Design of Circularly Polarized Transmit array Antenna using Low-Profile Dual-Linearly Polarized Elements

Asian Journal of Applied Science and Technology
Volume 4, Issue 4, Pages 38-43, October-December 2020
ISSN: 2456-883X www.ajast.net
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Design of Circularly Polarized Transmit array Antenna using Low-Profile Dual-Linearly
Polarized Elements
N.Khadarbasha1
& A.Yogeshwaran2
1,2
Assistant Professor, Dhanalakshmi Srinivasan Engineering College, Perambalur, India.
DOI: http://doi.org/10.38177/ajast.2020.4404
Copyright: ©2020 N.Khadarbasha et al. This is an open access article distributed under the terms of the Creative Commons Attribution License, which
permits unrestricted use, distribution, and reproduction in any medium, provided the original author and source are credited.
Article Received: 09 September 2020 Article Accepted: 17 November 2020 Article Published: 05 December 2020
1. Introduction
The transmit array antenna has attracted significant attention in past decades because of its advantages such as high
gain, inexpensive fabrication, and no insertion loss caused by the feeding network of a phased array at higher
frequencies. With simple planar structure, the transmit array has more advantages over lens antennas. In addition,
compared with the reflect array, in the transmit array the feed is placed directly in back of the aperture to avoid its
blockage losses, which usually results in higher aperture efficiency. For the transmit array, a feed antenna
illuminates the array in which the proper designed unit cells are used to transform the incoming wave with proper
phase to form a desired beam shape.
Two most important design criteria for a transmit array element are its phase range and transmission magnitude. In
order to obtain a transmit array with high aperture efficiency, unit cells with 360° transmission phase range and the
transmission magnitude as high as possible are needed. To date, many different efforts have been devoted to design
the transmit arrays with high performance.
To date, many different efforts have been devoted to design the transmit arrays with high performance. A wideband
transmit array antenna using four identical layers with the double loop elements is proposed [2]. A transmitarray
antenna consists of multiple layers of flat transmitting surface and an illuminating feed source, which is located on
an equivalent focal point.
The transmission coefficients of these elements are individually designed such that spherical phase front from the
feed source is converted into a plan phase front. One of the arrays act as a receiver, and it is illuminated by the
antenna feed source. The other array radiates into free space, and it acts as a transmitter. A coupling structure is
designed between the two array to obtain a specific phase and magnitude distribution. It is worthwhile to point out
that these techniques mostly use printed type elements mounted on substrate materials [3],[4].
ABSTRACT
A low-profile dual-linearly-polarized unit cell in X-band, and its capability is demonstrated by a circularly polarized transmit array. The unit cell
comprises three metallic layers etched on two dielectric slabs without air gap. Cross strips are inserted in cross slots on the top and bottom layers, and
the T-slot structure is etched on the middle layer. The proposed unit cell has high isolation between the dual polarizations, and its total thickness of
the unit cell is only 1 mm. Prototype of a 341-element transmit array, the incoming incident linearly polarized wave is transformed into the outgoing
circularly polarized wave, is simulated. The measured results show that the proposed transmit array realizes 3.5% (9.8-10.15 GHz), axial ratio
bandwidth and 4% (9.7-10.1 GHz) 1-dB gain bandwidth. The measured peak gain at 10 GHz is 21.9 dBi, with the aperture efficiency of 36%.
Keywords: Low profile, Dual polarization, Transmitarray.

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2. Proposed System
In transmitarrays, at least three layers with quarter-wavelength spacings are necessary to meet a full 360° phase
range requirement [13]. In our study, dual linear polarizations, low profile and a full 360° phase range are important
for the transmitarray element design. The designed transmitarray unit cell comprises of three metallic layers
sandwiched with two dielectric layers. Its configuration is shown in Figure 1. The substrate layers are made by
RO4003 with a relative permittivity of 3.55 and a thickness of H=0.5 mm.
Figure 1: Unit Cell Configuration of T-Slot Element
Table 1
3. Unit Cell Design
In transmitarrays, at least three layers with quarter-wavelength spacings are necessary to meet a full 360° phase
range requirement. In our study, dual linear polarizations, low profile and a full 360° phase range are important for
the transmitarray element design. The designed transmitarray unit cell comprises of three metallic layers
sandwiched with two dielectric layers. Its configuration, the substrate layers are made by RO4003 with a relative
permittivity of 3.55 and a thickness of H=0.5 mm.
For the proposed element, parallel resonant circuits are formed by the cross slot and the cross strip on the top and
bottom layers, and a transmission passband is realized. By independently adjusting lengths Lx and Ly, the
transmission phase of the corresponding polarization wave can be controlled. It is very difficult to realize
360°transmission phase on such a low profile structure by using three identical layers in our attempt, so we design
a T-slot element shown in Fig. 1(b), which is used to form a new resonance. By conducting several times simulation
experiments, we summarize the relation between Lx1 (Ly1) and Lx (Ly), as shown in Table 1. Through a rational
design of the ratio of Lx1 (Ly1) to Lx (Ly), the desired phase range of 360°can be realized. Values of the equivalent

40
capacitors and inductors for x-direction are not affected by the y-direction size, and vice versa. Therefore, the
designed unit cell can realize good polarization isolation performance.
The unit cell simulations are carried out using the commercial software Ansoft HFSS ver. 13. The mutual coupling
between identical elements is considered under periodic boundary conditions.
Transmission coefficient responses of the compound sandwich structure with different Lx's. It can be seen that with
increasing Lx's, the pass band center frequencies decrease. The transmission amplitudes and phases versus Lx at the
center frequency of 10 GHz for different Ly's, when the incoming wave is x-polarized.
4. Circular Polarization
In electrodynamics, circular polarization of an electromagnetic wave is a polarization state in which, at each point,
the electric field of the wave has a constant magnitude but its direction rotates with time at a steady rate in a plane
perpendicular to the direction of the wave. In electrodynamics the strength and direction of an electric field is
defined by its electric field vector. In the case of a circularly polarized wave, as seen in the accompanying
animation, the tip of the electric field vector, at a given point in space, describes a circle as time progresses. At any
instant of time, the electric field vector of the wave describes a helix along the direction of propagation. A circularly
polarized wave can be in one of two possible states, right circular polarization in which the electric field vector
rotates in a right-hand sense with respect to the direction of propagation, and left circular polarization in which the
vector rotates in a left-hand sense. Circular polarization is a limiting case of the more general condition of elliptical
polarization.
5. Conversion to and from Linear Polarization
Circularly polarized light can be converted into linearly polarized light by passing through a quarter-wave plate.
Passing linearly polarized light through quarter-wave plate with axes at 45° to its polarization axis will convert it to
circular polarization. In fact, this is the most common way of producing circular polarization in practice.
6. Simulation Results
Return Loss
Figure 2: Return Loss of T-Slot Element

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Radiation Pattern
Figure 3: Radiation Pattern for Designed Transmitarray at10GHz
Radiation Pattern 3D
Figure 4: Radiation Pattern in 3D form of designed Transmitarray
3D Polar Plot
Figure 5: Polar Plot of Transmitarray Antenna

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7. Conclusion
A circularly polarized transmit array antenna using a novel low-profile dual-polarized unit cell, that consists of
three metallic layers with two thin dielectric slabs in between Cross strips are etched in cross slots on the top and
bottom layers and the T-slot element is etched on the middle layer. The unit cell has the good dual polarization
characteristic and it is compact, the unit cell element has complete symmetry, the polarization of transmit array is
specified and its total thickness is 1 mm (0.033λ0). A 341-element circularly polarized transmit array realizes the
3-dB AR bandwidth of 3.5% (9.8-10.15 GHz), and its 1-dB gain bandwidth is 4% (9.7-10.1 GHz). The aperture
efficiency is 36% at 10 GHz frequency.
References
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Design of Circularly Polarized Transmit array Antenna using Low-Profile Dual-Linearly Polarized Elements

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