A NEW SATELLITE ANTENNA CONCEPT USING REFLECTARRAY ANTENNAS
Mei Fukaya1 , Ryota Obata1 , Shigeru Makino1 , Hiromasa Nakajima2 , and Michio Takikawa212Kanazawa Institute of Technology, 7-1 Ogigaoka, Nonoichi, Ishikawa, 921-8501 Japan
Mitsubishi Electric Corporation, 5-1-1 Ofuna, Kamakura, Kanagawa, 247-8501 Japan

ABSTRACTIn this paper, a new satellite antenna concept involving a Tx and an Rx reﬂectarray antenna is proposed. Eachantenna is composed of multiple horns and a single-layer
ﬂat reﬂectarray. It radiates scanning beams with different
radiation directions in the azimuth due to polarization.
Each scanning beam has a different radiation direction
depending on the frequency and covers an elongated area
in elevation. Each user in the service area selects the optimum frequency band, and the polarization is determinedby the position of the user. If a 3 dB gain reduction isallowed, half of the frequency band can be used, similar
to the conventional multiple-spot beam antenna.

with a total of two reﬂectors. In any of the above antenna
conﬁgurations, only one reﬂector is used for both Tx andRx. When Tx and Rx are far apart, for example, in theKa band, isolation between beams of the same type is anissue because Tx has a greater beam width. For Rx, since
the beam width is narrower, it is possible that the gain at
the beam edge will decrease.

Key words: Satellite antennas; Reﬂectarray antennas;
Multibeam Antennas.

1. INTRODUCTION
In recent years, antennas used in satellite communication have a conﬁguration with four types of beams,A, B, C, and D; these beams are produced by combining two frequency bands, f1 and f2 , and two orthogonalpolarized polarizations, V and H, as shown in Fig. 1. As
both a transmission frequency band (Tx) and reception
frequency band (Rx) are necessary for satellite communication, a total of eight types of beams are required. If
each beam is produced by a parabolic reﬂector and multiple horns, a total of eight antennas is required. However, the beams are generally produced with four antennas, each using a Tx and a Rx reﬂector.
Various antenna conﬁgurations using reﬂectarrays[1]have been reported to reduce the number of antennas.
Reference [2] demonstrates how to create a parabolic reﬂectarray. In this case, for example, a CT x beam canbe produced by the reﬂectarray and two beams, AT x andARx , can be produced by the parabolic reﬂector, resulting in the production of three types of beams. As a result,eight types of beams can be produced with a total of threereﬂectors. Reference [3] shows a ﬂat reﬂectarray that produces four kinds of beams by combining Tx/Rx and V/H.
In this case, the four kinds of beams are AT x , ARx , CT x ,and CRx ; hence, eight types of beams can be produced

Figure 1. Conventional beam arrangement.
In this paper, a new satellite antenna conﬁguration
containing a Tx and an Rx reﬂectarray antenna is proposed. Each antenna is composed of multiple horns anda single-layer ﬂat reﬂectarray. It radiates scanning beams
with different directions in the azimuth due to polarization by using the phasing elements, as shown in [3][4].
Each scanning beam has a different direction depending
on frequency and covers an elongated area in elevation
using multiple horns and beam squint characteristics ofthe reﬂectarray[5][6]. Each user in the service area selects the optimum frequency band and polarization depending on their position. If 3 dB gain reduction is allowed, half of the frequency band can be used, similar toconventional multiple-spot beam antenna conﬁgurations.

2. PROPOSED REFLECTARRAY

We consider the case where the whole frequency bandis used, from fL to fH . The center frequency, f0 , andthe frequency bandwidth, BW , can be expressed by Eq. 1

and Eq. 2, respectively.
fL + fH
2(1)BW = fH − fL

(2)

f0 =

The proposed antenna is composed of multiple horns
and a single-layer ﬂat reﬂectarray. The horns are arranged
such that the corresponding beams at f0 form an equilateral triangle with a two-beam-width period.
The geometrical conﬁguration of the reﬂectarray is designed to have beam squints with ±1 beam widths at fLand ∓1 beam widths at fH . Hence, as the frequencychanges from fL to fH , the beam direction varies continuously and linearly from -1 beam width to 1 beamwidth. Fig. 2 shows the frequency characteristics of radiation patterns when three beams are present in elevation;
here, the beam squints at fL and fH are at -1 beam widthand 1 beam width, respectively. The fH beam of Beam
1 and the fL beam of Beam 2 overlap at EL=-1 beamwidth; the same occurs at the EL=+1 beam width. Here,if a 3-dB gain reduction is allowed, the user can have abandwidth of BW /2, which is similar to a conventional
multiple-spot beam antenna conﬁguration. Similarly, auser at EL=-1 beam width can use the BW /2 bandwidth,i.e., from fL to f0 of Beam 2. A user at EL=-2 beamwidth can use the BW /2 bandwidth, from fH − BW /4
to fH of Beam 1 and from fL to fL + BW /4 of Beam 2.
Therefore, users within the range of El=-2.5 beam widths
to El=2.5 beam widths can avail similar services. Generally, by using N beams in elevation, it is possible toprovide similar services to users within the range of El=N+0.5 to El=N-0.5 beam widths. Therefore, as shown in
Fig. 3, vertically long areas having a beam width of 2N-1
are arranged√ in the azimuth direction, with a beam width
period of 3.

Figure 3. Coverage areas for a single polarization direction.
same area use the same frequency band, f1 or f2 with a
BW /2 bandwidth. The gain reduction amount is 0 to 3
dB depending on the position in the spot beam, which isa ﬁxed value independent of the frequency. On the other
hand, for the proposed antenna, although the user uses
a different frequency band (depending on their position),
the bandwidth is BW /2, which is the same as that fora conventional multiple-spot beam antenna. Further, theamount of gain reduction is 0 to 3 dB and depends on thefrequency.

Figure 4. Coverage areas for dual polarization directions.

3. DESIGN EXAMPLE OF A REFLECTARRAY
WITH SCANNING BEAM
Figure 2. Frequency characteristics of radiation patterns.
Next, the phasing elements are designed√so that thebeam direction in the azimuth differs by 3/2 beamwidths between the V-pol and H-pol beams, which corresponds to a horn. Therefore, the service area is covered with elongated beams that are staggered by V-poland H-pol, as shown in Fig. 4. In the case of a conventional multiple-spot beam antenna, users who are in theFig. 5 shows the geometrical conﬁguration of an offset
reﬂectarray antenna. In the ﬁgure, F is the position of ahorn antenna used as a primary radiator, F’ is the positionof an image horn produced by a plane reﬂector, and O
is the center position of the plane reﬂector. In this case,there are four degrees of freedom for the design parameters. The following four parameters are selected: theaperture diameter D, the distance from O to F, R, theangle formed by the straight line OF’ and a straight line
passing through O in the beam radiation direction, θ, anda clearance, c, to avoid blockage. The position of F’ isdetermined by R and θ, whereas the position of F is determined by D, R, and c; then, the position and orientationof the plane reﬂector are determined.

from the horns, respectively. For all three beams fromthe horns, the 19.0 GHz, 19.5 GHz, and 20.0 GHz beams
cross another beam at a level 3 dB blow their peaks. Further, the 19.0 GHz beam of Beam 1 and the 20.0 GHz
beam of Beam 2 as well as the 19.0 GHz beam of Beam
2 and the 20.0 GHz beam of Beam 3 almost overlap eachother. The deviation of the gain is 1 dB or less. Hence, we
can conﬁrm that the aimed beam arrangement was successful.

Figure 5. Design parameters of reﬂectarray geometricalconﬁguration.
The beam squint angle, θs , depends on the inclination
angle, θ, which is determined by Eq. 3[7],tan θs =λ − λ0tan θλ0(3)where λ0 and λ are wavelengths at f0 and f , respectively.
The required beam shift amount is 1 beam width at a frequency of fL or fH . The 3-dB beam width Θ3 can beapproximated by Eq. 4,
Θ3 = αλ0D(4)

where α is a constant dependent on the amplitude distribution on the aperture and is generally equal to approximately 70 deg. Using Eq. 3 and Eq. 4, the design parameter θ is determined by Eq. 5.
θ = tan−1 (λ0λ0tan(α ))λ − λ0D(5)λ is a wavelength at a frequency of fL or fH . If fL is selected, the fL beam deﬂects to El=+1 beam width and thefH beam deﬂects to El=-1 beam width, and vice versa.
Design examples are shown below, where fL is 19.0
GHz, fH is 20.0 GHz, and D is 1600.0 mm. θ is 24.6
deg, calculated using Eq. 5. In this case, the 19 GHz
beam deﬂects to El=+1 beam width. Then, R and c are
selected to be 2880.0 mm and 1280.0 mm, respectively,and three horns are placed. The reﬂectarray is a singlelayer ﬂat type as the ring-type phasing element is unable
to change the beam direction by polarization.
Fig. 6 shows the analyzed frequency characteristics ofthe radiation patterns. In the ﬁgure, the red, green, andblue lines indicate the radiation patterns at 19.0 GHz,
19.5 GHz, and 20.0 GHz, respectively. The broken, solid,
and dashed lines represent Beam 1, Beam 2, and Beam 3

Figure 6. Frequency characteristics of radiation patterns.

4. CONCLUSION
In this study, a new satellite antenna concept accomplished using a Tx and an Rx reﬂectarray antenna is proposed. This conﬁguration utilizes two characteristics ofthe reﬂectarray: the beam squint characteristics, which
can be realized using the geometric conﬁguration, and aphasing element, which can change the beam direction bypolarization.

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