Bandwidth Enhancement Using Annular Ring Microstrip Antenna With Slits

Bandwidth Enhancement Using Annular Ring Microstrip Antenna With Slits

Mr. Rahul B. Khadase. EXTC Department PIIT, New Panvel

Mr. Pragnesh N. Shah . EXTC Department PIIT, New Panvel

ABSTRACT

Microstrip Antenna (MSAs) consist of a metallic radiating patch on one side of thin dielectric substrate and other side is ground plane. Most important advantageous of MSAs are low profile, light weight and can be made conformal with host surface. So microstrip antennas are widely used as efficient radiators in many communication systems. One of the most interesting applications is their use in linear polarization. Linear Polarized radiation is obtained with single feed.

The size of the regularly shaped microstrip antenna operating in the ultra high frequency band is quite large. To design a smaller antenna at these frequencies with large bandwidth, the conventional microstrip antenna configurations, such as Annular Ring and circular configurations, need to be modified.

Here, An Annular Ring Microstrip Antenna with slits has been successfully fabricated and tested. This Annular Ring Microstrip Antenna with slits operates in 2.60 – 2.72 GHz frequency band for VSWR 2. This band is used for Indian Satellite (INSAT) Communication System. The impedance bandwidth is 116.5 MHz or about 4.38% is achieved. Gain of Antenna becomes 9.15 dBi. The Antenna and Radiation Efficiency are 90.68% and 97.46% respectively.

INTRODUCTION

1. Microstrip Antenna (MSA) Configuration

   A microstrip antenna in its simplest form consists of a radiating patch on one side of the dielectric substrate (r 10), which has a ground plane on the other side.

   Radiation from the microstip antenna can occur from the fringing fields between the periphery of the patch and the ground plane. The length L of the rectangular patch for the fundamental TM10 mode excitation is slightly smaller than /2, where is the wavelength in the dielectric medium, which in terms of free-space wavelength 0 is given as 0/l, where l is the effective dielectric constant of a microstrip line of the width W. The value of l is slightly less than the dielectric constant of r the substrate because of the fringing fields from the patch to the ground plane are not confined in the dielectric only, but are also spread in the air. To enhance the fringing fields from the patch, which account for the radiation, the width W of the patch is increased. The fringing fields are also enhanced by decreasing the r or by increasing the substrate thickness h. Therefore, unlike the microwave integrated circuit (MIC) applications, MSA uses microstrip patches with lower dielectric constant (r 2.5) and thicker h.

   ANNULAR RING MICROSTRIP ANTENNA

   Annular Ring

   An annular ring MSA (ARMSA) is shown in Figure 1.1.

   Figure 1.1 an Annular Ring MSA

   The outer and inner radii are a and b respectively. The ARMSA can be considered as a removal of a smaller inner concentric circle from the outer circle. The resonance frequency of the ARMSA is always smaller than that of the CMSA because of its larger resonant length. The resonance frequency of the ARMSA is given by:

   and gain but its area is also smaller. The most compact antenna among all these configurations is the HETMSA, but it has the least BW. However, gain is only slightly less than the other configurations. As a result, if BW and gain are the main requirements, RMSA or CMSA should be used. However, if compact size is required, then SCMSA or HETMSA should be

   = 2

   used.

2. Modified Annular Ring:-

Where c is the velocity of light and X nm represents the roots of the equation

Jn (CX nm) Yn (X nm) Jn (X nm) Yn (CX nm) = 0

Jn (x) and Yn (x) are the Bessel functions of the first and second kind, and C = a /b.

1.1-Comparison of Various Configurations for Broad B Table 1.2 gives a comparison of various regularly shaped probe-fed MSA configurations, such as rectangular, circular, semicircular, equilateral triangular, 30-60-90 triangular and annular ring.

Table 1.1- Comparison of Various Regularly Shaped Broadband MSAs ( er = 1, h = 0.5 cm, and d = 0.12 cm)

The substrate with er = 1 and h = 0.5 cm is taken to realize broad BW for all theses configurations. The patch dimensions are chosen in such a way that the resonance frequency of all these antennas operating in their fundamental mode is around

2.6 GHz. The RMSA and CMSA have the largest BW, but RMSA has larger gain and area. The ARMSA has a smaller area and BW than the CMSA, but the gain is comparable. An SCMSA has half the area of the CMSA and has a smaller BW, but its gain is only slightly less. An ETMSA has a smaller BW

Several variations of CMSAs are possible to realize a compact CP antenna. Two variations are shown in Figure 1.2. A CMSA with tuning stub along its periphery and cross-slots of equal lengths at its center is shown in Figure 1.2(a). With an increase in the slot length, the resonance frequency decreases and the tuning stub controls the excitation of the orthogonal modes. A quarter-wave transformer is used to obtain impedance matching with a 50-V microstrip line feed. Instead of rectangular cross-slots, four curved slots are cut along the periphery of the circular patch as shown in Figure 1.2(b). The orthogonal modes are excited by cutting another slot perpendicular to one of the curved slots. However, these compact CP configurations yield lesser AR BW and gain due to the smaller aperture area.

Several variations of circular ring MSAs are possible for generating CP, including an annular ring with an offset polarizer and a pair of narrow slits in the outer or inner circle of the annular ring, as shown in Figure 1.2(ce). In general, either the outer circle or the inner circle should produce two orthogonal modes, which are excited equally, and in-phase quadrature by properly locating the feed.

Figure 1.2 Compact CMSA with (a) cross slot with tuning

stub and (b) curved slot with tuning stub. Annular ring MSA with (c) an internal offset polarizer and slits in the

(d) outer and (e) inner circle.

2. RESULTS AND DISCUSSION

Fig.2.1 shows the geometry of Annular Ring MSA with Slits (width=3.5mm, depth=5mm). The Annular Ring MSA has a outer ring radius of a= 28mm and inner ring radius of b = 10mm .The dielectric used for the patch is (r) = 1 and the thickness of substrate h =5mm. he co-axial probe is fed of the patch at (x= 11, Y= 0). The radius of the feed conductor of co-axial probe is 0.6mm. The center frequency of this Annular Ring MSA is 2.655GHz

Fig. 2.1 Geometry Annular Ring MSA with Two Slits

Fig. 2.2 Geometry Annular Ring MSA with Four Slits

2.2.1Parametric study of Annular Ring MSA with Two Slits

1. Effect of Dielectic constant :

   Table No.2.1: Effect of Dielectric constant on BW, Gain, Efficiency and resonance frequency. Inner ring radius b = 10mm and outer ring radius a =28mm, thickness of the substrate h = 5mm, slits width =3.5mm, slits depth=5mm, Probe position= (X=11, Y=0 ), radius=0.6 mm.

   Table 2.1: Effect of Dielectric constant

   (Diel ectri c Cons tant) r	Low er Freq. GHz	Upper Freq GHZ	cente r Freq foG Hz	Band widt h MHz	Gain dBi	Antenn a Efficie ncy at fo	Radiati on Efficien cy at fo
   1.0	2.60 63	2.7228	2.65 66	116. 5	9.1577	90.687 7	97.4666
   1.1	2.51 81	2.6063	2.55 59	88.2	8.5172	82.293 7	94.7328
   1.2	2.44 25	2.4960	2.47 40	53.5	7.8112	74.071 5	92.0098

   • Comment :

     With increase in dielectric constant (r)

     1. Gain, Bandwidth, Antenna and Radiation efficiency decreases.

     2. Center, Upper and Lower frequency shift to lower side

2. Effect of Thickness:

   Table No.2.2: Effect of Thickness on BW, Gain, Efficiency and resonance frequency, inner ring radius b = 10mm and outer ring radius a =28mm., r =1slits width =3.5mm, slits depth=5mm, Probe position=(X=11, Y=0), Probe Radius=0.6mm.

   Table 2.2: Effect of Thickness

   Comment : -With increase in Thickness

   1. Bandwidth, Antenna efficiency and Radiation efficiency increases

   2. Lower frequency shift to lower side.

   3. Higher frequency shift to upper side.

3. Effect of Probe Radius :

   Table No.2.3: Effect of Probe Radius on BW, Gain, Efficiency and resonance frequency, inner ring radius b = 10mm and outer ring radius a =28mm. thickness of the substrate h

   = 5mm r =1 slits width =3.5mm, slits depth=5mm, Probe position=(X=11, Y=0), r = 1

   Table 2.3: Effect of Probe Radius

   Prob e Radi us	Low er Freq. GHz	Upper Freq GHZ	center Freq GHz	Band width MHz	Gain dBi	Antenna Efficiency at fo	Radiation Efficiency at fo
   0.4	2.57 79	2.7228	2.656 6	144.9	9.339 1	95.1224	97.5068
   0.5	2.58 42	2.7291	2.653 5	144.9	9.268 3	93.5300	97.5248
   0.6	2.60 63	2.7228	2.656 6	116.5	9.157 7	90.6877	97.4666
   0.7	2.61 89	2.7165	2.656 6	97.6	9.078 5	89.0259	97.4704
   0.8	2.64 40	2.7007	2.672 4	56.7	8.883 5	85.9957	97.4230

   • Comment :

     With increase in Probe Radius

     1. Gain, Bandwidth and antenna efficiency decreases.

     2. Lower frequency shift to upper side.

4. Effect of Inner Ring Radius :

   Table No.2.4: Effect of Inner Ring radius on BW, Gain, Efficiency and resonance frequency, outer ring radius a

   =28mm. Thickness of the substrate h = 5mm r =1 slits width

   =3mm, slits depth=5mm, Probe position=(X=11, Y=0), Probe Radius=0.6mm

   Table 2.4: Effect of Inner Ring Radius

   Table No.2.5: Effect of Outer Ring radius on BW, Gain, Efficiency and resonance frequency, inner ring radius a

   =10mm. Thickness of the substrate h = 5mm r =1 slits width

   =3.5mm, slits depth=5mm, Probe position=(X=11, Y=0), Probe Radius=0.6mm.

   Table 2.5: Effect of Outer Ring Radius

   Outer Ring Radi us (b)	Lowe r Freq. GHz	Uppe r Freq GHZ	Cente r Freq GHz	Band widt h MHz	Gain dBi	Antenna Efficien cy at fo	Radiatio n Efficien cy at fo
   26	2.804	2.908	2.858	103.	8.8868	86.8609	97.3710
   	7	6	2	9
   27	2.703	2.811	2.757	107.	8.7194	83.5586	97.3920 /td>
   	9	0	4	1
   28	2.606	2.722	2.656	116.	9.1577	90.6877	97.4666
   	3	8	6	5
   29	2.521	2.637	2.574	116.	9.0814	89.1696	97.4527
   	2	8	8	6
   30	2.442	2.562	2.496	119.	9.0642	88.6031	97.4596
   	5	2	0	7

   • Comment :

   With increase in Outer Ring Radius (a) (a)Bandwidth increases

   (b)Center Frequency shift to Lower side

   5.1.4 Results of Annular Ring with Two Slits

   10

   Simulated result

   8 Measured result

   vswr

   vswr

   6

   4

   2

   0

   1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2

   Frequency (GHz)

   Inner Ring Radiu s (b)	Lower Freq. GHz	Upper Freq GHZ	Center Freq GHz	Band widt h MHz	Gain dBi	Antenna Efficienc y at fo	Radiation Efficiency at fo
   9.0	2.6189	2.7669	2.6944	48.0	9.01 77	88.7815	97.5621
   9.5	2.6126	2.7448	2.6755	132. 2	9.07 88	89.6865	97.5192
   10.0	2.6063	2.7228	2.6566	116. 5	9.15 77	90.6877	97.4666
   10.5	2.6031	2.6913	2.6378	88.2	8.96 94	87.2560	97.3823
   11.0	2.6012	2.6615	2.6158	87.4	8.72 13	87.6425	97.2516

   Inner Ring Radiu s (b)	Lower Freq. GHz	Upper Freq GHZ	Center Freq GHz	Band widt h MHz	Gain dBi	Antenna Efficienc y at fo	Radiation Efficiency at fo
   9.0	2.6189	2.7669	2.6944	48.0	9.01 77	88.7815	97.5621
   9.5	2.6126	2.7448	2.6755	132. 2	9.07 88	89.6865	97.5192
   10.0	2.6063	2.7228	2.6566	116. 5	9.15 77	90.6877	97.4666
   10.5	2.6031	2.6913	2.6378	88.2	8.96 94	87.2560	97.3823
   11.0	2.6012	2.6615	2.6158	87.4	8.72 13	87.6425	97.2516

   • Comment :

   With increase in Inner Ring Radius (b) (a)Radiation efficiency decreases.

   (b) Center, Lower and Upper Frequency shifts lower side

5. Effect of Outer Ring Radius

Fig. 2.3 Simulated & Measured results of Annular Ring MSA with Two Slits shown in fig. 2.1 VSWR

0

-2

-4

Return loss in dB

Return loss in dB

-6

-8

-10

-12

-14

-16

120

100

Percentage (%)

Percentage (%)

80

60

40

20

0

Radiation Efficiency Antenna Efficiency

1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2

Frequency (GHz)

1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2

Frequency (GHz)

Fig. 2.7 Simulated results of Annular Ring MSA with Two Slits shown in fig. 2.1 Efficiency

Fig. 2.4 Simulated & Measured results of Annular Ring MSA with Two Slits shown in fig. 5.1 Return loss

Fig. 2.5 Simulated results of Annular Ring MSA with Two Slits shown in fig. 2.1 Elevation Pattern Gain Display (dBi).

10

9

(dBi)

(dBi)

8

7

6

5

1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2

Frequency (GHz)

Fig. 2.8 Simulated results of Annular Ring MSA with Two Slits shown in fig. 2.1 Directivity

10

8

6

(dBi)

(dBi)

4

2

0

1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2

Frequency (GHz)

Fig. 2.6 Simulated results of Annular Ring MSA with Two Slits shown in fig. 2.1 Gain

Fig. 2.9 Simulated results of Annular Ring MSA with Two Slits shown in fig. 5.1 Average Current Distribution.

2.1.5 Results of Annular Ring with Four Slits

10

8

vswr

vswr

6

4

2

10

8

6

(dBi)

(dBi)

4

2

0

1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2

Frequency (GHz)

0

1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2

Frequency (GHz)

Fig. 2.10 Simulated & Measured results of Annular Ring MSA with Four Slits shown in fig. 2.2 VSWR

0

Simulated result

Fig. 2.13 Simulated results of Annular Ring MSA with Four Slits shown in fig. 2.2 Field Gain

120

100

-2

Return loss in dB

Return loss in dB

-4

-6

-8

-10

-12

-14

Measured result

1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2

Frequency (GHz)

Percentage (%)

Percentage (%)

80

60

40

20

0

1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2

Frequency (GHz)

Fig. 2.11 Simulated & Measured results of Annular Ring MSA with Four Slits shown in fig. 2.2

Return Loss

Fig. 2.14 Simulated results of Annular Ring MSA with Four Slits shown in fig.2.2 Antenna and Radiation Efficiency

10.0

9.5

9.0

8.5

(dBi)

(dBi)

8.0

7.5

7.0

6.5

Fig. 2.12 Simulated results of Annular Ring MSA with Four Slits shown in fig. 2.2 Elevation Pattern Gain Display

6.0

1.8 2.0 2.2 2.4 2.6 2.8 3.0 3.2

Frequency (GHz)

Fig. 2.15 Simulated results of Annular Ring MSA with Four Slits shown in fig. 2.2 Directivity

Fig. 2.16 Simulated results of Annular Ring MSA with Four Slits shown in fig. 2.2 Average Current Distribution

CONCLUSION

An Annular Ring Microstrip Antenna with slits has been successfully fabricated and tested. This Annular Ring Microstrip Antenna with slits operates in 2.60 – 2.72 GHz frequency band for VSWR 2. This band is used for Indian Satellite (INSAT) Communication System. The impedance bandwidth is 116.5 MHz or about 4.38 % is achieved. Gain of Antenna becomes 9.15 dBi. The Antenna and Radiation Efficiency are 90.68% and 97.46% respectively.

REFERENCES

1. C. A. Balanis, Antenna Theory Analysis and Design, 2nd Edition, John Wiley and Sons, New York, 1997.

2. G Kumar and K. P. Ray, Broadband Microstrip Antennas, Artech House, 1992.

3. J. R. James and P.S. Hall, Handbook of Microstrip Antennas, Vol. 2, Peter Peregrinus Ltd., London, 1989.

4. Kin-Lu Wong, Compact and Broadband Microstrip Antennas, Wiley and Sons, Inc., New York, 2002.

5. IE3d Manual, Zealand Software Inc., Freemont, California, U.S.A., 1999.

6. IEEE Transactions and Propagation, Vol.48, No.7 July 2000