- 2080 Bhadra · 3+3+4 marks
Lumped vs distributed analysis, applications, protocols
Short answer
Lumped analysis treats R, L, C as point elements valid when circuit size is much smaller than wavelength; distributed analysis uses per-unit-length R, L, G, C and wave equations when size is comparable to wavelength. Applications include communication, radar, navigation, heating, medical, and radio astronomy. Two protocols: Wi-Fi (2.4/5 GHz, OFDM, CSMA/CA) and satellite (C/Ku/Ka bands, transponders, FDMA/TDMA/CDMA).
Differentiate between lumped and distributed circuit analysis. List out the areas of application of microwave system. Provide detail protocols of two microwave communication systems.
Lumped vs distributed circuit analysis
Lumped analysis treats R, L and C as concentrated at points connected by ideal wires. It is valid when the circuit size is much smaller than λ (a rule of thumb is l < λ/10). Distributed analysis treats R, L, G and C as spread along the line per unit length. Voltage and current then vary with position, which is needed when the size is about λ or larger.
| Lumped | Distributed |
|---|---|
| Size ≪ λ | Size ≥ λ/10 |
| Elements are discrete R, L, C | R′, L′, G′, C′ per unit length |
| V and I are the same along a wire | V and I vary with z (waves) |
| No propagation delay | Phase delay βz |
| KVL/KCL, ordinary ODEs | Telegrapher's equations (PDEs in z, t) |
| Example: a 50 Hz power circuit | Example: a 10 GHz microstrip line |
Distributed model of a length Δz of line:
o--R'Δz--L'Δz--+------o
|
G'Δz C'Δz
|
o--------------+------o
Areas of application of microwave systems
Communication (terrestrial links, satellite, cellular, Wi-Fi), radar (ATC, weather, military, automotive), navigation (GPS), broadcasting (DTH TV), remote sensing, industrial and domestic heating (2.45 GHz ovens), medical (diathermy, hyperthermia), and radio astronomy.
Detailed protocols of two microwave communication systems
1. Wi-Fi (IEEE 802.11 WLAN)
- Bands: 2.4 GHz ISM (2.400–2.4835 GHz), 5 GHz (5.15–5.85 GHz), and 6 GHz for Wi-Fi 6E.
- Channels: 20/40/80/160 MHz wide. At 2.4 GHz there are 13 channels 5 MHz apart, and only 1, 6 and 11 do not overlap.
- Modulation: OFDM with BPSK up to 1024-QAM (802.11ax). 802.11b used DSSS/CCK.
- Access: CSMA/CA with optional RTS/CTS. Duplexing is TDD.
- Rates: 11 Mbps (b), 54 Mbps (a/g), 600 Mbps (n, MIMO), about 9.6 Gbps (ax).
- Security: WPA2/WPA3 (AES).
2. Satellite communication
- Geostationary orbit at 35,786 km. The ground-to-satellite delay is about 120 ms, so one hop (up and down) takes about 240 ms.
- Bands: C band (uplink 5.925–6.425 GHz, downlink 3.7–4.2 GHz, written 6/4 GHz), Ku band (14/12 GHz), Ka band (30/20 GHz).
- A transponder receives the uplink, translates the frequency down, amplifies with a TWTA or SSPA, and retransmits. Typical transponder bandwidth is 36 MHz.
- Access: FDMA, TDMA, CDMA. Example: VSAT networks with QPSK/8PSK and DVB-S2.
- Uplink is at the higher frequency because the ground station can afford more power to overcome the greater loss.
✓ Answer checked by Claude Opus 5.5 (high effort)
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