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The Effects of Dielectric Size in Microstrips

A dielectric substrate that has a radiating patch on one side and a ground plane on the other is known as a radiating patch antenna, or a microstrip patch antenna. The patch sitting on top of the dielectric substrate is photo-etched onto this substrate from a conducting material such as copper. A trade-off is needed to obtain a balance between the size of the antenna and its performance.

Purpose
- A radiating patch antenna has a low-profile structure that is common for use with wireless applications. This enables the antenna to be placed inside of a small hand-held device such as a cell phone.
Specifications
- Greater performance required by an antenna is obtained from a larger antenna size. This is realized by using a thick dielectric substrate having a low dielectric constant of 2.2 to 12. The ground plane size can be as big as 9 inches by 12 inches.
Feed Type
- If an aperture-coupled feed type is used with the antenna, two layers of dielectric substrate may be present. A high-dielectric substrate is used for the top layer, with a thicker low-dielectric constant material on the bottom.
Issues
- When the thickness of the dielectric substrate for the antenna is increased, it amplifies the surface waves and spurious feed radiation. This has the effect of disturbing the bandwidth of the antenna. This is seen when an aperture-coupled feed is used for the antenna, as it produces a narrow bandwidth. Antennas of this type with multiple dielectric layers are difficult to fabricate and increase the cost of production.

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