Antennas

Antennas have been developed from a few hundred kHz to 10 GHz in particular:

• 2.1 GHz QFH antenna for airbourne repeater
• 5G Massive MIMO research antenna
• Bluetooth and Airplay antennas
• Miniature GSM/DCS chip antennas and matching networks
• X band slotted waveguide array
• Tri-band printed patch array
• NFC bracelet antennas at 13.56 MHz

• Printed slot antenna for a field disturbance detector
• Active loop antenna array (gradiometer) and preamp for a magnetic field search device
• Planar spiral antenna, backing cavity and balun used in a radar warning receiver
• Contactless card , long range/high power reader antenna
• Dual band UHF/2.5GHz Helical antenna

This 128 element "massive MIMO" basestation antenna was developed for a University. It is to be used for research into 5th generation "5G" mobile phone technology. 

QFH antenna at 2.1 GHz

This device was developed for an airbourne application where the antenna is placed underneath a helicopter or aircraft to receive signals from a mobile TV camera. It produces circular polarisation and has an extremely wide beamwidth with almost hemispherical coverage. A typical application is for transmitting television pictures from a motorbike to an airbourne repeater, such as in motor racing or marathons. The prototype below uses an "infinity" balun, where one of the radiating elements is the semi rigid feed. The "self phased" design relies on two elements tuned above and below resonance to produce a 90 degree phase shift with resulting circular polarisation:

A typical radiation plot is shown below. The measurements were recorded on an FSP spectrum analyser with zero Hz span, synchronised to a rotating table. The log mag data was imported into Excel, then displayed as a polar plot:

An attempt was made to productionise the antenna using a 3D printed former. However, the dielectric constant of the nylon material detuned the elements from 2.1 GHz to 1.7 GHz:

A dipole and sleeve balun at 2.5 GHz

This antenna was produced to test a rectenna array made for the BBC. By using a small RF power source and by holding it near the rectenna elements, the power produced by each one could be checked.

Dual band helical antenna

Radar test set with patch antenna

This miniature test set was developed to test a radar transponder that was developed by JWD Ltd. The patch was fabricated on Rogers RT5880.

Slotted waveguide array

This antenna was designed from first principles and made in reduced height waveguide. The guide was produced by photo-etching brass sheet, which was then folded over a mandrel and soldered.

Outdoor antenna test facility

A small outdoor antenna test facility is available with a remote controlled turntable. Although the system is not calibrated, it gives a rough indication of how well an antenna is performing. Whilst a swept S11 measurement might indicate a good input match, that alone does not guarantee the antenna is forming the expected beam pattern. The photograph below shows a very early prototype wireless speaker, with internal Airplay antenna being tested for a customer: