Popular intermediate frequencies (IF) for microwave and radar receivers operating in the 1–10 GHz RF range are typically which of the following?

Difficulty: Easy

Correct Answer: 30, 60 and 70 MHz

Explanation:


Introduction / Context:
Microwave and radar receivers use down-conversion from gigahertz RF to a convenient IF where filtering and amplification are practical. Standardized IFs simplify filter design and system interoperability.



Given Data / Assumptions:

  • RF range: 1–10 GHz (L-, S-, C-, X-bands).
  • Need IF high enough to separate images yet low enough for high-performance filters.


Concept / Approach:

Common IFs for microwave superhets include ~30 MHz, ~60 MHz, and ~70 MHz (and their near variants). These strike a balance between image rejection, filter availability (crystal/SAW), and achievable IF gains.



Step-by-Step Solution:

High RF (GHz) → mixer with LO → fixed IF (tens of MHz).Select IF values with mature filter tech (e.g., 70 MHz SAW/crystal filters).Achieve narrow, stable passbands and good dynamic range.


Verification / Alternative check:

Radar/receiver literature and module catalogs list 30/60/70 MHz IF chains as industry staples.



Why Other Options Are Wrong:

  • kHz IFs are far too low for modern microwave selectivity demands.
  • GHz IFs defeat the purpose of down-conversion.
  • 1.6/4.5/10.7 MHz are common in other contexts (e.g., 10.7 MHz for FM), not typical for microwave radar IF back-ends.


Common Pitfalls:

  • Assuming FM broadcast IF (10.7 MHz) is universal; microwave systems prefer higher IFs.


Final Answer:

30, 60 and 70 MHz

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