenna. Most of them can support backward wave propagation, but the ones with a ground plane provide better directive properties of the final leaky-wave structure. Leaky-wave capability of a microstrip-based periodic transmission line is numerically verified as fit for electronic beam steering applications provided the technological readiness of MEMS technology. Experimental samples, with static MEMS capacitors used as a reactive load, centered at 77 GHz are fabricated in a clean room and measured using a probe station. An alternative to a single antenna scanning system is designed and measured at 94 GHz. The antenna system is based on substrate integrated waveguide which was proved to be suitable and easy to fabricate technology in order to facilitate several antennas positioned next to each other to provide sufficient span of scanning angles. A design method for periodic transmission lines based on planar lines is developed and verified. The most important contribution of this method resides in a linear approach to the design, ease of use, and span of applicability up to millimeter-wave range. The central steps of the design method are pre-compensation of parasitic impedances and periodicity pre-compensation. It is numerically and experimentally verified at 77 and 26 GHz, respectively. It is shown that the leaky-wave antenna designed by this method is capable of providing needed scanning angle range in order to be used in future automotive radar and sensor applications. Eventually a detailed analysis of individual design steps is made resulting into a set of instructions and considerations when designing a periodic leaky-wave antenna or structure based on balanced one-dimensional periodic transmission line.