Aerospace and Electronic Systems - October 2018 - 34

Feature Article:

DOI. No. 10.1109/MAES.2018.160160

Beam Shaping of X-Band Stepped Choke Ring Antenna
for LEO Satellite Applications
M. Fallahzadeh, Iranian Space Research Center and K.N. Toosi University of
Technology, Tehran, Iran
H. Aliakbarian, K.N. Toosi University of Technology, Tehran, Iran
A. Haddadi, Amirkabir University of Technology, Tehran, Iran
S. Radiom, Iranian Space Research Center, Tehran, Iran

INTRODUCTION
Low Earth orbit (LEO) satellites operating below 1,400 km are currently in use for various applications, ranging from remote sensing
and weather forecast to voice and data communications and scientific
research. Because of their shorter distance to Earth, simpler, smaller,
and therefore lower-gain antennas with wider angular coverage can
be mounted on a LEO satellite to establish the communication link.
Regarding the wider angular coverage and the varying distance
of these satellites to the Earth, the beam shaping for the antennas on
the satellite becomes more significant. An ideal radiation pattern for
such applications is called an isoflux pattern that has a lower directivity than its far angles in the broadside direction, depending on the
altitude of the satellite [1]-[5]. Several antenna types have been used
to achieve an isoflux pattern, such as helix structures [1], [2], [3],
turnstile structures [4], multimode antennas [5], and choke ring antennas (CRAs) [6], [7]. Array antennas are not normally used due to
their physically large dimensions. On the other hand, helix structures
do have difficult implementation in frequencies higher than X band.
The CRAs, however, are very interesting especially because of their
radiation characteristics which allow obtaining high-quality circular
polarization. It is usually desired to have this polarization all over the
wide beam of a LEO satellite antenna.
CRAs are very popular as the feed of reflector antennas [8].
They are also being used for receiving global positioning system
signals [9] and other applications. The role of the set of concentric
rings that are positioned in the center of the CRAs manipulates the
propagation of surface waves on the ground plane to control the
current distribution on the antenna aperture and to shape the radiaAuthors' current addresses: M. Fallahzadeh, S. Radiom,
Iranian Space Research Center, Tarasht, Sama Square, No. 59,
Tehran, Iran. H. Aliakbarian, Faculty of Electrical Engineering,
K.N. Toosi University of Technology, Seyed Khandan Bridge,
P.O. Box 16315-1355, Tehran, Iran, E-mail: (h.aliakbarian@
ieee.org). A. Haddadi, Department of Electrical Engineering,
Amirkabir University of Technology, Tehran, Iran.
Manuscript received July 27, 2016, revised November 27, 2016,
December 11, 2017, and ready for publication January 22, 2017.
Review handled by D. Ciuonzo.
0885/8985/18/$26.00 © 2018 IEEE
34

tion pattern. The shape of the desired radiation pattern depends on
the application. There are also several modified versions of CRAs.
In [6], stepped concentric rings with periodic slots on the wall of
each ring has been proposed. In [10], a CRA has been optimized
to achieve a shaped isoflux beam for a LEO satellite. Such a radiation pattern using a three-dimensional (3D) choke ring structure is
reported in [11] by Hosseinmardi et al.
In this article, we focus on the design of a different 3D CRA with
descending stepped rings, as shown in Figure 1, to achieve maximum

Figure 1.

(a) SCRA with all design parameters, and (b) the fabricated antenna under
measurement in anechoic chamber.

IEEE A&E SYSTEMS MAGAZINE

OCTOBER 2018

Aerospace and Electronic Systems - October 2018

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