Microstrip Antennas in Portable Electronics

Key Takeaways

• Microstrip antennas are low-profile antennas with a two-dimensional flat structure and they offer low-radiation antenna characteristics. 

• Metal patches in microstrip antennas are usually either a rectangular or circular shape.

• Microstrip antennas are used in satellites, missiles, aircraft, space crafts, mobile phones, wireless communication systems, radars, and in remote sensing. 

Microstrip antenna

Antennas are an essential component of wireless communication in smart devices, and in handheld or portable smart devices, the antenna’s size matters. Microstrip antennas are most commonly used in wireless devices due to their easy integration and small size.  The design of a microstrip antenna influences its performance; it is critical to design microstrip antennas properly to ensure quality communication and signal integrity. 

The Characteristics of Microstrip Antennas

Microstrip antennas are low-profile antennas with a two-dimensional flat structure. They offer low-radiation antenna characteristics. 

How Are Microstrip Antennas Constructed?

A microstrip antenna consists of a metal patch of length usually equal to one-half wavelength. The length is maintained so that the antenna behaves as a resonator. The metal patch is mounted to the ground plane and the dielectric material is filled in between. Due to the presence of a conducting patch, a microstrip antenna is also known as a microstrip patch antenna. Generally, copper material is used to make the patch.

How Do Microstrip Antennas Operate?

When a thin microstrip antenna is excited from a feeding network, waves are generated and reflected in the dielectric material. When the waves reach the corners or edges of the metal patch, a fraction of the incident energy is radiated outwards.   

Conducting Patch Shapes

Conducting patch shapes can be rectangular, circular, triangular, elliptical, hexagonal, rhombic, pentagonal, etc. Rectangular or circular metal patch shapes are the most common in microstrip antennas. Since the surface area consumed by a circular patch is less than a rectangular patch antenna, they are suitable in array antenna construction. Irrespective of the shape of the patch, the radiation characteristics of both circular and rectangular patch antennas are the same. 

Dielectric Material

Dielectric material is used between the metal patch and the ground plane. The dielectric constant is very important in determining antenna performance. A thick dielectric material of low dielectric constant is preferred in microstrip patch antennas to give high antenna performance.  

The Advantages of Microstrip Antennas

Microstrip antennas are used in satellites, missiles, aircraft, space crafts, mobile phones, wireless communication systems, radars, and remote sensing. Some of the advantages of using microstrip antennas in these systems include:

• Easy to fabricate, modify, and customize.
• Simple and inexpensive construction.
• Lightweight and low volume.
• Suitable for array antennas.
• Conformity with planar and non-planar surfaces.
• Mechanical robustness.
• Compatible with monolithic microwave integrated circuits.
• Bandwidth expandability by increasing the dielectric material thickness.
• Linear and circular polarization are possible.
• Dual and triple frequency operation.

Methods of Feeding

There are different methods of feeding a microstrip patch antenna:

Microstrip Line Feed

In this type of feed, the patch antenna is directly connected with the microstrip feed line. It is easy to fabricate and match the microstrip line feeding system with the patch antenna. 

Coaxial Probe Feed

In coaxial probe feeding, the inner and outer conductors of the coaxial probe are connected to the microstrip patch and ground plane. This feeding method is a non-isolated or non-contacting feeding network. The advantages of coaxial feeding are easy fabrication, the minimization of spurious radiations, and efficient feeding. 

Slot on the Ground Plane or Aperture Coupled Feed

There is a coupling between the microstrip patch antenna and the feeding line through a slot in the ground plane. This feeding method offers pure polarization of the antenna. The minimization of the interference is a merit of aperture coupled feeding. 

Proximity Coupled Feed

This feeding method uses two dielectric substrates: the top and bottom dielectric substrates. The microstrip patch is placed on the upper side of the top dielectric substrate. The feeding line comes in between the two dielectric substrates. This feeding method is free from spurious radiation and offers the highest bandwidth.   

Coplanar Waveguide Feed

A coplanar waveguide is used for feeding the microstrip patch antenna.

When designing a microstrip antenna, performance can be enhanced by modifying the geometry of the metal patch or the thickness of the dielectric material. A properly designed microstrip antenna is essential for successful wireless communication in portable electronic devices.

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