High isolation MIC Ka band upconverter

A mixer is a critical element in almost every microwave communication system. The two most important parameters of an up-converter mixer are the LO to RF isolation and its P_-1dB. In many cases the LO frequency is too close to or even overlapping the RF frequency. In that case the rejection of the LO signal by a filter is difficult or sometimes even impossible. The LO signal could possibly saturate the following power amplifiers and/or be too high at the antenna port. A high LO to RF isolation mixer can solve this problem. An up-converter with a high dynamic range or high 1 dB compression point can simplify the amplifier chain by reducing the number of stages. There are a few techniques one can use to design an up-converter with high LO to RF isolation. In order to develop a manufacturable product and to achieve enough margin over the temperature range, we considered developing a “power combined” up-converter mixer for 40 GHz range, which is simple, inexpensive, and provides both high LO to RF isolation and high P_-1dB. We present a Ka band up-converter mixer with LO to RF isolation of better than 50 dB and 1 dB compression of 3 dBm at the RF port over a bandwidth of 2 GHz. The up-converter was implemented using thin film alumina technology 180° splitter