Cavity High-Pass Filter Selection Guide: Which Cutoff Frequency Do You Need?

TL;DR: Find Your Application

Match your application to the right cutoff frequency and part number.

Brand Comparison: Who Makes Cavity HPFs?

ZOMWAVE is the only cavity HPF supplier covering DC–40 GHz with a 5-day lead time.

Cavity vs LC vs Ceramic: Which Topology?

Bottom line: Weak-signal Rx / medium-high-power Tx → Cavity. Low-power test equipment → LC. In between → Ceramic.

1. L-Band: GPS and Satellite IF (1–2 GHz Cutoff)

Best for: Hardware engineers working on GPS receivers, satellite navigation, and L-band communication systems.

GPS L1 (1575 MHz) and L2 (1228 MHz) face out-of-band interference from DC–1 GHz switching ripple and clock harmonics. LC HPFs typically provide 20–30 dB stopband rejection; ZOMWAVE cavity HPFs deliver ≥50 dB — a 1000× difference in blocked interference power.

Selection: If your IF is 1700–2150 MHz, a 1.25 GHz cutoff preserves 500 MHz more passband margin than 1 GHz, at the cost of 3–5 dB less low-frequency rejection. For most GPS L1 applications, HPS-MAJMAJ-001G ($383) is the right call.

2. 5G Mid-Band (2–4 GHz Cutoff)

Best for: RF engineers working on 5G base stations, Massive MIMO, and S-band radar systems.

5G n77 (3.3–4.2 GHz) and n78 (3.3–3.8 GHz) transmit harmonics fall at 6.6–8.4 GHz (2nd harmonic). With IF in the 1–2 GHz range, a 4 GHz cutoff pushes the 3rd harmonic out of the passband while preserving the full n77 band.

Selection: HPS-MAJMAJ-004G ($400, 4–23 GHz passband, VSWR ≤1.6:1, IL ≤2 dB). In a 128T128R Massive MIMO array, channel-to-channel IL consistency (±0.3 dB) matters more than absolute IL — cavity HPFs outperform LC by ~0.5 dB in matching accuracy.

S-band radar (2–4 GHz): 2nd harmonics at 4–8 GHz may interfere with adjacent 5G/WiFi bands. Failing an EMI certification costs far more than the price difference between filter options.

3. C-Band and 5G mmWave IF (4–8 GHz Cutoff)

Best for: Systems engineers working on C-band satellite comms and 5G millimeter-wave IF conversion.

C-band satellite downlinks (3.7–4.2 GHz) have LO leakage in the 1–2 GHz range. A 5 GHz cutoff HPF placed before the upconverter filters this. HPS-MAJMAJ-005G ($400) also covers n79 (4.4–5 GHz).

5G mmWave (24–29 GHz) typically uses 6–12 GHz IF (X-band IF). HPS-MAJMAJ-6500 ($367, 6.5 GHz cutoff) — the lowest-priced model in the line — places the 2nd harmonic of n77/n78 (6.6–8.4 GHz) in its stopband with ≥50 dB rejection.

4. X-Band Radar (8–11.5 GHz Cutoff)

Best for: Engineers working on X-band radar, military, and avionics systems.

X-band radar (8–12 GHz) generates 1st harmonics at 16–24 GHz (Ku-band) and 2nd harmonics at 24–36 GHz (Ka-band). If your system also operates in Ku/Ka bands, start with a 9 GHz cutoff HPF to strip baseband noise before the bandpass filter.

HPS-MAJMAJ-009G ($450, 9 GHz cutoff, 9–28 GHz passband): ≥50 dB stopband rejection at 7 GHz, per ZOMWAVE internal test report (2023). For 21W CW, HPS-MAJMAJ-8500 ($450) — cavity HPF temperature rise is <15°C at 21W (25°C ambient). LC HPFs degrade significantly above 2W.

SMA return loss holds at 18–20 dB up to 28 GHz. No need to upgrade to 2.92mm unless your system extends above 26.5 GHz.

5. Ku/Ka-Band (11–40 GHz Cutoff)

Best for: Engineers working on Ka-band testing, millimeter-wave R&D, and satellite comm ground terminals.

Ka-band (26.5–40 GHz) requires 2.92mm connectors. SMA hits its cutoff around 18 GHz; above 18 GHz, VSWR degrades to >2.5:1, introducing unacceptable VNA measurement error.

ZOMWAVE HPS-MKJMKJ-011G ($833) covers 11–40 GHz — one of the few cavity HPFs reaching 40 GHz on the market. Pasternack’s equivalent tops out at 26.5 GHz ($695), leaving a 13.5 GHz gap.

For Ku-band only (12–18 GHz), HPS-MAJMAJ-011G ($467, 11.5 GHz cutoff, SMA) saves 44% — no point paying for Ka-band coverage you don’t need.

Summary: Decision Quick-Reference

Weak-signal Rx (GPS, radio astronomy) → Cavity, prioritize rejection. Medium/high-power Tx (5G BTS, radar PA coupled port) → Cavity, prioritize power. Low-power test (VNA calibration) → LC, prioritize IL.

All 29 models at ZOMWAVE High-Pass Filters — MIL-STD-202 certified, 5-day lead time.

FAQ

Q: SMA vs 2.92mm — when is 2.92mm mandatory?

A: Cutoff ≤11 GHz and system upper limit ≤28 GHz → SMA is fine. System upper limit >26.5 GHz (Ka-band) → must use 2.92mm. SMA above 18 GHz gives VSWR >2.5:1, which corrupts VNA measurements.

Q: Can I replace a bandpass filter with a high-pass filter?

A: No. A HPF only blocks low frequencies; a BPF blocks both low and high. For X-band radar with both LO leakage (low-frequency) and PA harmonics (high-frequency), a single HPF won’t cut it — either HPF+LPF in series or a BPF directly. The cost of skipping the right filter is usually less than one EMI failure retest.

Q: Is 2 dB insertion loss too high for GPS front-end?

A: GPS L1 front-end: antenna 290K, LNA NF 1.5 dB, HPF IL 2 dB → system NF ≈3.5 dB, noise temperature 288K. With insufficient stopband rejection (LC at 20 dB), out-of-band interference can push noise temperature to 500–1000K. 2 dB IL for 50 dB rejection is the right trade.

Q: Is 15W CW enough for high-power radar Tx?

A: Not at the PA output — PAs output >100W. The HPF belongs on the PA → directional coupler → HPF → antenna path, where coupled-port power is typically <20W (15W rating is fine). For >50W port power, contact ZOMWAVE for custom solutions.

About the Author ZOMWAVE Technical Team — RF and microwave components covering DC–110 GHz, serving 5G, satellite comm, and radar test applications.