Dipole Antenna Calculator

Calculate dipole antenna dimensions, wavelength, and electrical properties for optimal performance.

Design and optimize dipole antennas by calculating the correct length, wavelength, impedance, and radiation resistance for your desired frequency.

Examples

Click on any example to load it into the calculator.

2-Meter VHF Dipole

2-Meter VHF Dipole

Standard half-wave dipole for 2-meter amateur radio band (144-148 MHz).

Frequency: 146.52 MHz

Velocity Factor: 0.95

Type: 半波

70cm UHF Dipole

70cm UHF Dipole

Half-wave dipole for 70cm amateur radio band (420-450 MHz).

Frequency: 446.0 MHz

Velocity Factor: 0.95

Type: 半波

40-Meter HF Dipole

40-Meter HF Dipole

Half-wave dipole for 40-meter amateur radio band (7.0-7.3 MHz).

Frequency: 7.074 MHz

Velocity Factor: 0.95

Type: 半波

Insulated Wire Dipole

Insulated Wire Dipole

Half-wave dipole using insulated wire with reduced velocity factor.

Frequency: 146.52 MHz

Velocity Factor: 0.85

Type: 半波

Other Titles
Understanding the Dipole Antenna Calculator: A Comprehensive Guide
Master the fundamentals of dipole antenna design and learn how to calculate optimal dimensions for any frequency. This guide covers everything from basic theory to practical applications in amateur radio and wireless communications.

What is a Dipole Antenna?

  • Basic Principles
  • Types of Dipoles
  • Why Dipoles Matter
A dipole antenna is one of the most fundamental and widely used antenna designs in radio communications. It consists of two conductive elements, typically wires or rods, arranged in a straight line and fed at the center. The dipole is the building block of many more complex antenna systems and is essential for understanding antenna theory and practice.
The Physics Behind Dipole Operation
When an alternating current is applied to the center of a dipole, it creates an oscillating electric field between the two elements. This generates electromagnetic waves that radiate into space. The dipole's length determines its resonant frequency - when the antenna is exactly half a wavelength long, it resonates efficiently and radiates maximum power. This is why the half-wave dipole is the most common configuration.
Types of Dipole Antennas
Half-wave dipole: The most common type, with each element being λ/4 long (total length λ/2). It provides good impedance match (≈73Ω) and radiation pattern. Full-wave dipole: Each element is λ/2 long (total length λ). Higher gain but more complex impedance. Quarter-wave monopole: Single λ/4 element over a ground plane, equivalent to half-wave dipole. Folded dipole: Two parallel dipoles connected at ends, providing higher impedance (≈300Ω).
Why Dipoles Are Essential
Dipoles serve as reference antennas for measuring gain (dBi), are simple to construct and understand, provide predictable radiation patterns, and are the foundation for more complex antenna arrays. They're used in amateur radio, broadcast television, wireless communications, and many other applications.

Common Dipole Applications:

  • Amateur Radio: 2m, 70cm, HF bands for local and long-distance communication
  • Broadcast TV: Receiving antennas for VHF and UHF television signals
  • Wireless Networks: WiFi antennas and point-to-point links
  • Emergency Communications: Portable and temporary antenna systems

Step-by-Step Guide to Using the Calculator

  • Input Parameters
  • Understanding Results
  • Practical Applications
Using the dipole calculator is straightforward, but understanding the results and their implications is crucial for successful antenna design and deployment.
1. Determine Your Operating Frequency
Start with your desired operating frequency in MHz. For amateur radio, this might be 146.52 MHz (2m band), 446.0 MHz (70cm band), or 7.074 MHz (40m HF band). For other applications, use your specific frequency requirements. The calculator will automatically determine the wavelength and optimal antenna length.
2. Select Appropriate Velocity Factor
The velocity factor accounts for the fact that electromagnetic waves travel slower in conductors than in free space. For bare copper wire, use 0.95-0.98. For insulated wire, use 0.85-0.95 depending on insulation thickness. For coaxial cable, use 0.66-0.85 based on the dielectric material. This factor affects the actual physical length needed.
3. Choose Dipole Type
Select the appropriate dipole type for your application. Half-wave dipole is most common and provides good impedance match to 50Ω or 75Ω transmission lines. Full-wave dipole offers higher gain but requires impedance matching. Quarter-wave monopole is useful when you have a good ground plane available.
4. Interpret and Apply Results
The calculator provides wavelength, dipole length, antenna impedance, radiation resistance, and gain. Use these values to construct your antenna, match it to your transmission line, and understand its performance characteristics. Remember that real-world performance may vary due to environmental factors.

Amateur Radio Band Frequencies:

  • 160m: 1.8-2.0 MHz (long-distance HF communication)
  • 40m: 7.0-7.3 MHz (day/night HF communication)
  • 20m: 14.0-14.35 MHz (worldwide HF communication)
  • 2m: 144-148 MHz (local VHF communication)
  • 70cm: 420-450 MHz (local UHF communication)

Real-World Applications and Design Considerations

  • Amateur Radio
  • Professional Applications
  • Environmental Factors
Dipole antennas find applications across a wide range of communications systems, from simple amateur radio setups to complex professional installations.
Amateur Radio Applications
Amateur radio operators use dipoles extensively for both local and long-distance communication. On HF bands (3-30 MHz), dipoles can communicate worldwide using ionospheric propagation. On VHF/UHF bands (30 MHz-3 GHz), dipoles provide reliable local communication. The simplicity of construction makes them ideal for portable operations and emergency communications.
Professional and Commercial Use
Dipoles are used in broadcast television receiving antennas, wireless network infrastructure, point-to-point microwave links, and many other professional applications. Their predictable performance and ease of design make them cost-effective solutions for many communication needs.
Environmental and Installation Considerations
Dipole performance is affected by height above ground (higher is better), nearby conductive objects, and ground conductivity. For best results, mount the dipole at least λ/4 above ground and away from large metal objects. The antenna should be oriented horizontally for maximum radiation in the broadside direction.

Common Misconceptions and Design Myths

  • Length Myths
  • Impedance Confusion
  • Performance Expectations
Several misconceptions persist about dipole antennas that can lead to poor performance or unnecessary complexity in design.
Myth: Exact Length is Critical
While proper length is important, dipoles are relatively forgiving. A 5% error in length typically results in only a small change in impedance and minimal performance degradation. The antenna can be trimmed for optimal SWR after initial construction. This tolerance makes dipoles excellent for home construction.
Myth: 50Ω Impedance is Always Best
A half-wave dipole in free space has an impedance of approximately 73Ω, not 50Ω. While 50Ω is common for coaxial cable, the slight mismatch is usually acceptable. For better matching, you can use a balun or adjust the antenna height. The key is keeping the SWR below 2:1 for most applications.
Myth: Higher Gain Always Means Better Performance
While gain is important, it's not the only factor. A dipole's simple, predictable radiation pattern is often more valuable than higher gain from a more complex antenna. For many applications, the dipole's broad coverage and simplicity outweigh the benefits of higher gain antennas.

Expert Tips:

  • Always use a balun when feeding a dipole with coaxial cable to prevent common-mode currents
  • Consider using a center insulator to maintain proper spacing between elements
  • Test your antenna with an SWR meter and adjust length as needed for best performance

Mathematical Derivation and Advanced Concepts

  • Wavelength Calculation
  • Impedance Theory
  • Radiation Patterns
Understanding the mathematics behind dipole operation helps in optimizing design and troubleshooting performance issues.
Wavelength and Frequency Relationship
The fundamental relationship is λ = c/f, where λ is wavelength, c is speed of light (3×10⁸ m/s), and f is frequency. For practical calculations, we use λ = 300/f (MHz) in meters. The half-wave dipole length is then L = λ/2 = 150/f (MHz) meters. The velocity factor adjusts this to account for wave propagation speed in the conductor.
Antenna Impedance and Matching
A half-wave dipole in free space has a radiation resistance of approximately 73Ω and a reactance near zero at resonance. The actual impedance varies with height above ground and nearby objects. Impedance matching is crucial for maximum power transfer and can be achieved through baluns, matching networks, or antenna adjustments.
Radiation Pattern and Gain
A half-wave dipole has a figure-8 radiation pattern in the plane perpendicular to the antenna, with maximum radiation broadside to the antenna and nulls along the antenna axis. The gain is approximately 2.15 dBi (decibels relative to isotropic radiator). This pattern is ideal for many applications due to its broad coverage.

Key Formulas:

  • Wavelength: λ = 300/f (MHz) meters
  • Half-wave dipole length: L = 150/f (MHz) × velocity factor
  • Radiation resistance: Rr ≈ 73Ω (free space)
  • Antenna gain: G ≈ 2.15 dBi (half-wave dipole)