Small, High-Performance Antennas for IoT

Antenna design is a major pain point for IoT developers. In this article, I would like to bring another important point to your attention: IoT is all about smaller devices, which means, of course, you must make your antennas smaller. Trust me when I say antenna is the biggest component in your IoT product. Even when you select the smallest chip antenna, it requires a huge ground plane to radiate efficiently. When you cut down on the ground plane length, the antenna efficiency will reduce proportionally.

Chances are, you’re reading this precisely because you know miniaturization is no simple task.

According to the wavelength theory, the lower the frequency, the higher the wavelength or physical size of the antenna. The antenna length or size at lower frequencies such as 915MHz, 800MHz or 700MHz will be very large. This is one of the reasons why our smartphones are getting bigger.

Bigger smartphones might have better cellular reception capability as compared to smaller smartphones because the antenna size of bigger smartphones might be bigger too. However, many IoT applications require smaller sized products which are problematic to design, especially for lower frequency technologies such as cellular (2G, 3G, 4G, 5G, NB-IoT, Cat-M), Z-wave, Wi-Fi, LoRa, Satellite, Weightless and Sigfox. The smaller sized antenna will have reduced antenna performance or efficiency which will then result in the product failing certification (FCC, PTCRB, GCF, SAR, CE) and will also drastically reduce the field performance of the product. For example, an antenna with 50% / -3dB efficiency will deliver twice as much power than an antenna with 25% / -6dB efficiency.

Bulky antennas with large physical size are also prone to external inference from human touch, wall, human body loading or from other near-field interferers. Due to this, it’s always desirable to have smaller, high-performance antennas. Innowave have filed numerous patents on miniaturization technique for antennas without compromising antenna performance.

Innowave has designed a wearable IoT device with co-located multiple wireless technologies. The wireless technologies include cellular (HSPA+/WCDMA – 850/1900/2100 MHz and GSM/GPRS/EDGE – 850/900/1800/1900 MHz), Wi-Fi, GPS, and bluetooth. Other components in the product are a tri-axis accelerometer, touch sensor, speaker, microphone and battery. Innowave is able to design electrically small antennas for each wireless technology with patented antenna miniaturization techniques. With all these components included, the size of the product is just 81.5 mm (L) x 51.2 mm (W) x 13 mm (H) and weighs 57 grams. The product is shown in Figure 1 as below.

Figure 1: Miniaturized IoT device with Innowave patented antenna technology

This product has passed FCC, PTCRB and FCC-SAR certification.

The measurement setup in the Cetecom Milpitas, California is shown in Figure 2 below.

Figure 2: FCC, PTCRB and FCC-SAR certification test setup at Cetecom Milpitas, California.

We will be demonstrating the antenna tuning and measurement setup and results for custom-designed monopole antenna for Wi-Fi application with Innowave patented antenna miniaturization techniques.

Figure 3 shows the antenna tunning and measurement setup for Wi-Fi Antenna. The custom-designed monopole antenna is located inside the product with a 50 ohm SMA cable soldered onto the Wifi Chip RF Input/Output pin. We made a hole onto the enclosure to bring the 50 ohm SMA cable out to measure the antenna performance accurately as it will be used by the customer.

Figure 3: Antenna Tuning and measurement setup for Wi-Fi Antenna.

Figure 4 and Figure 5 below shows the tuning of a custom-designed Monopole antenna for Wi-Fi. Figure 4 shows return loss whereas Figure 5 shows input impedance. The return loss of less than -18dB is achieved across the Wi-Fi band, 2.4GHz to 2.5GHz.

Figure 4: Wi-Fi Antenna Return Loss (S11)

Figure 5: Wi-Fi Antenna input impedance (Z11)

This antenna is tuned, taking into account the loading effect of the human body, human touch and so on. Due to this, the field performance of the antenna will be very similar to Figure 4 and Figure 5.

To learn more about how you can benefit from our smaller antenna designs, please contact us.