Microstrip Patch Antenna

Microstrip patch antenna consists of a conducting patch on one side of a dielectric substrate whose other side is grounded. Unlike a microstrip line, a radiating patch is preferably printed on a low permittivity substrate for higher radiation efficiency.

This article provides an overview of the microstrip patch antenna, its properties, and its geometry. We discuss in detail its applications and limitations in the real-life world. We try to conclude the article by discussing what we learned about this antenna.

Development of Microstrip Patch Antenna

Microstrip antennas (MSA) received considerable attention in the 1970s, although the first designs and theoretical models appeared in the 1950s.

The concept of microstrip antenna dates back to 1952. Scientists like Deshchamps believed the microstrip was a microwave antenna. Nearly two decades later The practical application of microstrip antenna was seen. Howell and Munson may be regarded as the pioneer architects of microstrip antenna engineering.

Construction And Geometry of Microstrip Patch Antenna

A microstrip patch antenna consists of a thin metallic patch of any shape on a dielectric slab whose other side is grounded. The thickness of the dielectric slab is from 0.03λ- 0.05λ.

The dimensions of the patch are in the range λ/3 to λ/2 with the dielectric of the slab varying from 2.2 to 12. The choice of substrate is limited by the RF or Microwave circuit coupled with the antenna that has to be built on the same board.

Microwave circuit and antenna are usually etched together using photo-etching technology.

Patch Antenna

Working of Microstrip Patch Antenna

The working of microstrip patch antenna can be explained as:

The microstrip patch contains a conducting patch on a dielectric slab whose other side is grounded. When current through a feed line reaches the strip present on the antenna ,it leads to the generation of electromagnetic waves.

The waves from patch generate a radiation pattern as waves begin to radiate from the sides of the patch. The waves produced depends upon the thickness of the substrate, due to the small thickness of substrate , the waves get reflected from the edges.

It is important to note that the continuous structure of strip doesn’t let the emission of the radiation. After certain discontinuity , transmission of radiation again begins from the second side of patch.

Patch antenna only radiates certain portion of energy which makes it inefficient. It acts more of a like cavity than a transmitter .The inefficient radiation doesn’t allow it to be used widely.

Types of Microstrip Patch Antenna

There are various types of microstrip patch antenna:

• Square
• Rectangular
• Dipole
• Circular
• Ellipse
• Triangular
• Disc Sector
• Circular Ring

Square: The microstrip patch antenna which has a square-shaped radiating patch is called square type microstrip antenna. This type of antenna is widely used in many devices and can find large applications primarily due to its ease of design.

Rectangular: The microstrip patch antenna which has a rectangular-shaped radiating patch is called rectangular type microstrip antenna. This type of antenna is majorly used in communication systems because it offers flexibility in tuning.

Dipole: The microstrip patch antenna which has a radiating patch similar to the structure of dipole therefor it is called dipole type microstrip antenna. It is primarily know to offer broadband performance and is used in applications that demand broader frequency coverage.

Circular: The microstrip patch antenna which has a circular-shaped radiating patch is called circular type microstrip antenna. This type is suitable to perform circular polarization. It is also used in satellite and mobile communication.

Ellipse: The microstrip patch antenna which has a elliptical-shaped radiating patch is called elliptical type microstrip antenna. It offers a different radiation pattern than other types thereby can be used specifically when such radiation pattern in required.

Triangular: The microstrip patch antenna which has a triangular-shaped radiating patch is called triangular type microstrip antenna. It is a very uncommon type and can be advantageous due to its shape.

Disc Sector: The microstrip patch antenna which has a disc-sector-shaped radiating patch is called disc sector type microstrip antenna. Its major advantage is that it provides directional radiation and is used where specific angles are required.

Circular Ring: The microstrip patch antenna which has a circular ring-shaped radiating patch is called circular ring type microstrip antenna. It has the property of variation in radiation characteristics.

Types of Microstrip Antenna

Formulas Used in Microstrip Patch Antenna

Here are some important formulas associated with this antenna:

Dimensions of Patch Antenna

[Tex]Centre frequency(f_{c})= \frac{c}{2L\sqrt{є_{r}}} [/Tex]

[Tex]Wave number(k)= \frac{2π}{ƛ} [/Tex]

The radiation pattern of a rectangular microstrip patch antenna can be approximated by a simple formula.

For E-plane (phi = 90 degrees):

• E(θ)=[Tex]\frac{1}{jƛ} [/Tex] × ([Tex]\frac{I_{0}}{2} [/Tex])× sin(θ) × [sin(kl × cos([Tex]\frac{θ}{2} [/Tex])/cos([Tex]\frac{θ}{2} [/Tex]))

For H-plane (theta = 90 degrees):

• H(ϕ)=[Tex]\frac{1}{jƛ} [/Tex] × ([Tex]\frac{I_{0}}{2} [/Tex])× sin(θ) × [sin(kl × sin([Tex]\frac{θ}{2} [/Tex])/sin([Tex]\frac{θ}{2} [/Tex]))

Here,

E(θ) is the electric field in the E-plane (phi = 90 degrees).

H(ϕ) is the magnetic field in the H-plane (theta = 90 degrees).

θ is the polar angle in the E-plane.

ϕ is the azimuthal angle in the H-plane.

k is the free-space wave number

λ is the wavelength

l is the effective length of the microstrip patch.

I₀ is the current on the antenna.

Radiation Pattern of Microstrip Patch Antenna

Here is the radiation pattern of microstrip antenna:

Radiation Patterns of Microstrip Patch Antenna

• Generally we represent a normalized radiation pattern, a normalized radiation pattern is scaled relative to some value.
• The radiation pattern is quite broad a hemispherical coverage is provided by a patch antenna at an angle of 30⁰ to 180⁰.
• The radiation power as seen is low with narrow frequency band.
• It has lesser directivity around 5-7db. To have a greater directivity, an array can be formed by using these patch antennas.

Characteristics of Microstrip Patch Antenna

The major characteristic of microstrip is the radiating patch present on the grounded substrate. It is characterised by properties like light weight, low profile configuration, easy fabrication.

• The thickness of the substrate lies between 0.03λ- 0.05λ and we generally prefer thick substrate with low dielectric coefficient for better radiation efficiency.

• It shows both linear and circular polarization unlike microstrip dipole antenna which only shows linear polarization.

• It has flexibility in shape and can be of any shape like circular, elliptical, triangular, ring sector etc.

• It has a narrow bandwidth typically around 5% particularly due to its constraint in size.

• Sometimes the coupling between the patch and the antenna can result in fringing where the waves begin to emit from edges of patch into space making the patch appear larger than its usual dimensions.
  

Fringing Effect

Applications of Microstrip Patch Antenna

• They were suitable for many mobile applications, handheld devices, aircraft, satellite, missile, etc.
• The MSA are low profile, mechanically robust, inexpensive to manufacture, compatible with MMIC designs and relatively light and compact.
• They are quite versatile in terms of resonant frequencies, polarization, pattern and impedance
• They allow for additional tuning elements like pins or varactor diodes between the patch and the ground plane.

Advantages and Disadvantages of Microstrip Patch Antenna

There are some list of Advantages and Disadvantages of Microstrip Patch Antenna given below :

Advantages of Microstrip Patch Antenna

Microstrip technology has taken off since with the tremendous growth in communication , wireless as well as space-borne. This has been possible because of following advantages:

• It is Light weight, has low volume and thin profile configuration which makes it handy and conformal.
• Since it has low cost of fabrication ,it can readily be used for mass production at convenient cost.
• One can easily perform linear and circular polarization with microstrip antenna by applying a simple feed.
• This antenna can easily be integrated with microwave integrated circuits at industrial level.

Disadvantages of Microstrip Patch Antenna

Some limitations of microstrip antenna include:

• They have a narrow frequency range. They are applicable in the GHz range (f > 0.5 GHz). For lower frequencies their dimensions become too large.
• They have relatively low efficiency due to dielectric and conductor loss.
• They witness relatively high level of cross-polarization radiation.
• They generate low power.
• There is presence of spurious waves which generate surface waves lowering the effective bandwidth.

Conclusion

We can conclude that microstrip patch antenna is a very useful antenna and particular useful in communication systems where it serves the purpose of generating radiation patterns. We can select any particular type depending on our need of shape. We can also use different feeding methods for this antenna some of which include microstrip line feed, coaxial feed, aperture coupled feed, proximity coupled feed. These feeding methods are employed while designing the circuit . There are certain limitations of microstrip antenna due to the limited bandwidth of this antenna but variations are being made to improve them.

FAQs on Microstrip Patch Antenna

1. What are some other types of patch antenna?

Other types of patch antenna include dipole antenna, travelling microstrip antenna and slot microstrip antenna each having different use and shapes.

2. What are fringing fields in microstrip patch?

Due to the coupling between the microstrip patch and the antenna, then fractional electric field begins to emanate from the edges of patch in space. This results in the dimensions of patch appearing bigger. The fringing effect is a function of dimensions of patch and increases with increase in height of patch. At higher frequency the field begins to concentrate at the centre of the patch.

3. What are some characteristics that should be considered while selecting the substrate?

The major characteristics that should be considered are surface-wave excitation in substrate, anisotropy in substrate, copper loss. Some mechanical requirements like elasticity ,weight ,conformity and cost efficiency.