A NEW SATELLITE ANTENNA CONCEPT USING REFLECTARRAY ANTENNASShigeru 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 presentation, a new satellite antenna concept realized by a TX and a RX reflectarray antenna will be proposed. Each antenna is composed of multiple horns anda single layer flat reflectarray. It radiates scanning beams
with different radiation directions in azimuth due to polarization and each scanning beam with different radiation directions depending on frequency covers an elongate area in elevation. Each user in the service area selects the optimum frequency band and polarization determined by the position of the user. If 3 dB gain reductionis allowed, half of the frequency band can be used likethe conventional concept.
Key words: Satellite antennas; Reflectarray antennas;
Multibeam Antennas.

1. INTRODUCTION
In recent years, in satellite communication, an antennaconfiguration covering a desired service area uses fourtypes of beams, A, B, C, and D, that can be realized
by combining two frequency bands, f1 and f2 , and two
orthogonal-polarized polarizations, V and H, as shownin Fig. 1. As a transmission frequency band (Tx) andreception frequency band (Rx) are necessary for satellite
communication, a total of eight types of beams are required. If a type of beam is to be realized by a parabolicreflector and multiple horns, a total of eight antennas arerequired; however, it is generally realized with four antennas, using a Tx and Rx reflector, respectively.
Various antenna configurations using reflectarrays[1]have been reported for the purpose of reducing the number of antennas. Reference [2] shows a method of constructing parabolic reflectarrays. In this case, for example, in addition to the two beams AT X and ARX that canbe realized with a parabolic reflector, the beam CT X canalso be realized by the reflectarray, so it is possible to realize three kinds of beam. As a result, the eight types ofbeams can be realized with a total of three reflectors. And
if dual-band phasing elements are possible, CRX beam
can also be realized, so a total of two reflectors will realize eight types of beams. Reference [3] shows a flat

Figure 1. Conventional beam arrangement.

reflectoarray that realizes four kinds of beams combining Tx/Rx and V/H. In this case, it is possible to realize
four kinds of beams such as AT X , ARX , CT X and CRX ,so the eight types of beams can be realized with a totalof two reflectors. In any of the above antenna configurations, one reflector is used for both Tx and Rx. When Txand Rx are far apart such as Ka band, isolation between
beams of the same type is concerned because Tx has awider beam width. Also, in Rx, since the beam width isnarrower, it is feared that the gain at the beam edge will
decrease. In addition, it is necessary to connect Tx/Rx
duplexer, Tx OMT (Orthogonal Mode Transducer), andRx OMT to each horn.
In this presentation, a new satellite antenna configuration
realized by a TX and a RX reflectarray antenna will beproposed. Each antenna is composed of multiple hornsand a single layer flat reflectarray. It radiates scanningbeams with different directions in azimuth due to polarization by using the phasing elements as shown in [3][4].
Each scanning beam with different directions depending
on frequency covers an elongate area in elevation by using multiple horns and the beam squint characteristics ofreflectarray[5][6]. Each user in the service area selects
the optimum frequency band and polarization determinedby the position of the user. If 3 dB gain reduction is allowed, half of the frequency band can be used like theconventional multiple spot beam antenna configurations.

2.

PROPOSED REFLECTARRAY

Consider the case of using the frequency band from fL tofH . The center frequency f0 and the all frequency band
width BW are as Eq.1 and Eq.2, respectively.
fL + fH
2(1)

BW = fH − fL(2)

f0 =beam widths lengths. When the beams are arranged two
dimensionally as shown in Fig.√2, multiple elongate areas
are arranged in azimuth with 3 beam widths period asshown in Fig. 4.

An antenna is composed of multiple horns and a single
layer flat reflectarray. Horns are arranged so that the corresponding beams at f0 are arranged in an equilateral triangle with 2 beam widths period as shown in Fig. 2.

Figure 3. Frequency characteristics of radiation patterns.

Figure 2. Beam arrangement at center frequency f0 .
The geometrical configuration of the reflecarray is designed to occur beam squint with ±1 beam widths at fLand ∓1 beam widths at fH . So, as the frequency changes
from fL to fH , the beam direction varies continuously
and linearly from -1 beam widths to 1 beam width. Fig. 3
shows the frequency characteristics of radiation patterns
when three beams are present in elevation, in the case thatthe beam squints at fL and fH are -1 beam widths and 1beam width, respectively. The fH beam of Beam 1 andfL beam of Beam 2 overlap at EL=-1 beam widths; thesame occurs at the EL=+1 beamwidths. Here a user at
EL=0 can use the frequency band from f0 − BW /4 tof0 + BW /4 of Beam 2, if 3 dB gain reduction is allowed.
So, BW /2 band width can be used and is like the conventional multiple spot beam antenna configurations. Similarly, a user at EL=-1 beam widths can use BW /2 bandwidth from fL to f0 of Beam 2 and a users at EL=-2 beamwidths can use BW /2 band width from fH − BW /4 tofH 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 use similar services. Generally, by using N beams in elevation, it is possible toprovide similar service to users within the range of El=N+0.5 beam widths to El=N-0.5 beam widths. So, theservice area is an elongate area in elevation with 2N-1

Figure 4. Coverage areas for single polarization.
Next, the phasing elements are designed
so that the beam√
direction in azimuth differs by 3/2 beam widths between V-pol and H-pol beams corresponding to a horn.
So, the service area is covered with the elongate beams
staggered by V-pol and H-pol as shown in Fig. 5.
In the case of the conventional multiple spot beam antenna, users who are in the same spot beam use the samefrequency band f1 or f2 with BW /2 band width, and thegain reduction amount is 0 to 3 dB depending on the position in the spot beam, which is a fixed value independentof frequency.
On the other hand in the case of the proposed antenna, although the user uses a different frequency band depending on its position, its band width is BW /2, which isthe same as the conventional multiple spot beam antenna.
Furthermore, the amount of gain reduction is 0 to 3 dB,
which depends on the frequency.

Figure 6. Maximum gain reduction in service area (conventional multi spot antenna).

Figure 5. Coverage areas for dual polarizations.
3.

GAIN REDUCTION AT THE COVERAGE
EDGE

Here it is assumed that the gain reduction amount Gr dB
is expressed by Eq.3,Gr (Θ) = 12(Θ 2)Θ3(3)where Θ is an angle from peak gain direction and Θ3 is a
3dB beam width.
In the case of the conventional multiple spot beam antenna, the maximum gain reduction occurs √at the point
P of Fig. 6. In such a case, the point P is 3/3 beamwidths apart from the center of the beam, so Gr =4 dBand is independent of frequency.
On the other hand in the case of the proposed antenna,
the maximum gain reduction occurs at the point P on
the boundary line between V-pol beam and H-pol beamshown in Fig. 7. In the case where gain reduction √is thesmallest, the frequency f0′ of the beam spaced by 3/4
beam width in azimuth is used, so Gr =2.25 dB at f0′ . The
frequency at which gain reduction is the maximum is thefrequency separated by BW /4 from f0′ , and the beam isfurther separated by√0.5 beam widths in elevation. Therefore, the point P is 7/4 beam widths apart from the center of the beam of this frequency, so Gr =5.25 dB. As aresult, the gain decreases from 2.25 dB to 5.25 dB depending on the frequency to be used.

Figure 7. Maximum gain reduction in service area (proposed antenna).
horn which is a horn image by a plane reflector, and O
is a center position of the plane reflector. In the case, 4degrees of freedom for design parameters exist. Here thefollowing 4 parameters are selected ; an aperture diameter D, a distance R from O to F, an angle θ formed by
the straight line OF’ and a straight line passing through Oand heading in the beam radiation direction, and a clearance c to avoid a blockage. The position F’ is determinedby R and θ, the position F is determined by D, R, andc, and then the position and the orientation of the planereflector are determined.
The beam squint angle θs depends on the inclination angle θ and is determined by Eq.4[7],tan θs =4.

DESIGN EXAMPLE OF A REFLECTARRAY
WITH SCANNING BEAM

Fig.8 shows the geometrical configuration of a offset reflectarray antenna. In the figure, F is a position of a hornantenna as a primary radiator, F’ is a position of an image

λ − λ0tan θλ0(4)where λ0 and λ are wavelengths at the frequency f0 andf , respectively. Required beam shift amount is 1 beamwidth at the frequency fL or fH . The 3dB beam widthΘ3 can be approximated by Eq.5,
Θ3 = αλ0D(5)

GHz beam cross at a level 3 dB blow their peak. Further19.0 GHz beam of Beam 1 and 20.0 GHz beam of Beam2, and 19.0 GHz beam of Beam 2 and 20.0 GHz beam of
Beam 3 almost overlap each other. The deviation of thegain is 1 dB or less.
As a result, it was confirmed that the aimed beam arrangement was realized.

Figure 8. Design parameters of geometrical configuration of reflectarray.
where α is a constant dependent on the amplitude distribution on the aperture and is generally around 70 deg.
Using Eq.4 and Eq.5, the design parameter θ is determined by Eq.6.
θ = tan−1 (λ0λ0tan(α ))λ − λ0D(6)λ is a wavelength at the frequency fL or fH , and if fL isselected, fL beam deflects to El=+1 beam width and fH
beam deflects to El=-1 beam width, and also, the converse
also holds.

Figure 10. Frequency characteristics of radiation patterns.

Below, design examples are shown, where fL is 19.0
GHz, fH is 20.0 GHz and D=1600.0 mm. θ is 24.6
deg by using Eq.6. In the case, 19 GHz beam deflects
to El=+1 beam width. Then R and c are selected to be2880.0 mm and 1280.0 mm, respectively. Fig.9 shows
the geometrical configuration of the reflectarray model.
And three horns are placed. The reflectarray is singlelayer flat type and the phasing element is ring type and is
not a type to change the beam direction by polarization.

5. CONCLUSION
In this study, a new satellite antenna concept, realized using a TX and RX reflectarray antenna, respectively, wasproposed. This configuration utilizes two characteristicsof the reflectarray: the beam squint characteristics thatcan be realized by geometric configuration, and a phasing
element that can change the beam direction by polarization.
Although this antenna configuration is considered tofunction satisfactorily as a satellite antenna, there areproblems to be solved with respect to the earth station,
as mentioned below:• The frequency band to be used depends on the position, and not on the beam to which the user belongs.

Figure 9. Geometrical configuration of the reflectarraymodel.
Fig.10 shows the analyzed frequency characteristics ofthe radiation patterns. In the figure, red lines, green lines
and blue lines indicate the radiation patterns at frequency
19.0 GHz, 19.5 GHz and 20.0 GHz, respectively. The
broken, solid, and dashed lines indicate Beam-1, Beam2, and Beam-3 corresponding to each horn, respectively.
For all beams, 19.0 GHz beam, 19.5 GHz beam and 20.0

• The frequency band used by the user may be discontinuous, in some cases. In the case of a mobile user,
the frequency to be used suddenly changes from fL
to fH .
• In the frequency band used by the user, the power
density varies with the frequency.

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