A Theoretical Survey on Patch Antenna for Wideband Communication

Modern communication system is based on wideband communication. A wideband antenna is designed in such a way that it will receive a wide range of frequencies. Microwave frequency spectrum is classified as ranging from 1GHz to 100GHz and this range is divided into a number of frequency bands. These bands are defined as L Band, S Band, C Band, X Band etc. To fulfil the demands of many users patch antenna is designed in these bands. Among different types of antenna, Microstrip Patch Antenna is most popular in wireless communication system. Microstrip patch Antennas have many advantages over other familiar antennas because microstrip patch antennas are of low profile, low cost, low volume, light weight. Low efficiency, low gain and narrow bandwidth of patch antenna create major challenge to a designer. Slots are created on patch for preparing antenna for wideband applications. In this paper, we have surveyed upon various types of Microstrip Patch Antenna, feeding techniques, design equation Substrate Characteristics, Simulation tools etc.


Introduction
Antenna is designed in such a way that, it will transmit or receive electromagnetic waves that is antennas are of two types receiving and transmitting. Receiving antenna is kept at the place of most radiating place from transmitting antenna. Microstrip Patch Antennas (MPA) are printed directly on a circuit board. It is more familiar and suitable and essential for Mobile phone market, Satellite Communications, Radars, Aerospace etc. MPA has good return loss as well as Voltage Standing Wave Ratio (VSWR) and bandwidth (BW) [1]. MPA in its simplest form is shown in the figure 1. A dielectric substrate is situated between metallic patch and metallic ground. The dielectric constant of substrate lies between 2.2 and 12 [2]. All microstrip antennas can be divided into four basic categories ( Figure 2). This paper is organized into following sections. In section 2 we discuss Microstrip patch antenna. This is followed by feeding techniques for antennas in section 3. Section 4 is devoted to equations for designing rectangular patch antenna. Section 5 describes effect of substrate characteristics on the design of Microstrip patch antenna. In section 6 we discuss on some of the standard simulation software in use for microstrip antennas.

Microstrip Patch Antenna
Microstrip patch antennas came in introduction in 1970 but in focus in 1950. Microstrip antenna ( Figure 1) has a very thin (t<<λ0, whereλ0 is the free-space wavelength) metallic strip(patch) and height of dielectric substrate h and the value of h be (h<<λ0, usually 0.003 λ0<h<0.05 λ0). For a rectangular patch, if L be length of the element then usually λ0/3<L<λ0/2. Characteristics of dielectric substrate take important role in the antenna performance. If the substrate be thicker and dielectric constant be of lower, then antenna gives better efficiency and larger bandwidth but the size of antenna will be larger [4]. If we use substrate which is thin and of higher dielectric constant, then the element size will be small. This type of antenna is suitable to take challenge of modern communication [2].
The radiating patch may assume the shape of square, rectangular, circular, elliptical, triangular, thin strip(Dipole) or 70 any other configuration ( Figure 3). Usually rectangular and circular size patches are used for microstrip antennas. The following chart will give clear idea about patch antennas at a glance. Profile of Microstrip patch antenna is thin, fabrication is easy, polarization is linear and circular both, spurious radiation exists and bandwidth is 2-50%. These characteristics are important for getting information at a glance. Profile of microstrip slot antenna is thin, fabrication is easy, polarization is linear and circular both, spurious radiation also exists but bandwidth for such antenna is seen 5-30% [3], [5].

Feeding Techniques
Feeding technique is very important for antenna operation. Through feed energy is supplied to the antenna. There are two types of feeding techniques, one is contacting and other is non contacting. Microstrip line and coaxial probe are contacting feeding technique but aperture coupling and proximity coupling feeding techniques are non-contacting type [6]. Here, a microstrip patch is directly connected with a conducting strip or microstrip line whose width is smaller than patch width ( Figure 4). This technique is very easy and impedance matching by which is also simple. Here feed be placed at any arbitrary location inside the patch for impedance matching. But narrow bandwidth is a disadvantage of this scheme. Here, a radiator patch is connected with the inner conductor of the co-axial. Ground is connected with outer conductor of co-axial.

3) Aperture coupled feed
Here, a ground plane separates two different substrates whose dielectric constants are chosen independently so that distinct electrical functions of circuit and radiations are optimized. On the bottom side of lower dielectric constant substrate there is a microstrip feed line. The feed energy is coupled to the patch through slot on the ground plane. Radiating patch is kept on the top position of upper substrate. Usually an antenna designer uses a high dielectric constant substrate for bottom substrate and a thick, low dielectric constant material for the top substrate for optimizing radiations from the patch.

4) Proximity coupled feed
Here we use two dielectric substrates whose proper alignment or array or make up is necessary. Radiating metal patch is placed on top of upper substrate. Feed line is attached between two substrates. By this technique we can eliminate false or spurious feed radiation. As the electrical thickness of microstrip patch antenna is enhanced through this technique so the large bandwidth of 13 % is obtained. In this system electromagnetic waves are coupled so this feeding technique is called as electromagnetic coupling system or scheme [6]- [8]. The above feeding techniques are essential for designing an antenna. Because the study of different techniques will help a designer the knowledge about excitation and energy supply to the patch. Which technique can be used for better achievements in designing is also obtained from the above study.
Comparisons of different feeding techniques from the literature survey courtesy [10], [11].
International Journal of Research in Engineering, Science and Management Volume-3, Issue-11, November-2020 https://www.ijresm.com | ISSN (Online): 2581-5792 71 In the above table feeding techniques are tabled in the descending band width order. For all techniques impedance matching is easy.

Equations for Designing Rectangular Patch Antenna
The design equations are described in below [2], [8], 12]. Notations used are frequency of operation ( ) dielectric constant of the substrate (∈ ) height of dielectric substrate (h). Mainly these three parameters are essential for designing a patch antenna.

Calculation of effective dielectric constant ( )
Fringing effect has a role to calculate this. (2)

Calculation of effective length ( ) of patch
(3)

Calculation of length of patch (L)
Finally, the length of the patch of the antenna can be calculated by the following equation.

(5)
Calculation of ground plane dimensions A designer can use the following equations for designing ground and substrate dimension. (6) h being the substrate height. Lg and Wg are length of ground and width of ground respectively.

Port and radiation box design: After feed point detection the ports are designed. Through port excitation is provided and the radiation box dimension must be larger than ground or substrate.
There are two types of port mainly lumped and wave ports take part in excitation.

Advantages and disadvantages
Microstrip patch antenna several advantages and disadvantages.
Advantages: Low weight, Low profile, Thin profile, Linear and circular polarizations, capable of dual and triple frequency operation, at a time feeding lines and matching networks can be designed.
Disadvantages: Insufficient efficiency, insufficient or low gain, low power handling capacity, excitation of surface waves, polarization impurity, large ohm loss in feeding structure.

Effect of Substrate Characteristics on Microstrip Patch Antenna Design
For designing an MPA, a designer should select the substrate material and its thickness with priority. Researcher should have clear idea about the effect of changing substrate material and its thickness on the performance of the antenna. We list some of the commonly used substrate materials and their dielectric constants which are equally useful for MPAs [11].
Thick substrate but low dielectric constant has some advantages and disadvantages in design process. Advantages are we get excellent efficiency, larger bandwidth and for radiation in space the loosely bound fields. After using such substrate, we see antenna element size becomes larger and weight, dielectric loss and surface wave loss of antenna increase also.
If we use thin substrate whose dielectric constant is high, then we see smaller size antenna. Because, this type of substrate demands tightly bound fields for minimizing unexpected Higher dielectric constant material declines the antenna performance. Larger thickness of dielectric substrate reduces the size of antenna element and for such type of substrate resonance frequency decreases but at the cost of bandwidth. Higher dielectric constant material also decreases resonance frequency and increases bandwidth. These observations are obtained from different antenna simulation results and analysis.

Simulation Software for Microstrip Antennas
There are various simulation softwares by which we can design geometrical model, simulate, analysis the design, interpret the result and modify the design. There are HFSS, CST, IE3D, MATLAB simulation softwares.
HFSS: It is a commercial method solver for electromagnetic structures from Ansys. High Frequency Structure Simulator. General procedure for creating and analyzing a design is in the following.

Design of a MPA for Wideband Communication
After implementing suitable feeding techniques, design equations, impedance matching a designer can think to design a MPA for wideband communication. During designing the designer should care on impedance bandwidth which is just an ordinary bandwidth of antenna. Impedance bandwidth is the range of frequencies over which the return loss is accepted. Cuts of different sizes or more than one slots are drawn on radiating patch of microstrip patch antenna to implement patch antenna for wideband applications. After designing MPA has to analyze. For this S Parameter, Z Parameter, Radiation patterns are plotted in any simulation software. From analyzing it will be seen that the frequency range where MPA is working. Thus a huge number of people will obtain MPA as gift for wideband communication system. Because wideband communication gives faster communication with high data rates. Fig. 9. Inset feed microstrip patch antenna designed through HFSS It is an inset feed microstrip patch antenna which is designed through HFSS. If the slots are drawn on patch, then it will work in wide band application.

Conclusion
In this paper a theoretical survey on MPA has been done which addresses the feeding technique, design technique, advantage and disadvantages of MPA and the design techniques for designing MPA for wideband communication system. From analysis of this survey a designer can select best feeding techniques for minimizing the disadvantage. Also, a brief discussion is given on some of simulation software in use. MPA can be designed for each application and different merits have been compared with conventional microwave antenna. How dielectric constant of substrate affects the process is also explained here. This survey will help a designer in the designing process.