Linear Tapered Slot Vivaldi Antenna with Corrugated Edges for UWB Application

Rahul SinghaDr. Vakula D Prof. Sarma NVSN

National Institute of Technology, National Institute of Technology, National Institute of Technology,

Warangal Warangal Warangal

Abstract - This paper presents a design of Vivaldi antenna by varying its structural parameters properly to balance radiation pattern, return loss performance by minimizing size. The Linear Tapered Slot Vivaldi Antenna has been modified by adding suitable size corrugations on its edges tocontrol the complex mutual coupling at high scan angles.

The Vivaldi antenna is constructed using substrate of relative permittivity 3.27 and height 0.3807mm. The antenna is designed at frequency of 12GHz with dimensions of 41.97mm× 72.92mm× 0.3807mm. The simulation result showed that the proposed antenna provides frequency band from 3.1 GHz to 20 GHz at return loss and HPBW varies around near 900. The antenna has a smaller size, with improved HPBW and it can meet the requirements of UWB system.

Keyword: Ultra-wideband (UWB), Half power beam width (HPBW),corrugations and return loss.

INTRODUCTION

In modern communication system, ultra-wideband antennas have to satisfy the various requirements, such as sending more information, transmitting and receiving quality of the information.There are many other kinds of ultra-wideband antennas available such as Bow tie, Helical, Spiral, Log-periodic, Horn and Biconical. Vivaldi antenna is selected because of its superior broad band characteristics, good impedance matching to the feed line, good energy efficiency and easy manufacturing process [3-4]. Vivaldi antenna is a kind of travelling wave and non-period antenna with UWB property, which can be made of microstrip so that it is widely used in many applications and as phased arrays [1].Vivaldi structure is proposed by Gibson in 1979 [2]. Vivaldi antenna maintains symmetrical E plane, and H plane patterns and the planar structure is also symmetrical. The UWB antenna must maintain not only wide impedance bandwidth but also wide instantaneous bandwidth.

For ultra-wideband signal, the US Federal Communications Commission (FCC) defined frequency band as 3.1 to 10.6 GHz over which maximum power is radiated.The performance of corrugated vivaldi antenna will play an important role for the UWB Communication system. Vivaldi Antennas with corrugated structures are being developed for radar and communication systems [5].

Maksimovitchet al, introduced corrugations in vivaldi antenna withincreased antenna bandwidth.The radiation characteristics have been improved by the use of a comb structureetched along the antenna edges combined with resistive films [6].

In the presentpaper,Vivaldi antenna is designed for reduced size and increase in impedance bandwidth.A linear tapered slot antenna is designed for a frequency band 3.1 to 20 GHz.

DESIGN OF TAPERED SLOT VIVALDI ANTENNA

(A) Tapered Slot Antenna Design

Tapered slot Vivaldi antenna is a kind of directional antenna.It’s basically a flared slot line, fabricated on a single metallization layer andsupportedby a substrate dielectric.The shape of the Vivaldi antenna used in the present paper has linear tapered slot which inﬂuences the frequency range of the antenna. The opening of the taper is for high frequency matching and wide end of taper is for lower frequency matching. The design of tapered slot Vivaldi antenna is a trade-off between the antenna size and its bandwidth.Slot line starts to radiate significantly under the condition of

(1)

Where, sw is width of the slot.

In practice, the antenna does not radiate from a single point for a given frequency, but from a small sectionalong the line of the flare.The taper profile is the combination of three linear lines, one linear region for high frequency and others are for low frequency. Linear tapered slot antennas (LTSAs) are the best compromise between beam width and side lobe level. If the number of linear lines increasesgradually the linear tapered slot becomes a exponential. At the same time, beam of the radiation pattern becomes narrow.

Different tapered slots types are exist. The most common types are linear tapered (LTSA), exponentially tapered (VTSA) and constant width (CWSA). The beam widths of CWSAs are typically the smallest, followed by LTSAs and then VTSAs. Most TSA elements produce symmetric radiation patterns in the E and H planes.

In the present paper, corrugation is introduced at the edge of the proposed antenna. By corrugating the edge of the proposed antenna it is possible to suppress surface current along the longitudinal directionand resonant frequencyis reduced. In the array the corrugationsreduce the coupling between two antennas [7].

Fig. 1(a) Structure of linearVivaldi antenna

(B) Feeding Circuit of Vivaldi Antenna

A simple line feeding port is used forvivaldi antenna and at the end of the feed a radial stub is used, which is helpful for impedance matching.The tapered slot Vivaldi antenna is excited via themicrostrip to slot line transition. The transition construction exploits wideband features of a microstrip radial stub used as a virtual wideband short.

The microstrip is virtually shunted to the second half of the slot line metallization while the first half serves as a ground metallization for the microstrip line. It is necessary to transform the impedance of the input feeding microstrip line (50Ω) to the input impedance (100Ω) of the transition [8-10].The tapered slot Vivaldi antenna with feeding circuits is shown in Fig. 1(b).

Fig. 1(b) Feed structure of proposed antenna

TABLEI

DIMENSION OF THE LINEAR VIVALDI ANTENNA

Width, W / 72.92mm
Length, L / 41.97mm
l1 / 3mm
l2 / 16mm
l3 / 27mm
Cavity diameter, r / 2.9mm
G / 1.5mm
W50 / 0.9021mm
W100 / 0.2668mm
Radius of the microstrip stub, Rstub / 3.5mm

RESULTS AND ANALYSIS

Linear Tapered Slot Vivaldi antenna designed in the present paper is shown in Fig. 1. The parameters of the Vivaldi antenna are given in TableI.It has 0.017 mm thickness copper fins on the both sides of a “Roger TTM3”. The total length is 72.92mmby assuming a lower cut-off frequency at 3GHz. The width is 41.97mm which is sufficiently wide to reduce the reflection. The Tapered slot Vivaldi antenna designed with substrates of “Roger TMM3” (=3.27, ℎ=0.3807 mm, tan(δ) = 0) is simulated with HFSS 15.

Simulated results in Fig. 2 shows that this tapered slot Vivaldi antenna presents good UWB characteristics in terms of impedance bandwidth. Return loss is below -10 dB between 3.1 GHz and 20GHz.

VSWR represents of the antenna’s fitness; therefore, it is important that the VSWR be below 2 across the entire UWB spectrum (3.1–20 GHz).The simulated result presented in Fig 3 clearly shows that the VSWR curve for this antenna is less than 2 over the frequency range of 3.1GHz – 20 GHz.

Fig.2: Return loss of the linear Vivaldi Antenna (in dB).

Fig. 3. Simulated VSWR of Vivaldi Antenna.

Fig. 4 shows the value of real and imaginary impedance between 3.1 to 20GHz for the Vivaldi antenna. The figure shows a good matching of the antennas to the feed line and proposed antenna havethe values of impedance real part near 50 ohm and value of imaginary part near zero ohm.

Figure 4: Impedance plot for the Vivaldi antenna

The E-plane and H-plane radiation patterns for the frequencies of 10 and 12 GHz are shown in Fig.5. The x-y plane is the E-plane while the x-z plane is the H-plane. The HPBW is almost in between 900 to 1000at 10 GHz, 12 GHz.The designed antennas can be used in the entire UWB frequency band with a fractional bandwidth of 146% from 3.1 up to 20 GHz. It exhibits a voltage standing wave of less than 2.0 in a frequency range from 3.1 to 20 GHz.

Fig. 5(a) Radiation Pattern at 12 GHz (phi=00)

Fig. 5(b) E-field at 12 GHz (phi=00 and phi=900)

Fig. 5(c)Radiation Pattern at 10 GHz (phi=00)

Fig. 5(d) E-field at 10 GHz (phi=00 and phi=900)

CONCLUSION

In this paper, the effect of the antenna using corrugated structureon the tapered-slot antenna characteristics has been studied. And also reduced size is designed which has good impedance bandwidth of a Linear tapered slot antenna. The sidelobes of the radiation pattern are also improved. Theantenna has good beam widthfor array scanning and improved return loss.The proposed antenna can be easily integrated with a planar circuit.

REFERENCES

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