Innovative High-Gain Corrugated Horn AntennaCombining Horizontal and Vertical Corrugations

380
IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 5, 2006
Innovative High-Gain Corrugated Horn Antenna
Combining Horizontal and Vertical Corrugations
Jorge Teniente, Ramón Gonzalo, Member, IEEE, and Carlos del-Río, Member, IEEE
Abstract—An innovative kind of corrugated horn antenna is
proposed within this letter, the profile of the horn is based on the
combination of horizontal and vertical corrugations. The main
advantage of these profiles is the possibility of combining high-gain
with short profiles, meanwhile keeping the main performances of
the conventional corrugated horns. Besides, this horn results in
an easier manufacture process due to their smaller size and elim2 corrugations
inates the difficulties to manufacture the deep
at the throat of classical profiles. An example of a horn with 24
dB gain, 35 dB maximum crosspolar, and sidelobe levels and
20% bandwidth has been designed, fabricated and characterized.
These horns are a very promising alternative for future earth and
space applications.
Index Terms—Compact size, corrugated horn antennas,
Gaussian profiles, horizontal and vertical corrugations.
I. INTRODUCTION
E
XTREMELY low sidelobe horn antennas are often required for many current applications. This type of horn
antennas are really important nowadays to avoid interference
with other communication systems. The innovative concept
consisting on attaching a short choked antenna (horizontal
corrugations) to minimize the length at the initial part of the
horn together with a vertically corrugated profile to improve
the performance is proposed in this letter.
Horn antennas that combine horizontal and vertical corrugations were firstly developed four years ago as choked-gaussian
antennas with the main goal of achieving very high performances for stringent applications in a very compact antenna.
This type of corrugated horn is easier to manufacture than
normal corrugated profiles because they avoid deep throat
vertical corrugations necessary in usual corrugated horns. An
international patent was issued [1] and commercial exploitation
of the idea is now available.
Corrugated horns have always offered very broad bandwidth,
low crosspolar levels, low sidelobe levels and low return loss
making them a very attractive solution for many applications.
Over the last few years, the use of optimization simulating tools
has become a revolution in the design of compact corrugated
horns [2]–[5]. Actually, due to the high development of the optimization tools, the corrugated horns are usually no longer defined by means of a previously predetermined profile, and typi-
Manuscript received June 2, 2006; revised July 7, 2006.
The authors are with the Antenna Group, Electric and Electronic Engineering
Department, Public University of Navarra, Campus de Arrosad́ia, E-31006 Pamplona, Navarra, Spain (e-mail: jorge.tenienteunavarra.es; [email protected];
[email protected]).
Digital Object Identifier 10.1109/LAWP.2006.881919
cally the optimization focuses on inner and outer radius of each
corrugation as variables in the design process.
However, the overall size of the corrugated horn antennas is
becoming the real key issue. In the past, corrugated horns were
usually defined by conical profiles. Conventional conical profiles were huge when a horn with narrow beamwidth had to be
designed (gain above 20 dB) because they led to narrow flare angles and large apertures, resulting in very long profiles, heavy,
difficult to manufacture and expensive; see Fig. 1(a).
Olver et al. [6]–[8] proposed several profiles to reduce the
length of corrugated horn antennas and have used optimization
methods in them to reduce the excitation of higher order modes
with certain success; especially they have focused in the reduction of HE and EH modes and maximization of HE mode
content at the aperture. However, HE is a mode that naturally
couples in a corrugated horn. In fact, as it was said in [9], HE
mode doesn’t contribute to crosspolar level and if its phase is
carefully controlled, contributes to improve main beam radiation pattern and reduce sidelobe level. Advanced technology
designs should control the excitation of HE and reduce EH
modes to improve antenna performances.
When a comparison between conical and new profiles
[2]–[5], [9] is stated, see Fig. 1(a), it can be concluded that
nowadays, the length of corrugated horn antennas has reduced
a lot compared to old conical profiles. This length reduction
opens the design possibilities to higher gain with a reasonable
size.
In these advanced profiles of corrugated horn antennas
[2]–[5], [9], the output diameter size remains unchanged,
although its width defines the sidelobe level of the radiation
pattern, see Fig. 1(b). If required, prototypes with radiation
dB or even lower
pattern that presents sidelobe level below
can be made available. In such low sidelobe level designs, the
HE mode has significant amplitude at the aperture, at least
comparable to the HE mode [9].
It is also important to remark that size of these new technology corrugated horns is usually determined by the frequency
bandwidth. A narrow bandwidth specification can always be designed with a shorter and narrower aperture prototype, while
wide bandwidth requirements impose longer and wider profiles.
Bandwidth is usually a question of smoother profiles. In Fig. 1,
approximate pessimistic size values are given for a 20% bandwidth.
The design objectives for the corrugated horn antenna presented in this letter have been selected as typical parameters of
corrugated horns for space and earth applications, i.e., downlinks of DBS applications. No comparisons of performances of
this design with other advanced designs have been included be-
1536-1225/$20.00 © 2006 IEEE
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TENIENTE et al.: INNOVATIVE HIGH-GAIN CORRUGATED HORN ANTENNA
381
or chokes [1], see Fig. 2(a). This change has several advantages,
the first one is an easier manufacturing process because usually
) and difficult
throat vertical corrugations are deep (around
to machine. Other advantages are a reduction of length maintaining wide bandwidth and a better return loss response because the horizontal corrugations at the throat region are less
likely than the vertical corrugations to produce resonances that
lead to unwanted return loss spikes.
It is important to remark at this point that the rest of radiation parameters that exhibit the usual corrugated horns; circularly symmetric copolar pattern, bandwidth, low crosspolar
levels and low sidelobe level remain unchanged in this technology.
II. DESIGN AND RESULTS
Fig. 1. Size of new technology corrugated horn antennas versus directivity. (a)
Length (L). (b) Output aperture diameter (D ).
cause at the present moment no other author has presented any
high-gain corrugated horn based on other technologies rather
than conical technology described in [7]. For that case, the horn
length would be above 20 , see Fig. 1, which at 10 GHz leads
to a heavy and huge horn above 60-cm long. So, conventional
solutions to achieve these high-gain antennas have made use of
a reflector antenna or a lens horn antenna to overcome these limitations in microwave bands.
On the other hand, for higher frequencies, (mm and sub-mm
bands), corrugated horns with a gain above 26 dB have usually
been designed to avoid the complexity of reflectors at this short
wavelengths. In this case, the size as frequency increases is not
the real problem; the problem usually is the increased manufacture complexity. This problem would be also reduced by the use
of the proposed antenna configuration.
The main difference between the corrugated horn profiles
proposed in this letter and the advanced ones proposed by the
rest of authors is in the throat region and consists in the substitution of the throat vertical corrugations, which are usually
deeper to match the incident mode, with horizontal corrugations
To demonstrate the main properties of this innovative type
of horn profile, a corrugated horn antenna with 24 dB gain has
been designed, manufactured and measured. The design objectives were to obtain in at least a 20% bandwidth a design with
dB, crosspolar kevel below
a return loss lower than
dB, sidelobe level below
dB, and 24 dB gain at central frequency.
The Mician Wave Wizard software package was used for
simulation purposes. This software is an optimization (EM)
CAD tool for passive waveguide components and antennas, and
uses mode-matching techniques.
As it can be seen in Fig. 2(a) and (b), the designed 24 dB gain
corrugated horn meets the specification with a size of 10.5
long and 8.7 wide (the aperture width is given for overall aperture diameter, including last corrugation depth and metal thickness, usually other authors give this value for inner diameter
so the number we give is usually between 0.4 and bigger
and depends on last corrugation depth). Besides, in a 10% bandwidth the specifications are ever better, the sidelobe/shoulder
dB and the crosspolar level well below
level is around
dB.
This design was manufactured by a conventional milling machine at a central frequency of 10 GHz and measured in a far
field range anechoic chamber. Measurements show excellent
agreement, see Fig. 3, in spite of fabrication inaccuracies that
destroyed two corrugations in the flare region, (milling machine
made a bite during the manufacturing process), see Fig. 4. The
error in the machining process was probably the reason of a
measured crosspolar level slightly higher than expected, but still
close to the specifications. As it is said in [10], a perfectly constructed special purpose corrugated horn, when measured in a
very high performance anechoic chamber, gives exact agreedB. In fact, as
ment with theoretical radiation patterns till
it is shown in this case, manufacturing errors do not affect considerably to the performance of corrugated horn antennas, reinforcing one of the benefits of corrugated horns, manufacture
accuracy is not usually a real problem.
In the presented case, a random number generator to vary both
the length and the radius of each corrugation was used to test the
necessary accuracy in the manufacturing process. The results
confirmed that the needed accuracy is similar to any other kind
of corrugated horns.
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382
IEEE ANTENNAS AND WIRELESS PROPAGATION LETTERS, VOL. 5, 2006
Fig. 3. 24-dB gain horn antenna measurements. (a) Measured radiation pattern
at f . (b) Measured and simulated return loss response.
Fig. 2. 24-dB gain horn antenna simulations. (a) Simulated radiation pattern
at f and corrugated horn antenna profile. (b) Simulated radiation properties.
Regarding return loss measurement; the horn response
presents it below
dB in the whole frequency band including a coaxial to rectangular transition (this transition has
dB according to manufacturer)
a return loss better that
and a rectangular to circular transition (no manufacturer data
available of its VSWR response), so it is assumed that the
return loss meets the specification, no spike responses have
been detected.
III. CONCLUSION
A very compact and high performance 24-dB gain corrugated
horn antenna that combines horizontal and vertical corrugations
has been designed, manufactured and measured. Measured results meet the proposed specifications. By applying these innovative ideas, moderate to high-gain corrugated horns where
stringent requirements must be met; can nowadays be made
available in much reduced size than old corrugated technology
prototypes.
Fig. 4. Manufactured 24 dB gain corrugated horn (f = 10 GHz) and detail
of manufactured error in two corrugations (to compare size, 1 Euro coin was
photographed).
ACKNOWLEDGMENT
The authors would like to thank Dr. S. Loredo for the prototype measurement at the Oviedo University anechoic chamber.
They would also like to thank the reviewers for their useful comments in improving this manuscript.
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TENIENTE et al.: INNOVATIVE HIGH-GAIN CORRUGATED HORN ANTENNA
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