Loop Antenna Calculator
Created by: Natalie Reed
Last updated:
Compare square, delta, and quad-style full-wave loop dimensions before you choose the loop shape that best fits the site, supports, and feed arrangement.
Loop Antenna Calculator
Amateur RadioCompare square, delta, and quad loop dimensions with feed guidance for practical full-wave amateur-radio loop builds.
What is a Loop Antenna Calculator?
A loop antenna calculator estimates the wire length and physical dimensions for a full-wave loop built for a chosen amateur-radio frequency. That can mean a square horizontal loop, a delta loop, or a quad-style geometry. The key advantage of a loop is that it encloses roughly one wavelength of wire in a shape that can sometimes fit a property or portable site better than a single long straight dipole span, especially when several supports are available.
For hams, the appeal is not only the total length. It is how that total length breaks into side dimensions and how the feed arrangement changes the practical station plan. A square loop may fit a backyard with four decent supports. A delta loop may fit two trees and a mast. A quad-style layout may align better with a directional or support-driven build concept. The same frequency can therefore produce several physically different but electrically related antennas.
This calculator keeps those tradeoffs visible by showing total circumference, side length, and feed guidance together. That matters because full-wave loops are large enough that a design can be theoretically correct yet still unrealistic for the site. Operators often discover that the total wire length is not the hardest part. The challenge is whether the shape will actually fit the supports they have, with safe angles, useful height, and a feed arrangement that does not create extra headaches.
The result is a better planning tool for both fixed and portable stations. Instead of memorizing a single full-wave constant and then working everything out by hand, you can compare common loop styles directly and decide whether the antenna is a reasonable station choice before you start measuring wire, packing support lines, or ordering feedline and matching hardware.
How the Loop Antenna Calculator Works
The calculator uses a full-wave loop constant of about 1005 divided by frequency in MHz for square and delta loops, while the quad-style planning number uses about 984 divided by frequency. Those formulas estimate the total circumference required to place approximately one wavelength of wire around the loop. The selected geometry then converts that total into side lengths or other useful physical dimensions, including delta-loop side height guidance.
After the base dimensions are calculated, the tool applies a simple feed-position adjustment to the impedance estimate so the feedline advice is easier to interpret. The output is not meant to replace installation-specific measurement. It is intended to answer the early design questions that matter most: how much wire is required, how large each side becomes, what feed impedance neighborhood to expect, and whether the chosen loop is a realistic fit for the site or operating plan.
Loop antenna formulas
Square or delta full-wave loop (ft) = 1005 / frequency in MHz
Quad loop total length (ft) = 984 / frequency in MHz
Square side length = total length / 4
Delta side length = total length / 3, with height approximately 0.577 x side length
Example Calculations
Example 1: A 20 meter square loop
At roughly 14.2 MHz, a square loop needs a little over 70 feet of total wire, which means each side is a bit under 18 feet. That is far more manageable than many hams expect, and it explains why 20 meter loops can be practical when a site offers four decent support points even if a larger 40 meter version would be unrealistic.
Example 2: A delta loop with awkward supports
A delta loop can use roughly the same total wire as a square loop while fitting a very different support arrangement. If you have one high center support and two lower anchor points, the delta geometry may be easier to deploy than a neat four-corner square, even though the RF planning still begins with a full-wave circumference.
Example 3: Feedline strategy matters
A loop with feed impedance near the 100 ohm range can be easier to integrate with 75 ohm coax or a simple transformer than with an unexamined direct 50 ohm feed assumption. That does not make it difficult, but it does mean the antenna should be planned as a system rather than only as a wire length exercise.
Common Amateur Radio Uses
- Size a square, delta, or quad-style loop before buying wire or committing to a multi-support backyard build.
- Compare whether a loop shape will fit the available trees, masts, or portable supports better than a simple dipole.
- Estimate feed impedance neighborhood and matching expectations before choosing coax or transformer hardware.
- Check whether a 20, 30, or 40 meter loop is realistic for a POTA site with several available supports.
- Translate one full-wave circumference into side dimensions that are easier to visualize in the field or on a property map.
- Compare different loop styles for the same band without recalculating the full-wave wire requirement by hand each time.
Tips for Better Ham Radio Planning
Treat total wire length as only the first constraint. Side length, support spacing, and feedline routing often decide whether the loop is realistic. A loop that theoretically fits the site may still become awkward if the feed corner is too low, if the supports are not placed well, or if the shape forces poor wire angles that are hard to maintain in wind or portable conditions.
For portable or POTA use, think carefully about setup speed. A full-wave loop can work well when several supports already exist, but it is often slower to deploy than a center-supported dipole or vertical. That does not make it a bad choice. It means the loop is best when the site and operating style justify the extra layout work.
Frequently Asked Questions
What does a loop antenna calculator estimate?
A loop antenna calculator estimates the total wire length, side length, feed-impedance expectation, and basic feedline guidance for full-wave loops such as square, delta, and quad-style designs. Those numbers are useful because loop antennas are physically large enough that one design decision affects both available space and feedline strategy, especially when you move between horizontal loops, delta loops, and quad geometries.
Why do square, delta, and quad loops use similar total circumference numbers?
They are all built around roughly one electrical wavelength of conductor, so the total wire length stays in the same neighborhood for a given frequency. What changes is the physical layout, side length, feed-point behavior, and how the loop fits the available supports. In practice, the shape decision is often driven as much by the site and support geometry as by pure RF preference.
Is loop feed impedance always around 100 ohms?
Not exactly, but that is a useful planning range for many full-wave loop installations. Feed position, loop height, nearby objects, exact shape, conductor diameter, and whether the loop is horizontal or vertically oriented can all move the impedance. That is why the calculator presents a reasonable estimate and matching guidance rather than pretending every loop has one fixed feed-point number in all installations.
How should I choose between a loop and a dipole?
A loop is attractive when you have enough support points and want a full-wave antenna with different pattern and feed options from a simple dipole. A dipole usually wins on simplicity and faster deployment. A loop often wins when you can dedicate the space and want a more enclosed geometry that fits multiple supports or a property boundary better than one long straight wire.
Are loop antennas practical for POTA or field operating?
They can be, but support layout is the real question. A full-wave 20 meter loop can be practical if the site has several useful trees or masts. On 40 meters and below, the required span grows quickly. For many activators, a loop becomes a special-purpose portable option rather than the universal first choice, especially when quick setup matters more than experimentation.
Does the calculator replace final trimming and on-air testing?
No. Like other wire antennas, a loop still benefits from final trimming and real installation testing. The calculator gives the right order of magnitude and a smart first cut, but local height, feed arrangement, and support geometry can move resonance and feed impedance enough that final adjustment is still part of a successful build.
Sources and References
- ARRL Antenna Book, full-wave loop dimensions and feed-impedance guidance.
- ARRL Handbook, practical wire-loop antenna construction and installation notes.
- RSGB loop-antenna references covering square, delta, and quad-style amateur installations.