Question T9A05
From subelement T9 - T9A
Which of the following increases the resonant frequency of a dipole antenna?
Why is this correct?
Shortening a dipole antenna increases its resonant frequency because antenna length and frequency have an inverse relationship. A shorter antenna resonates at a higher frequency, while a longer antenna resonates at a lower frequency. Options A (lengthening) decreases frequency, while options B (inserting coils) and D (capacitive loading) are both loading techniques that electrically lengthen the antenna, making it resonate at lower frequencies despite physical shortening.
Memory tip
Remember the inverse relationship: shorter physical length equals higher frequency. Loading techniques (coils or capacitors) always electrically lengthen antennas to lower their resonant frequency, regardless of any physical shortening. When you see loading mentioned, think 'lower frequency.'
Learn more
In practical antenna work, this principle guides antenna tuning. If your antenna analyzer shows resonance below your desired frequency, you must physically shorten the antenna elements. Conversely, if resonance is too high, you either lengthen the antenna or add loading elements. Loading coils are common on mobile HF antennas where physical space limits antenna length, allowing operation on lower frequency bands.
Think about it
Why do you think antenna loading techniques always result in lower resonant frequencies, even when they might involve physically shortening the antenna structure?