Design of a Novel Microstrip Franklin Leaky-Wave Antenna Using the Eigenstate Approach

This paper presents the design of a novel periodic leaky-wave antenna (LWA) using modified microstrip Franklin unit cells. Two additional quarter-wave couple-line sections are used to allow the cell to work with the $n =-2$ fast-wave harmonic. It allows the use of low- $\epsilon _{\mathrm {r}}$ substrates so the designed LWA is cost-effective, can be easily integrated with radar front-end circuits, and avoids the excitation of surface waves. A novel application of eigenstate analysis leads to a simpler and more intuitive approach for the implementation of the reflection cancellation concept to eliminate open-stopband (OSB) effects. This is realized in the proposed structure with the use of a pair of interdigital fingers and different widths for the two lines forming the coupled section. A general design flow is also proposed for the design of the unit cell and LWA. Finally, a 40 cell LWA is fabricated on a Rogers 3003 substrate with $\epsilon _{\mathrm {r}} = 3$ . The measured results show that the beam scans continuously from −54° to +55° when frequency is varied from 54.7 to 70 GHz, and no visible OSB effect is observed near the broadside direction.