--- title: "Short note: Strip-lines against micro-strips" subject: "RF and Microwave Engineering" chapter: 2 key: "semester_7/rf_and_microwave_engineering:striplines-vs-microstrips-note" source: https://www.bctengineer.com/q/semester_7/rf_and_microwave_engineering/striplines-vs-microstrips-note site: BCT Engineering --- # Short note: Strip-lines against micro-strips RF and Microwave Engineering · Chapter 2: RF and Microwave Transmission Lines - Asked in: 2071 Magh, 5 marks - Video: [DSRM1: Stripline, Microstrip and Coplanar Line](https://www.youtube.com/watch?v=4vaZlMmC3zk) — RF4micro - 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/striplines-vs-microstrips-note - Whole chapter: https://www.bctengineer.com/md/semester_7/rf_and_microwave_engineering/chapter-2 ## Question Write a short note on microwave strip-lines against micro-strips. ## Short answer Stripline has a central strip between two ground planes, giving pure TEM propagation, no dispersion or radiation, but harder fabrication. Microstrip has a strip on a substrate over one ground, giving quasi-TEM behavior with dispersion and radiation, but easy fabrication and surface mounting. Microstrip is common for MMICs and antennas; stripline suits filters, couplers and high-isolation circuits. ## Answer **Stripline** and **microstrip** are planar transmission lines made by etching copper strips on dielectric substrates. They are used in microwave integrated circuits. ```text Stripline (triplate) Microstrip ==================== ground | dielectric εr | ____ strip (w) | ▬▬▬ strip | | dielectric εr | h | | ================= ground ==================== ground ``` | Feature | Stripline | Microstrip | |---|---|---| | Structure | Strip between two grounds, fully inside the dielectric | Strip on top of the substrate, one ground below | | Mode | Pure TEM | Quasi-TEM (fields partly in air) | | Effective εr | εeff = εr | 1 < εeff < εr | | Dispersion | None | Present at high frequency | | Radiation | None (shielded) | Some radiation from open top | | Losses | Lower radiation loss | Higher (radiation, surface waves) | | Fabrication | Harder (multilayer, buried) | Easy, single-layer PCB | | Mounting components | Difficult (buried strip) | Easy (surface mount, tuning) | | Bandwidth | Very wide | Wide | | Uses | Couplers, filters, power dividers | MMICs, patch antennas, amplifiers | **Choice:** microstrip is the most popular because it is cheap and components are easy to mount. Stripline is chosen where isolation, low radiation and no dispersion are needed, for example in high-performance couplers and filters. ## Check yourself The answer's key points as multiple-choice questions, with the correct option and why. 1. Which statement about the propagation modes is correct? A. Both stripline and microstrip support pure TEM B. Stripline supports pure TEM; microstrip is quasi-TEM C. Stripline is quasi-TEM; microstrip supports pure TEM D. Both are quasi-TEM because both use a dielectric Answer: B. A stripline is fully inside one dielectric, so the mode is pure TEM. In a microstrip the fields are partly in air, so the mode is quasi-TEM. (Key point: Mode of propagation) 2. How do the effective permittivities compare? A. Stripline: eps_eff = eps_r; microstrip: 1 < eps_eff < eps_r B. Stripline: 1 < eps_eff < eps_r; microstrip: eps_eff = eps_r C. Both have eps_eff = 1 D. Both have eps_eff = eps_r Answer: A. All the stripline field is in the dielectric, so eps_eff = eps_r. The microstrip field is partly in air, which gives a value between 1 and eps_r. (Key point: Effective permittivity) 3. Why is microstrip the more popular choice, and when is stripline preferred? A. Microstrip is shielded and non-dispersive, so it is used for couplers B. Stripline is cheaper and easier to mount parts on, so it is used for amplifiers C. Microstrip is cheap and easy to mount components on; stripline is chosen where isolation, low radiation and no dispersion are needed D. Both are identical, so the choice is only a matter of colour Answer: C. Microstrip is a single-layer PCB with an open top for mounting. Stripline is shielded and non-dispersive, so it suits high-performance couplers and filters. 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