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 2.5dB is measured at 62GHz with a 2-dB bandwidth of 83%, while a high directivity factor of 33dB is simultaneously obtained at 58-62GHz. Over the entire design frequency range of 30-90GHz, we achieve good phase unbalance of 90±6.0°, return loss, and isolation lower than -23 and -16dB, respectively.