What’s An Inverted-F Antenna | Radiation Pattern, Uses & More

An inverted-F antenna is a variation of quarter-wave monopole antennas that are widely used in telecommunication. The antenna features a conductive rod set at a 90° angle with a conductive ground plane. This type of antenna is fed at the base.

Because of its similarities to planar inverted-F antennas or PIFAs, people assume they serve similar functions. But in reality, a slot antenna resembles an inverted-F antenna or IFA better when it comes to performance. 

The most common antenna application is seen in mobile phone design when it comes to IFAs. That’s possible because of their small antenna size. There are other benefits to this antenna that make them so important in modern life. Keep on scrolling to learn all about IFAs.

What is An Inverted-F Antenna?

An inverted-F antenna or IFA has a short circuit arm that’s λ/4 in length and shorted at one of the ground plane’s terminals. The feed is at the base of the antenna.

Moreover, an inverted antenna is created by halving a slot antenna to create an open circuit. As we already said, the performance of IFA is similar to a slot antenna but it’s smaller, making it more useful for small devices. For example- mobile phones or notebook computers.

Here’s how an IFA is structured and how it appears from different viewing angles.

Inverted-F Antenna

Interestingly, the position of the shorting pin with respect to the feed pin of an IFA is what controls its input impedance and allows better impedance matching. The shorter the distance of the feed from the shorting pin, the less input impedance you get.

As you know, 50 Ω is the most commonly required input impedance for practical antenna designs. To attain this input impedance, the shorting pin has to be closer to the feed of the antenna as opposed to the open end.

Using a thick conductor to build an IFA improves bandwidth and decreases resistance as well.

Basics of Inverted-F Antenna

To expand your understanding of inverted-F antennas, here are some other basics that will clear the concept.

  • The first F-type antenna came about in the 1940s. The design of this antenna was different than the one we know today. The feed, instead of being at the base of the antenna was in connection with a point along the length.
  • The shorting pin is responsible for introducing an inductance to the input impedance.
  • On the other hand, the open end is responsible for the conductance of the input impedance.
  • It’s possible to get impedance at resonance if the two reactive components cancel one another. In that case, only the radiation resistance will remain.
  • The width of the shorting pin has to be fractional compared to the wavelength, between 0.05λ to 0.1λ.
  • IFA design doesn’t always have to be non-planar. A wire-type, non-planar construction is also possible.
  • It’s a widely used antenna for mobile devices. 

Importance of Inverted-F Antennas

Because of their similar performance to slot antennas but smaller size, inverted-F antennas are widely used in designing mobile phones, tablets, and even in wireless transmission. Your Wi-Fi, GSM, and Bluetooth may be using this antenna. Not only that, they are used in the manufacturing of vehicles. 

As the use of these antennas is so widespread, you can imagine just how it has affected the way we communicate. Even in military test ranges, they came in handy for judging telemetry applicants. 

Planar inverted-f antennas are also used in military vehicles because of their efficiency. For a broader bandwidth, multi-band antennas can be constructed with IFAs.

Radiation Pattern of Inverted-F Antenna

You’ll get an almost omnidirectional radiation pattern from an IFA. That’s because the slot is meant to be complementary to the dipole. Based on Babinet’s principle, both the patterns of dipole and slot are supposed to be identical.

Here’s what the radiation pattern of an inverted-F antenna looks like. As you can see, it’s in the shape of a donut.

Radiation Pattern
Radiation Pattern

Tips to Design An Inverted-F Antenna

IFAs can vary in impedance based on their structure. You can make the following adjustments to your design to get the desired result.

Tip 1

A closer positioning of the feed and shorting pin reduces the impedance in IFAs. Place the shorting pin closer to the side of the ground plane that has the feed and farther from the open end. It’ll give you a lower impedance of about 50 Ω, which is utilized in many devices.

Tip 2

You need to ensure that the width and height of the ground plane are as much as the length of IFA, which is λ/4. A smaller height will result in a loss of bandwidth as well as efficiency. 

So, make sure your design is in accordance with these proportions.

Other Monopole Antenna Types You Should Know About

There are many other types of monopole antennas. The following are some of the most common ones.

  1. Helical Antenna 

When a single or multiple conducting wires are wound to form a helix, it’s called a helical antenna. The most common design parameter is called a monofilar, which consists of a single helical wire. 

Helical antennas can be directional or omnidirectional. Directional helical antennas are usually positioned on a ground plane with the feed line connecting the ground plane and the bottom of the helix. They have two modes of operation. One is their normal mode, the other is axial.

  1. Whip Antenna

A whip antenna has a straight wire or rod connected at the bottom to a transmitter or radio reception system. 

One of the best things about this antenna is its flexible structure makes it durable. These antennas are useful to construct portable radios, telescope tubes, etc.

  1. Folded Unipole Antenna

This antenna is made with a perpendicular metal rod connected to a ground plane at the base. The top of this metal rod has some vertical wires attached to it, forming a sort of skirt. 

These wires lead to a metal ring that is closer to the base of the rod. The antenna is fed between the ground plane and this metal ring. 

Analysis of the IFA


What is the gain of an inverted-F antenna?

An inverted-F antenna is a comparatively high gain performance with its beams being concentrated over a good distance. You can expect to obtain 8.5- 12dB easily. The gain variation is also good at a little above 1 dB. Overall, IFAs are good at transmitting power in the desired direction.

How is the PIFA antenna? 

PIFA or planar inverted-F antenna is a resonant patch antenna that possesses great SAR qualities. It’s very popular when it comes to building mobile devices. omnidirectional radiation pattern and small size are what make their usage so widespread.

What is a meander antenna?

It’s a microstrip antenna that’s much smaller than the IFA. In fact, this antenna’s largest dimension doesn’t exceed λ/10. They are made by a conductor with lots of vertical and horizontal turns. More turns make the antenna more efficient. They’re increasingly being used in smaller wireless devices.

Others antenna

Final Words

Antennas are getting smaller and smaller every year. The invention of the quarter wave antenna like the IFA in the 1940s paved the way for portable devices. This mobile phone antenna is also useful in making vehicles. 

Technology has advanced to a degree that there are much smaller microstrip antennas available. Making it possible to carry smaller and smaller devices with you.

Our basic guide on inverted-F antenna covers all the primary aspects but there’s a lot more to these antennas. Leave us a comment if you have any questions. We would love to help you out.

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