Moxon antenna

Moxon antenna. The Moxon antenna is a compact, two-element directional antenna design known for its excellent front-to-back ratio and relatively simple construction. It was developed by the British radio amateur and antenna designer Leslie Moxon, who described it in his influential book HF Antennas for All Locations. The design is a derivative of the classic Yagi–Uda antenna, but uses a rectangular, folded shape to achieve its performance characteristics in a smaller physical footprint, making it particularly popular among amateur radio operators on bands like the 20-meter band.

Design and geometry

The fundamental geometry consists of a driven element and a single parasitic element, typically a reflector, arranged to form a rectangle or a shallow "V" shape. The two long sides are the main radiating sections, connected by shorter ends that fold back towards each other, a concept somewhat analogous to a quad antenna but with only two sides. Critical performance parameters like impedance matching and optimal directivity are highly dependent on precise dimensions, including the lengths of the elements and the spacing between them, which are often calculated for specific target frequencies like the 14 MHz amateur band. Designers frequently use software modeling tools, such as those based on the method of moments, to optimize these proportions before construction.

Radiation pattern and performance

Its most celebrated performance characteristic is an exceptionally high front-to-back ratio, often exceeding 20 dB, which greatly reduces reception and transmission of unwanted signals from the rear. This results in a sharp, single-lobed radiation pattern directed broadside to the plane of the rectangle, providing useful gain comparable to a two-element Yagi–Uda antenna but in a more compact form. The design typically exhibits a moderate SWR bandwidth and good efficiency, with the folded configuration contributing to a manageable feed point impedance that often matches well to common coaxial cable like RG-58 without a complex balun.

Construction and materials

Construction is notably straightforward, often utilizing common materials such as aluminum tubing or copper wire supported by a non-conductive frame made of PVC pipe, fiberglass, or wood. The joints at the corners can be fashioned using simple insulator blocks or plastic brackets, with the driven element fed directly at the center of one side. Many builders document their projects for platforms like QRZ.com, showcasing adaptations for portable operation or permanent installation, with some designs even integrated into antenna rotator systems for Amateur radio direction finding or contesting.

Applications and usage

Its primary application is within the amateur radio service, where its compact size and directional performance are highly valued for DXing on the high frequency bands from limited spaces, such as urban lots or during Field Day events. The antenna is also employed in other radio services requiring directional gain without a large aperture, including some low-frequency experimental communications and certain types of radio direction finding equipment. Its design principles have influenced other compact antenna projects within the American Radio Relay League community and are frequently discussed in publications like QST.

History and development

The antenna is named for its inventor, Leslie Moxon, who first published the design in the 1950s and later featured it prominently in his 1982 book published by the Radio Society of Great Britain. Moxon's work built upon foundational antenna theory developed by figures like Shintaro Uda and Hidetsugu Yagi, applying the concept of coupled parasitic elements in a novel, space-saving configuration. While not as ubiquitous as the traditional Yagi–Uda antenna, its design has been preserved and promoted through the ongoing work of the Amateur Radio Research and Development Corporation and remains a staple topic in antenna modeling software and amateur radio literature worldwide.

Category:Radio frequency antenna types Category:Amateur radio