**3.1 Vivaldi antenna design**

The design guidelines for a Vivaldi antenna are the following:

*Characterization of Printed Podal Vivaldi Antenna (8–18 GHz) on RT Duroid with Single… DOI: http://dx.doi.org/10.5772/intechopen.88727*


The separation between the conductors is smaller than one-half free space wavelength (λ0/2) [5] and the waves travelling down the curved path along the antenna are tightly bound to the conductors in the propagating section. The energy gets radiated into the air in the radiating section where the slot width is increasing beyond the one-half wavelength. Radiation from high-dielectric substrates is very low and hence for antenna applications significantly low dielectric constant materials are chosen.

Apart from these, the design parameters are as follows:

1. antenna length;

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printed circuit easily.

structures.

Vivaldi antenna.

polarization.

slot antenna, Vivaldi antenna.

**3. Principle of operation**

section and radiating section.

**3.1 Vivaldi antenna design**

**2. Vivaldi antenna**

ate gain.

dimensions are governed by wavelength of operating frequency, antenna miniaturization is a challenging and difficult task. Planar/printed antennas offer good solutions for the above class of problem. Vivaldi antennas are preferable in many applications due to high gain, simple structure and easy fabrication. They are mostly used in ultra-wideband and broadband applications. Printed antennas are being increasingly used as they are low profile and can be integrated on any

Most of the wireless communication systems suffer from co-channel interference and multipath effects. The co channel interference and multipath effects are addressed by using horn antennas that are placed in LOS, but these antennas are too bulky to be integrated with the rest of the wireless systems and suffer high cost of fabrication. For military and commercial applications wideband width antennas with high gain are preferred and Vivaldi antenna or planar tapered slot antenna (TSA) are better choice. As these antennas are support for multifunction communication applications because of their consistent impedance matching over a very broad operating frequency range, stable directional patterns, low profile and planar

The Vivaldi and TSA's offer broadband operation, with low sidelobes but moder-

**Problem definition:** The objective is to design the single cavity and double cavity Vivaldi antenna operating from 8 to 18 GHz frequency to achieve VSWR less than 3:1 and comparison of antenna performance for single cavity and double cavity

A Vivaldi antenna gives significant advantages of efficiency, high gain, wide bandwidth and simple geometry. The Vivaldi antenna, having an exponentially tapered slot profile, is a type of tapered slot antenna (TSA). Lewis et al. [1] introduced tapered slot antenna as a broadband strip line array element capable of multi octave bandwidths in his study in 1974. Vivaldi antenna, is an exponentially tapered slot antenna, was originated by Gibson [2]. These antennas operate in the frequency range from below 2 to above 40 GHz and offer significant gain and linear

Yngvesson et al. [3] compared three different TSAs, linearly tapered slot antenna (LTSA), constant width slot antenna (CWSA) and Gibson's exponentially tapered

Gazit [4] proposed two important changes to the traditional Vivaldi design. The use of a low dielectric substrate (cu clad, ε = 2.45) instead of alumina and an antipodal slot line transition. This type of transition offers relatively wider bandwidth but,

The Vivaldi antenna belongs to travelling wave antennas. The principle of operation of the surface wave antennas can be divided into two sections: propagating

antipodal slot line transition has high cross polarization problem.

The design guidelines for a Vivaldi antenna are the following:

**134**


Depending on the dimensions of the transmission line the characteristic impedance is calculated and the vivaldi antenna is printed on both sides of the substrate with a dielectric constant, εr = 2.2 and thickness of the substrate is h = 0.508 mm. The length and width of the antenna are optimized.

## **3.2 Construction**

From **Figure 1**, the parameters of Vivaldi antenna are described as:

**Figure 1.** *Vivaldi antenna.*


The antenna consists of a tapered slot etched onto a thin film of metal. This can do either with or without a dielectric substrate on one side of the film. The tapered slot antennas work over a large frequency bandwidth and produce a symmetrical end-fire beam with appreciable gain and low side lobes. An important step in the design of the antenna is to find suitable feeding techniques for the Vivaldi.

The taper length should be on the order of one wavelength in the lowest working frequency. Besides, the taper length is also dependent on the cavity diameter and antenna length. An increase in the taper length improves the bandwidth.

The taper rate can be defined by an exponential.

$$\mathcal{Y} \quad = \; \pm A e^{R\mathbf{x}} \tag{1}$$

**137**

antenna.

**Figure 2.**

except some parameters are stub start angle = 90° stub angle = 80° taper length = 6.86455 cavity diameter = 1.582

*feeding arrangement of single cavity Vivaldi antenna.*

*Characterization of Printed Podal Vivaldi Antenna (8–18 GHz) on RT Duroid with Single…*

the stub angles of tapered strip line feed also change. The length and width of double cavity Vivaldi antenna are 37.5 and 15 mm respectively. **Figure 3(a)–(c)** shows the front view, back view and feeding arrangement of double cavity Vivaldi

*(a) Front view of single cavity Vivaldi antenna; (b) back view of single cavity Vivaldi antenna; and (c)* 

Parameter values for single cavity antenna is same as double cavity parameter list

The VSWR-frequency plot for the Vivaldi antenna without SMA connector seems to have a high VSWR, which means the reflection of power is more and also

the reflected wave amplitude is high from frequency 8 to 18 GHz.

*DOI: http://dx.doi.org/10.5772/intechopen.88727*

where *A* = *Sw*/2, (*R*=)ln ( \_ *a* \_ *Sw*) La and *a* is the antenna aperture at *La*, *Sw* is the slot width at the antenna origin and *R* is the taper rate.

## **3.3 Bandwidth consideration**

To achieve a wider bandwidth, the following aspects need to be considered:


The length and width of the single cavity Vivaldi antenna are 38.5 and 15 mm respectively. **Figure 2(a)** and **(b)** shows the front and back view of simulated design of single cavity Vivaldi antenna which is excited using strip line [6] shown in **Figure 2(c)**.

The double cavity Vivaldi antenna is compared with this single cavity Vivaldi antenna. The size of single cavity antenna is more than the double cavity antenna, *Characterization of Printed Podal Vivaldi Antenna (8–18 GHz) on RT Duroid with Single… DOI: http://dx.doi.org/10.5772/intechopen.88727*

#### **Figure 2.**

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• WSL—width of slot line;

• WST—width of strip line;

• L—length of the taper;

• H—height of the taper;

• R—exponential factor; and

• d—height of the conductor.

where *A* = *Sw*/2, (*R*=)ln

**3.3 Bandwidth consideration**

feeding the antenna;

antenna; and

Vivaldi.

The antenna consists of a tapered slot etched onto a thin film of metal. This can do either with or without a dielectric substrate on one side of the film. The tapered slot antennas work over a large frequency bandwidth and produce a symmetrical end-fire beam with appreciable gain and low side lobes. An important step in the design of the antenna is to find suitable feeding techniques for the

The taper length should be on the order of one wavelength in the lowest working frequency. Besides, the taper length is also dependent on the cavity diameter and

*y* = ± *AeRx* (1)

To achieve a wider bandwidth, the following aspects need to be considered:

• the transition from the main input transmission line to the slot line is done for

• it is designed for a low reflection coefficient to match the potential of the

• the dimensions and shape of the antenna, to obtain the required beam width,

The length and width of the single cavity Vivaldi antenna are 38.5 and 15 mm respectively. **Figure 2(a)** and **(b)** shows the front and back view of simulated design of single cavity Vivaldi antenna which is excited using strip line [6] shown in

The double cavity Vivaldi antenna is compared with this single cavity Vivaldi antenna. The size of single cavity antenna is more than the double cavity antenna,

side lobes and back lobes, over the operating range of frequencies.

La and *a* is the antenna aperture at *La*, *Sw* is the slot width

antenna length. An increase in the taper length improves the bandwidth.

The taper rate can be defined by an exponential.

( \_ *a* \_ *Sw*)

at the antenna origin and *R* is the taper rate.

• RST—radius of strip line stub;

• DSL—diameter of slot line cavity;

**136**

**Figure 2(c)**.

*(a) Front view of single cavity Vivaldi antenna; (b) back view of single cavity Vivaldi antenna; and (c) feeding arrangement of single cavity Vivaldi antenna.*

the stub angles of tapered strip line feed also change. The length and width of double cavity Vivaldi antenna are 37.5 and 15 mm respectively. **Figure 3(a)–(c)** shows the front view, back view and feeding arrangement of double cavity Vivaldi antenna.

Parameter values for single cavity antenna is same as double cavity parameter list except some parameters are

stub start angle = 90° stub angle = 80° taper length = 6.86455 cavity diameter = 1.582

The VSWR-frequency plot for the Vivaldi antenna without SMA connector seems to have a high VSWR, which means the reflection of power is more and also the reflected wave amplitude is high from frequency 8 to 18 GHz.

### **Figure 3.**

*(a) Front view of double cavity Vivaldi antenna; (b) back view of double cavity Vivaldi antenna; and (c) feeding arrangement of double cavity Vivaldi antenna.*

To lower the VSWR, a connector is attached to the antenna for the required band of frequencies. **Figure 4(a)** and **(b)** shows the simulated single cavity Vivaldi antenna and double cavity Vivaldi antenna with SMA connector in CST software respectively. The designed SMA connector in CST software is shown in **Figure 5**.
