Finding the Right RFID Antenna Design

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Finding the Right RFID Antenna Design

Article by Mobile Mark

If you are selecting an RFID antenna design for a new RFID installation, the choices may seem daunting. There are many factors to consider such as: Operating Environment, Coverage Range, and Potential Interference. It is important to select the RFID antenna design that matches the environment, which can be as diverse as a temperature-sensitive Cold Chain Management application or a large-volume Homeland/Port Security active tracking application or a high traffic/high impact Distribution & Warehousing settings with heavy equipment and obstructed range. By matching the RFID antenna design to the application it is possible to achieve optimal coverage, quicker registration of the RFID tag and greater hit-rates for tag reading. The right antenna will save the RFID user time and money by providing more reliable and more accurate reporting.Frequency: RFID manufacturers design systems to operate on a variety of frequencies depending on the application and the location. Current RFID systems include: HF at 13 MHz, UHF (orUltraHighFID) at 915 MHz (or 868 MHz in Europe), and RTLS (Real Time Location Systems) at 2.4 GHz. HF applications have been around longer and include applications such as the tagging and tracking of library books. Most UHF applications are newer than HF applications, so there are more unanswered questions as we move through the learning curve. For the sake of focus, this paper will cover RFID Antenna Designs for UHF frequencies.

Orientation of the tags: Polarization is important for optimal signal transfer. Site antennas that communicate with each other are installed so that they have the same polarization, for example both would be vertically aligned or horizontally aligned. Because it is difficult to know that orientation of the small RFID tags placed on many items, RFID manufacturers typically use circularly polarized RFID antenna designs. The circularly polarized radiation pattern makes it possible to get reliable read capture rates when tags are coming from all directions. Circularly polarized reader antennas provide higher read probability for those important high traffic settings. However, in some settings, such as a RFID smart shelf application, where the tags are read in close proximity to the reader, a linearly polarized RFID antenna design might be preferable.Polarization direction: RFID reader antennas are typically designed to be circularly polarized in a particular direction. In the US, the standard configuration is right-hand circularly polarized and in Europe it is left-hand circularly polarized. The RFID modem manufacturers will generally mark on the spec sheets whether the RFID antenna design is RHCP or LHCP. In actual use, the circular polarization direction makes no difference since the tags are generally linear.

Gain: Antennas for the RFID Readers are used to direct and shape the RFID signal from the Reader. Antennas of different gains exhibit radiation patterns of different shapes which allow the network installer to optimize the coverage area. Higher gain antennas throw the signal further but with a narrower beam; lower gain antennas will provide a wider (rounder) coverage area. Outdoor installations, such as in a car lot, may require a high gain panel antenna but close-in applications, such as tracking items on a conveyer belt, will call for a lower gain antenna. Selecting the right level of gain for the application is important; for example, an RFID reader installed to read packages coming in one dock door should not be reading tags on packages coming in through a neighboring dock door. RFID manufacturers will often certify a variety of antennas for their Readers.

Impact on RF performance: RF signals do not penetrate metal and will be deflected when they hit metal. At a minimum, RFID manufacturers will tell you that item level Tags need to be placed on items in such a way that they are not shielded by metal. Other materials, such as water, can also pose an RF problem; it is difficult to read an RFID tag through liquid.

Impact on durability of antenna: Networks that are set up outdoors will need to be designed to handle a range of weather conditions. This may include large swings in temperature, or resisting moisture damage. Most RFID manufacturers in the US will provide detailed installation instructions with pointers such as “don’t cover drain holes”. These are important guideline; understanding how the antenna should be installed will go a long way towards eliminating problems down the road.

Unusual settings: Every installation is unique but some settings pose more challenges than others. The Fork Lift setting, for example, provides ample challenges for antenna design; the all-metal construction blocks efficient signal transfer while not providing enough backing for a solid ground plane. Look for an RFID antenna design with sufficient shielding and with a mounting solution that allows the antenna to be mounted to the load back rest of a forklift truck for palletized scanning.

Another challenging setting involves tracking items that are removed from and replaced in fixed locations such as a retail display or production conveyor belt. A Near Field Loop Antenna offers maximum power density in close proximity to the antenna. The read range for this particular RFID antenna design is tag dependent but is typically up to 3 feet. The high forward directivity of the Near Field Loop Antenna combined with extreme isolation adjacent to the antenna results in fewer instances of misread tags.

Connections: It is important to know which connector is used as the RFID reader termination. The connector on the Reader Antenna will need to mate with that connector. Some RFID antenna designs have the mating connector directly on the antenna; for others the connector is located on a cable pigtail exiting from the RFID Reader.

Useful accessories: Jumper cable assemblies can be provided by many RFID manufacturers or by many antenna manufacturers. Jumper cables allow for the antennas to be positioned further from the RFID reader which increases the variety of installations possible.

Developer’s Kit option: It should be clear from the preceding article that it is useful to keep your options open when setting up a new RFID installation. Most manufacturers recognize that wireless settings will vary and will therefore certify several different RFID antenna designs for their RFID Readers. Requirements will vary from setting to setting. In some cases the RFID installation will work better with more gain and in other cases it will work better with less gain. Similarly, some settings will require circular polarity and other settings will operate better with linear polarity. Mobile Mark offers a pre-packaged RFID Developer’s Kit which allows network designers to experiment with different RFID antenna designs. Nine different models are available ranging from a compact strip style antenna with 2.5 dBi gain and linear polarity to a powerful panel antenna with 10 dBic gain and circular polarity. A Developer’s Kit allows the network designer to take all the issues raised in this white paper into consideration. It is a convenient way to see the impact of different RFID antenna designs on a specific installation.

About Mobile Mark, Inc.:

Mobile Mark, Inc. designs and manufactures site, mobile and device antenna for 600 MHz – 9 GHz. Applications include GPS Tracking & Fleet Management, Cellular GSM/CDMA, LTE, WiMAX, WiFi, RFID, Public Safety, Military and Machine-to-Machine (M2M). Engineering and custom design services available. Mobile Mark’s global headquarters, which include research facilities and manufacturing plant, are located near Chicago, IL. An additional manufacturing and sales facility is located near Birmingham, UK. Complete information on various RFID antenna designs can be found on the Mobile Mark website.

Contact:Eleanor Sylvan, VP MarketingMobile Mark, Inc.Tel: 847-671-6690esylvan@mobilemark.com www.mobilemark.com

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Antennas question by Tractor: Can I hook up two HDTV antennas to my TV to get a better signal?
I want to get the best possible signal of over-the-air channels on my HDTV. It’s sometimes hard to get the channels to come in. If I get a splitter and hook up several HDTV antennas on different sides of my home, would that be beneficial? Thanks for any answers.

Antennas best answer:

Answer by marty
One good external aerial on a 15 foot mast should be sufficient ,you could always add in internal aerial signal amplifier if needed.More aerials does not equal a better tv picture in fact it could have the opposite effect.