There is an inherent trade-off between LO drive level, input RF power and intermodulation distortion. As a minimum, LO power should generally be at least 7 dB higher than the highest expected RF power to avoid mixer compression. This value of 7 dB actually depends on the specific mixer (i.e. T3 mixers relax this tolerance to about 4 dB), but 7 dB can always be used as a conservative estimate. Thus, if you have RF powers not to exceed +5 dBm, then you can use medium barrier (“M-type”) diodes with LO drive around +10 to +13 dBm. If a higher LO drive is available in the system, then a better choice may be to use a high barrier diode because the intermodulation distortion generated during the mixing process will be suppressed more fully. Keep in mind that under normal operation, the greater the difference between the LO and RF power, the lower the intermodulation products.
1 dB compression can refer to the property in a mixer, amplifier, balun, or other non-linear element that saturates with excessive input power. It is the point at which the loss increases by 1 dB.
Mixers are excellent linear frequency converters in the sense that every dB change in input power results in a dB change in the output and the actual power ratio is the conversion loss. When too much RF power enters the mixer, this dB for dB relationship will cease and the conversion loss will begin to increase. The 1 dB compression point is therefore defined as the RF input power required to cause the conversion loss to increase by 1 dB. This compression point is the maximum recommended RF input power to the mixer.
Our Nonlinear Device Models for Microwave Office and ADS are available here: https://www.markimicrowave.com/engineering/resources/non-linear-device-models/ However, the devices you listed (M2-0218, MT3-0113LCQG, and M1-0310) do NOT have models available for them. All M1, M2, M4, M8, and M9 mixers are considered ‘Legacy’ mixers. These hybrid mixers are built using three dimensional constructions from low dielectric softboard, discrete diodes, and ferrite by hand. While they have some attractive features (most importantly low loss across broad bandwidths) they are typically not preferred because they are less repeatable, have poorer isolations and spurious performance, and are more expensive to produce (especially in volume). Because they are not very repeatable and because they are a hybrid construction it is not possible to create accurate models for them. The MT3-0113LCQG is also a hybrid assembly, but it uses some handbuilt components combined with a monolithic mixer core. While it is much more repeatable and high performance (and is therefore frequently recommended for designs) it is also not very amenable to the creation of physics based nonlinear models.
Clayton,
That is a really good question. Using the existing T3 mixers with the ADM amplifiers you will see similar results to what you would have seen with the legacy A0010 LO drive amplifier. Designing and building the ADM amplifiers is allowing us to advance the technology in the driver amplifiers, but the first generation is intended to match the previous performance, but with a more reliable package, positive only bias option, and better pricing. We are currently in development on the next generation of ADM amplifiers that will offer superior performance and more ease of use improvements. Additionally, look for these amplifiers to be integrated with our upcoming T3 MMICs to make multi-chip module T3As.
It turns out that tuning/testing for image rejection does not guarantee that a unit will have good sideband suppression as an SSB, and of course, this work the other way as well. While the units are essentially identical in design, they are tuned and tested differently. Also, IR’s are non-reciprocal when up/down converting in terms of sideband selection. An IR that converts with a lowside RF will upconvert a highside RF.
Note that neither of these mixers is recommended, however. Our current recommendation is to purchase an MMIQ mixer and to select a IF quadrature hybrid from our catalog or from this table.
Since our inception over 30 years ago, Marki Microwave has developed a long and successful history in space applications. Our capabilities cover both space and Hi-Rel for military applications, supporting die, surface mount, connectorized, and waveguide products.
Most of Marki Microwave’s catalog can be upscreened in-house to meet the various qualification requirements of GEO and LEO applications, including:
Our test flows support the overall MIL specification requirements for the various active and passive products Marki Microwave builds. These documents define the general requirements as well as the quality assurance and reliability requirements of such circuits used in military and other high reliability programs. Our qualification plans are designed to meet the following standards:
Marki mixers are remarkably robust, with many of our mixers lasting in harsh conditions in the field for decades without failure or degradation. There are very few known degradation mechanisms for our mixers, and the two most common are thermal/handling damage and DC current application.
Thermal and handling damage usually occur in concert to surface mount components during the assembly process. The application of excessive heat combined with improper care in handling can cause obvious mechanical damage to the part.
The other major failure mode is the application of excessive current. While we have never seen a mixer damaged from excessive RF input power, damage due to excessive DC is quite common. This is particularly common in IQ mixer structures where a DC offset is used to improve sideband suppression. The addition of DC connected circuitry can expose the mixer to increased risk of damage due to ESD discharge as well, since the mixer is generally protected by RF shielded cables and connectors from any discharges.
To test if your mixer is still good perform the following tests:
– Take a handheld multimeter, and set it to the ‘diode’ setting. The diode setting will measure how much voltage is required to drive 10 mA of current from the positive to the negative lead. For a standard silicon Schottky diode this value would be 0.7 Volts. For most Marki low barrier diodes it will be around 200-300 millivolts. Measure from the center pin of the IF to the grounded case. Next reverse the leads, with the positive lead on the ground and the negative lead on the IF center pins. Now compare the measurements. If they are roughly the same, then the diodes are ‘alive’, and if one is significantly different, the diodes are likely ‘dead’. If one voltage is higher than the others it indicates that one of the diodes in the ring is probably burned out.
– If possible, measure the conversion loss of the mixer. The conversion loss of each side should be within the datasheet spec for conversion loss. Ensure that you are supplying sufficient LO power. If you are driving it below the datasheet spec, then it will have high conversion loss.
After you have these results you can send an email including your findings to support at markimicrowave. Unfortunately when diodes are burned out due to the application of DC current, this is considered field damage and the parts are not returnable under the warranty, so please be extremely careful when using this technique for IQ compensation, and consider one of these alternative methods.
See What happens when you underdrive a mixer? for information about this.
Additionally, the intermodulation distortion IP3 will become worse, phase matching will become more difficult, and performance over temperature becomes more difficult.
It is always better to select the lowest drive level mixer available and add efficient amplifiers to boost your LO signal level than to starve the mixer.
For a comprehensive answer to this question, see the Mixer Basics Primer. The triple balanced mixer is best thought of as a “doubly-double balanced” mixer in which two double balanced mixers are driven in a push-pull configuration. Thus, the primary difference between the double balanced and triple mixer is that the double balanced mixer uses 4 nonlinear elements (i.e. diodes) while the triple balanced mixer uses 8 nonlinear elements (i.e. 2 double balanced mixers with 4 diodes each). In general, a double balanced mixer cannot have (significantly) overlapping IF and RF/LO bands due to the circuitry involved. Therefore, a typical Marki Microwave double balanced mixer such as the MM1-2567LSM has RF/LO bands ranging from 25-67 GHz and an IF band from DC-30 GHz. A triple balanced mixer (denoted by the Marki MM2 and T3 mixer lines) can have overlapping RF/LO and IF bands at the expense of requiring an additional diode quad. Triple balanced mixers also generally do not have DC IF response and tend to have slightly worse isolation performance compared to double balanced mixers.
In our understanding, AM-PM conversion occurs as nonlinear devices saturate. This is why limiters in particular are not a good idea in low phase noise paths, and is also why amplifiers tend to have a bit of a sweet spot just above P1dB. However, this is a really deep question that will involve lots of experimentation over the coming years.
For now the safe advice is to design the chain to aim the input power at right about the compression point of each nonlinear device and try not to add too much extra nonlinear stuff if you don’t need it. It’s basically the balance of “Power good” and “AM-PM conversion bad”.