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Gallery Example 7

PCB Layout Antipodal Vivaldi Antenna With Exponential Taper Slot Edge

Example 7: Antipodal Vivaldi Antenna With Exponential Slot Edge PCB

We had the pleasure of evaluating this pretty PCB antenna. It goes by the formal name of an antipodal PCB Vivaldi antenna with exponential slotted edges. Although, it is better known as a Palm Tree antenna! This design is by Iain, the author of the HexAndFlex Blog.

Our antenna testing services were used to evaluate this antenna to find out just how wide-banded it really is. It displayed positive gain from 1.5 to almost 18 GHz. Accounting for return loss and reasonable pattern directivity, the antenna is useful from about 1650 MHz to 9300 MHz. Realized radiation efficiency and return-loss/VSWR are great across this operating band.

Excel gain files are available for download here. Also, a 3D plot-file is available here, and can be used with our free 3D pattern plotting software.

Gallery Example 6

Photo 1 Pagoda 2 FPV LHCP Measured at Antenna Test Lab Co

Example: 6 LHCP Miniature Omnidirectional Antenna

This Example Test Report features a small LHCP omnidirectional antenna designed by Maarten Baert. It is a sophisticatedly simple design with three PCBs on a semi-rigid coax with an SMA connector. This inexpensive antenna was designed for the 5.8 GHz WiFi market, targeting FPV (first person view, AKA remote person view) drone control transceivers. 

This antenna performs very well, and has essentially 0 dBi gain in the intended sideways directions, where its axial ratio is around 2 dB. Radiation is verified as LHCP with a cross-polarization rejection ratio (in the sideways directions) of close to 20 dB. Realized radiation efficiency is 78% at 5.8 GHz, impressive for an C band antenna made with inexpensive FR4. 

The linked test report spreadsheet details full measured Gain Magnitude, LHCP, RHCP, and axial ratio data over the entire 3D sphere (approximately 400 physical test directions and 101 test frequencies). 

Excel data files are available for download here.

The 3D plotfile can be downloaded here. You can render rotatable and scalable 3D plots at any of the 101 test frequencies on your desktop with this free downloadable software


Our Published Antenna Testing Articles


Our Published Articles

Providing antenna insights is our passion! Some of our published articles are linked here; 

How to Pre-Test Your Product’s Antenna, EDN June 2017
The Many Benefits of Testing Your Antenna
The Benefits of Antenna Testing
Frequent Forum Contributions
In the November 2017 Issue: The Top 10 Excuses For Not Testing Your Antenna! 
Our No-Math Whitepaper on Circularly Polarized Antennas.


We also have written and published many antenna evaluation tutorial articles on this site too.

There lots of sample antenna test reports and patterns available here too.

To find out how we can help, just ask !

Thank You For Your Quote Request!

Thank you for contacting us. We will quickly review your request, and get back to you ASAP ! Now may be the time to familiarize yourself with antenna testing methods and boost your technical awareness with our educational section.

Return Loss and VSWR

Explained Without The Math !

VNA VSWR Antenna Tuning Before Efficiency Testing In Anechoic Chamber

VNA VSWR Antenna Tuning Before Efficiency Testing In Anechoic Chamber

RF energy travels through transmissions lines (coax cables or PCB traces) like sound travels through an empty room. It is susceptible to reflections an bounces. When sound waves hit the hard tiled walls of an empty room, you can hear strong echoes. The loss or reduction of the echoed waves is nearly zero. Imagine the difference when you are in a clothes packed walk-in closet … no echos. The fabric around you absorbs sound, and the loss of the sound bounces is high (high return loss). When we send RF down a coax or PCB trace we want it to go into the antenna (then radiate out into the world). We do not want it to bounce back at us like sound in an empty room.

Return Loss

This bounce back reflection is called “return”. Return loss is the measure of how small the “return” or reflection is. We want a small return, so a large loss on the return “echo” is good. Smaller return loss is bad, and means less energy is going into our antenna. RF engineers often measure return loss on a “dB” logarithmic scale, which can make it seem complicated. However, just remember greater the loss is indicated by bigger numbers and is better for your antenna. Here are some examples of the logarithmic scale, or loss in decibels:


Return Loss & VSWR Table

Return Loss in dB
What It Means
VSWR Number
0 dB
100% reflection, no power into the antenna, all reflected back
1 dB
80% reflection, 20% power into the antenna
2 dB
63% reflection, 37% power into the antenna
3 dB
50% reflection, 50% power into the antenna
5 dB
32% reflection, 68% power into the antenna
6 dB
25% reflection, 75% power into the antenna
8 dB
16% reflection, 84% power into the antenna
10 dB
10 dB (10% reflection, 90% power into the antenna)
15 dB
15 dB (3% reflection, 97% power into the antenna)
20 dB
20 dB (1% reflection, 99% power into the antenna)

As you can see, higher return losses mean more power into the antenna. Although more return loss is better here, there is little benefit above 10 dB return loss, since more that 90% of available power is already being delivered to the antenna.


It officially stands for Voltage Standing Wave Ratio. This dimensionless ratio (no measurement units) is the same parameter as return loss, just measured in a different scale. VSWR is someone old fashioned and was often measured by the transmitter itself while transmitting into an antenna. 

Measuring Return Loss

Measuring return loss during antenna design or verification is a powerful performance tool. Without good return loss, an antenna CANNOT accept your RF energy, and therefore cannot have it available to radiate. It is imperative that return loss goals and specifications be met. However, return loss does not tell the whole story. While it is true that poor (low number) return loss means that an antenna cannot radiate: It is NOT true that good return loss guarantees effective antenna radiation. Unfortunately, every week, we see antennas in our lab that radiate poorly, yet have a good return loss. Knowing (not assuming) your radiation efficiency is one of the many benefits of antenna testing

Radiation Efficiency

The problem is that internal losses or radiation inefficiency in an antenna can also create good return loss, since the lost energy is not being reflected (returned) to the transmitter. But how do we tell if our good return loss is due to radiation (desired) or internal absorption (undesirable)? The most accurate way is to have the antenna evaluated at an antenna test lab, and verify its radiation efficiency. Good radiation efficiency is the ultimate goal for most antennas.

Bench Checks

There are two other indications of poor radiation efficiency that can be checked on a test bench:

  • Hand proximity. While monitoring return loss, move your hand in close proximity to your antenna, about 6 inches away. If you see changes in return loss, that means the antenna is “interacting” with it’s surroundings. This is a good indication of radiation, and that return loss is probably not being dominated by internal losses.
  • Bandwidth. Good return loss over a very wide range of frequencies is hard to obtain. Thus, if wide band “good” return loss is observed, there may be serious losses in the antenna matching components. (You probably have not accidentally discovered a wonderful new wide band efficient matching topology!)

Your Next Steps

Are you ready for antenna insights? Partner with an antenna testing service and get results. You may contact us here

What is an Anechoic Chamber?

person in electromagnetic RF anechoic chamber with quad ridged horn antenna

Antenna Test Lab Co’s Anechoic Chamber

The Basics

An anechoic chamber is a shielded room that has absorbing material applied to the walls, ceiling, and floor. Chambers may be table top sized enclosures, but are normally room sized enclosures where engineers can enter and work. The absorbers on the inside surfaces are often pyramidal shape, and give the room an unique “science fiction” look. You may have also heard that they are very expensive. So why would anyone go to all of this trouble? Because there are many benefits to antenna testing!

The Flashlight Comparison

At Antenna Test Lab Co, we often find that comparing antennas and radio wave energy to light is helpful to our customer’s understanding of basic concepts. We often illustrate the anechoic chamber’s functionality with the following flashlight comparison.

Pyramidal RF Absorber Anechoic Test Chamber For Antenna Testing Services

Closeup of Pyramidal RF Absorber

Imagine your task was to “pattern” a flashlight. In other words, your job is to measure and create a map of where the device shines light, where it does not, and how much light goes where. It may seem intuitive, and that is because nature has equipped us with eyes, very sophisticated built-in light sensors. We are used to simply “seeing” light and it’s patterns, so it is easy to visualize a flashlight’s pattern.

However, we cannot see radio energy, directly so we have to measure it with radio receivers and antennas. Luckily, the propagation is very similar, so continue to visualize light from the flashlight. Now back to our task … patterning the flashlight. Imagine you have a light-meter, and will use it to measure the flashlight’s output in various directions to create the pattern of the flashlight beam. We would be using an antenna a receiver to do the same for patterning an antenna.

You start the job and quickly discover that your light meter readings are being interfered with by the sun. Outdoors on a sunny day, your light meter is picking up lots of sunlight, and confusing that with the flashlight’s light. You need “shielding”.


So you go indoors, to a windowless room, with the lights turned off. In this “dark room”, all of the observed light is from your flashlight under test. The room is shielded against outside light, just like the metal walls of an anechoic chamber shield our equipment from outside radio signals. Inside the chamber, only the radio frequency (RF) waves from the antenna or transmitter under test are measurable. This would be the perfect solution, if it were not for one problem … reflections ! 


A Mirrored Room With Infinite Reflections

A Mirrored Room With Infinite Reflections

Imagine the room you just chose was lined with mirrors. It is still a “dark room” and it is fully shielded from outside light. However, the mirrored wall/ceiling/floor reflections will cause chaos with your flashlight measurements. What can be done? 

You decide to paint over the mirrored walls, floor, and ceiling with a flat black paint. A paint so black that you can’t see it, one that absorbs all light. Now you have an optical anechoic chamber. The light that would bounce from the mirrors is like an echo, and anechoic means without echos. Now your flashlight under test appears to be in free-space. There is no ambient light, and the walls are not visible. 

Pyramidal RF Anechoic Absorbers Antenna Testing Company

Our Absorbers In The Anechoic Chamber

In the RF world, the reflective walls of the shielded room are made “invisible” or “anechoic” by covering them with RF absorbing materials. The most common absorber is a carbon loaded foam pyramid. Sharp tips on the absorbers keep RF waves from bouncing off, allowing the waves to slowly transition from air to the lossy carbon inside of the foam. This gradual taper from tip to core is the secret to RF absorbers. The amount of RF that bounces off of anechoic chamber walls is often 0.1% to 1% (-30 to -20 dB) of the original wave. The low level of reflections in our chamber allow us to accurately measure your antennas gain, efficiency, and radiation patterns. Find out more about how we do it in this educational article

Anechoic Absorber Tips


Our Anechoic Chamber

The walls, ceiling, and floor of our chamber are treated with over 2000 absorbing pyramids! The absorbers are between 12″ and 18″ long. We have an additional absorber in our chamber, called a ferrite tile. The ferrite tiles absorb RF at frequencies too low for the foam pyramids, and extend the anechoic ability of our chamber down to frequencies far below many antenna testing chambers. We routinely test antennas down to 300 MHz.

See It For Yourself

Drop us a note, and see how we can help get your antenna project and costs on track ! Many successful companies partner with an antenna testing service, and reap the benefits.

Circularly Polarized Antenna Testing Services


LHCP/RHCP, Co/Cross Polarization, Axial Ratio

And Cross Polarization Rejection Ratio

By Dave3457 - Own work, Public Domain, https://commons.wikimedia.org/w/index.php?curid=9862801

Our antenna evaluation service gathers full “vector data” during testing, which means your antenna’s gain and phase are both measured. We do this in every test direction, and for each test frequency. Then we do the complex math for you, and report all standard circularly polarized (CP) parameters in easy to read spreadsheets. Specialized post processing or graphing is made easy when your data is in our spreadsheet format. Virtually any plot can be created, including  overlaying co-polarization and cross-polarization parameters on the same graph. 

An example of our typical CP spreadsheet report can be found here. We have also created a no-math white-paper explaining CP antenna concepts, which can be found here

Your test results will include the following data in Excel format: RHCP Cavity Backed Spiral Antenna GPS Testing Spherical Pattern Measured in Far Field Anechoic Chamber

  • All of the features of standard passive antenna testing are included
  • LHCP Gain in dBi
  • RHCP Gain in dBi
  • Total Gain Magnitude in dBi
  • Axial Ratio in dB
  • Graphs of LHCP, RHCP, and Axial Ratio vs frequency for the preferred antenna direction (data is available for all test directions)
  • Raw orthogonal vector gain and phase data

Please Contact Us and see how we can help you with your antenna evaluation.