Novel Slotted mmWave CPW Branch Line Coupler for MMIC and Sub-THz Applications

This paper presents a novel mm-wave branch line coupler with an enhanced isolation up to 72dB between the input ports, whereas a conventional branch line coupler usually gives less than 40dB of isolation. Similarly, there was also a small increase in the return loss. The two slots are situated a half wavelength apart acting as resonators and bandpass filters. The shape of the slot is rectangular with smaller sides equal to a half of the transmission line (TL) it is placed on (whether the Z(0) or Z(0)/root 2 ohm TL). The two slots must be identical to output symmetrical resonance frequencies. This is a promising coupler design particularly in an integrated microwave circuit such as, mixer or multiplier circuits at high frequencies (mmWave).