I'm kind of speechless at the moment, but I think this is going to change EVERYTHING in terms of VNAs.
Analog Devices' ADL5960 10 MHz to 20 GHz integrated vector network analyzer front end supports various LO interface configurations
Image of Analog Devices' ADL5960 Analyzer Front EndADI's ADL5960 is a wideband, small form factor vector network analyzer front-end comprising a resistive bidirectional bridge, down conversion mixers, programmable IF amplifiers and filters, and a highly flexible local oscillator (LO) interface. The bridge provides >14 dB of directivity up to 17 GHz. The primary transmission line from RFIN to RFOUT is wideband matched to 50 Ω with only 1.1 dB loss at low frequencies, increasing to 1.8 dB loss at 20 GHz.
The ADL5960 supports several different LO interface configurations that simplify the clocking design of a vector network analyzer (VNA) solution as well as the interfacing of the device to an analog-to-digital converter (ADC). The frequency divider and multipliers in the LO interface enable measurement sweeps beyond the operating frequency range of the LO source, enabling operation over the full 20 GHz frequency range of the ADL5960 using a 6 GHz synthesizer. The IF frequency offset mixer, driven through the offset interface formed by the OFP and OFM pins, enables further simplification by allowing the swept RF and LO interfaces to share the same frequency source. The frequency of the IF output signals is then determined by the low-frequency source driving the OFP/OFM interface. When this interface is driven at the ADC sample frequency with the divide by 4 enabled, it automatically centers the IF output signal in the first Nyquist zone.
https://www.digikey.com/en/product-highlight/a/analog-devices/adl5960-analyzer-front-end
The way I understand the block diagram, you only need 2 "low speed" (Sampling 1-100MHz) ADC per VNA channer, and one of these ICs. From the image below, everything for a channel except the ADC and the DSP.

Price is
168 USD for one off at Digikey. My jaw is still on the floor.
I think we are months away of having very cheap 20GHz VNAs on the market.