Fraunhofer distance for D=1 m and λ=0.1 m is at least?
A 10 m
B 20 m
C 2 m
D 100 m
Answer: B. 20 m. The common far-field criterion is R ≥ 2D²/λ, which gives 20 metres.
Given E- and H-plane HPBWs of 30° and 20°, and ΩA≈θEθH, directivity is near?
A 17.2
B 34.4
C 137.6
D 68.8
Answer: D. 68.8. Convert the beamwidths to radians: ΩA≈0.5236×0.3491=0.1828 sr, so D≈4π/ΩA≈68.8.
Link budget with Pt=0 dBm, gains 10 dBi each, and 100 dB path loss gives Pr?
A −90 dBm
B −60 dBm
C −80 dBm
D −110 dBm
Answer: C. −80 dBm. The link budget is 0 + 10 + 10 − 100 = −80 dBm.
At 1 GHz across 1 km, free-space path loss is about?
A 92.4 dB
B 72.4 dB
C 82.4 dB
D 102.4 dB
Answer: A. 92.4 dB. FSPL = 20log₁₀(4πR/λ); with λ≈0.3 m and R=1000 m, it is about 92.4 dB.
In a four-element equal-phase array, broadside array-factor magnitude relative to one element is?
A 4
B 2
C 1
D 8
Answer: A. 4. Four equal phasors add coherently at broadside, giving an array-factor magnitude of four.
EIRP for Pt=5 W and linear gain 10 is?
A 5 W
B 15 W
C 500 W
D 50 W
Answer: D. 50 W. EIRP equals transmitter power times linear gain: 5×10 = 50 watts.
VSWR=2.5 gives what reflection-coefficient magnitude?
A 0.143
B 0.600
C 0.750
D 0.429
Answer: D. 0.429. |Γ| = (VSWR−1)/(VSWR+1) = 1.5/3.5 ≈ 0.429.
With radiation efficiency 0.8 and |Γ|=0.5, total efficiency is?
A 0.60
B 0.40
C 0.20
D 0.80
Answer: A. 0.60. Mismatch efficiency is 1−|Γ|² = 0.75; total efficiency is 0.8×0.75 = 0.60.
Aperture efficiency 0.6 with D/λ=10 yields parabolic-dish gain near?
A 59.2
B 98.7
C 592
D 986
Answer: C. 592. G≈η(πD/λ)² = 0.6(10π)² ≈ 592, or about 27.7 dBi.
For four equal in-phase elements in a broadside array spaced λ/2, first nulls lie at what angles from array axis?
A 60° and 120°
B 45° and 135°
C 30° and 150°
D 90° only
Answer: A. 60° and 120°. For a broadside four-element array, the array-factor nulls occur when cosθ=±1/2.
Using Ψ=kd cosθ+β, d=λ/2 and β=−π/2 steer the maximum to?
A 30° from axis
B 90° from axis
C 60° from axis
D 120° from axis
Answer: C. 60° from axis. Here kd=π; Ψ=0 gives πcosθ−π/2=0, so θ=60°.
Spacing of one wavelength in a broadside array creates array-factor maxima at?
A 45° off-axis
B Only broadside
C No maxima
D Endfire
Answer: D. Endfire. At d=λ, the broadside array factor repeats at endfire, creating grating lobes if the element pattern permits.
When λ=0.3 m, d₁=200 m, and d₂=800 m, first Fresnel radius is about?
A 3.46 m
B 6.93 m
C 9.80 m
D 13.9 m
Answer: B. 6.93 m. r₁=√(λd₁d₂/(d₁+d₂)) = √48 ≈ 6.93 metres.
Field ellipse with 3 dB axial ratio has major/minor ratio near?
A 1.00
B 2.00
C 3.00
D 1.41
Answer: D. 1.41. The linear ratio is 10^(3/20), approximately 1.41.
For an ideal lossless half-wave dipole with D=1.64, gain in dBi is near?
A 1.64 dBi
B 0 dBi
C 4.26 dBi
D 2.15 dBi
Answer: D. 2.15 dBi. 10log₁₀(1.64) is approximately 2.15 dBi for an ideal lossless dipole.
Ideal quarter-wave monopole above a ground plane has directivity near?
A 0 dBi
B 2.15 dBi
C 5.15 dBi
D 8.00 dBi
Answer: C. 5.15 dBi. Its hemispherical pattern gives about 3 dB more directivity than a half-wave dipole: roughly 5.15 dBi.
Front-to-back power ratio of 20 dB means forward power is?
A 20 times rear power
B 10 times rear power
C 100 times rear power
D 400 times rear power
Answer: C. 100 times rear power. A power ratio in decibels is 10log₁₀(Pf/Pr); 20 dB corresponds to a ratio of 100.
Receive power for Ae=0.05 m² in S=2 mW/m² is?
A 10 μW
B 100 μW
C 25 μW
D 1 mW
Answer: B. 100 μW. Received power is S×Ae: 0.002×0.05 = 0.0001 watt.
Free-space loss rises how much when frequency doubles at fixed range?
A +3 dB
B +6 dB
C +1 dB
D +12 dB
Answer: B. +6 dB. FSPL is proportional to frequency squared, so doubling frequency adds 20log₁₀2 ≈ 6 dB.
Linear gain for a 20 dBi antenna equals?
A 10
B 20
C 100
D 200
Answer: C. 100. Linear gain is 10^(20/10) = 100.
With half-wavelength spacing and zero phase progression, two equal elements have an array-factor null along?
A Broadside
B Array axis
C Every direction
D No direction
Answer: B. Array axis. Along the axis, the path phase difference is π for half-wavelength spacing, so equal fields cancel.
Given Z0=25 Ω and ZL=50 Ω, |Γ| is?
A 1/2
B 1/5
C 2/3
D 1/3
Answer: D. 1/3. |Γ|=|ZL−Z0|/(ZL+Z0)=25/75=1/3 for real impedances.
Two equal reflected paths arriving 180° apart cause what?
A Destructive interference
B Constructive interference
C Polarization rotation only
D Frequency doubling
Answer: A. Destructive interference. Equal-amplitude components with opposite phase cancel, producing a deep multipath fade.
If |Γ|=0.2, what incident-power fraction is reflected?
A 4%
B 20%
C 2%
D 40%
Answer: A. 4%. The reflected-power fraction is |Γ|², or 0.04 = 4 percent.
Opposite-handed circular polarizations have what ideal polarization loss factor?
A One-quarter
B Zero
C One-half
D One
Answer: B. Zero. Ideal right- and left-hand circular polarizations are orthogonal, so coupling is zero.