V-band CPW 3-dB tandem coupler using air-bridge structure

We present a uniplanar coplanar waveguide 3-dB tandem coupler operating at V-band frequencies. The uniplanar structure is monolithically fabricated by using two-section parallel-coupled lines and air-bridge crossovers replacing the conventional multilayer or the bonded structures. Due to an optimized tandem structure and nonbonded crossovers minimizing the parasitic components, a maximum coupling of 2.5 dB is measured at 62 GHz with a 2-dB bandwidth of 83%, while a high directivity factor of 33 dB is simultaneously obtained at 58-62 GHz. Over the entire design frequency range of 30-90 GHz, we achieve good phase unbalance of 90±6.0°, return loss, and isolation lower than -23 and - 16 dB, respectively.