Antenna Design Examples
Some examples of antenna designs RadioCAD Limited have executed over the last ten years.
Here we have an IP64 waterproof VHF direction finding antenna for determining bearing to target on 121.5 MHz the international aircraft and maritime distress frequency. It comprises three dipoles arranged at 120°. Each comprises two helical sections (whips). The sprung nature of the elements contained within their plastic IP64 tubes allows them to connect to the central triangular PCB by spring pressure only. This market-leading design has been in continuous production since 2006.
RadioCAD designed the antenna and direction finding circuitry.
This antenna was designed to work on both the EU and US license free bands at 868 and 915 MHz. It has a simple mesh reflector to increase gain and reject signals coming from behind.
Here we have a simple omni-directional helical whip that uses the transmitter module PCB as a planar counterpoise. Helical sections can be used to reduce the overall length of an antenna. I have found one can reduce to λ/8 whilst retaining the performance of a λ/4 straight dipole. The use of straight and helical sections serves to reduce the antenna Q and thereby improve useable bandwidth. This design of both antenna and module executed by RadioCAD Limited was in continuous production from 2003 until very recently.
PCB antennas are frequently used to save component and assembly costs as they can be printed onto the same PCB as your transceiver design. However getting good performance from them can be time consuming and will usually require more than one spin of a PCB to perfect them.
Log-periodic antennas can be frustrating to design as printed structures because of the need to trim both the length of the dipole elements and their position on the transmission line boom in order to get a flat broadband response.
Here is an example of a glass LPDA structure printed on a core sheet of glass with thinner laminated outer sections for physical protection. It’s a great looking item designed as an indoor UHF TV aerial. Glass has a relatively high εr allowing structures to be significantly shrunk in size whilst retaining performance.
Usually at RadioCAD we benchmark antennas in the anechoic chamber. However larger antenna have to be trimmed and measured outside. The antenna under test here is mounted at some height above the turntable in order to minimise the effect of ground reflections.
At RadioCAD’s Cowden test facility we do the full range of CAI benchmarking tests.
In addition to antennas I have also designed a number of PCB baluns as impedance transformers for balanced to unbalanced operation.
The PCB balun on the left is a TEM design whereas the balun on the right is a more conventional coplanar design.
Contact RadioCAD for more information.