Chip vs. PIFA: Selecting the Proper Antenna for a Booming IoT Medical Trade
According to a recently published market research report on transparency, the IoT medical device market will see an increase through 2026. These devices may include vital signs monitoring devices, imaging systems, breathing devices, implantable cardiac devices, infusion devices, anesthesia machines, and neurological devices, hearing aids, fetus monitoring devices, and ventilators. “
With this shift in perspective, developers in the medical technology industry can identify significant hardware innovations even at the passive level. The passive manufacturer Abracon recently updated its selection of dielectric resonator antennas and reaffirmed its commitment to solutions for IoT medical devices.
Abracon’s guide to chip selection covers several classifications, including Wi-Fi, cellular, and medical. Image courtesy of Abracon
Dielectric resonator antennas, commonly known as chip antennas because of their small size (only 2 mm x 1.25 mm), offer certain advantages over planar printed circuit board antennas. In this article, we’ll compare the two and discuss how each can play a role in an evolving embedded landscape.
Design advantages of chip antennas and PIFA
Both chip antennas and planar inverted-F antennas (PIFA) have their own design complexities that require the expertise of an RF designer to navigate.
Chip antennas can be successfully matched with a passive network of inductor and capacitor components, creating a well-matched transceiver system. In comparison, PIFAs require significantly more simulations and possibly additional rotations of the board to optimally tune the RF chain.
Some other practical considerations in choosing a chip antenna include the lower frequency operating frequency that may make PIFA structures unsustainable and ground level clearances which determine the space constraints for the rest of the board.
Which parameters determine the antenna geometry?
IoT devices differ in their application, and RF design requirements such as antenna pattern, gain, and directivity vary depending on the application.
Both PIFA and chip antennas have an omnidirectional antenna pattern, which is ideal due to the mobility of an IoT device. Image (modified) courtesy of 5G Technology World
Antenna polarization (either vertical, horizontal, or circular) has a major impact on power reception. An omnidirectional pattern generates energy in a uniform “donut”, which means that both the receiver and the transmitter can be at different angles of incidence to one another.
Another parameter, the permittivity (also known as dielectric constant), has a great influence on the determination of the final dimensions, which should correspond to a quarter wavelength. The wavelength is inversely proportional to the dielectric constant for a given frequency.
PCB layout size restrictions can be greatly simplified with a small ceramic chip antenna compared to a monopole or PIFA. Image courtesy of Abracon
When printing on FR4 with a dielectric constant of 4.4, a printed monopole measures ~ 23mm. Ceramic chip antennas, however, have significantly higher dielectric constants, which allow much smaller geometries and possibly lower losses at very high frequencies.
Antenna Considerations: Form Factor, Frequency, and Range
Using the Blumio blood pressure monitor as an example, a designer must weigh cost and operating frequency considerations against both the fixed form factor size of the portable device and the wireless range between the transmitter and receiver.
The Blumio Radar-based Blood Pressure Monitoring Development Kit, natively connected to meters, can be designed to provide wireless functionality. Image courtesy of Blumio
A design scenario can develop as follows: A development kit is expanded to include wireless functions that communicate with a vital monitoring station near the patient. Because the device and its receiver are in the same location, a designer can select an operating frequency in the MBAN range (2360 GHz to 2400 GHz). Because of the higher operating frequency, several antenna structures become viable competitors.
There is a cost tradeoff between the one-time engineering (NRE) cost of developing a well-tuned PIFA and the large-scale production costs associated with the additional passive components required for a matching network and chip antenna.
To delve deeper into this conversation, the designer must also address the end market. Larger production costs can be tolerated to a lesser extent – for example, a medically oriented product family (Pro: Chip antenna); However, a commercial product family intended to be sold in millions of units would benefit from a smaller parts list (pro: PIFA).
Final thoughts on competing antenna parameters
Chip antennas, like planar PCB antennas, have advantages and disadvantages that affect the design process. In addition to the RF parameters selectivity, sensitivity, efficiency and power, there are also considerations to be taken into account.
Some of these considerations include, but are not limited to, the designers’ expertise in relation to RF, the volume of production of the application, and constraints on antenna geometry due to form factors.
Choosing an antenna structure for tiny medical IoT designs can be a challenging process. If you’ve been working on a project like this recently, what decisions did you make? Let us know in the comments below.