Need help

Heaven431

Sep 18, 2026
2
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Sep 18, 2026
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2
Can anyone please help me answer these questions?
1. Why do antennas integrated on bulk CMOS substrates typically have low radiation efficiency, and what techniques can be used to improve their efficiency?
2. A 50 Ω on-chip transmission line operates at 140 GHz. Which type of loss is most significant at this frequency, and how would you modify the transmission-line cross-section to minimize it?
3. In a phased array, why is the input impedance of an element is not the same as when that element is simulated alone, and how does this difference affect the front-end amplifier driving the element?
4. An absorber demonstrates 100% absorption. Physically, where is the incident electromagnetic energy dissipated, and what experimental measurement would provide convincing evidence that the reported absorption is not merely a simulation artifact?
5. An antenna is reported to have 100% radiation efficiency. What experimental measurement would convincingly verify that the reported efficiency is not a simulation artifact?
 

Sunnysky

Jul 15, 2016
577
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Jul 15, 2016
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577
Too many questions unrelated. Pre-exam questions?

At 140 GHz surface roughness is a significant addition to path length and losses with eddy current , dielectric loss although skin effect is deeper than sqrt(f) it is still a small fraction of any typical conductor thickness.

The best test for absorption loss from s11 matching and s21 attenuation. Grapene nanotube surfaces would be the best thermal absorbers but never 100% and would exceed conductor loss. Reflected power would reduce incident power from 100% so be perfectly absorptive one must meet the challenge of matching the input impedance is essential if this is conducted vs radiated.

An IR thermal camera would be an obvious measurement to see the peak and null current losses with standing waves.

What tolerance did you assume for 100% loss? Or was this a trick question to test your practical experience?
 
Last edited:

Sunnysky

Jul 15, 2016
577
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Jul 15, 2016
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577
Skin Effects are a result of internal dielectric Eddy Currents.
Proximity losses are a result of external Eddy Currents such as parallel paths of Ferrite touching the conductor traces.
 

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