Two generations of ultra-low-loss IR-blocking filters. HERD-2 is the current generation; HERD-1 remains listed for setups built around it.
1st generation
The first HERD filter. Non-magnetic, inline, with the leaky-waveguide structure that drains high-frequency radiation into an absorptive region while microwave signals pass undisturbed.
2nd generation · current
The current generation. Carbon-based non-magnetic absorbers thermalized to a gold-plated copper body, a deeper stopband measured to 145 GHz, and four connector families.
Both generations work the same way: a leaky coaxial waveguide drains Cooper-pair-breaking radiation into an absorptive region off the signal path, and both are non-magnetic and matched to 50 Ω up to 20 GHz.
HERD-2 changed the materials and the manufacturing process. Its carbon-based absorbers are thermalized to a gold-plated copper body, so the filter needs no additional thermalization; HERD-1 performs best with copper braids on its body. The stopband is deeper, more than 60 dB from 70 GHz and measured to 145 GHz, where HERD-1 gives more than 50 dB from 60 GHz. HERD-2 also comes in four connector families instead of one.
HERD-1 keeps the lower specified insertion loss, under 0.1 dB against 0.15 dB typical. If your setup is built around HERD-1, it stays available; new setups start with HERD-2.
Sources: HERD-2 datasheet Rev. 3 · Application note
| Specification | HERD-1 | HERD-2 current |
|---|---|---|
| Insertion loss | <0.1 dB | <0.15 dB typ. (DC–8 GHz) |
| Passband | DC–12 GHz | DC–13.5 GHz |
| Stopband | >50 dB above 60 GHz | >60 dB above 70 GHz, measured to 145 GHz |
| Matched to 50 Ω | to 20 GHz | to 20 GHz |
| Thermalization | Copper braids on the body recommended | None needed; mounting holes provided |
| Absorbers | Absorptive region off the signal path | Carbon-based, non-magnetic, thermalized to the body |
| Connectors | SMA F/F | SMA / SMP / SMPM / SMPS, custom on request |
| Construction | Non-magnetic | Non-magnetic, gold-plated copper, 0 K–320 K |
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