Wideband
Systems
Work on wideband systems has included studies of
current technology as well as theoretical publications on the
antenna problems and manufacture of a wide variety of prototype
antennas. These include
- dual and quadridged horns for various bands. Typically a
Return Loss of -8 dB can be achieved over a 4:1 band
- ridged corrugated horns of high performance over more
than an octave
- reflector systems covering 1 to 18 GHz
- phase monopulse reflector covering 2 to 18 GHz
- reflector systems covering 8 to 18 GHz for high power
- printed antennas for octave-plus coverage
Relevant projects include
- Printed notch antennas with bandwidths in excess of an
octave. Some of these were omnidirectional and some were
directional with gains in excess of 6 dBi. Figure 1 shows a typical antenna and
Figure 2 shows a plot of Return
Loss. Versions in FR-4 and high grade Rf substarte have
been manufactured. Versions have been successfully
fabricated from sheet metal for operation at much lower
frequencies, including versions for operation on
aircraft.
- Offset reflector operational between 8 and 18 GHz. The
feed horn was an exponential horn of circular
cross-section and waveguide stepped transitions were
designed and built to access standard rectangular
waveguide (Figure 3). Gain and
radiation patterns were predicted using mode-matching and
PO software. The measured results were in excellent
agreement with prediction (Figure 4 and
Figure 5). These antennas were
built by Thomas
Keating Limited.
- Quadridge horns of novel design with greater than 3:1
bandwidths. These were designed for use as a monopulse
feed to a reflector and therefore had to have very small
apertures at the lowest frequency. It proved possible to
design a horn with an aperture as small as 0.25
wavelength. The match is then dominated by the aperture
mismatch. By careful modelling of the ridges which
protruded outside the aperture, a match of better than
2.5:1 across a band of 4:1 was achieved. Good agreement
between predicted and measured performance was achieved (Figure 6). These antennas (Figure 7) were built by Thomas
Keating Limited.
- A side entry coupler (Figure 8)
to cover 8 to 18 GHz with good insertion loss and Return
Loss. This is used with a Free Electron Laser
- A ringloaded corrugated horn with a coaxial output fed
through a dual ridged waveguide section (Figure 9). This covered 8 to 18 GHz.
Figure 1 Omnidirectional notch antenna
with octave bandwidth
Figure 2 VSWR of two versions of an
omnidirectional notch running from F to 3F.
Figure 3 Wideband horns and transitions
Figure 4 Predicted and measured gain
(dBi) for wideband reflector
Figure 5 Measured and predicted
radiation patterns in Circular Polarisation for wideband
reflector
Figure 6 Measured and predicted gain
for small Quadridged horn
Figure 7 Cutaway view of Quadridged
horn using SOLIDWORKS
Figure 8 Side Entry Coupler for 8 to 18
GHz showing entry of FEL arm
Figure 9 Ringloaded Corrugated Horn for
8 to 18 GHz
 Above:- Section from SolidWorks
Right:- Photograph of Completed Horn
|
 |
|
