Wiz, you should be able to measure the cable loss (S21) to 40 GHz and adjust your measurements. You will need to use 3.5mm connectors (K connectors) and not SMA. If you place the cable before the pre-amp the cable loss will add directly to the pre-amp noise figure. If the preamp precedes the cable you do not do this. This pre-amp will cost some $. Other suitable coaxial connectors are the 2.4 mm and 1.0 mm. Using a mixer/oscillator that allows fundamental mixing to 40 GHz would really simplify the measurements. With harmonic mixing a little work is involved in determining the actual frequency of a signal. A spectrum analyzer that will handle this without external mixers is the Tektronix 2784. Although it used harmonic mixing above 28 GHz it has a neat feature that causes the actual frequencies to stand out. It sweeps 28-40 GHZ using two different first IF frequencies (3.5 and 10 GHz). The false signals are green or red and the actual signals are yellow. I have used waveguides in the past and hope I don't have to use them again. Dave Cuthbert Micron Technology
From: owner-emc-p...@majordomo.ieee.org [mailto:owner-emc-p...@majordomo.ieee.org] On Behalf Of Wiz Sent: Thursday, February 12, 2004 8:37 AM To: EMC Forum Subject: High Frequency Measurements Hello, I have a need to make radiated measurements up to 40 GHz. I uses a low loss cable that gives me enough dynamic range up to 18GHz. The cable is very short and I have to move my measurements equipment out to the antenna. I know I need to get a pre-amp and mixer, but what do I do about the cable loss? I have called many places and I cannot find good enough cable to measure to 40 GHz. The other alternative is waveguides as I understand. Those would, I assume, be coupled directly to the input of the mixer. This does not allow for antenna height adjustments form 1 to 4m as required. I have seen other test reports where high frequency data was taken where the antenna was held at about 1meter. I can understand this since emissions will likely be very directional at those frequencies. Is it acceptable to make measurements with the receive antenna at 1 meter only? Thanks for any information you can provide… Wiz
