Compact 20 MHz Balun for Miniature Antennas Using CRLH Transmission Lines

This article presents the design of a highly miniaturized 5.1 cm × 4.8 cm balun designed to operate at the center frequency of 20 MHz. Two branches are formed by splitting the input signal, one with a positive phase-shift and the other with a negative one. Complementary Right-Left-Handed Transmission (CRLH) is proposed as unit cell of the line to generate the positive and negative phase-shifts. Lumped inductors are added to further reduce the footprint of the structure. This results in a very compact balun (around 300 times smaller than the wavelength) presenting a balanced property with an insertion loss ranging from -5 dB to -7 dB on the two branches and a phase difference of 180° between the two differential ports in the 15–25 MHz frequency band.