Broadband design and optimization of balanced subharmonically pumped mixer for Ka-band LMCS subscriber terminal.

摘要

Downconverter is a key building block in an LMCS/LMDS receiver front-end module for use in the subscriber terminal (CPE-Custom Promises Equipment). It requires the design of a high-quality and small-size broadband mixer, which is critical for the CPE system architecture. Balanced mixer is known to have some advantageous features over its single-diode counterpart, namely, good RF-to-IF and LO-to-RF isolations, and rejection of AM noise from the LO source and some spurious responses. Subharmonically pumped (SH) mixers present additional advantages when operating with an LO at 1/2 RF signal frequency. Combining the advantages of balanced and subharmonically pumped schemes, we study and design new balanced SH mixers.; In this work, we present a generic approach, which can be used to estimate the optimum loading conditions at various idler frequencies and also to give the best performance of balanced SH mixers for generic circuit model. As an attempt in validating our approach, we design, on the basis of the microstrip technique, a balanced SH mixer at 14 GHz that was optimized at its 2 f_LO + f_RF frequency. The circuit was realized on a 10 mil thick TMM3 substrate. The measured conversion loss is less than 9 dB over the RF frequency range of 13.5–15.5 GHz and 7.2 dB at 14 GHz with the IF frequency of 500 MHz. More than 30 dB isolations between ports are achieved.; In this work, a general method of design is developed for broadband design for performance improvement of a class of uniplanar double-Y baluns. According to the developed technique, we design two kinds of broadband double-Y baluns on two platforms related to the infinite and finite ground planes: CPW-slotline and CPW_fgp structures. They are realized in MHMIC format, respectively. The designed CPW-slotline balun exhibits a rather good performance with a low insertion loss of less than 1 dB and a flat response over 2–3 octave frequency range. Also, the designed CPW _fgp balun demonstrates a less than 1.5-dB insertion loss over the DC-to-22 GHz frequency range.; Finally, two new architectures of uniplanar broadband balanced SH mixers with the infinite and finite ground planes are proposed and fabricated on 10-mil thick alumina substrate. The proposed uniplanar balanced SH mixer with infinite ground planes achieves a very flat conversion loss of 9.5–11.6 dB over a wide bandwidth of 24–38 GHz RF driven by a subharmonic L4 source of 11.5–18.5 GHz. (Abstract shortened by UMI.)