Direct answer
Use a YIG-tuned filter when the passband must move across an octave or more and remain a roughly constant absolute width. Use a cavity filter when the band is fixed, insertion loss and power handling matter more than tunability, and you can accept a bandwidth that is a percentage of centre frequency. A switched cavity bank is the third option when you need both low loss and several discrete bands — it is not a faster YIG filter. Electrical tuning and cavity Q are different purchases; one driver will not turn either part into the other.
Key takeaways
- YIG buys a moving, near-constant absolute bandwidth; a cavity buys Q at one frequency.
- A YIG preselector costs real insertion loss where a cavity costs little; the gap widens with stage count.
- Compare absolute bandwidth at each operating frequency; a fixed cavity’s fractional width is not a tuning law, and YIG bandwidth can vary as it tunes.
- If the frequency plan is a short list of channels, a switched bank usually beats both extremes.
- Compare the model’s limiting and damage conditions at its installed input plane; a sphere-transfer example is not a high-power rating.
A filter comparison that starts with Q-factor is already answering the wrong question. The useful split is whether the passband has to move. For continuous narrowband tracking over broad coverage, investigate a YIG-tuned filter. For fixed channels, compare a cavity or a bank against the actual passband, rejection, loss and power requirements. That is the decision this page is for; the rest of the YIG technology section is the mechanism.
Side by side
| Criterion | YIG-tuned filter | Fixed cavity | Switched cavity bank |
|---|---|---|---|
| Coverage | Continuously moving passband within model range | One designed passband | Union of the installed passbands |
| Bandwidth check | Measure at low and high tuning points | Document absolute / fractional width at its centre | Document width and overlap for each path |
| Loss and rejection | Verify structure, frequency, alignment and power | Verify poles, bandwidth and construction | Include cavity and switch response |
| Power check | Separate linearity, limiting and damage conditions | Verify model power and thermal limits | Include both filter and switch ratings |
| Readiness | Coil / driver settling to required alignment | Check any adjustment or switched path | Measure switch and path readiness |
The conclusion
Use a YIG-tuned filter as a tracking preselector — in a spectrum analyser, a wideband EW or monitoring receiver, or any front end whose LO walks a multi-octave band. You are buying a moving, near-constant absolute bandwidth. Budget the model’s insertion loss, documented settling and coil power. A generic loss range is not an acceptance limit.
Use a cavity filter on a fixed channel — a SATCOM transponder, a radar on a known frequency, a base-station duplex path, a high-power transmitter. Compare the documented resonator Q, insertion loss and power conditions for that cavity. A fixed design gives up continuous electrical tracking.
Use a switched cavity bank when the frequency plan is a short list. That is the honest way to combine low loss with more than one band. It is not a YIG filter with extra switches, and it will not cover the spaces between the cavities.
What each one actually is
A YIG filter couples one or more spheres to small loops and moves their common resonance with an electromagnet. Bandwidth is a function of loop spacing and stage count. Frequency is a function of coil current. What YIG is is the material reason that works at all.
A cavity filter uses geometric resonators. Coaxial and waveguide implementations need their own Q, loss, size and power evidence; no universal ranges or frequency cutoff are retained here. A fixed cavity does not track the RF band by coil current.
Why the bandwidth shape matters
Example, assumed inputs: an idealized tracking passband stays 30 MHz wide at 2 GHz and 18 GHz. Its fractional widths are 1.5% and about 0.17%. Separate fixed filters each specified as 2% wide at those centres would be 40 MHz and 360 MHz wide. This arithmetic illustrates different specification choices; it is not a claim that a YIG filter has perfectly constant width or that one cavity tunes across that span.
Micro Lambda’s public bandpass-filter explanation, section 1 describes approximately 20% bandwidth expansion per octave for its discussed structures. Treat that as manufacturer guidance, not a universal tuning law; verify width and rejection across the model’s range.
Image rejection is a filter decision
The reason a receiver has a preselector at all is the image: a second RF, 2 × IF from the wanted signal, that the mixer cannot tell apart. RF, IF and LO is the frequency-plan version. The hardware version is this page.
- For continuous narrowband tracking over the plan discussed here, investigate a tracking filter. A fixed filter or switched bank can also work if its passbands cover the wanted channels and its rejection meets the moving image requirement; one filter per tune position is not inherently required.
- For a fixed channel, centre a bandpass cavity on the wanted passband and verify rejection at the image offset. A band-reject or notch design instead centres its rejection on the unwanted frequency.
Insertion loss ahead of the first gain stage adds directly to noise figure. Record the measured filter loss at its intended location and include it in the receiver noise budget. Put the same filter after the LNA and you spend linearity and recovery instead. Neither placement is free; compare actual loss and blocker performance at the proposed location.
What to pick, by job
- Analyser, EW receiver, monitoring front end. YIG. Coverage binds. Pair it with the YIG oscillator and budget settling once, together.
- SATCOM channel, radar on a known frequency, transmitter harmonic filter. Cavity. Loss and power bind. Waveguide if the power or the frequency says so.
- A radio with six known bands. Switched bank. Do not buy a YIG filter and then only ever park it on six currents.
- Radar that must tune. Split the problem. The tracking piece can be YIG; the high-power piece on the transmit side stays a cavity. See radar RF components.
The same three-way split — wide-and-slow, agile-and-noisier, fixed-and-quiet — is the oscillator comparison written for sources rather than filters. If you are pairing a YTO with a YIG preselector, read both before you budget settling.
Write the blocker scenario first
A bandpass filter must preserve the wanted band while rejecting the blocker. A notch or band-reject filter targets the unwanted frequency instead. Compare a tracking design and fixed or switched alternatives under the same frequency plan, including channels covered by a single fixed passband.
| Field | Required condition | Candidate evidence / result |
|---|---|---|
| Wanted frequency range / width | Fill: channels, modulation, tuning and temperature error | Fill: passband coverage and clipping margin |
| Image / blocker position | Fill: IF, LO side and unwanted frequencies | Fill: rejection at each required location |
| Interferer level | Fill: level at filter input, including prior gain | Fill: linearity, limiting and damage checks |
| Allowed loss / placement | Fill: budget before or after the LNA | Fill: installed loss and receiver impact |
| Readiness / switching time | Fill: command sequence, alignment tolerance and deadline | Fill: measured tuning or switch completion |
Coordinate the record with the RF, IF and LO plan. For a moving filter, repeat loss, rejection and readiness measurements across the required band; a static plot does not establish tracking performance.
Takeaway: Select the route that meets the complete passband, blocker, power and timing record rather than a class-wide loss or Q range.
Frequently asked questions
Can I tune a cavity electrically?
Not in the sense that matters here. Production cavities are aligned with screws. Some designs add a varactor or a motor; the tuning range is a sliver of what a YIG filter covers, and the Q usually falls as you pull it. Treat a cavity as fixed unless the datasheet shows otherwise.
Why is a YIG filter so much lossier?
It is not automatically lossier under every comparison. Coupling, bandwidth, resonator count and operating frequency determine the actual loss. Compare model evidence at the same passband and rejection requirements rather than applying a generic YIG or cavity range.
Will a YIG filter reject a high-power interferer better?
Spectral rejection does not establish power tolerance. Check the model’s limiting, linearity and damage conditions at the actual input plane. The cited YIG manufacturer’s 0 to +10 dBm sphere-transfer example is not a rating for every filter; cavity power handling also requires its own specification.
When is a switched bank the real answer?
When you have a known list of bands, need cavity-like loss, and can spend switch time instead of coil settling. Continuous coverage between those bands is what you give up.
Sources
- Key differences between RF band reject and band pass YIG filters — Micro Lambda Wireless Accessed October 8, 2026.
- How to Design a Frequency-Tunable Bandpass Filter Using YIG Resonators — RF Essentials Accessed August 28, 2026.
- Waveguide vs Coaxial Cavity Bandpass Filters — RF Essentials Accessed August 28, 2026.
- The Role of the Preselector Filter in a Receiver Front End — RF Essentials Accessed August 28, 2026.
