The half loop antenna is a practical and space-efficient solution for amateur radio operators who want reliable multiband HF performance without complex matching networks or large towers. The design shown above is a proven configuration that supports 80, 40, 20, and 15 meter bands, making it ideal for both regional and DX operation.
Originally developed and shared by UR0GT, this antenna has gained popularity due to its simplicity, mechanical stability, and consistent on-air results.
Overview of the Half Loop Antenna Design
A half loop antenna is essentially one half of a full wave loop, installed vertically and fed at one end near ground level. Despite using only half the wire of a full loop, it behaves efficiently across multiple harmonic bands.
In this design, the total wire length is approximately 28.1 meters, supported by a vertical mast on one side and a sloping support on the other. The antenna is fed with 75-ohm coaxial cable, which provides a reasonable impedance match across the supported bands without requiring an external tuner in many installations.
Half Loop Antenna –Physical Dimensions and Construction
The antenna consists of a single continuous wire and a short vertical support tube at the feed point.
Key physical characteristics include:
- A sloping wire section approximately 28.1 meters long made from 2 mm wire
- A vertical height of about 12.8 meters on the far support
- A 2.5-meter vertical tube at the feed point
- Grounding at both the support and feed locations for improved stability and noise reduction
The sloped geometry helps provide a mix of low and medium takeoff angles, making the antenna effective for both short-range and long-distance contacts.
Multiband Performance Characteristics
One of the strongest advantages of the half loop antenna is its natural multiband behavior.
On 80 meters, the antenna provides solid NVIS and regional coverage, making it suitable for nighttime ragchews and emergency communications. On 40 meters, it offers a balanced radiation pattern that works well for both regional and intercontinental contacts. On 20 and 15 meters, the antenna becomes more directional, with lower radiation angles that favor DX operation.
Because the antenna is resonant on multiple harmonic bands, efficiency remains high compared to shortened or heavily loaded designs.
Feeding and Matching Considerations
The antenna is typically fed with 75-ohm coax, which provides a good compromise match across all supported bands. While SWR may vary depending on installation height and ground conditions, many operators report acceptable SWR levels without the need for an antenna tuner.
Proper grounding at the feed point and support mast is strongly recommended. This improves RF stability and helps reduce common-mode noise.
Half Loop Antenna –Installation Tips
This antenna can be installed using a single tall support and a secondary anchor point such as a tree or smaller mast. Because it is a single-wire design, mechanical stress is low and wind loading is minimal.
For best results:
- Install the antenna as high as practical
- Maintain clear space around the wire where possible
- Use good quality insulators and weatherproof connections
Even in modest suburban installations, this antenna performs remarkably well.
This antenna design is based on the original half loop concept and dimensions published by UR0GT.
Source: http://antentop.org/016html/016_p58.htm
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