Ithayakumaran Lakshman

Ithayakumaran Lakshman, ENGD2009 Electromagnetics, T21801678

Design and Simulation of a Patch Antenna
Abstract—Microstrip antennas or Patch antennas became more popular due to its very small size that can be easily fabricated on the printed circuit board. This transaction will give a brief introduction on Microstrip antenna, its working, relationship between the dimensions of antenna and its operating frequency, discussion on S-parameters. And moreover it contains the designing of 5.8GHZ antenna and analysis using CST studio suite.

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Index Terms—Microstrip Antenna, Resonant, Substrate,
Antennas are transducers which are used to transmit and receives information through long distances. The role of antenna is efficiently done by radiating electromagnetic energy in the desired directions. There are variety of antenna used according to the requirements. Here we are interested in Microstrip antenna which are more commonly used in PCBs. Mostly all portable devices which contains the feature of communicating or transfer of information uses this type of antennas. This Microstrip antenna designs also varies according to the requirements such as in satellite communications, GPS systems and cellular applications.
Task 1: Patch Antenna
What is a patch, or Microstrip, antenna and how does it work?
Microstrip or a patch antenna is a printed type antenna, where a metallic patch is placed on a dielectric material and supported by a ground plane. And its most common known application is mobile phone application where the antenna is fabricated on the PCB of mobiles.

Fig. 1 Simple design of Microstrip or Patch antenna
Here the Microstrip transmission line is used to feed the power to the Microstrip antenna and the transmission line is
connected with the patch as in the manner of impedance matching happen between transmission line and the patch.

Radiation will happen through the width (w) sides only and the magnitude of radiation will increase with the width (w).
And impedance matching also depends on the value of width.

Radiation in space will increase with the height (h) of dielectric material to some extend and it will stop radiate beyond to the limit of that height.

Fig. 2 Radiation in a simple Microstrip antenna
What is the relation between the patch antenna dimensions and its resonant frequency?
W = c2fr2?r+1L = Leff – 2?L
Wg = 6h + W
Lg = 6h + L
h = 0.025?
Leff = c2fr?reff ?reff = ?r+12 + ?r-12(1 + 12hW)-1/2
c = fr?
fr- Resonant Frequency
c-Speed of Light in space
?-Wavelength of Light in space
?r- Dielectric constant of Substrate
L-Length of Patch
W-Width of Patch
Lg-Length of Substrate
Wg-Width of Substrate
Leff-Effective Length of Patch
?reff-Effective Dielectric constant
?L-Fringing Length
h-Height of Substrate
Task 2: s-parameters (scattering matrix)
What are S-parameters for two-port networks?
‘S’ parameters are mathematical representation of how RF energy propagates in a multiport network 7
As we consider the high frequency such as microwave frequency, the network parameters such as h, z and y parameters cannot be used because;
Equipment is not readily available to measure total voltage at the port network.

Short circuit and open circuit are difficult to achieve on broad range of frequencies.

Active devices such as power transistors and tunnel diodes will not have stability for open and short circuit condition.

So to resolve the issue scattering (‘s’) parameter is introduced in case of microwave frequency analysis
‘S’ parameter is defined as,
Sij = biaj = Normalized reflected wave at ith portNormalized incident wave at jth port
Fig. 3 Representation of Two-Port Network
bi = Reflected voltage at ith portZoiaj = Incident voltage at jth portZojS11 = b1 / a1 = (V1- / Zo1) / (V1+ / Zo1) = V1- / V1+
S12 = b1 / a2 = (V1- / Zo1) / (V2+ / Zo2) = (V1- / V2+)Zo2Zo1S21 = b2 / a1 = (V2- / Zo2) / (V1+ / Zo1) = (V2- / V1+)Zo1Zo2S22= b2/ a2 = (V2- / Zo2) / (V2+ / Zo1) = V2- / V2+
What is the importance of S11 parameter in one-port antenna measurements?
From the above expressions for the ‘S’ parameters, it is an apparent truth that a single port antenna only can have ‘S11’ parameter because only the ‘S11’ depends on the reflected and incident voltage of port_1
And the S11 represents how much input power given to device is reflected back at input port, and hence is known as reflection coefficient or return loss.

For example,
If S11 = dB, then all the power is reflected from the antenna and nothing is radiated.

If S11 < around -10dB means that at least 90% input power is delivered to device and reflected power is less than 10%
Task 3: CST Software
What is CST Studio suite?
CST Studio suite is package of tools for design, simulate and optimize the Electromagnetic systems such as Antennas.

How can a patch antenna be modelled? What is the basis of the technique used by CST to do this?
According to the operating frequency of desired antenna dimensions of the components can be calculated with the equations mentioned in TASK 2. And then each parts of the Antenna can be designed with the use of “Modeling” tab in CST Studio by choosing the appropriate materials (FR-4 for substrate and Copper for other parts) and dimensions of each component.

Task 4: Designing a Patch Antenna
Design a patch antenna that operates at 5.8 GHz (ISM Band: 5.725 GHz – 5.875 GHz) and simulate it using the CST Studio Suite

Fig. 4 Top view of Patch Antenna

Fig. 5 Side view of Patch Antenna

Table. 1 Parameters of designed Antenna

Fig. 6 S11 Results for initial design (in dB)

Fig. 7 Farfield Directivity
CONCLUSIONFrom this Course Work on Design and Simulation of a Patch Antenna, a Patch Antenna has successfully designed with the help of CST Studio suite and corresponding S11 parameters and radiation patterns were studied.

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