Finding enough space for HF antennas is becoming increasingly difficult. Small backyards, limited roof access, and portable operation often force radio amateurs to compromise between antenna size and performance.
This compactopen sleeve dipole antenna solves that problem rather elegantly.
The open sleeve dipole antenna combines operation on both the 40 and 20 meter amateur bands while remaining considerably shorter than a conventional full-size dipole. Despite the reduced dimensions, performance remains surprisingly good, making it an attractive solution for portable stations, field operation, temporary installations, and restricted urban environments.
A Practical Space-Saving Design
The antenna is built from standard 450-ohm ladder line or ribbon cable. Its total length is approximately 17.17 meters, noticeably shorter than a traditional half-wave dipole for 40 meters.
The reduction in length comes from a clever arrangement at the antenna ends. Instead of extending the dipole elements fully outward, the outer sections are folded back toward the center of the antenna.
This approach shortens the overall span by nearly five meters while only slightly affecting electrical behavior. On crowded rooftops or small properties, those missing five meters can make the difference between installing an antenna or not installing one at all.
The Open Sleeve Principle
One of the more interesting aspects of this antenna is the use of the “Open Sleeve” or “Skeleton Sleeve” technique.
Rather than feeding two completely separate dipoles, the antenna uses electromagnetic coupling between nearby conductors. The primary radiator handles the 40 meter band, while a second nearby conductor resonates on 20 meters without a direct electrical connection to the feed point.
In this design, the lower conductor of the ladder line forms the main 40 meter radiator together with the folded end sections. The remaining upper conductor acts as the parasitic radiator for the 20 meter band.
The result is a remarkably simple dual-band antenna with no traps, loading coils, or switching components.
Feed System and Choke
The Open sleeve dipole antenna uses standard RG-58C/U coaxial cable as the feeder.
Because coaxial cable is unbalanced while the antenna itself is symmetrical, a common-mode choke should be installed as close as possible to the feed point. This suppresses unwanted sheath currents that would otherwise distort the radiation pattern and introduce RF into the station equipment.
The illustrated choke uses ferrite sleeves placed directly over the coaxial cable. Small ferrite toroids recovered from discarded monitor cables or data cables often work surprisingly well for this purpose.
Even a simple current balun made from several ferrite cores provides sufficient suppression on both the 40 and 20 meter bands.
Open Sleeve Dipole Antenna – Dimensions and Construction
The antenna is mechanically simple and can be assembled in a single afternoon.
The main radiator length is approximately 17.17 meters overall, while the active open sleeve section measures around 9.4 meters. The spacing between the folded sections is about 10 centimeters.
Using copper-clad steel ladder line improves mechanical durability, especially for portable operation where repeated deployment places stress on the conductors. Commercial products such as MFJ-18H250 ladder line are suitable, although almost any quality 450-ohm window line can be adapted successfully.
Performance on the Air
Computer simulations performed using EZNEC show surprisingly respectable results for such a compact structure. At 7.15 MHz on the 40 meter band, the antenna produces a calculated gain of approximately 6.6 dBi. On 14.15 MHz for the 20 meter band, the gain rises to roughly 8.3 dBi in the direction of maximum radiation.
Part of this improvement comes from a slightly narrower radiation pattern compared to a conventional dipole.
The standing wave ratio remains below 2:1 across both amateur bands:
- 7.0 to 7.3 MHz
- 14.0 to 14.35 MHz
That allows direct operation with many modern transceivers without requiring an external antenna tuner.
Portable and Temporary Installations
This antenna is especially attractive for portable operation. Field Day stations, temporary contest setups, emergency communication deployments, and vacation operation all benefit from its reduced physical size and lightweight construction.
The ladder-line structure also rolls up easily for transport.
Still, the design does have one weakness. Because of the large surface area created by the window line, snow and ice accumulation can become problematic during winter operation. Strong wind loading also increases compared to ordinary wire dipoles.
For that reason, the antenna is generally better suited for temporary or seasonal use rather than permanent year-round installation. The open sleeve dipole is a clever example of practical antenna engineering. It manages to cover two popular HF bands with a compact structure, simple materials, and no complicated matching networks.
For radio amateurs dealing with limited space, portable setups, or temporary installations, this antenna offers an excellent balance between simplicity, portability, and usable performance. Sometimes the best antenna solution is not the biggest one, but the smartest one.
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