Bandwidth enhancement of triangular microstrip antenna using dual stub Mr. Govind Agarwal Mr. Atif Rizwan Mr. Rajeev Kumar Singh Mr. Rajarshi Sanyal Student Student Student Asst. Professor ECE department ECE department ECE department ECE department MCKV Institute of MCKV Institute of MCKV Institute of MCKV Institute of Engineering ,Howrah Engineering ,Howrah Engineering,Howrah Engineering ,Howrah

Abstract—A new stub loaded equilateral triangular microstrip antenna(ETMSA) has been proposed . The new structure has the enhanced bandwidth of 13.63% in the Ku band.Stub loading technique is used to enhance the bandwidth performance. Two rectangular stubs are inserted on the radiating edge of the patch. The gain of the antenna is stable at about 5.78 dBi.Detailed analysis of the patch has been done in this paper using MOM based IE3D simulator.
Index Terms—Bandwidth enhancement,ETMSA,Secondary stub effect,STUB effect. ————————————————————
1 Introduction
Microstrip antenna are very popular in wireless communication systems due to their several advantages like low cost,thinprofile,light weight etc.,but on the other hand,microstrip antenna suffers due to its bandwidth problem [1].The most straightforward way to overcome the low bandwidth problem is to use the thicker substrate [2]. Unfortunately , the thick substrate results in impedance mismatch,large radiation loss [3] [4]. There are several techniques of Bandwidth enhancement processes. Lots of slotting mechanisms [5] i.e. wide rectangular type slot [6] [7] , circular slot [8] , U type slot [9], etc. are adapted for bandwidth enhancement [10] . Another procedure for Bandwidth enhancement is Bow-Tie shape antenna [11] and slot antenna with EBG structure [12].
2 ANTENNA DESIGN AND SIMULATION
The proposed antenna is designed using RT/Duroid 5880 substrate material and dielectric constant εr=2.2. The patch geometry is the equilateral trianglular shape with arm length L=10.2mm. This triangular antenna radiates at fr=13.4GHz. Using the cavity model and assuming perfect magnetic sidewalls,the equilateral triangular patch antennaThe formula used for calculating the resonant frequency is, fr=2c/3L√εr The optimum coaxial probe feeding location at 3.875mm from the vertex of antenna as given in fig 1a and 1b.

Fig. 1a. Geometry of equilateral triangularmicrostrip antenna

Fig. 1b return loss performance of equilateral triangular patch .

2.1 EFFECT OF DUAL STUB LOADING

The dual stub of length L1 and L2 are loaded on radiating edge as shown in fig. 2a. The return loss performance is shown in fig. 2b.The difference on stub of length L1 = 4mm is fixed and L2 is varying. The length ratio L2/L1 vs bandwidth is shown at the optimum value of L2/L1 = ½. The maximum bandwidth of 13.63% is achieved at center frequency fc = 13.193 GHz as shown in fig. 2c.

Fig. 2b..S-parameter plot for return lossvs frequency

Fig. 2a.View of triangular microstrip patch antenna with dual stub

Fig. 2c.Plot for bandwidthvs stub length

Table 1a. EFFECT OF STUB LENGTH VARIATION

DIELECTRIC CONSTANT(εr ) | STUB LENGTH(L1) IN mm | STUB LENGTH(L2) IN mm | CENTER FREQUENCY IN GHz | % OF BANDWIDTH ENHANCEMENT | 2.22 | 4 | 2 | 13.193 | 13.63 | 2.22 | 4 | 2.5 | 13.3062 | 12.829 | 2.22 | 4 | 3 | 13.6095 | 9.878 |

Table 1b.STUB LENGTH VS BANDWIDTH LENGTH OF SECOND STUB (L2) IN mm | BANDWIDTH IN GHz | 3 | 1.34443 | 2.5 | 1.70713 | 2 | 1.79825 |

2.2 RADIATION PATTERN
The co-polarized field components and also cross-polarized field components are almost stable in the entire operating bands as shown in fig. but at the upper cut off frequency 14.47 GHz , the co-polarized fields are disturbed as shown in fig. 3a, 3b and 3c.

Fig. 3a Simulated radiation pattern at 12.66 GHz

Fig. 3b Simulated radiation pattern at 13.19 GHz
..

Fig. 3c Simulated radiation pattern at 14.47 GHz

2.3 GAIN

The almost better gain of maximum 6dBi (approx.) has been achieved within the operating range of 12.66 GHz – 14.47 GHz. The peak gain of 5.77 dBi achieved at fc = 13.19 GHz.

Fig 4a Plot for gain vs stub length

As L2/L1 tends to unity,the peak gain falls sharply as shown in fig.

Fig 4b Plot for gain vs frequency

Fig. 5.Current distribution using dual stub.

Table 2. STUB LENGTH VS PEAK GAIN LENGTH OF SECOND STUB (L2) IN mm | PEAK GAIN IN dBi | 2 | 5.77953 | 2.5 | 4.77801 | 3 | 3.69842 |

CONCLUSION

The double stubs loaded triangular microstrip antenna has been proposed for enhanced bandwidth operation. A 13.63% bandwidth enhancement has been achieved with two unequal length stub loading . Within the enhanced bandwidth , the considerable gain has also been achieved. Simulation studies have been performed on the proposed antenna. The design is very useful . The proposed antenna is applicable in Ku band.

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