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Numerical simulation of a rectangular microstrip patch antenna for 3.35 GHz applications

This paper described the design and numerical simulation of a rectangular microstrip patch antenna for applications at 3.35 GHz. The numerical simulation carried out with the aid of AWR software. The initial design was done by mathematical calculation. Then the initial design is modeled and numerically simulated to get the optimal design. Optimized parameters are length of the patch and width of the feed line. Based on the optimal results obtained a minimum return loss of -15.98 dB and bandwidth below the return loss of -10 dB is 93 MHz (3.311 - 3.404 GHz).


Introduction
The rectangular microstrip patch antenna (RMPA) is the popular antenna with its simplicity. Various wireless systems have offered to use the RMPA such as radar applications [1], cellular communication [2], Wi-fi [3] and WiMAX [4]. The RMPA printed on the double side of PCB (printed circuit board). The printing is very necessary for an accurate design. If the RMPA has already been printed and to be incompatible, it cannot be changed but must replace it with another design. Therefore, before printing, the most optimal design must be obtained. The optimal design obtained at a lower cost by numerical simulations. This paper discussed the RMPA design with a resonant frequency of 3.35 GHz which is one of the bands for broadband communication applications. The design initialized with mathematical calculations and then investigated numerically simulation with the help of AWR software. An iterative investigation is carried out on the dimensions of the design of the RMPA namely the patch length and the width of the feed line to get optimal results.

Antenna Design
The RMPA configuration showed in Fig. 1 The theoretical calculations have been formulated, the design of the RMPA can be done as follows:

Patch Dimension
Patch dimension consists of width (W) and length (L). The dimension can be calculated with this equation [5]: and (4) where v0 is the speed of light in free space, fr is resonance frequency, is dielectric constant of substrate and h is height of the substrate.

Feed Line Dimension
In this design, the feed line used is a microstrip line with it dimension consists width (Wf) and length (Lf) of the feed line. The need for the dimension is adjusted to the required characteristic impedance (Zc) which is can be calculated with [5][6]: If the type of substrate has been determined, then for Zc = 50 Ω can be achieved by setting the Wf. The length of the Lf can be adjusted to the dimensions of the ground plane, or use the equation [6]: = 0 4√ reff (6) where 0 is the free space wavelength.

Ground Plane Dimension
The ground plane is grounding for the microstrip antenna system which generally covers the entire underside of the substrate. The wider the ground plane, the better, but smaller ground plane dimensions are desirable. The ground plane dimension for RMPA can be given by λ/4 from the edge of the patch [6] or by using: = 6ℎ + (7) = 6ℎ + where Lg is length of the ground plane and Wg is width of the ground plane.

Numerical Modelling
The numerical value of the design RMPA using Eq. (1) through (8) showed in Table 1. This value is the value of initial design for numerical simulation. The numerical modelling of RMPA shown in Fig. 2.  Step: 0.01

Simulation Result and Discuss
The numerical results of the simulation from the initial design in the form of return loss shown in Fig.  3. Based on this result, the minimum return loss value is -10.2 dB on the 3.69 GHz frequency. It is not very good for needs in a 3.35 GHz application. Therefore, the parameters of the initial calculation results need to be set to produce an optimal design. There are many possible combinations of parameters, but in this paper, the initial step taken is to set the length of the patch (L). Fig. 4 shown the return loss value generated from numeric simulation with each variation of L as stated in the legend.   In Fig. 5 can be seen that a good result is achieved at Wf = 1 mm with a minimum return loss reaching -15.98 dB. The bandwidth below the return loss of -10 dB is 93 MHz (3.311 -3.404 GHz). This result is the optimal decision from the two sequential changes in variation, namely length of the patch and then width of the feed line. Numerical simulation is very helpful to get optimal design results before it is done for fabrication. One is that it can reduce fabrication costs due to errors that will occur. Comparison of the results of the initial design and after optimization from the numerical simulation showed in Table  2. It shown that this optimization is enough with the iteration of change in L and Wf. Table 2. Comparison of the initial and optimal design.

Conclusion
This paper has explained the steps of the RMPA designing with numerical simulation. Based on the optimal results obtained a minimum return loss of -15.98 dB and bandwidth below the return loss of -10 dB is 93 MHz (3.311 -3.404 GHz). The results show that the design can be applied for the communication system for 3.35 GHz.