Three phase resolution transmitarray element for electronically reconfigurable transmitarrays

n
ring slot, it is helpful to analyze the equivalent circuit of
 in Table I.
the structure. As presented in [14], the equivalent circuit of
the element can be represented as shown in Figure 3.
 2. Frequency Response of The Transmitarray Element
 For the equivalent circuit, the two C-patches placed on
the top of two substrates are modeled as a parallel circuit The performance of the element should be validated be-
containing two series LC tanks () 1, !) 1, ) 2, !) 2). The fore implementing a transmitarray. ANSYS HFSS software
ring slot loaded with a rectangular gap is represented by version 13 is used to simulate and to optimize the proposed
a parallel LC tank (1, 1) placed in parallel with a element. To obtain the transmission phase and magnitude, a
series LC tank (2, !2). The substrate with a thickness method is to use the waveguide simulator. Since the center
 108
 Vol. 2019, No. 2, December
frequency of the element is 11.5 GHz, the WR-90 standard 0
waveguide is suitable to be used as waveguide simulator.
In the simulation, the element is placed in the open-end of -2
two WR-90 standard waveguides. Two excitation ports are
assigned at the other ends of two waveguides to measure -4
the transmission coefficients. Before the final version of an
 -6
electronically reconfigurable transmitarray is implemented,
 State 1 
the performance of the element is first evaluated using ideal State 2 
 -8
 State 3 
RF-switches. In this case, metallic strips are used as ideal p- Tran smissio nMag n itu d e(d B)
i-n diodes. For the ON state of a diode, the metallic strips -10 
are inserted on the gaps. For the OFF state, the metallic 10.0 10.5 11.0 11.5 12.0 12.5
strips are removed. Frequency (GHz)
 (a)
 Figure 4 shows the simulated transmission coefficients 200
of the proposed element for three phase states. As it can State 1 
 State 2 
be seen, the transmission magnitude of three phase states 100
 State 3 
at 11.5 GHz is greater than −1 dB. The common −3 dB
transmission bandwidth of three phase states is 16.5% 0
from 10.6 GHz to 12.5 GHz. As shown in Figure 4(b),
the transmission phase curve successfully changes when we -100
change the state of four diodes. Three phase curves have a
 -200
step of 120◦ at 11.5 GHz. However, the step of 120◦ is not TransmissionPhase (°) 
maintained for frequencies far from 11.5 GHz, due to the -300
non-linearity of the phase curves. 10.0 10.5 11.0 11.5 12.0 12.5
 Frequency (GHz)
 (b)
III. EXPERIMENTAL VALIDATION OF THE ELEMENT
 Figure 4. (a) Simulated transmission magnitude and (b) transmission
 A prototype of the element is implemented to validate phase of the proposed element.
the performance of the proposed element. The element is
fabricated by standard PCB fabrication technique. A small
metallic strip that acts as an ideal switch in the ON state is
soldered across the rectangular gap of ring slot layer. That
metallic strip is removed for the OFF state of the switch,
as shown in Figure 5.
 The method to measure the frequency response of the
element prototype is also to use waveguide simulators. This
technique requires two WR-90 standard waveguides whose
open-end size is 22.86 × 10.16 mm2. Since the element’s
shape is a square while the aperture of the waveguide is
rectangular, two rectangular-to-square transitions are imple-
mented and they are used as an adaptor to put the element Figure 5. (Simulated transmission magnitude (left) and transmission phase
in the middle of two waveguides. A metallic plate with a (right) of the proposed element.
hollow of 14×14×1.5 mm3 is inserted between two parts of
the element to ensure that two substrates are separated by
 IV. TRANSMITARRAY DESIGN
an air gap of 1.5 mm. Figure 6 presents the measurement
system. The measurement of the transmission coefficients A square transmitarray antenna is designed with 12 × 12
is performed using Agilent E5071C Vector Network An- elements to validate the radiation characteristics and beam
alyzer. The measurement system has been calibrated at steering capacity. As the periodicity of each element is 14
the ends of two straight waveguides, not including the mm, the transmitarray size is 168×168 mm2, corresponding
two rectangular-to-square transitions. Figure 7 shows the to 6.44_> × 6.4_> at 11.5 GHz. A small aperture horn
measured transmission coefficients in comparison with that antenna is used as the feed source for the array. Its aperture
of the simulation. As shown in Figure 7, the measured is 32 × 23 mm2 and its directivity is 11 dB. The horn
results agree well with simulated results. antenna is placed at a focal length of 150 mm corresponding
 109
Research and Development on Information and Communication Technology
 Figure 6. The measurement system.
to an F/D ratio of 0.89. The transmitarray in 3D and the Since the transmitarray antenna is based on the element
simulation environment are shown in Figure 8. which provides three phase states as discussed above, after
 calculating the theoretical compensation phase of each
 In the design of a space-fed array antenna, to steer the
 element using equations (1) and (2) for a main beam at
main beam to direction (\,q), the transmission phase of
 direction (\, q), the real phase k(G ,H ) of the element at
each element can be calculated using equations (1) and (2) 8 8
 the position with the coordinates G , H on the transmitarray
as follows: 8 8
 is quantized using equation (3). This corresponds to the
  

 φ(G8,H8) = :0 38 − sin \(G8 cos q + H8 sin q) , (1) three phase states:
 q ◦ ◦ ◦
 2 2 2 0 , −60 < φ(G8,H8) < −60 ,
 38 = (G8 − G 5 ) + (H8 − H 5 ) + (I8 − I 5 ) , (2) 
  ◦ ◦ ◦
 k(G8,H8) = 120 , 60 < φ(G8,H8) < 180 , (3)
where (\, q) is the direction of main beam, G8, H8 and  ◦ ◦ ◦
 th 240 , 180 < φ(G8,H8) < 300 ,
I8 are the coordinates of the 8 element, G 5 , H 5 and 
 th
I 5 are the coordinates of the feed source, and :0 is a where k(G8,H8) is the quantized phase of the 8 element at
propagation constant. the position with the coordinates G8, H8.
 According to equation (1), the phase distribution on the In order to evaluate the beam steering capabilities of
transmitarray aperture is depicted in Figure 9. In this figure, the transmitarray, various phase distributions obtained by
the desired main beam direction is \ = q = 0◦. arranging the suitable transmission phase are designed.
 110
 Vol. 2019, No. 2, December
 0
 1
 Phase (°)
 2
 -2
 358
 3
 336
 4
 309
 -4
 281
 5
 254
 6
 226
 State1 - Measured
 -6
 7
 199
 State1 - Simulated
 171
 8
 State 2 - Measured
 144
 State 2 - Simulated
 9
 -8
 116
 State 3 - Measured
 10
 89
 Tran smissio nMag n itu d e(d B)
 State 3 - Simulated
 61
 11
 -10 
 34
 12
 10.0 10.5 11.0 11.5 12.0 12.5
 6
 1 2 3 4 5 6 7 8 9 101112
 Frequency (GHz)
 (a)
 Figure 9. Theoretical compensation phase distribution required in the
 broadside transmitarray.
 300
 State1 - Measured State 2 - Measured
 State1 - Simulated State 2 - Simulated
 200
 State 3 - Measured State 3 - Simulated
 100
 0
 -100
 -200
 TransmissionPhase (°) 
 -300
 10.0 10.5 11.0 11.5 12.0 12.5
 Frequency (GHz)
 (b)
Figure 7. Measured and simulated transmission coefficients of the
prototype: (a) transmission magnitude and (b) transmission phase.
 Figure 10. Phase distribution for the main beam pointed at different
 angles: (a) \ = 0◦, q = 0◦ or 90◦, (b) q = 0◦, \ = 10◦, 20◦, 30◦,
 Figure 8. Simulation system for 12 × 12-element transmitarray. and (c) q = 90◦, \ = 10◦, 20◦, 30◦.
 111
Research and Development on Information and Communication Technology
 25 V. CONCLUSION
 20
 The three-phase-state element for reconfigurable trans-
 15
 mitarray has been presented in this paper. Both simulation
 10
 and measurement results validated good phase shifting
 5
 capability and a wide −3 dB transmission bandwidth. While
 0
 the prototype is still passive, where the ideal metallic strips
 -5
 are used as p-i-n diodes, simulation results indicated that
 -10
 the fully populated reconfigurable transmitarray can provide
 -15
 Radiationpattern (dB) 
 a wide scan angle with low scan loss. Further study and
 -20
 implementation of real p-i-n diodes will be deployed in an
 -25
 -90 -80 -70 -60 -50 -40 -30 -20 -10 0 10 20 30 40 50 60 70 80 90 electronically tunable version of the transmitarray.
 Theta (°)
 (a)
 25 ACKNOWLEDGMENT
 20 This research is funded by the Vietnam National Foun-
 15 dation for Science and Technology Development (NAFOS-
 10 TED) under grant number 102.01-2016.35.
 5
 0
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In comparison with the 1-bit element for reconfigurable Microwave Theory and Techniques, vol. 57, no. 8, pp. 1874–
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[11] A. Clemente, L. Dussopt, R. Sauleau, P. Potier, and Nguyen Huu Minh was born in Vietnam
 P. Pouliguen, “1-Bit reconfigurable unit cell based on PIN in 1992. He received his Bachelor of En-
 diodes for transmit-array applications in X-band,” IEEE gineering in Electrical Engineering from
 Transactions on Antennas and Propagation, vol. 60, no. 5,
 the International University, Ho Chi Minh
 pp. 2260–2269, 2012.
[12] B. D. Nguyen and C. Pichot, “Unit-cell loaded with PIN City in 2019. He is currently working as
 diodes for 1-bit linearly polarized reconfigurable transmi- a hardware engineer for Homa Techs Inc.
 tarrays,” IEEE Antennas and Wireless Propagation Letters, His interests mainly focus on passive and
 vol. 18, no. 1, pp. 98–102, 2018. active transmitarrays, PCB antenna design.
[13] F. Diaby, A. Clemente, L. Di Palma, L. Dussopt, K. Pham,
 E. Fourn, and R. Sauleau, “Linearly-polarized electronically
 reconfigurable transmitarray antenna with 2-bit phase resolu-
 tion in Ka-band,” in 2017 IEEE International Conference on
 Electromagnetics in Advanced Applications (ICEAA), 2017,
 pp. 1295–1298. Nguyen Binh Duong was born in Vietnam
[14] B. D. Nguyen and M. T. Nguyen, “Three-bit unit-cell with
 low profile for X-band linearly polarized transmitarrays.” in 1976. He received the B.S. degree in
 Applied Computational Electromagnetics Society Journal, electronic and electrical engineering from
 vol. 38, no. 9, 2019. Ho Chi Minh University of Technologies,
 Ho Chi Minh, Vietnam, in 2000 and the
 M.S. and Ph.D. degrees in electronic en-
 gineering from the University of Nice-
 Sophia Antipolis, France, in 2001 and 2006
 Nguyen Minh Thien was born in Viet- respectively. From 2001 to 2006, he was as a Researcher at
 nam in 1995. He received his Bachelor of the Laboratoire d’Electronique d’Antennes et Telecommunication,
 Engineering in Electrical Engineering from University of Nice-Sophia Antipolis, France. His research interests
 the International University, Ho Chi Minh focus on millimeter antenna, reflector, reflectarray and FSS.
 City in 2017. He is currently pursuing a
 Master program in the School of Electrical
 Engineering, International University. His
 research interests mainly focus on design
high gain antenna array, unit-cell design for passive reflectarray,
transmitarrays, electronically reconfigurable transmitarray.
 113