Disconnecting the Dots: Stellar Constellations with Stellar Connectorized Parts

In case you missed IMS in San Diego last week, we showed off a mmWave up- and down-conversion chain using a fully coaxial connectorized lineup operating at 81GHz. This system shows the power and flexibility of our complete 1.0mm connectorized product family. We showcased several new connectorized modules, including the AMM-0001M and MM1-30100LM, that feature 1.0mm connectors along with our new M-package devices (MPDR-00110M2) that enable connectorized operation up to 110GHz.

In this chain, we upconverted a 1GHz 5G NR modulation to 81GHz, demonstrating that a high performance signal generator and analyzer can be built in a single afternoon with Marki’s complete 1.0mm product family. Here’s a glimpse of the demo circuit at our IMS booth:

Figure 1. mmWave Connectorized Up- and Down-Conversion Chain.

Our modulated signal flows from left to right – starting in the top left corner, the LO signal is split between the up- and down-conversion chains with a PD-0126. The 20GHz LO source is generated by the SMB100A, courtesy of Rohde & Schwarz. Our 5G modulation starts at the bottom left with the SMM100A feeding our QH-0226. At the output, the FSW probes our up-converted channel at 81GHz via the MPDR-00110M2 and monitors the down-converted 1GHz 5G modulated signal on the IF port of MM1-30100LM.

Figure 2. LO and Signal Source (left) with Output Signal Probes (right).

Many thanks to Rohde & Schwarz for lending us equipment to test this signal chain and Southwest Microwave for lending us the 1.0mm cables and adapters used to build this lab bench set up. Without these, you wouldn’t have caught the stellar constellations we showed on the big screen!

Before we take a look at the signal link performance, let’s break down this circuit:

Figure 3. mmWave Connectorized Up- and Down-Conversion Chain Block Diagram.

In the signal path, we have a single-sideband upconversion using the MMIQ-40100LM with the I and Q ports fed by the 90° and 0° ports on the QH-0226 respectively. Following the upconversion, have a noise-suppressing filter MFBC-00020M in series with MPDR-00110M2 to emulate channel loss and split power to probe and demodulate the 81GHz signal directly with the FSW. For the downconversion, we used a MM1-30100LM fundamental double balanced mixer which features excellent 8.5dB typical conversion loss with RF/LO operation from 30-100GHz. The LO on the 30-100GHz mixer and 40-100GHz IQ mixers are driven by two series AMM-0001M (11.5dB gain, 19dBm P_sat from 45-95GHz) on both the up- and down-conversion chains.

To generate the 80GHz clock on the upconversion chain, a 20GHz LO source is multiplied up to 80GHz using a single MMQ-40125HM, a passive quadrupler with output frequency range from 40 up to 125GHz. This is pre-amplified with a single AMM-7473PC with over 20dBm output power from 0.4-22GHz. A 77-108GHz bandpass filter (MFBC-00020M) after the passive quadrupler provides additional 1F, 2F, and 3F harmonic suppression.

On the downconversion chain, an alternative approach is used: the 20GHz LO is passively doubled to 40GHz with an MMD-2060LU followed by a passive MMD-20100HM mmWave doubler to multiply the 40GHz clock up to 80GHz. Similar to the upconversion chain, MFBC-00020M provides additional harmonic suppression at the output of the 40 to 80GHz multiplier. A AMM-7473PC pre-amplifies the 20GHz clock input to the first doubler while an AMM-6702UC5 pre-amplifies 40GHz input into the second doubler. Two ATN06-0067 balance the power between upconversion and downconversion chains to allow LO generation using a single source.

As some might have noticed, we’re driving a 2-26GHz quad hybrid with a 1GHz signal. This might contribute to a higher EVM due to the slightly degraded phase and gain balance, however this precise combination of cables and parts yielded an optimum EVM. Stayed tuned for more test results as we tune the IQ phase and gain balance to further improve EVM!

So how well does it perform? In this setup, the LO is set with 10dBm input power at 20GHz. The 5G signal source is set at 1GHz center frequency, -3dBm average power, 100MHz channel bandwidth, and 64QAM modulation. When connecting the SMM straight to the FSW, the EVM is ~0.25%. When upconverted and downconverted through our signal chain, we achieve ~3% EVM – the constellation spread suggests noise as the primary source of this error. Directly probing at 81GHz shows ~4% EVM – this degradation is likely due to the attenuation and noise seen on the lossy 18” 1.0mm cable.

Figure 4. EVM and Constellation for 1GHz and 81GHz Signal Link - RF = -3dBm, LO = 10dBm.

Let’s adjust some parameters to see how well this link performs. First, we will decrease the LO power:

Figure 5. EVM and Constellation for 81GHz Signal Link – Decreasing LO Drive.

As expected, decreasing LO drive results in increased EVM as the LO drive is no longer sufficient to drive the MM1-30100LM and MMIQ-40100LM. Just another reminder to avoid starving the mixer of LO drive.

Now let’s adjust the RF level - we will sweep the RF level from -10dBm up to 5dBm in the next few plots:

Figure 6. EVM and Constellation for 81GHz Signal Link – Increasing RF Drive.

This power sweep demonstrates the typical EVM bathtub curve providing insight into the system’s operating limits. From the constellation diagrams, we see a focal point with -3dBm average input power where the EVM is optimized. At low input powers (like -10dBm), EVM is dominated by the noise performance of the system. In other words, our RF power is underdriven resulting a low signal-to-noise ratio and in turn causing a high EVM. Further increasing the power to 5dBm yields increased EVM as the mixer begins compressing. Nonlinear operation due to compression results in increased intermodulation distortion which further degrades EVM. Here’s an example bathtub:

Figure 7. EVM [%] vs Input RF Power [dBm] Bathtub Curve.

Still not happy with the EVM? Good news! Our newly minted mmWave connectorized parts make prototyping a breeze – you can swap out any of the parts in our chain to improve your system without having to bust out a new PCB. Prototyping signal chains up to 110GHz has never been easier with Marki’s wide selection of connectorized mmWave mixers, filters, amplifiers, power dividers, and so much more!

Feel free to reach out to support@markimicrowave.com with any questions or needs to help fill out your next signal chain!