Mini‑Circuits ANNE‑50L+ 50 ohm 1W SMA coaxial terminator
The Mini‑Circuits ANNE‑50L+ is a very good choice for many purposes—let’s evaluate it specifically for your radio astronomy calibration use case (receive-only, around ~1.42 GHz). Below I’ll walk through its merits, limitations, and how “good” it is in terms of your calibration needs.
✅ What the spec sheet tells us
From the manufacturer datasheet:
- Impedance: 50 Ω typical. (AllDataSheet)
- Frequency range: DC to 12 GHz for this part (some distributor lists say DC-18GHz but the official datasheet states up to 12 GHz for this model). (DigiKey)
- Maximum continuous power rating: 1 W (with derating at elevated temperatures). From the datasheet: “1 W. Up to 100 °C, derate linearly to 325 mW at 100 °C.” (minicircuits.com)
- Return loss / S-parameter typical: The datasheet (from “‐VIEW.pdf”) shows typical return loss dropping with frequency: e.g. at 50 MHz ~55 dB, at 1000 MHz ~46 dB, at 4000 MHz ~30.84 dB. (minicircuits.com)
- Connector type: SMA male (plug) termination. (DigiKey)
🎯 How this matches your calibration use case (receive-only, L-band ~1.42 GHz)
Because you’re working on radio astronomy (e.g., your feed for ~1420 MHz) and you’re looking to use a dummy load/termination for calibration (rather than transmit), key factors are: good impedance match (low reflections), stability, known temperature noise behaviour, plus ease of using as a “cold reference” or termination.
- At ~1.42 GHz, the ANNE-50L+ shows very good return loss (around 40+ dB typical at 1000 MHz; at 1.4GHz it will likely be in that ballpark). That means reflections are very low, which is excellent.
- Because the frequency band is well within the specified DC-12 GHz (in fact well within the flat region of the spec), the termination’s behaviour will be well-controlled at your frequency.
- Since you’re not transmitting large power, the 1W power rating is more than adequate for a receive-only termination. Thermal/heat dissipation is minimal in your case.
- The termination is compact (SMA, coaxial), which is convenient.
Thus, in terms of electrical impedance match and frequency range, this part is very well suited for your receive-only calibration termination.
⚠️ Some caveats / things to watch
While the part is good, for precision radio-astronomy calibration you should check/consider the following:
- Physical/thermal stability
- The load’s resistor will generate Johnson (thermal) noise according to its physical temperature. For calibration you ideally know the physical temperature of the termination. If the termination is mounted in a warm environment or changes temperature, that will affect your calibration baseline.
- Even though power handling (1 W) is more than you need, your termination may still warm slightly if ambient temperature changes or if the connector/cable has losses. It might be wise to mount the termination in a well-thermalised enclosure or monitor its temperature if you’re aiming for high accuracy.
- Return loss under real conditions
- The datasheet shows “typical” performance. Manufacturing tolerances and connector/cable transitions may degrade that somewhat. For the best calibration you might want to measure the actual VSWR/return loss at your frequency.
- Ensure that the connector transition (SMA male) to whatever cable/adapter you use does not introduce additional reflection/imbalance.
- Noise temperature vs ambient
- The load will contribute a noise temperature roughly equal to its physical temperature (i.e., if it is at 290 K, then ~290 K noise). If you want to calibrate to a “cold” reference you might still want a cooler termination (or better yet, a matched termination inside a cooled block) depending on your accuracy goals.
- If you are just doing relative calibration (versus comparing antenna to termination), this is fine. But for absolute calibration of system noise temperature, you might prefer a termination whose temperature you can control and know precisely.
- Connector/cable and stray inductance/capacitance
- Even though it’s specified to 12 GHz, as you go higher frequencies or if your calibration extends beyond 1.4 GHz, pay attention to the connector/cable transitions. For instance, if your cable is long or has losses, that may alter the effective impedance or noise contribution.
- Thermal coefficient and stability
- The datasheet doesn’t necessarily give the temperature coefficient of the internal resistor explicitly (or at least not in the snippets I saw). If high precision is required and ambient temperature swings, then you may want a termination with known low TCR or place it in a controlled thermal environment.
🔍 My judgement: Is it good enough for your use?
Yes — for your described use (L-band ~1.42 GHz, receive-only, using a good termination for calibration) the ANNE-50L+ is very suitable and likely an excellent practical choice.
If you were doing extremely high precision noise-calibration (say measuring system noise temperature to ± a few Kelvin or doing absolute calibration of cosmic line intensities to high precision), then you might ask for even more demanding specs (e.g., ultra-low TCR, specially mounted termination in a temperature‐controlled block, etc.). But for most radio-astronomy calibration use, this part is more than adequate.
🧩 My recommendation
- If you have budget: Buy the ANNE-50L+ and also consider building or purchasing a second termination for a “hot” reference (if you plan two-point calibration) or a cooled termination for a “cold” reference.
- Mount the termination in a short cable run from your receiver so that cable losses and mismatch are minimal. Use the same connector type as your receiver input to minimise adapter transitions.
- Monitor its ambient temperature (or put in an enclosure with a small temperature sensor) so you can log the physical temperature during calibration—then you know the noise contribution.
- Perform a reflection/VSWR check (if you have a VNA) at ~1.42 GHz just to confirm the termination and cable+connector assembly are behaving well.