Rhombic Antenna Calculator
Calculate approximate dimensions and characteristics of a Rhombic antenna.
3
Inputs
Live
Math
3
Related
Enter parameters and click Calculate to view results
Formula & Theory
λ = 300/f
Leg Length = λ × Multiplier
Overall Length =
2Lcos(θ/2)
Overall Width =
2Lsin(θ/2)
This formula is used to calculate antenna parameters for rhombic antenna calculator.
Overview
The Rhombic Antenna Calculator helps RF engineers, amateur radio operators, broadcast engineers, and HF communication system designers estimate the physical dimensions of a rhombic antenna using its operating frequency, leg length multiplier, and included angle. The calculator determines the free-space wavelength, individual leg length, overall antenna length, overall antenna width, and a recommended installation height. It also provides typical gain, feed-point impedance, and termination resistance values commonly associated with rhombic antennas. This calculator is useful for designing high-frequency (HF) directional antennas used in long-distance communications, international broadcasting, military radio systems, point-to-point links, and amateur radio DX operation.
Input Guide
Enter Frequency, Leg Length (× λ), Included Angle exactly in the units shown by this rhombic antenna. Check the operating band, unit prefix, and decimal position before calculating; these are the inputs used by the formula.
- Frequency — use MHz.
- Leg Length (× λ).
- Included Angle — use °.
Output Guide
The results describe the calculated rhombic antenna values for the inputs you entered. Check each value against the available space, selected components, feed system, and operating conditions before making a final design decision.
How This Calculator Works
The Rhombic Antenna uses λ = 300/f Leg Length = λ × Multiplier Overall Length = 2Lcos(θ/2) Overall Width = 2Lsin(θ/2) . Supply Frequency (MHz), Leg Length (× λ), Included Angle (°) in the displayed units, then use the calculated values as the first engineering target for this specific antenna types design or analysis.
Design Notes
A rhombic antenna is a travelling-wave wire antenna consisting of four long wires arranged in a diamond (rhombus) shape and supported above ground. Unlike resonant antennas, a properly terminated rhombic absorbs energy at the far end instead of reflecting it back toward the feed point, producing a highly directional radiation pattern over a broad frequency range. Rhombic antennas are valued for their wide bandwidth, relatively high gain, simple construction, and stable performance across multiple HF bands. Typical leg lengths range from one to several wavelengths, while included angles commonly fall between 40° and 90°, depending on the desired gain and beamwidth. This calculator provides first-order geometric dimensions using free-space assumptions. Actual antenna performance is influenced by ground conductivity, support height, termination resistor accuracy, wire sag, nearby structures, terrain, and operating frequency.
Build and Tuning Notes
Install the antenna in a large open area with sufficient clearance because rhombic antennas require considerable physical space. Support the wires at a consistent height using non-conductive masts or towers and maintain adequate wire tension to minimise sag. If unidirectional operation is required, terminate the far end with a non-inductive resistor close to the characteristic impedance of the antenna. Use a balanced feed line or an appropriate balun to minimise common-mode currents. After installation, verify impedance, VSWR, and radiation characteristics using an antenna analyser or Vector Network Analyzer (VNA). For professional communication systems, validate the design using antenna modelling software and field-strength measurements before final deployment.
Frequently Asked Questions
What is a rhombic antenna?
A rhombic antenna is a large travelling-wave wire antenna formed by four long wires arranged in a diamond shape. It provides high directional gain, broad bandwidth, and efficient long-distance HF communication.
What does this Rhombic Antenna Calculator calculate?
The calculator estimates wavelength, individual leg length, overall antenna length, overall antenna width, recommended installation height, and typical electrical characteristics based on the selected operating frequency and antenna geometry.
Why are rhombic antennas terminated with a resistor?
A terminating resistor absorbs the travelling wave at the end of the antenna, preventing reflections that would otherwise create standing waves and distort the directional radiation pattern.
Which frequencies are rhombic antennas commonly used for?
Rhombic antennas are primarily used in the HF spectrum, typically between approximately 3 MHz and 30 MHz, where they provide excellent long-distance skywave communication and broadband performance.
What is the typical gain of a rhombic antenna?
A well-designed rhombic antenna typically provides approximately 10 to 15 dBi of forward gain, although the exact value depends on antenna dimensions, operating frequency, termination, installation height, and ground conditions.
Why does a rhombic antenna require so much space?
Each side of the antenna is typically one or more wavelengths long. At HF frequencies, wavelengths are tens of metres long, resulting in antennas that can occupy hundreds of square metres of land.
Can a rhombic antenna operate over multiple frequency bands?
Yes. One of the primary advantages of a rhombic antenna is its wide operating bandwidth. A single antenna can often provide useful performance across multiple HF amateur, broadcast, and communication bands without significant retuning.
Is this calculator sufficient for final antenna construction?
No. The calculator provides theoretical dimensions for initial design. Final construction should consider local terrain, support structures, wire characteristics, termination resistor selection, feed system design, and electromagnetic modelling or field measurements to achieve optimum performance.
Alex Warren
B.Sc. in Electrical & Electronic Engineering (EEE)
Alex specialises in antenna design and wave propagation. His expertise helps ensure these calculators present practical RF concepts, useful design estimates, and clear engineering guidance for students, HAM operators, and wireless professionals.