The dual-band 144/430 MHz Square Loop Antenna is one of the most efficient and compact VHF/UHF antennas that amateur radio operators can build at home. Designed to cover both the 2-meter and 70-centimeter bands, this antenna offers excellent gain, low noise reception, and impressive SWR when constructed correctly. Its simple geometry, easy-to-source materials, and reliable performance make it ideal for beginners and experienced hams alike.
This design uses a full-size copper loop for the 144 MHz band and a pair of short radiating elements to tune the antenna for 430–435 MHz. Unlike commercial dual-band antennas that rely on traps, coils, or complex matching networks, this model achieves dual-band operation through a cleverly calculated combination of resonant loop length and UHF radiator phasing. The result is a clean, wideband, and low-noise antenna suitable for indoor, balcony, attic, or outdoor installations.
Understanding the Dual-Band Loop Concept
At the heart of this square loop antenna is a square loop with each side measuring 510 mm. The perimeter of the loop is close to one full wavelength at 144 MHz, making it a naturally resonant radiator for the 2-meter band. Loop antennas at VHF frequencies are well known for their stable impedance characteristics, quiet receive operation, and minimizing local electrical noise, especially indoors.
For 430 MHz operation, the loop becomes electrically much longer—nearly three wavelengths. At this point, the UHF radiation is dominated by the two short lower elements, each measuring 435 mm and spread at an angle of 60°. These act as phasing elements and provide the correct impedance transformation for 70-centimeter operation. This combination is what makes the antenna function seamlessly across both bands without requiring traps or stubs.
Square Loop Antenna – Construction Details and Dimensions
The square loop antenna can be built using copper wire, copper tubing, or even aluminum rods. The recommended wire thickness for the loop is around 6.7 mm, which helps stabilize impedance and improves broadband response. The loop ends should be spaced exactly 5 mm apart at the feed point to maintain the correct electrical tuning.
The lower radiating elements are equally important and should be cut to 435 mm. The 60-degree separation helps match the UHF impedance to the feed line while also establishing the proper directional pattern. The central support can be made from PVC pipe or any electrically non-conductive material. Ferrite rings are mounted at the feed point to act as a 1:1 choke balun, preventing common-mode currents from flowing back onto the coaxial shield.
Ferrite Marking in Drawing
“Ферритовые кольца 10×20 50ВЧ2 2000НМХ1”
This means:
- Ferrite rings: 10 × 20 mm
- Material 50ВЧ2 (Russian ferrite mix for VHF/UHF)
- About 2000 permeability (good for choking common mode)
- Any mix for VHF/UHF can be used.
They prevent coax from radiating.
Feedline and Matching
A standard 50-ohm coaxial cable is attached directly to the feed point, where the loop ends and UHF elements meet. The ferrite choke, specified in the diagram (ferrite rings 10×20 mm, material 50ВЧ2), ensures the antenna behaves symmetrically and eliminates stray RF radiation on the coax. This improves SWR and prevents pattern distortion, especially when the antenna is used indoors or near walls.
Square loop antenna – Performance and Radiation Characteristics
On the 144 MHz band, the square loop antenna operates as a full-wave resonant antenna, providing a smooth, nearly omnidirectional radiation pattern. This makes it ideal for repeater access, simplex communication, and general VHF operation. The loop design also significantly reduces man-made noise, offering cleaner audio and more stable signals than a typical vertical antenna.
On 430 MHz, the short radiators create a higher-gain, slightly directional pattern with efficient radiation and low SWR across most of the 70-centimeter band. Users typically report gain in the range of 4–5 dBi, making it competitive with many commercial dual-band verticals. Because the antenna is physically compact, it performs exceptionally well indoors, on apartment balconies, and in attic installations.
One of the strongest advantages of this dual-band loop is its simplicity. There are no traps, coils, or complicated matching sections. Every dimension is directly tied to the operating wavelength, ensuring predictable results. The loop design naturally rejects local electrical noise, making it an excellent choice for urban operators.
Suggested Alternates for Ferrite Rings
If 10×20 mm 50ВЧ2 ferrite rings are not available, you can use any high-permeability ferrite for VHF/UHF choke/balun.
Good Substitutes (Common Worldwide)
1. Mix 43 Ferrite Rings (most common)
- Size: FT50-43, FT82-43, FT114-43, FT140-43
- Works well for 144–430 MHz
- Most available on Amazon, RF stores
2. Mix 61 Ferrite Rings (better for UHF)
- More effective at 300–500 MHz
- Ideal for 70cm band
- Sizes: FT82-61, FT114-61
3. Fair-Rite Snap-On Chokes (easy to install)
- Mix 43 or Mix 61
- Clamp-on style
- Use 2–3 pieces on coax
- Good for people who don’t want to remove the connector
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