Analysis of the radiation characteristics of CRLH LWAs around broadside

A study of the characteristics of lossy composite right/left-handed (CRLH) leaky-wave antennas (LWAs) is presented. It is analytically shown that the fulfilment of the Heaviside condition in this media leads to an undistorted phase constant, a frequency-independent attenuation constant and a purely real characteristic impedance. In addition, closed-formed expressions for the efficiency and radiation rate of the antenna, valid around the transition frequency, are derived. It is found that the antenna efficiency depends on the individual efficiencies of the series and shunt branches of the unit cell, which are decoupled. Also, it is shown that the simultaneous presence of series and shunt radiation resistors is not necessary to obtain radiation at broadside. However, in this case the antenna efficiency will always be below of 50%. Full-wave simulations results are included to demonstrate the validity of the developed circuit-based theory.