Frequency and Parameter Considerations for UHF Chip Antennas and ISM Bands

Real-world applications in the UHF radio frequency band

Chip antennas are surface mount parts used together with PCB traces to complete the required length to transceive center frequency of the design. They are useful for designs with center frequencies requiring transmission and reception of wavelengths in the ultra high frequency (UHF), and above, bands.

Some of the most common frequencies in both the United States and throughout the world are 433 MHz, 915 MHz, and 2.4 GHz. So how do you choose the right chip antenna for your application? The best place to start is with your application and your operating frequency. We’ll be looking at three chip antennas each operating in a single band within the ISM region of UHF transceivers. We’ll cover center frequencies within the bands at 433 MHz, 915 MHz, and at 2.4 GHz.

Background for UHF and ISM Bands

The UHF band is composed of frequencies between 300 MHz and 3 GHz. The UHF band is regulated by the International Telecommunications Union (UTI) worldwide, specifying three regions that incorporate regulatory agencies for specific countries and/or areas within each region. In the United States, this is the Federal Communications Commission (FCC).

Within the band, there exist dedicated frequencies for industrial, scientific, or medical (ISM) purposes. These ISM bands were originally reserved for non-telecommunication purposes, such as microwave cooking. Amateur radio enthusiasts also used the ISM bands with the knowledge that if there was a microwave or other ISM-type device nearby, it may interfere with their broadcasts.

As electronics evolved into the present day, use of the ISM band continues to grow. Although regulated, the space does not require a license by the regulatory agencies to operate within. The agencies establish limits to electrical field strength at a distance of 3 meters, or about 10 feet, from the transceiver. These short-range applications employ low-power electronics and they have small form factors suitable for chip antennas. The applications for use of chip antennas are too many to name here but some include wireless local area networks (WLAN, including WiFi), Bluetooth, keyless locks, smart home applications, and manufacturing inventory tags.

Radio frequency identification (RFID) chip antenna

Defining Characteristics of UHF Chip Antennas in ISM Band

Chip antennas use radio frequency for wireless communication to transmit and receive data. Each antenna specifies the operating frequency and power rating within which they operate. UHF chip antennas are characterized by:

Antenna Frequency: The operating frequency at which the antenna receives and transmits information. It is the number of cycles of a wave per second.

Center Frequency: The central frequency between the upper and lower cutoff frequencies.

Bandwidth: The range of frequencies over which the antenna operates correctly.

Gain: The antenna efficiency plus directivity, measured in decibels.

Impedance: A quantity within the antenna that minimizes the wave.

Power Rating: The actual amount of power (in watts) of radio frequency energy the antenna may transceive.

In the UHF bandwidth, most devices operate at short range, transceiving within a smaller radius of about 10 feet. The power available for UHF transmission is typically smaller, in lower wattages, to support short range. Short range avoids competition for the communication space, so it is available to multiple users, simultaneously, in different locations. To avoid multiple users in the band, single frequencies are reserved for specific functions, such as ISM. These single band systems are available for use with UHF chip antennas.

Parameters to Consider When Selecting a Chip Antenna

Chip Antennas use PCB layout to get the correct length and impedance matching for proper transmission and reception. The transceiver vendor includes guidelines for layout of the chip antenna. Typically, the chip is placed on the PCB with ground planes adjacent rather than underneath the chip. Proper layout also includes impedance matching, usually with a pi filter, to obtain optimal performance of the transceiver.

Impedance matching requirements are specified by your vendor’s datasheet. Vendors provide development boards for use in validating critical layout patterns and for measuring actual impedance on the built board with a network analyzer. Use these test boards to discover optimal layout for the antenna, but with the caution that you’ll need to apply these techniques with consideration to the uniqueness of your final custom PCB.

Typical layout considerations for chip antennas illustrated on Johanson datasheet

The UHF chip antennas we’ll look at today are single band utilizing one operating frequency.

ISM 433 MHz Radio Band Chip Antenna

The radio band with center frequency 433 MHz is used for ISM devices in Region 1 of the ITU areas of the world that include Europe, Africa, the former Soviet Union, Mongolia, and the Middle East west of the Persian Gulf, including Iraq. The power output of this band, otherwise known as the 70-centimeter band, is specified by the Electronic Communications Committee (ECC) of the European Conference of Postal and Telecommunications Administrations (CEPT) at ECC Rec. 70-03.

Dedicated to ISM devices as well, it is used for hand-held radios for communication within Europe, for wireless instruments, and for digital devices such as car key locks, and all low power devices operating at short range.

Operating one of these short-range devices within the ISM band in Europe, or other parts of ITU Region 1, will require an antenna that tranceives at 433 MHz. If you have a design specifying a device that operates at 433 MHz, take a look at the ISM chip antenna offered by Yageo, the ANT1204F002R0433A.

This is a low power short-range, sub-GHz lead-free chip antenna for use at 433 MHz. It is compact in size with omnidirectional radiation for use in smart meter, industrial remote control, and other ISM band equipment. For development, a reference design within an evaluation board is available.

ISM 915 MHz Radio Band Chip Antenna

The radio band with center frequency of 915 MHz is part of the band dedicated to industrial, scientific, and medical (ISM) radio frequency. The power output of this band is given by the FCC which specifies electrical field strength and distance in FCC Sections 15.247 and 15.249.

Transmission distances approximate 3 meters and make the band useful for short-range, low-power wireless communications systems. It works well in small form factor applications. Some small form factor applications using this operating frequency in the ISM band include monitoring and collecting highway tolls, home weather stations, automated meter reading, industrial monitoring, home security, and (radio frequency identification) RFID tag technology.

If your design is using 915 MHz for its application, take a look at the ISM chip antenna offered by Johanson Technology, the 0915AT43A0026E.

Johanson miniature RF ceramic chip antennas are made using Low-Temperature Cofired Ceramic (LTCC) Technology which has the ability to embed low and high dielectric constants inside our antenna. This enables them to have great detuning resilience and extreme temperature stability (~2ppm) behavior.

Our ceramic chip antennas offer SMD manufacturability in standard or small form-factor designs/applications (i.e. ISM), provide great reliability and versatility while maintaining industry demanding performance. These antennas are easy to tune to any unique PCB environment. For qualified opportunities, we offer 2 complimentary (free) RF layout design reviews if you choose to use one of our components!

ISM 2.4 GHz Radio Band Chip Antenna

The radio band with center frequency of 2.4 GHz is also part of the ISM spectrum of the UHF band. The power output of this band is specified by the FCC in Sections 15.247 and 15.249.

This is part of the band dedicated to ISM, as well, and it is used for a variety of applications and protocols including Bluetooth and wireless local area networks (WLAN). There are a variety of protocols used within this frequency spectrum, several of which are IEEE 802.11 and IEEE 802.15.4 (otherwise known as Zigbee).

The band included 2.4 GHz has become very popular over the past several decades and is becoming crowded with use. Some of the applications that crowd the spectrum are WiFi devices such as gamepads, toys, PC peripherals, and audio devices. Using Zigbee in the spectrum are home entertainment and control, smart lighting, advanced temperature control, safety and security, movies and music, sensor networks, and more.

Should your design specify a device operating at 2.4 GHz, take a look at the ISM chip antenna offered by Pulse, the W3008.

This is a lead-free surface mount ceramic chip antenna for use in Bluetooth, wireless local area networks, and WiFi. It operates with protocols IEEE 802.11b/g, ZigBee IEEE 802.15.4, 2.4 GHz WLAN, and 2.4 GHz ISM band systems. Pulse offers test boards for tuning validation.

Pulse Larsen Antennas contains an online library including not only the technical datasheet but also 2D CAD layout and 3D STEP file to assist in design with this chip antenna. One of the layouts illustrated in the documentation includes the following:

One terminal configuration for Pulse Larsen chip antenna W3008

Chip antennas are effective low-cost parts to use for designs employing the ISM radio frequency band. The low-cost parts are implemented in a small form factor suitable for surface mount onto printed circuit boards that fit within small devices. Octopart can help you find the right chip antenna for your UHF necessities.

If you have comments or suggestions on chip antenna part selection, drop us a note in our Slack chat room or in comments below.

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