Compact fractal shaped, unequal length branch-line coupler for dual-band applications

This paper presents a novel, compact, fractal shaped, unequal length branch-line coupler for dual band applications. The proposed planer topology exhibits compact size as well as dual band characteristics with quadrature phase difference centered at 900 MHz (GSM band) and at 2.4 GHz (ISM) band, with a band ratio of 2.7. Explicit design equations of the proposed coupler are analytically derived using ABCD parameter and rigorous trigonometric identities. The perfect topology of the design is obtained iteratively by EM simulations. Novel coupler shows good in-band performance with a sharp attenuation at around mid frequency (1.6 GHz). Most importantly, the work demonstrates the compatibility between fractal and stub tapped technique and the provision of an alternative approach and new concept of designing MMICs.