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Vsevolod Kryukov
Vsevolod Kryukov

Inset Fed Patch Antenna Calculator

Typical CharacteristicsBandwidthGainSizeImpedancePatternPolarization1% - 5%6dBi 30Ω - 200ΩUnidirectionalLinearThe microstrip patch antenna takes on many forms and has been widely used in the past due to its low profile and ease of manufacturing. There are many different types of microstrip patch antennas, and many of them can be found in the MicrowaveTools Antenna A-Z database. While this type of antenna is not used as much as it once was, the theory behind this antenna has led to many of the more modern antennas such as the IFA, PIFA, and FICA antennas. All the equations for determining the size and impedance of an inset fed patch antenna are at the end of this post. Matlab scripts are provided.

Inset Fed Patch Antenna Calculator

A well designed patch antenna can have a peak gain between 6 and 8dBi, and as such it is considered to have a directional pattern (click to rotate 3D image below) which is linearly polarized along the width of the patch.

The rectangular patch is one of the more common types of patch antennas. This antenna is designed using a rectangular piece of electric conductor situated above a ground plane. The rectangular piece of copper measures long. Note that the wavelength depends on the material situated between the ground plane and the patch; meaning when air is between the patch and ground, the length of the rectangle electric conductor is of the free-space wavelength (). If the antenna is loaded with different dielectrics, the length of the antenna decreases as the dielectric constant increases.

The natural input impedance of a patch antenna dependent on where within the patch the feed is located. It is possible to match the patch antenna from below 30Ω to above 200Ω. If the feed is located closer to the edge of the patch the input impedance will be high, if the feed is located closer to the center of the patch the impedance will be low. Below is the standard input impedance of an inset fed patch antenna at 2.45GHz.

The 50Ω bandwidth of a patch antenna designed to have a resonance of 2.45GHz is shown below. This type of antenna is inherently a high Q antenna, meaning that this antenna is relatively narrow banded.

There are many different ways to feed a patch antenna, the inset fed patch antenna is fed via a microstrip feed line connected to a specific point within the patch. Through varying the location of where the microstrip connects to the patch antenna the measured input impedance can be controlled. In the reflection coefficient shown above was matched to a 50Ω microstrip line.

The Microstrip patch antenna is a little different than many antennas, as the structure itself does not radiate, but rather the edge gaps between the patch and the ground plane. This can be visualized below. line is situated directly above where the patch radiates from, this effects the pattern of the patch antenna and what applications it can be used in. The areas where the patch radiates from are shown below.

The inset patch design has three distinct geometrical regions. The first is the actual patch itself. The second is the feed line. Finally, the third part is the ground plane. It is possible to derive the parameters of patch antenna using a few different techniques. This article will focus on the cavity model approximation in most situations and will fall back on the transmission line model to derive parameters such as the input impedance of the patch.

It is possible to determine the width of the patch, w, using Equation (1). The width of a patch antenna is good starting point when designing a microstrip patch antenna. This is due to the width not having a significant impact on the operational frequency of the antenna, and tends to have the largest effect on the bandwidth and the input impedance (excluding dielectric height and constant) of the patch antenna.

The length of the patch is determined by the electrical length of the antenna rather than the physical length of the antenna. The effective dielectric constant impacts the speed at which electric energy travels through this media. This effectively changes the resonant frequency of the antenna. To design the length to match the required resonant frequency Equations (3), (4), (5) are used.

After calculating the patch length, the feed line characteristics can be determined. There are many different feeding types that can be implemented in a patch antenna; in this particular patch antenna an inset microstrip feed will be used.

In order to determine the approximate input impedance of the patch antenna, many different approaches have been derived. One in particular is derived in [1] by analyzing the patch antenna as two slot radiators. In this derivation the admittance is calculated using Equations (6), (7), and (8).

Once the edge impedance is derived, the next design parameter is to properly interface the feed line impedance with the patch antenna impedance. The current to voltage ratio changes as a function of across the length of the patch antenna. This results in an impedance change seen from the edge of the patch decreasing as a squared cosine function moving towards the center. Equation (9) is then used to determine the input point for the feed line from the edge of the patch or Equation (10) from the center of the patch.

The final design consideration of the patch antenna is to ensure a large enough ground plane is used for this particular derivation. Equations (11) and (12) determine the minimum ground length and width that should be used with this particular design.

The patch cutout for the feed inset should be > 2 times the microstrip width. This means that on each side of the feed line there should be a distance of 1/2 the microstrip width on each side of the microstrip between the microstrip feed line and the patch antenna.

This paper presents the transmission line model for analyzing the microstrip line inset fed patch antenna and also presents a curve fit formula for locating the exact inset length to obtain 50 Î input impedance. Accuracy of the formula is compared with the results obtained from the EM simulator.

In this paper, an inset feed rectangular microstrip patch antenna has been designed and simulated at the frequency of 3GHz and the dependency of antenna performance parameters like return loss, VSWR and other antenna parameters have been successfully studied with the variation of the notch gap using CST microwave studio. We have varied the notch width(g) as the proportion of the Length(L), Width(W) of the patch and the width of the microstrip feed line (Wf) to study the performance parameters of patch antenna. FR-4 with dielectric constant of 4.3 is used as a substrate for the designed antenna. The designed rectangular microstrip patch antenna with inset feed technique is very useful for various applications in Industrial, Scientific and Medical sectors which operates at 3GHz range. It shows that the return loss decreases within some certain values of the notch width (g) and after those values the return loss and VSWR started to increase with the corresponding notch gap. Although the return loss and VSWR change with varying the notch gap but no significant changes were observed in case of gain, directivity and bandwidth. The resonant frequency of our designed antenna was almost same with the variation of the notch gap and it remained almost fixed from 2.944 GHz-2.978 GHz.

insetpatch = patchMicrostripInsetfed(Name,Value) sets properties using one or more name-value pair. For example, insetpatch = patchMicrostripInsetfed('Length',0.2) creates an inset-fed patch of length 0.2 m. Enclose each property name in quotes.

The microstrip patch antenna is used in a wide range of applications since it is easy to design and fabricate. The antenna is attractive due to its low-profile conformal design, relatively low cost and very narrow bandwidth.

It is known that the antenna impedance will be higher than an accepted value if fed from the edge, and lower if fed from the center. Therefore, an optimum feed point exists between the center and the edge. This model uses an inset feeding strategy which does not need any additional matching parts to find this optimal point.

Use the pcbStack object to convert the patch antenna into a pcb stack so that the shape of the top layer can be extracted from the Layers property. Convert into a linear array of 4 elements. The patch is extracted from the Layers property of the pcbStack and the shape is copied and converted into a linear array.

Use the pcbComponent object and convert the corporate power divider into a PCB Component. Create a new pcbStack object to construct the cascade of power divider corporate and patch antennas. Assign all the properties of the pcbComponent to the pcbStack and then add the top layer of the corporate power divider with the patch antenna array and visualize it.

There are a variety of wearable antennas, such as planar dipoles, monopoles, planar inverted-Fs and microstrip patches. Microstrip antennas are planar and can be easily made onto a printed circuit board (PCB), which makes them a practical antenna type due to their low cost and easy fabrication. Figure 1 shows the structure of a planar microstrip inset fed patch antenna, where the resonant frequency is related to the width W1 and length L1 of the patch, the substrate thickness h and permittivity εr of the dielectric. The antenna is printed on a dielectric substrate with permittivity εr = 3.38 and h = 1.254mm. The antenna consists of an inset patch and a 50 Ohm microstrip feed line on the top side of the substrate, and a ground plane of 1mm thickness on its bottom side [1].

Verma, R. K., Yadava, R. L., & Balodi, D. (2022). An inset-feed on-chip frequency reconfigurable patch antenna design with high tuning efficiency and compatible radome structure for broadband wireless applications. Scientia Iranica, 29(6), 3304-3316. doi: 10.24200/sci.2021.56226.4612

R. Kumar Verma; R. L. Yadava; D. Balodi. "An inset-feed on-chip frequency reconfigurable patch antenna design with high tuning efficiency and compatible radome structure for broadband wireless applications". Scientia Iranica, 29, 6, 2022, 3304-3316. doi: 10.24200/sci.2021.56226.4612


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