Miniaturised patch hybrid couplers using asymmetrically loaded cross slots

A miniaturised planar-circuit-type 3-dB patch hybrid coupler using asymmetrically loaded cross slots is presented. By loading a pair of cross slots on the squared patch, the overall size of the proposed patch hybrid coupler can be significantly reduced because of its inductive loading effect. A class of cross-slot patch hybrid couplers is then theoretically characterised and their good performance is realised by varying the cross slots width or length towards equalisation of the amplitudes at two output ports. Next, the cross slots are properly meandered so as to reduce their overall size by about 89%. Finally, two patch hybrid couplers with patch sizes of about 0.24λg squared and 0.18λg squared are designed and fabricated, respectively. All the predicted results are verified by experiment.