Antenna projects
A horizontally polarised omni, (slotted waveguide array) at 9.4 GHz in 0.4mm brass sheet
Designed using MATHCAD, measured gain = 5 dBi, S11 = 15dB, B = 300 MHz.
Each slot is the negative of a dipole (Babinets principle) with the E and H fields reversed. It is straight forward to
trim the aperture distribution to obtain sidelobe reduction by adjusting the slot offset.
The antenna can be made for a few pounds in production quantities by photo-chemical machining
(carried out by TECAN in Dorset):
Unfolded x-band antennas on a sheet
Measuring the input match of the pin probe and guide
Prototype spiral, backing cavity and Marchand balun, 0.5 to 4 GHz.
Very inefficient, but wideband and gives circular polarisation - good for radar warning receivers
where gain is not important. The cavity loading (exponentially tapered 377ohm/square Aquadag paint)
is ineffective here due to skin depth. Better to use a dipped honeycomb structure
Helix at 900 MHz.
These work well to 3 GHz but higher frequencies require
very thin supports although the accuracy of the turns has only a small effect on return loss and pattern.
Air is by far the best dielectric.
This example was matched with a quarter-wave transformer and designed from
the "Antenna Engineering Handbook", Jasik, 1961.
Dual wideband "U-slot patch" antenna
These patches give a 25% return loss bandwidth with a modest ground plane spacing. It was found that 0.8mm FR4 backing required significant rescaling over a pure copper foil implementation, even at 750 MHz.
Even greater bandwidths can be obtained using a complementary ground plane design. Wideband, half-space radiation - and no balun required.
A range of RFID loop antennas for high power investigations
Contact details:
JWD Ltd
Telephone/Fax: +44 (0)1403 261251, Mob: 07973 173808
email:
julian @ jwdltd.demon.co.uk
