Measurements for microwave differential and IQ devices

In the past, devices that require true-mode differential drive (+-180 degree) or true-mode IQ drive (0 and 9 degree) have been difficult to measure at RF and microwave frequencies. At microwave frequencies, baluns and 90 degree hybrids have poor performance, and are very difficult to use in on-wafer test. True-mode VNAs have allowed non-linear measurements of compression, but require input and output frequencies to be the same. To date, no method has been presented that can allow measurements of differential harmonics, differential mixers, or IQ mixers without the use of baluns or hybrids at high frequency, or with high accuracy. This paper presents a new method that provides fully corrected measurements for all these cases, over swept frequency or swept power, or swept phase without the use of baluns. It is suitable for on-wafer applications and extensible to mm-wave frequencies.