New-Tech Europe Magazine | May 2018

Figure 2 shows a basic structure using interconnected Mini- Circuits parts to multiply a 6 GHz signal from a synthesized signal generator up to 24 GHz. Coaxial amplifiers are used to correct the signal levels; reflectionless filters suppress unwanted harmonics at the multiplier output and absorb any signal reflections between elements in the chain; and an ultra- wideband splitter/combiner is used to distribute 24 GHz to each of the two mixer LO ports. Note that this block diagram represents a concept that may be modified to the user’s requirements. Depending on the user’s actual application frequency, real-world losses and parasitic effects, different combinations of multipliers, filters, amplifiers and attenuators may be added to the chain to achieve the ideal signal frequency and power. Case 1: Spectrum Analyzer Measurement System with Up/Down Converter Now that we have a means of frequency conversion between 4 GHz and 28 GHz and a 24 GHz source for our mixer LO, we can combine these elements to build a variety of useful setups. One example is the spectrum analyzer measurement setup depicted in Figure 3.

Figure 1: Up/down-conversion between a 4 GHz test signal from a spectrum analyzer and a 28 GHz device under test.

generator to 28 GHz to the DUT. For uplink testing, the same mixer can be used to convert 28 GHz from the DUT back down to 4 GHz into the analyzer. Mini-Circuits’ MMIC mixer model MDB-44H+ is ideal for this application. The mixer has an IF frequency range of DC to 15 GHz and an LO/RF frequency range of 10 to 40 GHz. It can be used as an up- and down-converter and provides low conversion loss with excellent harmonic suppression. The mixer is conveniently available mounted on a test board (TB-973- MDB44HC+) with 2.92mm Female connectors (required for frequencies above 26.5 GHz), readily allowing interconnection with 3.5 mm and

SMA connectors on test cables, DUTs and test equipment. Building a 24 GHz LO Source In order to realize the frequency conversion capability illustrated in Figure 1, a 24 GHz source is required for the LO to the mixer. To avoid the cost of a high-frequency generator, we’d like to use a 6 GHz signal source to generate the desired LO signal. In order to minimize component count and further reduce cost, we’d also like to split one LO source to drive both the up-converter and down-converter. The mixer MDB-44H+ operates on an LO level of +15 dBm, so our LO source should deliver two 24 GHz channels at +15 dBm.

Figure 2: Basic structure to generate 2x 24 GHz LO sources at +15 dBm for up-conversion and down-conversion between spectrum analyzer and DUT.

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