Final answer:
The radiation resistance of a thin line center-fed half-wavelength antenna with sinusoidal current distribution is 73 ohms. Option 1 is correct.
Step-by-step explanation:
The radiation resistance of a thin line center-fed λ/2 (half-wavelength) antenna with a sinusoidal current distribution is 73 Ω (ohms). This value represents the resistance that accounts for the power radiated by the antenna when it is driven at its resonant frequency. Radiation resistance does not usually have an imaginary component, as it is a real value representing the radiation efficiency of the antenna. Hence, the correct answer to your query is 73 Ω.
The radiation resistance of a thin line center-fed λ/2 antenna with sinusoid current distribution is 73 Ω.
The resonance of currents on an antenna that is 1/4 their wavelength is analogous to the fundamental resonant mode of an air column closed at one end, since the tube also has a length equal to 1/4 the wavelength of the fundamental oscillation.