Microstrip Patch Antennas For RFID Readers

The advantages of microstrip antennas make them a perfect candidate for use in RFID (Radio Frequency Identification) applications. Microstrip patch antennas are being promoted for new high-speed RFID Reader Systems. This antenna style provides for a low profile, aesthetically pleasing and low cost as well as highly effective and efficient antenna design. Microstrip patch antennas are well suited for RFID Reader systems due to their versatility, conformability, low cost and low sensitivity to manufacturing tolerances.

Many recent patch antenna efforts have been focused on demonstrating broadband properties capable of high-speed data transfer. This has been seen in the Wi-Fi 802.11b/g market, High Gain Base Stations, automotive collision avoidance radars as well as many other applications. The RFID market is benefiting from these new materials and designs.

The dielectric constant (permittivity) plays a major role in the overall performance of a patch antenna. It affects both the width, in turn the characteristic impedance and the length resulting in an altered resonant frequency and reduced transmission efficiency. Some manufactures have been using the G10 fiberglass substrate (also known as FR4) but the permittivity (er ) of the substrate alters from batch to batch, sometimes even between different sheets of the substrate. In addition, FR4 has a high loss tangent and is highly frequency dependent. This has become an issue for RFID applications above 800 MHz.

The radiation efficiency of the patch antenna depends largely on the permittivity (er ) of the dielectric. Ideally, a thick dielectric, low er and low insertion loss is preferred for broadband purposes and increased efficiency. The advantages of microstrip antennas are that they are low-cost, conformable, lightweight and low profile, while both linear and circular polarization is easily achieved. These attributes are desirable when considering antennas for RFID Reader systems.