--- title: "Microwave vs low frequency and five system protocols" subject: "RF and Microwave Engineering" chapter: 1 key: "semester_7/rf_and_microwave_engineering:microwave-differences-five-protocols" source: https://www.bctengineer.com/q/semester_7/rf_and_microwave_engineering/microwave-differences-five-protocols site: BCT Engineering --- # Microwave vs low frequency and five system protocols RF and Microwave Engineering · Chapter 1: Introduction - Asked in: 2082 Baisakh, 4+4 marks - Answer checked by Claude Opus 5.5 (high effort) on 2026-10-14 - Page: https://www.bctengineer.com/q/semester_7/rf_and_microwave_engineering/microwave-differences-five-protocols - Whole chapter: https://www.bctengineer.com/md/semester_7/rf_and_microwave_engineering/chapter-1 ## Question Find the unique differences between microwave and conventional low frequency systems. Mention detail specifications/protocols of any five microwave communication system. ## Short answer Microwave systems are distributed, use S-parameters, waveguides, and line-of-sight propagation, while low-frequency systems are lumped with Z/Y/h parameters. Five microwave systems: Wi-Fi (2.4/5 GHz, OFDM, CSMA/CA), cellular (GSM/LTE/5G, TDMA/OFDMA), satellite (C/Ku/Ka bands, transponders), terrestrial microwave links (6-38 GHz, QPSK to 4096-QAM), and Bluetooth (2.4 GHz FHSS, GFSK). ## Answer #### Unique differences: microwave vs conventional LF systems | Point | Conventional LF | Microwave | |---|---|---| | Circuit size | Much smaller than λ | About λ | | Analysis | Lumped, KVL/KCL | Distributed, Maxwell's equations and transmission lines | | Parameters | Z, Y, h | S-parameters | | Guides | Wires, twisted pair | Coax, waveguide, microstrip | | Devices | BJT, FET, triode | Klystron, magnetron, TWT, Gunn, HEMT | | Skin effect and radiation | Negligible | Significant | | Propagation | Ground wave and sky wave | Line of sight | | Bandwidth | Small | Very large | #### Specifications/protocols of five 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. **4. Terrestrial microwave link (point-to-point backhaul)** - Bands: 6, 7, 8, 11, 13, 15, 18, 23 and 38 GHz, with E-band at 70/80 GHz. - Line of sight with at least 60% of the first Fresnel zone clear. Hop length 30–50 km at 6 GHz, a few km at 23–38 GHz. - Modulation: adaptive QPSK up to 4096-QAM. Channel width 7–56 MHz (up to 112 MHz). - Duplexing: FDD with a duplexer. Protection: 1+1 hot standby, and space or frequency diversity. - Parabolic dishes of 0.3–3 m, 30–45 dBi gain. **5. Bluetooth (IEEE 802.15.1)** - Band: 2.4 GHz ISM. 79 channels of 1 MHz (Classic) or 40 channels of 2 MHz (Low Energy). - FHSS at 1600 hops/s. Modulation GFSK (1 Mbps), with π/4-DQPSK or 8DPSK for EDR (2–3 Mbps). - Piconet of 1 master and up to 7 active slaves, using TDD slots of 625 µs. - Range: 10 m (Class 2, 2.5 mW) to 100 m (Class 1, 100 mW). ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Which description fits Bluetooth (IEEE 802.15.1) Classic? A. FHSS at 1600 hops/s, 79 channels of 1 MHz, piconet of 1 master and up to 7 active slaves B. OFDM with 20 MHz channels and CSMA/CA C. TDMA with 200 kHz carriers D. DSSS with 3 non-overlapping channels Answer: A. Bluetooth hops among 79 channels at 1600 hops/s and a piconet has one master with up to 7 active slaves. (Key point: Bluetooth) 2. For a point-to-point terrestrial microwave link, what path clearance is required? A. At least 6% of the first Fresnel zone B. At least 60% of the first Fresnel zone clear C. Complete blockage of the Fresnel zone is acceptable D. Clearance only of the direct ray Answer: B. At least 60% of the first Fresnel zone must be free of obstacles to avoid diffraction loss. (Key point: Terrestrial link clearance) 3. Which set correctly describes GSM? A. OFDMA, 20 MHz carriers, TDD B. GMSK, 200 kHz carriers, TDMA with 8 slots per carrier, FDD C. CSMA/CA, 5 MHz carriers, TDD D. FHSS with 79 channels of 1 MHz Answer: B. GSM uses 200 kHz carriers, GMSK modulation, 8 TDMA slots per carrier and FDD (uplink 890-915 MHz, downlink 935-960 MHz). (Key point: Cellular GSM) 4. What does a satellite transponder do to the uplink signal? A. Demodulates it and stores it for later B. Translates it to a lower frequency, amplifies it (TWTA/SSPA) and retransmits C. Reflects it back unchanged at the same frequency D. Converts it to a higher frequency to reduce loss Answer: B. A transponder receives the uplink, shifts it down in frequency, amplifies and retransmits to avoid feedback between receive and transmit. 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