Building a DIY antenna is one of the most rewarding parts of being a radio amateur. If you are looking for a compact, high-gain alternative to a standard dipole or vertical for the VHF/UHF bands, the Full Wave Loop Antenna is an excellent project.
Why Choose a Full Wave Loop Antenna?
The Full Wave Loop is a favorite among homebrewers for several reasons:
- Lower Noise Floor: Because it is a closed-loop system, it often picks up less man-made “static” than a vertical antenna.
- Slight Gain: It offers approximately 2.1 dBd of gain over a standard dipole.
- Broadband Nature: It is relatively forgiving and provides a decent SWR bandwidth.
The rectangular full wave loop shown above is specifically optimized for 145 MHz (VHF) but can be easily scaled for UHF ham bands and the FM broadcast band by adjusting its physical dimensions.This antenna is popular because of its low noise, balanced radiation pattern, and good impedance characteristics, making it ideal for both transmitting and receiving applications.
Understanding Full Wave Loop Antenna Design
A full wave loop antenna has a total perimeter equal to one wavelength (λ) at the operating frequency. In the illustrated design:
- The loop is rectangular rather than circular, making it easier to construct.
- The feed point is located at the bottom center.
- A small gap (about 1.5 cm) is maintained at the feed point to connect a coaxial feed line.
- The vertical and horizontal sides are proportioned to optimize impedance and radiation efficiency.
Key Labeled Sections (as shown in the diagram)
- A (Top horizontal): ~0.175 λ
- B & E (Vertical sides): ~0.367 λ
- C & D (Bottom horizontal sections): Symmetrical
- F (Feed gap): ~1.5 cm
This configuration provides a good match for common coaxial cable when used with a simple balun or choke.
Full Wave Loop Antenna Dimensions Table
The table below provides approximate dimensions for full wave rectangular loop antennas across VHF, UHF ham bands, and the FM radio band. Dimensions are calculated using the free-space wavelength formula and may require slight trimming for best SWR.
Formula:
Wavelength (λ) = 300 / Frequency (MHz)
The dimensions and configuration shown in this article are based on the original concept and layout by HS3FYV, adapted here for educational purposes and for scaling across VHF, UHF amateur radio bands, and the FM broadcast band.
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