Suure jõudlusega kahekordne pääsuriba + Sälgu õõnsuse filter

Suure jõudlusega kahekordne pääsuriba + Sälgu õõnsuse filter

Designing a Dual Passband + Sälgu õõnsuse filter that combines two wide passbands with a narrow, deep rejection notch in between is one of the most demanding challenges in RF engineering. The customer’s specification defines strict requirements for bandwidth, attenuation, and environmental durability — all within a compact mechanical footprint. This article explains the technical requirements, design considerations, and implementation strategies for achieving such high-performance RF filtering.

Here is a buyer’s demand.

It is a L passband + notch combined filter.
power handling: vähem kui 30 dBm.
connector type: SMA female for input and out put.
center frequency: (960+1230)/2: 1095 MHz
passband frequency 1: 960 ~ 1015 MHz
passband frequency 2: 1045~1230 MHz
insertion loss < 1 dB
ripple : +- 0.5 dB
stop band 1: 70 dB attenuation achieved relative to the passband ripple midpoint for frequencies lower than 690 MHz
stop band 2: 70 dB attenuation achieved relative to the passband ripple midpoint for frequencies higher than 1390 MHz
suppression: 30 db attenuation achieved relative to the passband ripple midpoint for frequency 1028.5 kuni 1031.5 MHz
Vswr: better than 1.6
suurus: small as possible
temp: -40 ~70 degrees Celsius
keskkond: pass salt spray test
tuning: screw
material: brass or aluminium
coating: jah

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1. Technical Requirements Overview

The target product is a dual passband cavity filter with an integrated notch, defined by the following key parameters:

• Pääsupael 1: 960–1015 MHz
• Pääsupael 2: 1045–1230 MHz
• Notch Band: 1028.5–1031.5 MHz, ≥30 dB attenuation
• Stopband 1: below 690 MHz, ≥70 dB attenuation
• Stopband 2: ülal 1390 MHz, ≥70 dB attenuation
• Insertion Loss: <1 dB, Ripple: ± 0,5 dB
• Vswr: <1.6
• Power Handling: <30 dBm
• Pistik: SMA female input/output
• Töötemp: –40°C to +70°C
• Keskkonna-: Pass salt spray test
• Tuning: Mechanical screw tuning
• Materjal: Brass or aluminum with protective coating
• Suurus: As compact as possible

These parameters demand a precision-engineered cavity structure capable of delivering both high selectivity and low loss.

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2. Major Design Challenges

1. Extremely Narrow Notch (3 MHz)
   The rejection notch (1028.5–1031.5 MHz) is only 0.3% of the center frequency, requiring an exceptionally high-Q cavity resonator and accurate coupling control to ensure ≥30 dB attenuation without degrading the passbands.
2. 70 dB Stopband Rejection
   Saavutamine 70 dB suppression below 690 MHz and above 1390 MHz is a high-order filtering requirement that typically demands multi-cavity coupling or complex dual-mode structures.
3. Low Insertion Loss over Wide Passbands
   With broad passbands (960–1015 and 1045–1230 MHz), maintaining <1 dB insertion loss is difficult. High-Q cavities, low-loss plating, and precision machining are essential.
4. Miniaturization vs. Electrical Performance
   The customer’s request for minimal size directly conflicts with Q-factor and attenuation goals. Engineering tradeoffs must be made between compactness and RF performance.

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3. Recommended Implementation Approaches

A. Machined Multi-Cavity Filter (Preferred Solution)

• Eelised: Excellent Q-factor, stable thermal performance, and precise control over notch frequency.
• Disain: Multi-cavity resonator with a dedicated notch cavity and mechanical screw tuning.
• Materjalid: Brass or aluminum, nickel/silver plating for corrosion resistance.
• Drawbacks: Larger size and higher manufacturing cost.

B. Hybrid Dielectric–Cavity Filter

• Eelised: Smaller size, integrates ceramic resonators for the notch.
• Drawbacks: Temperature drift and limited 70 dB stopband rejection.

C. Compact Microstrip Filter

• Eelised: Minimal volume and low cost.
• Drawbacks: Limited deep rejection and higher insertion loss.

For military or UAV video transmission applications, the machined cavity structure remains the most reliable way to achieve the required dual passband + notch performance.

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4. Materials and Coating

To ensure corrosion resistance and compliance with the salt spray test:

• Brass: Nickel plating (optional gold plating on contacts)
• Aluminum: Hard anodized and sealed surface
• Proper sealing around SMA connectors and housing joints ensures long-term reliability.

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5. Tuning and Temperature Stability

The mechanical screw tuning allows fine adjustment of the passbands and notch. For stability under vibration and temperature changes, locking nuts or adhesive sealants are recommended.
Thermal drift is minimized by selecting low-expansion materials and tight mechanical tolerances.

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6. Testing and Quality Validation

Before shipment or batch production, igaüks Dual Passband + Sälgu õõnsuse filter should undergo comprehensive testing:

• S-Parameter (S11/S21) measurements from 300 MHz–2 GHz
• Vswr <1.6 across passbands
• Stopband attenuation verification (690 MHz and 1390 MHz)
• Salt spray and temperature cycling tests
• Power handling kuni 30 dBm
• Aging and vibration stability validation

A full RF test report should accompany every prototype and production batch.

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7. Manufacturing and Consistency

• Machining tolerance: ±0.02–0.05 mm for cavity dimensions.
• Connector interface: Ensure low reflection and solid grounding.
• Batch calibration: Each filter may require individual fine-tuning due to the narrow notch bandwidth.

Initial small-batch prototyping (3–5 units) is strongly recommended before mass production.

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8. Risk Assessment and Customer Communication

Because this Dual Passband + Sälgu õõnsuse filter targets high selectivity and compact size, it’s important to clarify the customer’s top priorities:

• Is 70 dB rejection mandatory, or can it be slightly reduced?
• Is compact size more critical than <1 dB insertion loss?
• Can the notch bandwidth be widened slightly to improve manufacturability?

Confirming these factors early helps balance design complexity and production cost.

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9. Kokkuvõte

The Dual Passband + Sälgu õõnsuse filter is technically feasible but requires precision mechanical and RF engineering.
A multi-cavity design remains the best approach to achieve low insertion loss, narrow deep notch rejection, and strong environmental durability.
Close collaboration between the customer and the RF design team ensures successful prototyping and optimized production.

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KKK -d

Based on buyer’s specifications, our engineering team has completed the simulation the Combline Filter and prepared the following proposed parameters for your review and confirmation:

Simulated Technical Specifications (for reference):

• Pääsupael 1: 960–1015 MHz
• Pääsupael 2: 1045–1230 MHz
• Insertion Loss: ≤1.5 dB (≤1.0 dB at center frequency)
• Passband Ripple: ≤±0.5 dB
• Vswr: ≤1.36
• Out-of-Band Rejection: ≥70 dB @ 690 MHz–DC; ≥70 dB @ 1390–3000 MHz
• Suppression Between Passbands: ≥30 dB @ 1028.5 MHz; ≥30 dB @ 1031.5 MHz
• Takistus: 50 Oh!
• Pistiku tüüp: SMA-Female
• Töötemperatuur: –40°C to +65°C
• Salt Spray Protection: Three-proof coating on the housing surface
• Simulated Size (for reference): 112 × 54 × 36 mm (TBD)

An RF comb filter is a type of radio frequency (RF) filter whose frequency response looks like the teeth of a comb — it has a series of equally spaced passbands or stopbands across the frequency spectrum.

Siin on jaotus:

• Funktsioon:
  It allows (or rejects) signals at specific, regularly spaced frequencies.
• Working principle:
  The comb-like pattern is achieved through signal delay and interference (in digital or analog domains) or through resonant structures (in microwave/RF hardware).
• Types:
  • Band-pass comb filter: Passes multiple narrow bands at regular intervals.
  • Band-stop (notch) comb filter: Rejects multiple narrow bands at regular intervals.
• Rakendused:
  • RF and microwave systems for channel selection or interference rejection
  • Frequency synthesizers and spectrum analyzers
  • Optical and acoustic signal processing
  • Multi-carrier communication systems

Näide:

A 1 GHz RF comb filter may pass signals at 1 GHz, 2 GHz, 3 GHz, jne., while attenuating others in between.