Size reduction and harmonic suppression of a CPW directional coupler using an inductive loading technique

In this paper, an inductive loading technique is applied to design a compact coplanar waveguide (CPW) directional coupler. The proposed structure can achieve both a significant reduction of size as well as harmonic suppression. The proposed structures take advantage of the coexistence of CPW and series asymmetric coplanar strip (ACPS) stubs. A very compact 10dB CPW directional coupler, operating at 30 GHz, is designed to illustrate the technique. In comparison to a conventional directional coupler, this coupler offers harmonic suppression and an approximately 50% reduction in area. The measured results agree well with simulation. The wideband response reveals that the proposed directional coupler is well-behaved with no spurious harmonics up to 140 GHz.