Super-Open-Bouundary Quadridge Hornn Antennas
Vicente Rodriguez
ETS-Lindgren L.P.
13011 Arrow Point Dr. Cedar Park TX 78613 USA
Vince.Rodriguez@ets-lindgren.com
Abstract—The present work shows the cooncept of the open
boundary quadridge horn (OBQH) introducced in 2005 [1] now
scaled to lower frequencies. The concept has been taken to
extremes by also opening the feed cavity of the horn leaving a
fully unbounded antenna. The resulting antenna, although large
in size, offers excellent VSWR and gain. The antenna is designed
nted to the wall of a
to perform both as a standalone unit or moun
chamber nested in the absorber treatment. In addition to the
antenna introduced in [2] a secondary antenn
na operating over a
higher frequency range is also introduced.
I. INTRODUCTION
While attending technical symposiumss and trade shows
related to antenna measurements the author became aware of a
need in the industry to perform more accuurate measurements
at lower frequencies. The lowest frequency of interest in all
these cases is around 100MHz. At thesse frequencies the
preferred anechoic chamber or range to perform the
measurement is a taper anechoic chamberr. Taper chambers
have their own limitations. Among them is the need for a horn
antenna. Logarithmic periodic dipole arrayy (LPDA) antennas
have a geometry that is opposite that of the taper chamber. As
frequency increases the radiating element moves
m
further away
from the taper walls. This separation causess the taper chamber
not work as intended creating an illumination that has a lot of
ripple across the quiet zone (QZ). In
I addition when
performing Radar Cross Section or any othher test where there
a pulse involve LPDA can distort the pulsse because of their
radiation mechanism. So Horns are needded at these lower
frequencies and because of their large phhysical size it is a
better approach to have a dual linearly polaarized horn, whose
polarization can be switched by using RF sw
witches, rather than
mechanically rotating the antenna which potentially could be
extremely large.
In reference [1] a horn is introduced thhat had no metal or
dielectric flare. This horn operated horn was
w a dual linearly
polarized horn for the S-Ku band. Based on this development
the horn introduced in [3] was developed. This
T horn improved
some of the deficiencies on the pattern off similar horns that
operated in the same 400MHz to 6GHz range.
r
The pattern
problems were corrected using the same teechniques shown in
[4]. To create a horn for the 100MHz to 1G
GHz range the most
sensible approach was to scale the hornn developed in [3]
which is shown in fig. 1.
978-1-4244-9561-0/11/$26.00 ©2011 IEEE
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Fig. 1 The 300MHz to 6GHz dual poolarized Open Boundary Quad Ridge
Horn developed in [3].
While the development of the horn
h
described in reference [3]
has shown that the design is scalable the problem is that
scaling a horn is in some caases mechanically a very big
challenge and in many cases the result is an antenna that
although having the expectted performance it is not
economically feasible to manufa
facture.
II. SCALIN
NG ISSUES
The horn shown in figure 1 was scaled and analysed
numerically using CST MW stuudio. The results show that the
resulting antenna had the expeccted performance for the range
of interest. However at 1.67m by
b 1.67m by 1.52m (see figure
2)
Fig. 2. The 100MHz to 1GHz Open Bouundary Quad-ridge horn (OBQH)
showing the dimensions in ft.
This was a physically veryy large antenna with a lot of
weight. The weight of the ridgges can be reduce by using an
aluminium honeycomb sandw
wich structure where the low
weight honeycomb is sandwichhed between to thin sheets of
aluminium. This structure is very strong and rigid while
having a very low weight. Annother approach is to have the
ridges hollowed as shown in figgure 3.
AP-S/URSI 2011
through connector to get the signals to the inputs of the
antenna.
The actual; implementation of the design is shown in fig. 6.
The braces between the ridges are towards the front of the
horn as the mechanical designer deemed that no braces were
necessary close to the feed. The ridges are an aluminum
honeycomb sandwich and the overall weight of the horn was
only 69kg. The performance of the horn was adequate for the
use as a measurement antenna. The measured VSWR, and
measured cross port isolation are shown in figures 7 and 8.
The computed patterns where used to obtain the Half Power
Beamwidth shown in figure 9.
Fig. 3. The same OBQH with the hollowed ridges for weight reduction.
The holes on the ridges do not have a significant effect of
the performance. This is evident in figure 4 where the results
of the horn with and without the hole are compared.
Fig 5. The OBQH antenna with open cavity. The dielectric struts for
additional mechanical support of the ridges are also modelled.
Fig. 4. The VSWR with and without the hole. Additionally the result with a
smaller gap between the ridges at the feed point is shown.
The problem of the high weight of the ridges has two
possible solutions as to how to mechanically implement the
design. One is to hollow the ridge and the other is to use a
honeycomb sandwich. The feed cavity is a more complicated
problem. The horns described in [2] and [3] had cavities
machined of a single piece. This approach means that the horn
can be mounted by the flange to the shield of the chamber to
maintain the shielding integrity of the enclosure. However, for
the scaled horn this cavity is 45cm in diameter and the flange
is 1.01 m in diameter. Machining the internal features of the
cavity becomes extremely difficult and expensive. It is not
practical to do so. A different approach must be used to
implement this horn. Octagonal cavities have been used in the
past in place of circular ones. The cavity can then be
manufactured of smaller pieces fastened together to complete
the octagonal cavity. The results for the octagonal cavity
versus the circular cavity show almost no change. This
brought up the idea of having a totally open horn where the
cavity is also “open boundary”.
III. THE SUPER-OPEN BOUNDARY HORN
Figure 5 shows the horn with the open cavity. The trade off
of this design is that when mounted on the wall of an anechoic
enclosure it is necessary to have a penetration panel with feed
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Fig. 7. Computed S11 from the Horn shown in figure 5.
The concept of the open cavity was also applied to the higher
frequency model 3164-08 [5]. The results show that the
Super-OBQRH concept can be used at different frequency
ranges. While the horn in [5] has a lower frequency of
700MHz, the Super-OBQRH version can be pushed down to
450MHz and is even usable down to 400MHz. Figures 10 and
11 show the resulting design and its performance.
IV. CONCLUSION
The paper has shown the limitations of scaling horn designs. [2]
The limitations on the machining of large parts forced the
designer to arrive to a design that could be implemented. The
result is a horn of moderate size with a good performance
from 100MHz to 1.5GHz. This horn can be used as a feed in [3]
taper chambers or in large rectangular chambers or in outdoor
ranges. The low VSWR (under 2:1 from 105MHz to 1GHz)
makes it also usable for pulse and radar applications.
[4]
REFERENCES
[1]
V. Rodriguez, “An Open-Boundary Quad-ridged Guide Horn Antenna
for Use as a source in Antenna Pattern Measurement Anechoic
Chambers” IEEE Antennas and Propagation Magazine, Vol. 48, No. 2,
April 2006.
Fig. 8. Measured cross port isolation.
[5]
V. Rodriguez “Open Boundary Quadridge Horn Antenna for the 80
MHz to 1 GHz Range: A Dual Polarized Solution for Testing Antennas
in the VHF and UHF Ranges” 2010 Proceedings of the Fourth
European Conference on Antennas and Propagation. Barcelona, Spain
12-16 April 2010
V. Rodriguez, S. Weinreb “A Lower Frequency (UHF and S-Band)
Open Boundary Quadridged Horn Antenna and the Use of the S to Ku
band Horn as a Feed for Reflectors” 29th Annual Antenna
Measurement Techniques Association Symposium AMTA 2007, St.
Louis MO, Nov. 4-9 2007
V. Rodriguez, “Recent Improvements to Dual Ridge Horn Antennas:
The 200MHz to 2GHz and 18GHz to 40GHz Models” 2009 IEEE
International Symposium on EMC. Austin, TX Aug 17-21 2009.
3164-08 Open Boundary Quad-Ridged Horn Antenna. www.etslingren.com/3164-08
Fig. 10. The 400MHz to 10GHz Super Open Boundary Quad-Ridged Horn.
Fig. 9. Computed half power beamwidth.
Fig. 6. A picture of one of the Super-OBQH with open cavity.
Fig. 11. VSWR of the antenna featured in Fig 10.
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