Fast and Easy Design of a Key Fob Antenna

Cabin Comfort Solution

Problem Statement:

Have you ever wondered how the doors of your car unlock with just the click of a button, even at a distance of more than 30 feet? The remote keyless entry device, commonly known as “key fob,” is an engineering marvel that fits into the palm of your hand. Now try to imagine carrying a key fob the size of an iPad. That would be pretty inconvenient! This could have happened, if the designers of the key fob antenna gave up at an early stage in the design process.

A key fob operates at 434 MHz, and an antenna at such a low frequency is generally as big as an iPad. If we try to reduce the size, the frequency increases. And this is exactly the problem engineers were facing while designing an antenna that fits into a small 6 x 4 x 1 cm key fob casing for the CATIA Bleu car. For such small dimensions the antenna started resonating at around 3GHz. How did engineers fit an antenna into the small key fob casing while still meeting the lower frequency requirement?

  • Since Antenna Magus didn’t have an antenna that fulfilled the constraints, we designed a parametric patch antenna in CST Studio considering the physical constraints of the casing. Simulation revealed that the antenna resonated at a little above 3 GHz.
  • We optimized the antenna length, width and ground plane dimensions, which brought the frequency down to 2.8 GHz.
  • Next, we introduced meander lines into the patch to increase antenna length, which further reduced the frequency to around 2.5 GHz. At this stage, the key fob started interfering with the Bluetooth and WiFi antennas on board the Bleu car.
  • So we used the “matching circuit” macro that provided the exact values of lumped elements (capacitors, inductors) required to tune the antenna to the key fob frequency.
  • The last step was to delete the matching circuit and to introduce those lumped elements in to the geometry and re-simulate to verify if the antenna is really resonating at 434 MHz.

And voila! It worked like a charm.

Thus, we succeeded in designing an antenna within the size constraints while resonating at a lower frequency of 434 MHz. Also, interference to the Bluetooth and and WiFi systems was avoided and harmony was established between the RF systems in the Bleu car.

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Katie Corey

Katie manages SIMULIA's social media, blog and online communities. As a writer and technical communicator, she is interested in and passionate about creating an impactful user experience. Katie is a native Rhode Islander and loves telling others about all it has to offer. As a self-proclaimed nerd, she enjoys a variety of hobbies including history, astronomy, science/technology, science fiction, geocaching, true crime, fashion and anything associated with nature and the outdoors. She is also mom to four amazing furbabies (2 cats and 2 dogs).

Deepak Goyal

Dr. Goyal is a Senior Technical Specialist, currently playing the role of simulation consultant in SIMULIA's Aerospace & Defense Industry growth team. He received his M.S. & Ph.D. degrees in Aerospace Engineering at Texas A&M University in August 2003 & December 2007 respectively. He is a recipient of American Institute of Aeronautics and Astronautics (AIAA) open topic graduate award in the year 2006. In academia, he has conducted extensive FAA, NASA & AFOSR funded research in tape laminated composites, textile composites & materials with complex microstructures. Since January 2008, he has been working with Dassault Systèmes SIMULIA Corp. where he has provided training & consulting services to SIMULIA’ s customers in various industries. Dr. Goyal has published several journal papers in highly reputed peer-reviewed international journals and has also reviewed scholarly articles of other researchers for leading journals in the area of Composites Materials.

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