Instructions to Candidates
- This post-test contains 20 multiple-choice questions. Answer ALL questions.
- Each question carries equal marks. There is no negative marking.
- Questions are restricted to the first three levels of Bloom's taxonomy: Level 1 – Remember, Level 2 – Understand, and Level 3 – Apply.
- Select the single best option for each question.
- The interactive quiz below allows self-marking with explanations. A full written answer key is also provided at the end of this document.
- Time allowed: 40 minutes.
Tips: Read each stem carefully. For "Apply" questions, work out the calculation on paper before selecting an option — unit consistency (watts, metres, dB, degrees) is essential.
Bloom's Taxonomy Coverage (Levels 1–3 Only)
| Level | Skill Tested | Question Numbers | Count |
|---|---|---|---|
| Level 1 — Remember | Recall definitions, symbols, and standard facts about antennas | Q1, Q2, Q3, Q4, Q5, Q6, Q7 | 7 |
| Level 2 — Understand | Explain concepts, interpret patterns, and relate parameters | Q8, Q9, Q10, Q11, Q12, Q13, Q14 | 7 |
| Level 3 — Apply | Use formulas to compute gain, wavelength, beamwidth, power density, and aperture | Q15, Q16, Q17, Q18, Q19, Q20 | 6 |
Part A — Quiz (Attempt All Questions)
Part B — Post-Test Answers & Explanations
Each answer below includes a concise explanation and its Bloom's taxonomy level, suitable for post-test review and moderation purposes.
| Q | Answer | Explanation | Bloom Level |
|---|---|---|---|
| 1 | (c) | An antenna is a transducer: it converts electrical energy from a transmission line into radiated electromagnetic waves (transmit mode), and the reverse on reception (reciprocity). | Remember |
| 2 | (b) | The far field (Fraunhofer) region is defined by R > 2D²/λ. Inside this region, angular field distribution is independent of distance and the wave approximates a plane wave. | Remember |
| 3 | (d) | Isotropic radiator: equal radiation intensity in all directions. It is a theoretical lossless reference source, not physically realisable. | Remember |
| 4 | (c) | Directivity is defined as maximum radiation intensity divided by the average radiation intensity: D = Umax/Uavg. It is a dimensionless ratio (expressed in dBi relative to isotropic). | Remember |
| 5 | (b) | A half-wave dipole has a feed-point impedance of approximately 73 + j42 Ω; with end effect it is usually quoted near 73 Ω (resonant length slightly less than λ/2). | Remember |
| 6 | (a) | Beamwidth (HPBW) is the angular separation between the two directions where the power pattern falls to one-half its maximum value (i.e., −3 dB points). | Remember |
| 7 | (d) | Standard relations: HPBW (degrees) ≈ 70 λ/D for large uniform apertures; Aeff = λ²G/(4π); and directivity of a short dipole is 1.5. HPBW ≈ 2π/N is not standard. | Remember |
| 8 | (b) | Wire antennas (dipoles, loops) are low-directivity, broad-beam radiators. High directivity is achieved with aperture antennas (horns, dishes), arrays, or Yagi-Uda structures. | Understand |
| 9 | (c) | A parabolic reflector collimates rays from a feed at the focus into a narrow beam — high directivity/gain with high aperture efficiency, the standard choice for satellite ground stations. | Understand |
| 10 | (b) | Near the horizon (low elevation), sky waves can travel very long distances via ionospheric reflection, and the horizon itself is the limiting geometry for direct waves. Ground wave at VHF is limited; "waves travel slower horizontally" is false. | Understand |
| 11 | (b) | Grazing/large separation from a ground plane produces image currents that cancel the radiated field, driving input resistance toward zero — a very poor match to the feed line. | Understand |
| 12 | (c) | End-fire means maximum radiation along the array axis (θ = 0° and 180°), as in a Yagi-Uda or properly phased linear array. Broadside is perpendicular to the axis. | Understand |
| 13 | (c) | Gain G = ηD. For an efficiency of 55% (0.55) and D = 10, G = 5.5 ≈ 7.4 dB. The distractor 10 dB (10 W/W) ignores the efficiency loss. | Understand |
| 14 | (d) | All statements are true: reciprocity holds (same radiation pattern transmit/receive), the same effective aperture formula applies on receive, and polarisation must be matched to avoid polarisation mismatch loss. | Understand |
| 15 | (b) | λ = c/f = 3×10⁸ / 3×10⁹ = 0.1 m = 10 cm. | Apply |
| 16 | (b) | EIRP = Pin × G(linear) = 50 W × 10 = 500 W. EIRP(dBm) ≈ 57 dBm; 50 W × 100 dB is a common misuse of dB as a linear multiplier. | Apply |
| 17 | (c) | HPBW ≈ 70λ/D = 70(0.1)/0.5 = 14°. This illustrates the inverse relation between aperture size and beamwidth. | Apply |
| 18 | (b) | S = Prad/(4πR²) = 1000/(4π·10⁶) ≈ 7.96×10⁻⁵ W/m². The 2πR² option is a frequent error (spherical surface area is 4πR²). | Apply |
| 19 | (c) | Aeff = λ²G/(4π) = (0.1)²×10/(4π) = 0.1/(4π) ≈ 7.96×10⁻³ m² ≈ 0.008 m² (≈ 80 cm²). | Apply |
| 20 | (c) | Prec = S × Aeff. With S from Q18: 7.96×10⁻⁵ × 7.96×10⁻³ ≈ 6.33×10⁻⁷ W ≈ 0.63 μW. Note that idealised Friis with Gt = 10, Gr = 10, R = 1 km, λ = 0.1 m gives Pr = PtGtGr(λ/4πR)² ≈ 6.3×10⁻⁷ W — consistent. | Apply |