Novel CRLH TL metamaterial and compact microstrip branch-line coupler application

A novel resonate-type composite right/left handed transmission line (CRLH TL) is presented based on a high-low impedance section and a capacitive gap on the conductor strip, and a Minkowski-loop-shaped complementary split ring resonators (ML- CSRRs) etched on the ground plane. Influence of different iteration orders on the performance of novel CRLH TL and miniaturization mechanism are investigated in depth by electrical simulation (an analysis of circuit model) together with planar electromagnetic (EM) simulation. The close-form results of negative refractive index and complex propagation constant are provided by constitutive parameters retrieval method. For application, a compact branch- line coupler (BLC) centered at 0.88 GHz (GSM band) is designed, fabricated and measured. The upper signal line of CRLH impedance transformer is constructed as Koch curves of first order to facilitate further integration of the BLC. Exact design method for fractal implementation is involved. Measurement results indicate that the proposed coupler achieves a comparable 81% size reduction and good in-band performance with regard to already covered ones. The concept, validated by consistent measurement data, is of practical value for other components design.