How do I select a vector network analyzer for measurements up to 110 GHz?

How do I select a vector network analyzer (VNA) for measurements up to 110 GHz? The VNA is the fundamental RF test instrument for measuring S-parameters, and selecting one for high-frequency work (up to 110 GHz) requires careful evaluation of frequency range, dynamic range, and the waveguide/connector ecosystem: (1) Key specifications: frequency range: 10 MHz-26.5 GHz: covers sub-6 GHz and some FR2. Suitable for most commercial RF work. 10 MHz-50 GHz: covers 5G NR FR2 (24.25-52.6 GHz). 10 MHz-67 GHz: covers the full V-band (57-66 GHz, 802.11ad/ay, radar). 10 MHz-110 GHz: covers the W-band (75-110 GHz, automotive radar at 77 GHz, 6G research). Requires waveguide frequency extenders above 67-70 GHz. Dynamic range: 80-100 dB: adequate for passive components. 110-130 dB: needed for high-isolation devices, multiplexers, amplifiers. 130-145 dB: achievable with high-end VNAs (needed for on-wafer mmWave device characterization). Number of ports: 2-port: sufficient for most 2-port devices. 4-port: needed for differential, multiport, and balanced device measurements. IF bandwidth: 1 Hz to 15 MHz. Narrow IFBW (1-10 Hz) maximizes dynamic range but slows the measurement. Wide IFBW (100 kHz-1 MHz) for fast production testing. (2) Frequency extension: above 67-70 GHz, the VNA uses frequency extender modules (mmWave heads): the VNA itself operates to 67 GHz (coaxial). Frequency extenders multiply the RF and LO signals to reach higher bands. Common extender bands: WR-15 (50-75 GHz), WR-10 (75-110 GHz), WR-06 (110-170 GHz), WR-03 (220-325 GHz). The extender connects to the DUT via a waveguide flange. Major extender manufacturers: Virginia Diodes (VDI), OML, Keysight. (3) Calibration at mmWave: connector type changes with frequency: 1.85 mm (DC-67 GHz), 1.0 mm (DC-110 GHz), waveguide flanges above 67 GHz. Calibration kits are frequency-specific and extremely expensive ($5,000-30,000 per kit). TRL (Thru-Reflect-Line) calibration is preferred at mmWave due to the difficulty of making precision SOLT standards. On-wafer calibration: requires a probe station (Cascade, FormFactor) with GSG probes and impedance standard substrates (ISS). (4) High-end VNA options: Keysight PNA-X N5247B: to 67 GHz, 145 dB dynamic range, NF measurement, gain compression, IMD. With extenders: to 1.1 THz. Price: $150,000-300,000. Rohde & Schwarz ZNA67: to 67 GHz, 140 dB DR, intuitive UI. Price: $120,000-250,000. Anritsu VectorStar MS4647B: to 110 GHz native (no extenders needed). Price: $200,000+. Copper Mountain CobaltFx: to 110 GHz, modular, lower cost alternative ($40,000-80,000).