Which of the following is NOT a basic resonant form of antennas?

Which of the following is NOT a basic resonant form of antennas?

• A. Center Fed
• B. End fed
• C. Loop
• D. Parabolic Dish

Answer: (D)

Antenna shapes that are inherently resonant support standing waves at the design frequency, allowing efficient radiation with a simple feed. A center-fed dipole is a classic resonant radiator because its total length is about half a wavelength, enabling a standing wave to form with equal currents at the two halves. An end-fed version relies on the same idea, with the length and a matching network tuned so the structure resonates near the target frequency. A loop antenna becomes resonant when its circumference is around a wavelength (or a multiple thereof), producing a standing wave around the loop and efficient radiation. A parabolic dish, by contrast, is a reflector. Its surface doesn’t itself establish a simple resonant standing wave at a single frequency; instead, it collects or focuses energy from a separate feed located at the focus to form a directed beam. Because it’s a reflector assembly rather than a basic radiating element, it’s not considered a basic resonant form of antenna.

Antenna shapes that are inherently resonant support standing waves at the design frequency, allowing efficient radiation with a simple feed. A center-fed dipole is a classic resonant radiator because its total length is about half a wavelength, enabling a standing wave to form with equal currents at the two halves. An end-fed version relies on the same idea, with the length and a matching network tuned so the structure resonates near the target frequency. A loop antenna becomes resonant when its circumference is around a wavelength (or a multiple thereof), producing a standing wave around the loop and efficient radiation.

A parabolic dish, by contrast, is a reflector. Its surface doesn’t itself establish a simple resonant standing wave at a single frequency; instead, it collects or focuses energy from a separate feed located at the focus to form a directed beam. Because it’s a reflector assembly rather than a basic radiating element, it’s not considered a basic resonant form of antenna.