Antenna in Test Lab
The original aim for this antenna was to be a general purpose antenna that worked down to 400MHz. The results are now in and I am really pleased with them. The antenna was tested by AntennaTestLab in a full anechoic chamber with a 3D positioning system to automatically rotate the antenna. ATL use a dual polarized (horizonal and vertical) Vivaldi antenna to measure the radiation pattern. By recording both the amplitude and phase of each antenna they can use clever math to calculate the circular polarized gain. Clever stuff eh?! Take a look at ATL’s writeup here
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Now tested by AntennaTestLab. Part 3 to follow shortly. For now see results here
Electromagnetic simulation software can be very expensive. While some software is cheaper, it often comes with either technical or artificial limitations. There are however a couple of free alternatives.
NEC2 – Originally written by Lawrence Livermore National Labs, NEC2 was open sourced many years ago. Since then a couple of users have created good free or low cost front ends for it. 4NEC2 is my personal favourite. The best feature is it’s speed, especially if you can find a copy of NEC2/MP that makes good use of multiple core moderns processors. The big limitation is with dielectrics. Everything in NEC2 is either wire, free-space or earth.
OpenEMS – A Finite Difference Time Domain (FDTD) tool that uses MATLAB or the excellent free Octave as a front end. It was created by Thortsten Liebig at the General and Theoretical Engineering University in Germany. As suggested in FDTD, OpenEMS uses a time-domain approximation of Maxwells equations to calculate the results. The big advantage of OpenEMS over NEC2 is that it can handle bulk dielectric materials with different EM properties, I will need this to simulate an antenna on FR4 with an Er~=4. While it may not seem it at first, being able to generate geometry mathematically in is another advantage. This is especially true for a spiral antenna. Hence this is the package I decided to learn and use for this project.
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My original Palm Tree Vivaldi Antenna has proved amazingly popular. Much more so than I originally intended. The design aim for this was primarily for it to be small and portable.
When deciding what to do next I decided to create a survey and see what other people were interested in.
R&D Survey Results
The overwhelming response was that people wanted a bigger version that would cover lower frequencies. I can understand this, there are loads of interesting signals below 800MHz.
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Why Spacing Matters
Firstly, the antenna array I am designing is a fixed in-phase array. Hence we assume that the total path length from each antenna to the single input/output connection are the same length. This makes the design and analysis much simpler, especially for an ultra-wide-band design.
In my design signals that arrive at right angle to the antenna will add up co-herently (in-phase)
Signals arriving from boresight add up in phase
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Antenna being tested in anechoic chamber
My Vivaldi Antenna was recently tested by Antenna Test Lab who offer an excellent professional antenna testing facility. Antenna Test Lab are able to provide customers with full 2D/3D antenna measurement using their anechoic antenna testing chamber. Read more ›
I am conducting a quick survey to help discover what developments people would most like to take my UWB antenna forward. I would be really grateful if you could take a few minutes to have your say.
My next project after successfully building my Ultra-Wideband Vivaldi antenna is to use it to create a UWB antenna array. I will assume that most readers are at least slightly familiar with the concept of an array, I will give a quick introduction, but for those that want some background reading here is a good site to look at.
In essence we create when we sum the output of multiple antennas to increase the gain and directivity. Of key importance when we do this is to control the phase of the incoming signal that we are adding. I will be building one of the simplest forms of array, where all antennas are summed with an equal phase offset. This will have the effect of increasing the gain on the antenna boresight (and reducing the gain at other angles (I will get to grating lobes in another post)).
All antennas fed with equal phase offset.
The simplest way to do this is with a ‘corporate’ feed that consists solely of 2 way Read more ›