Patent ID: 8188808

Claim:
A branchline coupler structure using slow wave transmission line effect having both large inductance and large capacitance per unit length, the branchline coupler structure comprising: a plurality of quarter-wavelength transmission lines, at least one of which comprises a high impedance arm and a low impedance arm, wherein a high impedance of the high impedance arm is relative to a low impedance of the low impedance arm; the high impedance arm comprising a plurality of narrow cells and having an inductance of nL and a capacitance of C/n; and the low impedance arm comprising a plurality of wide cells and having an inductance of L/n and capacitance of nC, wherein: the wide and narrow cells are relative to each other, and the wide and narrow cells are adjacent each other to form a signal layer having step discontinuous alternative widths; and wide cells of the low impedance arm comprise portions of the signal layer having widths wider than the narrow cells that are arranged over floating metal strips and the narrow cells of the high impedance arm comprises portions of the signal layer having widths narrower than the wide cells that are arranged over a ground plane.