TECS-18143 Camera Ready.pdf

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Transactions on Engineering and Computing Sciences - Vol. 13, No. 1

Publication Date: February 25, 2025

DOI:10.14738/tecs.131.18143.

Lekshmi, B. S. K., & Raglend, I. J. (2025). Design of Compact Vivaldi Antenna Arrays for AESA Radar System. Transactions on

Engineering and Computing Sciences, 13(1). 28-43.

Services for Science and Education – United Kingdom

Design of Compact Vivaldi Antenna Arrays for AESA Radar System

Babu Saraswathi K. Lekshmi

Department of Electrical and Electronics Engineering,

Noorul Islam University, India

I. Jacob Raglend

Department of Electrical and Electronics Engineering,

Noorul Islam University, India

ABSTRACT

This paper demonstrates a low-profile, wide band, miniaturized, Stripline fed

double layered exponentially tapered slot antenna with a wide-scan capability and

10% bandwidth at the X-band frequency has been designed, fabricated, and tested.

The antenna is optimized with a total size equal to 14.2x24.1x1.4 mm3 and is

capable of achieving the desired bandwidth experimentally. The 9-element array

and feeding network based on 1:9 T-junction power divider was employed to

compose the linear array. The array elements are operating with return loss lower

than 10 dB at X-band frequency. Measured results of single elements in isolated and

array environment are achieved, both have a wide 3-dB beam width better than

107o in the E- and H- planes, which is capable of a linear array with wide scan angle

±55o. The linear array has a half power beamwidth of 11 degrees with side-lobe

level of -12dB at 10GHz with a gain of 12dBi. These features make the antenna array

fit for X-band airborne radar applications.

Keywords: Dual layered Exponentially tapered slot antenna, slotline, X-band, wide beam,

Radar, Return loss, AESA antenna, Stripline.

INTRODUCTION

Lewis et al. introduced tapered slot antenna (TSA) in 1974 [1]. It is a key candidate for wide- scan arrays operating at a wide band frequency. Vivaldi antenna is a category of TSA used in an

Ultra wide band (UWB) technology. It was first designed by Gibson [2] in 1979, has an

exponentially tapered slot line. Vivaldi arrays are small in size, simple and weightless, easy to

fabricate, enable compact arrays and they are highly efficient for wideband phased array

antennas [3-5].

Phased arrays are essential to function over wide scan angle and wide bandwidths to offer

multiple operations, which is proficient of simultaneous and time interleaving, electronic

warfare and communication functions [6-10]. In response to that need, a design of TSA for

airborne radar applications has been offered in this paper. The TSA with Strip line feed

network, which is capable of operating in 8GHz to 12GHz frequency and scan angle above ±60o

in H- and E-planes. The present work concentrates on the design of the slot taper to increase

power transformation and decrease reflection. The exponential tapers have been designed

using a close form equation [8]. The three parameters decide the performance of the

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Lekshmi, B. S. K., & Raglend, I. J. (2025). Design of Compact Vivaldi Antenna Arrays for AESA Radar System. Transactions on Engineering and

Computing Sciences, 13(1). 28-43.

URL: http://dx.doi.org/10.14738/tecs.131.18143

exponential tapered slot antenna, viz. i) Opening of the slot which decides the operating

frequency, ii) smoothness of the exponentially TSA, which reduces the phase error across the

frequency and iii) balun limits the antenna bandwidth. The whole design of the antenna has

been repeated using an electromagnetic simulator, High Frequency Structure Simulator (HFSS)

[11].

Several studies about the phased array antenna for wide-scan and wideband applications have

been recently proposed [12-15]. The Bengt et al. [12] developed a slotted waveguideantenna

with achieving scan area less than ±40° in X-band. Chen and Wang [13] designed an array and

feeding network, but the measured outcomes were not revealed in their work to confirm the

performance of the array. When designing an array antenna, complications related to the

incorporation of antenna element and feeding network such as the mutual coupling effect

between elements need to be enunciated.

In this paper, a nine-element linear X-band antenna array has been designed and the radiation

characteristics of the array are studied numerically and tested experimentally. A number of

intermediate steps were done, to reach the design of the X-band array and summarized in this

paper as given below. In Section 2, the design of exponential tapered slot antenna has been

explained. This antenna element is used to constitute the X-band antenna array. The design of

the array with uniform distribution is presented to analyze the element in an array

environment, which is described in Section 3. In Section 4, the design of T-junction power

divider which is used for feeding the 9-element linear array has been explained. Measured

results are offered in Section 4 and the conclusions are condensed in Section 5.

TAPERED SLOT ANTENNA DESIGN

Parametric Study

Tapered Slot Antenna or Vivaldi antenna is fed with Strip line-feed which comprises of a Strip

line-to-slot line transition, a Strip line stub, a slot line cavity and a tapered slot. The design

parameters of a tapered slot antenna with square cavity and radial stub strip line feed are given

in Figure 1. The Specifications of each parameters of Tapered slot antenna are given in Table 1.

Table 1: Design Specifications of double layered TSA

Parameters Specifications

(in mm)

Strip line width (WST) 0.5

Angle of radial strip line stub (AR) 130o

Antenna width (b) 14.2

Antenna length (d) 24.1

Length of slot line cavity from ground plane (LG) 8.9

Aperture height (H) 8.5

Taper Length (L) 10.6

Opening Rate (R) 0.36

Slot width (WSL) 0.2

square slot line cavity (DSL) 2.6x2.6

Radius of radial strip line stub (Rr) 2.02

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Transactions on Engineering and Computing Sciences (TECS) Vol 13, Issue 1, January - 2025

Services for Science and Education – United Kingdom

Distance from the transition to the taper (LTA) 1

Distance from the transition to the slot line cavity (LTC) 1

Figure 1: Definition of parameters of Tapered slot antenna.

The RTDuroid 5880 dielectric substrate is used for this design with relative permittivity εr = 2.2

and thickness t = 0.7 mm. The strip line/slot line transition is indicated by WST (strip line width)

and WSL (slot line width). The exponential taper shape is defined by the opening rate R and two

end points P1 (z1, y1) and P2 (z2, y2)

y = c1e

Rz +c2 ------------------- (1) [3]

Where,

c1 =

c2 =

The length of exponential taper (L) is z2-z1 and the height of aperture (H) is 2(y2-y1)+WSL. For

linearly tapered slot antenna (LTSA), the opening rate R is zero and taper slope is constant,

which is given by so= (y2-y1)/(z2-z1).

LTC

LTA AR

WST

WSL

DSL