13th European Conference on Antennas and Propagation (EuCAP 2019)

Multiple Scanning Beam Antenna Configuration forSpace Applications Using Reflectarrays
Shigeru Makino1 , Hiromasa Nakajima2 , Michio Takikawa2 ,1 (Kanazawa Institute of Technology): 7-1 Ogigaoka, Nonoichi, Ishikawa, 921-8501 Japan, makino@neptune.kanazawa-it.ac.jp
2 (Mitsubishi Electric Corporation): 5-1-1 Ofuna, Kamakura, Kanagawa, 247-8501 Japan

Abstract—In this presentation, a new satellite antenna configuration 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 withdifferent radiation directions in azimuth due to polarization andeach 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 andpolarization determined by the position of the user. If 3 dB gain
reduction is allowed, half of the frequency band can be used likethe conventional multiple spot beam antenna configuration.

I. I NTRODUCTION
In satellite communication, a multiple spot beam antennaconfiguration covering a desired service area uses four typesof beams, A, B, C, and D, that can be realized by combining
two frequency bands, f1 and f2 , and two orthogonal-polarizedpolarizations, V and H, as shown in Fig. 1. As a transmission
frequency band (Tx) and reception frequency band (Rx) arenecessary for satellite communication, a total of eight typesof beams are required. If a type of beam is to be realized
by a parabolic reflector and multiple horns, a total of eight
antennas are required; however, it is generally realized withfour antennas by sharing Tx and Rx bands with one antenna.

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 can be realized with aparabolic reflector, the beam CT X can also be realized by thereflectarray, so it is possible to realize three kinds of beam.
As a result, the eight types of beams 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 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 total of
two reflectors. In any of the above antenna configurations,
one reflector is used for both Tx and Rx. When Tx and Rx
are far apart such as Ka band, isolation between beams of thesame type is concerned because Tx has a wider beam width.
Also, in Rx, since the beam width is narrower, it is fearedthat the gain at the beam edge will decrease. In addition, it isnecessary to connect Tx/Rx duplexer, Tx OMT (Orthogonal
Mode Transducer), and Rx 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 horns anda single layer flat reflectarray. It radiates scanning beams withdifferent directions in azimuth due to polarization by using thephasing elements as shown in [3][4]. Each scanning beam withdifferent directions depending on frequency covers an elongate
area in elevation by using multiple horns and the beam squint
characteristics of reflectarray[5][6]. 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 like theconventional multiple spot beam antenna configurations.
II. P ROPOSED 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.

Fig. 1. Conventional beam arrangement.

Various antenna configurations using reflectarrays[1] havebeen reported for the purpose of reducing the number offL + fH
2(1)BW = fH − fL

(2)

f0 =

13th European Conference on Antennas and Propagation (EuCAP 2019)

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 beamwidths period as shown in Fig. 2.

Fig. 3. Frequency characteristics of radiation patterns.

Fig. 2. Beam arrangement at center frequency f0 .

The geometrical configuration of the reflecarray is designed
to occur beam squint with ±1 beam widths at fL and ∓1 beamwidths 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 arepresent in elevation, in the case that the beam squints at fL andfH are -1 beam widths and 1 beam width, respectively. ThefH beam of Beam 1 and fL beam of Beam 2 overlap at EL=-1
beam widths; the same occurs at the EL=+1 beamwidths. Herea 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 band width from fLto f0 of Beam 2 and a users at EL=-2 beam widths can use
BW /2 band width from fH − BW /4 to fH of Beam 1 andfrom fL to fL +BW /4 of Beam 2. Therefore, users within therange 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 to provide similar service to users within therange of El=-N+0.5 beam widths to El=N-0.5 beam widths.
So, the service area is an elongate area in elevation with 2N1 beam widths lengths. When the beams are arranged two
dimensionally as shown in√Fig. 2, multiple elongate areas arearranged in azimuth with 3 beam widths period as shown inFig. 4.
Next, the phasing elements √are designed so that the beam
direction in azimuth differs by 3/2 beam widths between Vpol and H-pol beams corresponding to a horn. So, the service
area is covered with the elongate beams staggered by V-poland H-pol as shown in Fig. 5.

Fig. 4. Coverage areas for single polarization.

In the case of the conventional multiple spot beam antenna,
users who are in the same spot beam use the same frequency
band f1 or f2 with BW /2 band width, and the gain reduction
amount is 0 to 3 dB depending on the position in the spot
beam, which is a fixed value independent of 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 is the sameas the conventional multiple spot beam antenna. Furthermore,
the amount of gain reduction is 0 to 3 dB, which depends onthe frequency.
III. G AIN 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)13th European Conference on Antennas and Propagation (EuCAP 2019)

Fig. 6. Maximum gain reduction in service area (conventional multi spot
antenna).
Fig. 5. Coverage areas for dual polarizations.

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 beam widths apart fromthe center of the beam, so Gr =4 dB and is independent offrequency.
On the other hand in the case of the proposed antenna, themaximum gain reduction occurs at the point P on the boundaryline between V-pol beam and H-pol beam shown in Fig. 7. In
the case where gain reductionis the smallest, 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 reductionis the maximum is the frequency separated by BW /4 fromf0 , and the beam is further separated√ by 0.5 beam widths inelevation. Therefore, the point P is 7/4 beam widths apartfrom the center of the beam of this frequency, so Gr =5.25
dB. As a result, the gain decreases from 2.25 dB to 5.25 dB
depending on the frequency to be used.
IV. D ESIGN EXAMPLE OF A REFLECTARRAY WITHSCANNING BEAM

Fig.8 shows the geometrical configuration of a offset reflectarray antenna. In the figure, F is a position of a horn antenna
as a primary radiator, F’ is a position of an image horn which isa horn image by a plane reflector, and O is a center position ofthe plane reflector. In the case, 4 degrees of freedom for design
parameters exist. Here the following 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 O and heading in the beam radiation direction, and aclearance c to avoid a blockage. The position F’ is determinedby R and θ, the position F is determined by D, R, and c, andthen the position and the orientation of the plane reflector aredetermined.

Fig. 7. Maximum gain reduction in service area (proposed antenna).

The beam squint angle θs depends on the inclination angle
θ and is determined by Eq.4[7],tan θs =λ − λ0tan θλ0(4)where λ0 and λ are wavelengths at the frequency f0 and f ,respectively. Required beam shift amount is 1 beam width at
the frequency fL or fH . The 3dB beam width Θ3 can beapproximated by Eq.5,λ0(5)Dwhere α is a constant dependent on the amplitude distribution
on the aperture and is generally around 70 deg. Using Eq.4and Eq.5, the design parameter θ is determined by Eq.6.
Θ3 = αθ = 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.

13th European Conference on Antennas and Propagation (EuCAP 2019)

Fig. 8. Design parameters of geometrical configuration of reflectarray.

Fig. 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 be 2880.0 mm and 1280.0mm, respectively. Fig.9 shows the geometrical configurationof the reflectarray model. And three horns are placed. Thereflectarray is single-layer flat type and the phasing element
is ring type and is not a type to change the beam direction bypolarization.

V. C ONCLUSION
In this study, a new satellite antenna configuration, realizedusing a TX and RX reflectarray antenna, respectively, wasproposed. This configuration utilizes two characteristics ofthe reflectarray: the beam squint characteristics that can berealized by geometric configuration, and a phasing elementthat can change the beam direction by polarization.
Although this antenna configuration is considered to function satisfactorily as a satellite antenna, there are problemsto 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.
• The frequency band used by the user may be discontinuous, in some cases. In the case of a mobile user, thefrequency to be used suddenly changes from fL to fH .
• In the frequency band used by the user, the power density
varies with the frequency.
R EFERENCES

Fig. 9. Geometrical configuration of the reflectarray model.

Fig.10 shows the analyzed frequency characteristics of theradiation patterns. In the figure, red lines, green lines andblue lines indicate the radiation patterns at frequency 19.0GHz, 19.5 GHz and 20.0 GHz, respectively. The broken,solid, and dashed lines indicate Beam-1, Beam-2, and Beam-3
corresponding to each horn, respectively. For all beams, 19.0
GHz beam, 19.5 GHz beam and 20.0 GHz beam cross at alevel 3 dB blow their peak. Further 19.0 GHz beam of Beam 1
and 20.0 GHz beam of Beam 2, and 19.0 GHz beam of Beam
2 and 20.0 GHz beam of Beam 3 almost overlap each other.
The deviation of the gain is 1 dB or less.
As a result, it was confirmed that the aimed beam arrangement was realized.

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