This paper presents the design and development of simple vertical slot loaded rectangular monopole microstrip antenna for triple band operation. The proposed antenna is excited through microstripline feed arrangement. The low cost glass epoxy substrate material is used to fabricate the antenna. The antenna operates between 2.77 to 8.29 GHz. giving linearly polarized broadside radiation characteristics with a peak gain of 3.8dB. The proposed antenna may find applications in WLAN.
In recent years the microstrip antennas are becoming increasingly popular because of their small size, lightweight, low cost, easy to fabricate and compatible to microwave integrated circuits [1-2]. However, the modern communication systems such as wireless local area networks (WLAN) often require antennas possessing two or more discrete frequency bands, which can avoid the use of multiple antennas. The single, dual and triple band microstrip antennas are designed by cutting slots of different geometries like bow-tie, rectangular, square ring, annular ring etc. on the radiating patch [3-12].In this paper a vertical slot loaded rectangular monopole microstrip antenna is presented for triple band operation giving better radiation characteristics. This kind of study is found to be rare in the literature.
II. DESIGNING OF ANTENNA
The conventional rectangular microstrip antenna (CRMSA) is fabricated on low cost glass epoxy substrate material of thickness h = 1.6 mm, loss tangent 0.02 and dielectric constant er = 4.2. The artwork of is developed using computer software AUTO CAD to achieve better accuracy. The antennas are etched by photolithography process. The bottom surface of the substrate consists of a tight ground plane copper shielding.
Figure 1 shows the geometry of CRMSA This antenna is designed for the resonant frequency of 3.0 GHz using the equations available in the literature for the design of rectangular microstrip antenna on the substrate area A-SUBSTRATE x B-SUBSTRATE . This antenna consists of a radiating patch of length L and width W. A quarter wave transformer of length Lt and width Wt is incorporated to match the impedances between Patch and microstripline feed of length Lf and width Wf. A 50 Ω semi miniature-A (SMA) connector is used at the tip of the microstripline to feed the microwave power.
Figure 2 shows the geometry of vertical slot loaded rectangular monopole microstrip antenna (VSRMMSA) which has all the dimensions same as present in CRMSA.
A vertical slot of width 2 mm and length SV= 1.8 cm is placed on the patch to achieve triple band operation. The designed parameters are tabulated in Table No 1.
Table No 1
Figure 3 shows the variation of return loss versus frequency of CRMSA. It is clear from this figure that, the antenna resonates at 2.8 GHz which is very close to the designed frequency of 3 GHz. The CRMSA exhibits the band width of 2.15% which is determined by the relation
Where FH and FL are the higher and lower cut off frequencies of return loss curve when it is below -10dB value. The proposed antennas are simulated by HFSS 15.0 version software
Figure 4 shows the variation of return loss versus frequency of VSRMMSA when the slot is on left side of the central line of the patch. It is seen from this figure that the antenna resonates for triple bands f1, f2 and f3 with respective bandwidths BW1=2.52% (2.81-2.74GHz), BW2=4.72%(7.37-7.03 GHz) and BW3=1.46% (7.56-7.45 GHz). The BW1 is due to fundamental resonance of the patch while BW2 and BW3 are due to the insertion of the slot on the radiating patch.
Figure 5 shows the variation of return loss versus frequency of VSRMMSA when the slot position on the right side about the central line. It is seen from this figure that, the antenna operates for three bands f4, f5 and f6 with respective band widths BW4 = 1.08 % (2.77-2.74 GHz), BW5= 2.53(7.20-7.02 GHz) and BW6 = 1.58(8.29-8.16 GHz).
Figure 6 shows the variation of return loss against the frequency of the VSRMMSA when two slots are places symmetrical about the central line on the patch, It is observed that the antenna resonates for a single band f7 with the bandwidth BW7=14.23(5.95-5.16GHz). The bands BW4 to BW6 all merge in to a single band giving a bandwidth of 14.23%.
Figure 7 and 8 show the radiation pattern of CRMSA and VSRMMSA. It is seen from these figures that the patterns are linear and broad sided. The gain of the proposed antennas is measured by absolute gain method. The power transmitted ‘Pt’ by pyramidal horn antenna and power received ‘Pr’ by antenna under test (AUT) are measured independently. With the help of these experimental data, the gain (G) dB of AUT is calculated by using the equation,
where, Gt is the gain of the pyramidal horn antenna and R is the distance between the transmitting antenna and the AUT. The maximum gain CRMSA and VSRMMSA measured in their operating bands are found to be 1.01 dB and 3.8 dB respectively.
From the detailed study, it is concluded that, the CRMSA can be made to operate at three frequency bands between 2.77 to 8.29 GHz by loading vertical slot on the radiating patch. The maximum bandwidth of 14.23 % is achieved with linear broad side radiation pattern. The peak gain of 3.8 dB is achieved by the VSRMMSA. The proposed antennas are simple in their geometry and are fabricated using low cost glass epoxy substrate material. These antennas may find applications in wireless local area network(WLAN).
 Kin-Lu Wong, Compact and Broad band microstrip Antennas, A Wiley-Inter Science Publication, John Wiley & Sons. Inc. 2004
 Garg Ramesh , Bhatia Prakesh, Bahl Inder and Boon Apisakittir (2001), Microstrip Antennas Design Hand Book, Artech House Inc.
 Behera. S and Vinoy. K. J, “Microstrip square ring antenna for dual band operation,” Progress In Electromagnetics Research, PIER 93, 41–56, 2009.
 Roy . J. S, Chattoraj, and N. Swain, “ short circuited microstrip antenna for multi-band wireless communications,” Microwave and Optical Technology Letters, Vol .48, 2372-2375, 2006.
 Sadat, S , M. Fardis F. Geran, and G. Dadashzadeh,” A compact microstrip square-ring slot antenna for UWB applications,” Progress In Electromagnetic Research PIER 67, 173-179, 2007.
 Shams. K. M Z , M. Ali, and H. S. Hwang, “A planar inductively coupled bow-tie slot antenna for WLAN application,” Journal of Electromagnetic Waves and Applications, Vol.20, 86-871, 2006.
 Kuo, J. S and K. L. Wong, “A compact microstrip antenna with meandered slots in the ground plane,” Microwave and Optical Technology Letters, Vol. 29, 95-97, April 2001.
 Sharma A. and G. Singh, “Design of single pin shorted Three – dielectric layered substrates rectangular patch microstrip antenna for communication system,” Progress In Electromagnetic Research PIER 2. 157 – 165, 2008.
 Ang. B. K and B.K Chung,“A wideband microstrip patch antenna for 5-6 GHz Wireless communication,” Progress In Electromagnetic Research PIER 75, 397-407, 2007.
 Eldek .A. A, A .Z. Elsherbeni and C.E. Smith, “ Characteristics of bow-tie slot antenna with tapered tuning stubs for wideband operation,” Progress In Electromagnetic Research PIER 49, 53 – 69, 2004.
 Waterhouse R.B, “Broadband stacked shorted patch Electronic Letters” Vol.35, 98-100, Jan. 1999.
 Ge,Y, K. P. Esselle and T. S. Bird, “A broadband E-shaped patch antenna with a microstrip compatible feed,” Microwave and Optical Technology Letters, Vol .42, No. 2, July 2004.
 Bahl, I. J and P. Bhartia, Microstrip Antennas, Artech house, New Delhi, 1980.