Miniaturized and Reconfigurable Rat-Race Coupler Based on Artificial Transmission Lines

A miniaturized and reconfigurable rat-race coupler realized in inexpensive PCB technology is proposed. Miniaturization is achieved by exploiting the theory of right- and left-handed artificial transmission lines. The frequency agility allows the rat-race coupler to operate at two bands centered at 900 MHz and 1.7 GHz, therefore covering many industrial and communication standards. The frequency selection is operated by CMOS switches, controlled by only 1-bit signal, for adapting the equivalent electrical length of the four branches of the coupler. Moreover, the dimension is significantly reduced with respect to standard realizations at the same frequencies, with required areas of about 3% at 900 MHz and 10.4% at 1.7 GHz. The proposed design has been fabricated and measured, showing good performance in both operative frequency bands.