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Passive components behavior and application protocols

Short answer

At microwave frequencies parasitic lead inductance, stray capacitance and skin effect make resistors, capacitors and inductors self-resonant, so distributed stubs and cavities replace lumped parts. Wi-Fi uses OFDM and CSMA/CA in 2.4/5/6 GHz; cellular uses TDMA/OFDMA with frequency-reuse cells; satellite links use C/Ku/Ka transponders with about 240 ms round-trip delay.

Compare the behavior of microwave passive components at low frequency bands against microwave bands. Prepare the detail real-world protocols of any three major applications of microwave communication systems.

Behaviour of passive components: low frequency vs microwave

At low frequency a resistor, inductor or capacitor acts as an ideal lumped element. At microwave frequencies its leads and body are a large fraction of λ, so parasitics (lead inductance, stray capacitance, skin effect) dominate.

ComponentLow frequencyMicrowave band
WireShort circuitInductor (about 1 nH/mm) and a transmission line
ResistorPure RR with series lead L and shunt C; at high f, the C shorts it
CapacitorPure CSeries LCR; above its self-resonance it acts as an inductor
InductorPure LTurn-to-turn C causes self-resonance; above it, it acts as a capacitor
RealisationDiscrete partsDistributed: stubs, line sections, cavities, chip parts
Real resistor at microwave frequency:
      Ls       R       Ls
  o--^^^^---/\/\/---^^^^--o
        |              |
        +------||------+
              Cs (stray)

So at microwave frequencies L and C are made from short-circuited or open-circuited stubs, and resonators are made from cavities.

Real-world protocols of three 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. Cellular mobile (GSM / LTE / 5G NR)

  • GSM: 900/1800 MHz, 200 kHz carriers, GMSK modulation, TDMA with 8 time slots per carrier, FDD (uplink 890–915 MHz, downlink 935–960 MHz).
  • LTE (4G): 700 MHz–2.6 GHz, 1.4–20 MHz bandwidth, OFDMA downlink and SC-FDMA uplink, up to 64-QAM, MIMO, FDD or TDD.
  • 5G NR: FR1 below 6 GHz and FR2 at 24–52 GHz (mm-wave), up to 400 MHz bandwidth, flexible numerology, massive MIMO and beamforming.
  • Architecture: mobile station, base station (BTS/eNodeB/gNB), core network. Frequency reuse in hexagonal cells, with handover between cells.

3. 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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