Planar blade antenna

Image of the Planar blade antenna.

Antennas for airborne communications systems must have good omnidirectional coverage and efficiency, and must be well matched to the transceiver. For high performance aircraft, aerodynamic effects should be minimised and installation should be simple, to reduce aircraft modification costs. The antenna must also be designed to cope with environmental phenomena such as lighting strikes, rain and hail erosion, UV degradation, water ingress and static charge build-up. These factors invariably require the antenna to be enclosed in a fin-radome and mounted on the centre line of the fuselage, with a DC discharge or connection path to the ground or reference plane of the feed electronics.

Blade antennas meet these requirements in the VHF, UHF and microwave bands due to their small size, light weight and low drag. There are a large variety of blade topologies and designs, some of which include integrated impedance matching networks to comply with bandwidth specifications.

The blade antenna included in the Antenna Magus database for the Verison 2.4 release is a simple planar meander-monopole blade, with a base-feed and a conducting leading edge for mechanical support and lightning protection. This topology is simple and lends itself to housing in an radome structure.

The blade can either be designed for optimal S11 or optimal size. When designing for a good 50 ohm match the antenna will have a +- 3 dB front to back ratio and will be approx. 50% larger than when designing for optimal size. The optimal size design results in a near perfect omnidirectional pattern with a front to back ratio of less than 1dB. The two images below show typical S11 vs frequency and 3D gain patterns for these two design approaches.

Typical S11 for the two different design approaches available in Magus. Note the different reference impedances used.
Typical total gain patterns at the center frequency of the two design approaches available in Magus. Design for 50 ohm (top) , design for size (bottom).