Enhancement of Antenna Parameters of a Rectangular MSA with Optimized Inset Fed Using HFSS

Author Name(s): Basheer Ali Sheik *, Dr. P V Sridevi and Dr. P V Rama Raju
Author Email: basheeralis@yahoo.com

Abstract

Microstrip Antenna (MSA) plays a very important role in wireless communication systems (such as Mobile & Satellite Communications, Military applications, WLAN and Internet of Things (IoT)). The MSA has a compactable nature in design of antennas in wireless systems such as miniaturized size, easy to fabrication,  low weight and low cost.  But it has limitations too; those are narrowband, low gain, low directivity, and high cross polarization in H-plane due to impedance mismatching between high input impedance of patch at edge and low impedance of feed line (transmission line). This problem can be overcome with bring down the input impedance of patch to use shorting pins, different EBG structures, and different optimized feed methods. In this paper is going to reduce impedance mismatch with newly proposed formulas for inset fed method. This will go to be enhancing the antenna parameters and to improve the uniform distribution of current density on patch with diminishing the inductive load at junction of patch and feed line. Finally new optimized formulas for depth and gap of inset fed will be defined by iterative process in HFSS 14v. It yields the best and optimized results of antenna parameters in given frequency of operation, height of the substrate and dielectric constant.

Introduction

MSA has been in any shape (Tree, human body, square, rectangular, circular, trapezoidal, elliptical, etc.). The most popular MSA shape is rectangular shape, because it’s very easy to design, analyze and fabricate compared to other shapes of patch. MSA has been excited with different feed methods (such as edge fed, inset-fed, coaxial fed (or probe fed), proximity and aperture coupling) [1] – [3]. The impedance mismatching occurred at junction of feed line and patch edge, this degrade the performance of MSA [4]-[11]. To overcome this problem with shorting pins, EBG (Electro-magnetic Band Gap) design structures and optimized feeding methods.  These techniques are to concentrate on diminishing input impedance of patch and/or find where the impedance on patch is low to join the feed line at there. The shorting pins used to decrease the inductance between patch and ground. So these are used to improve the performance of antenna and have low cross- polarization due to paired pins [12]. But this model has a drawback, which is not applicable in design of array of antennas due to increasing the design problems such as danged the substrate while drilling for insetting pins and manufacturing cost become huge.

The next method to go for diminishing the impedance mismatching between patch and feed is using EBG structure on MSA. This is very effective method to improve the antenna parameters. This is three types of structures; those are 1D, 2D and 3D [13]-[17]. But these are more costly for complicated design.

So next method to go for reduce impedance mismatch between patch and feed is using an optimized feed method. We have five methods to feed (excite) the patch. In their, inset fed is more popular to simple design, give better results especially in array feed network and low cost. Based on these advantages, this paper is going to design optimized inset fed. Before going to optimized design of inset fed, here go to discuss some basics of inset fed. The inset fed means, the feed line is not join the edge of patch. The feed line inset is into the patch and join where the patch impedance is nearly equal to feed line impedance. Inset fed depends on depth and gap of notch (shown in Fig. 1). These two are mainly depended on length of patch, operating frequency, and height or thickness of substrate. Depth means how much the feed line inset into the patch. To determine the location of depth based on current distribution on patch, which is like cosine square function. The maximum current distribution is center of patch and electric field is zero. I.e., the impedance is minimum ( zero) at center and maximum at edge of patch.  The gap is mostly useful for separate/isolate the feed line from patch, and to develop some amount of capacitance for reduce inductive load of patch [18]-[24]. Whatever the advantages of inset fed, it has drawbacks too. The drawbacks are high cross polarization in H-plane due to unbalancing of current distribution at junction of patch and feed line and become complicate to design at higher frequencies due to increasing of width of feed line. But these formulas of depth and gap defined complicatedly so far. To avoid that problem and get best results with newly proposed formulas for depth and gap of notch, and improve the antenna parameters and low cross polarization.

The aim of this paper is trying to develop of empirical expressions to gap and depth of notch for enhancing the antenna parameters of the rectangular micro strip antenna. The optimized depth and gap of notch can be generated internal capacitance that will be compensating the inductive load and reducing/dwindling the impedance mismatch between the patch and feed line, and the current density distribution on patch is also uniform, which is dwindling cross-polarization. The design and simulation had done on Ansoft HFSS v14.

Conclusion

The impedance mismatch between the patch and feed-line is playing a very big important role as it will be decided the performance of the patch antenna parameters. The impedance mismatch can be decreased by optimized inset fed. Inset fed depended on depth and gap parameters. If changing them the overall capacitance and inductance in between the patch and transmission can be affected. Here defined new formulas (optimized) for depth and gap of inset fed, these formulas are very useful to increase the directivity (antenna parameters) of the patch antenna. By the experimental analysis, is getting the best results in the case–IV. Here by changing height of substrate, operating frequency and dielectric constant of substrate. This can be easily analyzed results of MSA that decrease the return loss, increase gain as well as directivity of the patch. It can be concluded that the newly defined formulas of depth and gap of inset fed have more pronounced effect on performance of antenna parameters.

References

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