Design of Microstrip Antenna with Greater Bandwidth at Frequencies

of GHz and THz

HUMBERTO CESAR CHAVES FERNANDES, TARCISIO DA SILVA BARRETO AND OTÁVIO

PAULINO LAVOR

Department of Electrical Engineering

Federal University of Rio Grande do Norte - UFRN

University Campus Lagoa Nova

BRAZIL

humbeccf@ct.ufrn.br, tarcisiofip2@gmail.com, otavioplavor@gmail.com

Abstract: - This paper presents a microstrip antenna with circular patch that operates at a frequency of

1 THz, with a circular opening in the ground plane, resulting in an increase in bandwidth. At GHz

frequencies, the circular opening in the ground plane is performed to obtain a wide pass band. Its

prototype is built and measurements are compared with simulated data. Results of loss by insertion

and radiation patterns in plans E and H are presented.

Key-Words: - Circular patch, THz, Bandwidth.

1 Introduction The structure of a conventional microstrip antenna

comprises a radiating metal patch, embedded in a

grounded dielectric substrate. As an improvement in

the switches of the microstrip antenna, various

modifications are found in the literature.

Recent strategies for increase bandwidth include

variations in ground plane size and the shape of the

connection between the feed line and the patch [1-

3], as well as the use of PBG structures (Photonic

Band Gap). The increase in bandwidth resulting

from these factors is subject to decrease the antenna

merit factor by decreasing the dielectric constant

[4].

In case these PBG structures, the dielectric

constant decreases significantly, causing a large

shift in frequency for a higher value. Thus, a change

in the ground plane becomes interesting, since it has

a simpler construction and causes a less

displacement of the frequency. At low frequencies,

the modified ground plane with curved branches

was used to improve bandwidth [5] and the

truncated plane was used in design of UWB antenna

(Ultra Wide Band) [6, 7]. The CSRR

(Complementary Split Ring Resonator) was also

used in the ground plane in antennas for UWB

applications [8]. Other modifications had been made

in the radiating element as in [9-11].

At high frequencies, microstrip antennas have

been well reported. By example, in [12], it is

presented a new supply technique using a

waveguide transformer. Other studies are described

in [13-15].

In this paper, it proposes a microstrip antenna

with circular patch designed for the frequency of 1

THz. A circular opening is made in the ground plane

in order to obtain better results for the bandwidth,

when compared to a standard antenna, namely,

without change. The analysis is also performed at

low frequencies, so that the prototype is applicable

to UWB (Ultra Wide Band) communication system

which occupies the frequency range from 3.1 to 10.6

GHz and another shows a change in bandwidth in

center frequency of 2.5 GHz.

2 Design of the Antenna In frequency of THz, for standard antenna, it

proposes a microstrip antenna with circular patch of

radius r = 24.6 µm, fed by a microstrip line of length

b= 21.9 µm and width w = 2.26 µm. The substrate is

silicon with relative permittivity (εr) of 11.9 and a

thickness of 5 µm. The material used for patch,

power line and ground plane is gold. A modification

is made making a circular opening of radius R in the

center of the ground plane. Figure 1 shows the

geometry of the antenna.

Mathematical and Computational Methods in Electrical Engineering

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Fig. 1. Geometry of the antenna. a) patch, b) ground plane.

In the case of antenna that operates at

frequencies of GHz, it is designed a antenna for the

frequency of 6.5 GHz and other for the frequency of

2.5 GHz. For the frequency of 6.5 GHz, the used

substrate is fiberglass (FR4) with relative

permittivity (εr) 4.4 and thickness 1.58mm. The

dimensions are r = 6 mm, b = 4 mm, w = 3 mm and

R = 11 mm. The material used for patch, power line

and ground plane is copper.

3 Results

Simulations were carried to obtain return loss versus

frequency, well as bandwidth. Three different values

of R are considered and S11 as function of frequency

can be seen in figure 2.

Fig. 2. Simulated S11 for standard antenna and with circular

opening at THz.

Here it can be seen that with the increase of R, there

is a frequency offset to the left, however, it also an

increase in bandwidth. While the standard antenna

has a bandwidth 67.5 GHz, antennas with circular

openings has a bandwidth of 90.5 GHz, 115.5 GHz

and 145.7 GHz for R = 10 µm, 15 µm and 20 µm,

respectively. For any value of R, a better impedance

matching is realized.

Figures 3 to 6 show the radiation patterns for these

antennas, where the angle ϕ is between 0° and 360°.

Fig. 3. Radiation pattern of the standard antenna at THz.

Fig. 4. Radiation pattern of the antenna with circular opening.

R=10µm.

Fig. 5. Radiation pattern of the antenna with circular opening. R=15µm.

Fig. 6. Radiation pattern of the antenna with circular opening.

R=10µm.

Mathematical and Computational Methods in Electrical Engineering

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In the following, experimental results of this

analysis are shown in frequencies of GHz. For the

frequency of 6.5 GHz, the picture of the antenna is

shown in Figure 7.

Fig. 7. Picture of the designed antena for 6.5 GHz.

Figure 8 shows the results for S11 versus

frequency comparing the simulated results with the

measured. In this model were obtained three

operating bands, one ranging from 2.5 to 2.9 GHz,

or 15% bandwidth with a center frequency of 2.7

GHz, another ranging from 3.7 to 7.5 GHz which

corresponds to 68% of bandwidth to the center

frequency of 5.6 GHz and another ranging from 8.8

to 10.9 GHz corresponding to 21% of the bandwidth

to the center frequency of 9.85 GHz.

Fig. 8. Measured and simulated values of S11.

For this configuration, the model constructed has

frequencies in the range of UWB, which qualifies

for applications in UWB communication systems.

Figure 10 shows the radiation pattern for this

antenna, where the angle ϕ is between 0° and 360°.

Fig. 9. Radiation pattern of the antenna with circular opening on the

ground plane.

For designed antenna for 2.5 GHz, the results are

presented below. Figure 10 shows the values of

return loss as a function of operating frequency for

the antenna pattern and proposed.

Fig. 10. Values of return loss as a function of operating frequency for

the standard and proposed antenna for 2.5 GHz.

One can observe a change in the return loss of

the antenna when using the proposed structure.

Through values it is possible to observe an

improvement in bandwidth for the proposed

configuration. The standard antenna has a return

loss of -22.41 dB and a bandwidth of 27 MHz, while

the proposed antenna has a return loss of -35.25 dB

and a bandwidth of 282 MHz.

Figures 11 and 12 show the radiation pattern of

the standard and proposed antenna for 2.5 GHz,

respectively.

Mathematical and Computational Methods in Electrical Engineering

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Fig. 11. Radiation pattern of the standard antenna.

Fig. 12. Radiation pattern of the proposed antenna.

The proposed antenna was built, since its large

increase in bandwidth. The images can be seen in

figure 13.

Fig. 13. Picture of the designed antena for 2.5 GHz.

Figure 14 shows the measured and simulated

data for the fabricated antenna where is possible

make a comparison between measured and

simulated data.

Fig. 14. Measured and simulated data of return loss for the proposed

antenna.

The graph shows a comparison of return loss for

the measured and simulated data in a range of 1 at

4.5 GHz. It is possible to see an approximation of

the measured data in relation to the simulated.

Another parameter measured is the input impedance

and can be seen in Figure 15.

Fig. 15. Input impedance of the proposed antenna.

In the resonant frequency of 2.7 GHz, the

measurement of input impedance is 49.7 – 0.6j Ω,

being a value very close to 50 Ω.

4 Conclusion A microstrip antenna with circular opening in the

ground plane was proposed and designed for

frequency of 1 THz, give a better bandwidth. The

same analysis was performed at frequencies of 6.5

and 2.5 GHz. Antenna were fabricated and

Mathematical and Computational Methods in Electrical Engineering

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measurements were performed, obtaining good

results. An antenna shown to be applicable to UWB

telecommunication system and the other had a

change in the bandwidth of 27 to 282 MHz in center

frequency of 2.5 GHz. New results of loss by

insertion and radiation patterns in the E and H

planes were presenteds.

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Mathematical and Computational Methods in Electrical Engineering

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