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How kHz, MHz, GHz, THz Signals Are Generated and Fed to an Antenna

 

Frequency Signal Generation and Antenna Feeding

How kHz, MHz, GHz, THz Signals Are Generated and Fed to an Antenna

There are both devices (hardware) and mathematics involved in generating and feeding frequency signals to an antenna.

1. Devices That Generate Frequency Signals

Core Idea: An antenna does not create frequency—it radiates whatever signal is fed into it.

Main Signal-Generating Devices:

  • Oscillator:
    • Produces a repeating electrical signal (sine wave)
    • Example: Crystal oscillator using Quartz for stable frequency
  • Signal Generator:
    • Adjustable frequency source (kHz to GHz)
    • Used for testing antennas and circuits
  • RF Transmitter:
    • Used in real-world systems (radio, mobile, WiFi)
    • Contains oscillator, amplifier, and modulator
  • Frequency Synthesizer:
    • Generates a wide range of frequencies from a reference signal

2. How the Signal Is Fed Into the Antenna

  1. Oscillator creates AC signal
  2. Signal is amplified
  3. Sent through a transmission line (e.g., coaxial cable)
  4. Reaches antenna terminals
  5. Antenna converts electrical signal into electromagnetic waves

3. The Math Behind Frequency

Wave Equation:

f = v / λ

  • f = frequency (Hz)
  • v = speed of wave (~3 × 10⁸ m/s)
  • λ = wavelength

Antenna Length Formula:

L = λ / 2 (half-wave antenna)

L = c / (2f)

Example:

  • Frequency = 100 MHz
  • Wavelength = 3 meters
  • Antenna length ≈ 1.5 meters

4. Circuit Math (Oscillator Formula)

LC Circuit Frequency:

f = 1 / (2Ï€√LC)

  • L = inductance
  • C = capacitance

Changing L or C changes the frequency.

5. Frequency Ranges and Methods

Range Generation Method
kHz RC / LC oscillators
MHz Crystal oscillators
GHz Microwave oscillators, PLL
THz Lasers, advanced semiconductor devices

6. Summary

  • Antenna does NOT decide frequency
  • Circuit and oscillator decide frequency
  • Antenna must be matched to that frequency

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