Doppia banda passante ad alte prestazioni + Filtro a cavità Notch

Doppia banda passante ad alte prestazioni + Filtro a cavità Notch

Progettare a Doppia banda passante + Filtro a cavità Notch che combina due bande passanti larghe con una stretta, la tacca di reiezione profonda nel mezzo è una delle sfide più impegnative nell'ingegneria RF. Le specifiche del cliente definiscono requisiti rigorosi per la larghezza di banda, attenuazione, e durabilità ambientale, il tutto con un ingombro meccanico compatto. Questo articolo spiega i requisiti tecnici, considerazioni di progettazione, e strategie di implementazione per ottenere un filtraggio RF ad alte prestazioni.

Ecco la richiesta di un acquirente.

È una banda passante L + filtro combinato notch.
gestione della potenza: meno di 30 dBm.
tipo di connettore: SMA femmina per ingresso e uscita.
frequenza centrale: (960+1230)/2: 1095 MHz
frequenza della banda passante 1: 960 ~ 1015 MHz
frequenza della banda passante 2: 1045~1230 MHz
perdita di inserzione < 1 dB
ondulazione : +- 0.5 dB
fermare la banda 1: 70 Attenuazione dB ottenuta rispetto al punto medio dell'ondulazione della banda passante per frequenze inferiori a 690 MHz
fermare la banda 2: 70 Attenuazione dB ottenuta rispetto al punto medio dell'ondulazione della banda passante per frequenze superiori a 1390 MHz
soppressione: 30 Attenuazione db ottenuta rispetto al punto medio dell'ondulazione della banda passante per la frequenza 1028.5 A 1031.5 MHz
VSWR: meglio di 1.6
misurare: piccolo possibile
temp: -40 ~70 gradi Celsius
environment: pass salt spray test
tuning: screw
material: brass or aluminium
coating: SÌ

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1. Panoramica dei requisiti tecnici

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

• Passband 1: 960–1015 MHz
• Passband 2: 1045–1230 MHz
• Notch Band: 1028.5–1031.5 MHz, ≥30 dB attenuation
• Stopband 1: below 690 MHz, ≥70 dB attenuation
• Stopband 2: above 1390 MHz, ≥70 dB attenuation
• Insertion Loss: <1 dB, Ripple: ±0.5 dB
• VSWR: <1.6
• Power Handling: <30 dBm
• Connettore: SMA female input/output
• Temp. operativa: –40°C to +70°C
• Environmental: Pass salt spray test
• Tuning: Mechanical screw tuning
• Materiale: Brass or aluminum with protective coating
• Misurare: 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. Principali sfide progettuali

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
   Achieving 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. Approcci di implementazione consigliati

UN. Filtro multicavità lavorato (Soluzione preferita)

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

B. Filtro dielettrico ibrido a cavità

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

C. Filtro a microstriscia compatto

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

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

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4. Materiali e rivestimento

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. Accordatura e stabilità della temperatura

IL 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. Test e convalida della qualità

Before shipment or batch production, each Doppia banda passante + Filtro a cavità Notch 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 fino a 30 dBm
• Aging and vibration stability validation

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

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7. Produzione e coerenza

• 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. Valutazione del rischio e comunicazione al cliente

Because this Doppia banda passante + Filtro a cavità Notch 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. Riepilogo

IL Doppia banda passante + Filtro a cavità Notch is technically feasible but requires precision mechanical and RF engineering.
UN 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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Domande frequenti

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):

• Passband 1: 960–1015 MHz
• Passband 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
• Impedance: 50 OH
• Tipo di connettore: SMA-Female
• Temperatura operativa: –40°C to +65°C
• Salt Spray Protection: Three-proof coating on the housing surface
• Simulated Size (for reference): 112 × 54 × 36 mm (TBD)

UN 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.

Ecco un riepilogo:

• Funzione:
  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.
• Applicazioni:
  • RF and microwave systems for channel selection or interference rejection
  • Frequency synthesizers and spectrum analyzers
  • Optical and acoustic signal processing
  • Multi-carrier communication systems

Example:

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