Design and Analysis of Down-Conversion Gate/Base-Pumped Harmonic Mixers Using Novel Reduced-Size 180 ^\'63irc Hybrid With Different Input Frequencies 
J.-J. Kuo, C.-H. Lien, Z.-M. Tsai, K.-Y. Lin, K. Schmalz, C. Scheytt, H. Wang, Microwave Theory and Techniques, IEEE Transactions On 60 (2013) 2473–2485.