An 18–50-GHz Double-Balanced GaAs Mixer Using Novel Ultrawideband Balun

In this letter, a novel multiconductor coupled line (MCL) balun is presented for the implementation of a wideband double balanced mixer (DBM). The proposed balun utilizes an artificial transmission line (ATL) (composed of periodical shunt stubs), and manages to shorten the length by 65.1% compared with the three-line balun. Besides, in order to provide a point for intermediate frequency (IF) extraction, two sections of coupled lines are exclusively added behind local oscillator (LO) balun. And this structure also transmits LO signals to the diodes for mixing. Through the aforementioned operations, a compact balun and an 18–50 GHz mixer in 0.15- $\mu \text{m}$ GaAs pseudomorphic high electron mobility transistor (p-HEMT) process are designed. The measured results show that within the operation frequency, the phase and amplitude difference of the balun are lower than 3.5° and 1.1 dB, respectively. The mixer dB conversion loss (CL) and 33 dB LO-to-RF isolation under 15 dBm LO power. The monolithic microwave integrated circuit (MMIC) area is $0.96\times1.68$ mm2, including all pads.