Power-Recycling Feedback System for Maximization of Leaky-Wave Antennas' Radiation Efficiency

A novel power-recycling feedback scheme is proposed for systematic maximization of the generally poor radiation efficiency of leaky-wave antennas (LWAs). In this scheme, the nonradiated power at the end of the LWA structure, instead of being lost in the terminating load, is fed back to the input of the LWA through a power-combining system, which constructively adds the input and feedback powers while ensuring perfect matching and isolation of the two signals. As a result, the radiation efficiency of the isolated (or open-loop) LWA η
₀
is enhanced by the system's gain factor G
_s
(G
_s
> 1) to the overall radiation efficiency of η
_s
= G
_s
η
₀
, which may reach 100% for any value of η
₀
in a lossless system. The design of the power-recycling system depends on η
₀
, which typically results from a tradeoff between required directivity and restricted size. The paper derives, for a rat-race-based implementation, the exact design equations, which determine both the rat-race impedance ratios and the feedback phase conditions of the system. The build-up of the steady-state regime from the transient regime at the onset of the system is explicated by transient circuit and electromagnetic simulations. Finally, an experimental power-recycling LWA system, including naturally ohmic and dielectric losses in addition to other imperfections, is demonstrated, where the isolated antenna efficiency η
₀
is enhanced from 38% to 68%, corresponding to a system efficiency enhancement of G
_s
= 1.8 . The proposed power-recycling feedback system applies to all LWAs and solves their fundamental efficiency problem in practical applications involving a tradeoff between relatively high directivity (higher than half-wavelength resonant antennas) and small size (smaller than open-loop LWAs or complex phased arrays).