Dual-band blade antenna

Lore & Background

The blade antenna designation was first adopted by ARINC in 1962 for the blade-like radome shape protecting the antenna in ARINC Characteristic 521C for Airborne Distance Measuring Equipment (DME). With increasing aircraft speed, drag increases, so antennas were placed in a blade-shaped radome to minimize aerodynamic fairing, reduce low air drag, and reduce corrosion compared to wire- or tube-type aircraft antennas. Dual-band blade antennas are available for both vertically polarized systems (VHF- and UHF-COM, DME, TACAN, IFF, SSR) and horizontally polarized systems (ILS-LLZ, ILS-GP, VOR, GBAS).

Most blade antennas provide more or less omnidirectional and directional antenna diagrams due to other fixed or movable protruding objects on the fuselage, but they can also provide directional coverage when needed, such as for ILS-LLZ and -GP use or four separate sectors for ACAS (TCAS). Omnidirectional vertically polarized dual-band blade antennas are available, for example, as VHF- and UHF-communication antenna type S65-8262-305, or as UHF-Communication and L-Band antennas like CNI8 Type UHF- und L-Band antennas, consisting of 1/4 λ monopoles. Horizontally polarized dual-band blade antennas are designed for reception of horizontally polarized VHF navigation systems (ILS-LLZ, VOR, GBAS) and provide additional support for UHF-Band reception of ILS-GP signals, using loop type antennas.

Multiband blade antennas for Emergency Location Transmitters (ELT) can support transmission on three frequencies: 406 MHz, 121.5 MHz, and 243.0 MHz, as in type S65-1231. The blade antenna is an attempt to create a broader-band monopole compared to a thin wire monopole, with most being trapezoidal in shape, sometimes with notches for better broadband performance.

Reader's Guide

Dual-band blade antennas are significant in aviation because they consolidate multiple frequency band functions into a single aerodynamic housing, reducing drag and corrosion while saving limited fuselage space. They serve both aeronautical mobile (route) service (AM(R)S) for VHF- and UHF-voice-communication and data-link, and aeronautical radio navigation systems (ARNS) including DME, TACAN, IFF, SSR, ILS-LLZ, ILS-GP, VOR, and GBAS. Their legacy lies in enabling efficient, low-drag antenna installations on modern aircraft, supporting both vertical and horizontal polarization as needed. The availability of omnidirectional and directional variants allows them to meet diverse operational requirements, from communication to navigation and collision avoidance. The design continues to evolve, with multiband versions supporting emergency locator transmitters on three frequencies.

Did You Know?

• The designation 'blade antenna' was first adopted by ARINC in 1962 for ARINC Characteristic 521C for DME.
• Omnidirectional vertically polarized dual-band blade antennas often consist of 1/4 λ monopoles.
• Multiband blade antennas for ELT can transmit on 406 MHz, 121.5 MHz, and 243.0 MHz.