Designing an UWB Hexagonal Fractal Microstrip Non-Antenna, or Be Vigilant

In the past few years, I regularly come across tasks for the development of UWB (ultra-wideband) microwave modules and functional units. And no matter how sad I am to talk about it, but almost all the information on the topic I draw from foreign sources. However, some time ago, in search of the information I needed, I came across a very interesting article that prompted a solution to all my problems. About how to solve problems did not work, I want to tell.

One of the constant "headaches" in the development of UWB microwave devices is the development of UWB antennas, which must have a set of specific properties. Among these properties are the following:

1. Coordination in the working frequency band (for example, from 1 to 4 GHz). However, it happens when it is necessary to agree in the frequency range from 0.5 GHz to 5 GHz. And here comes the problem of dropping in frequency below 1 GHz. I got the impression that the 1 GHz frequency has some mystical power - you can get close to it, but it is very difficult to overcome, because this violates another requirement imposed on the antenna, namely
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2. Compactness. After all, it is no secret to anyone that very few people now need a waveguide horn antenna of enormous dimensions. Everyone wants the antenna to be small, light and compact so that it can be shoved into the case of a portable device. But when compactifying an antenna, it becomes very difficult to comply with point 1 of the requirements for an antenna, since The minimum frequency of the operating range is closely related to the maximum antenna size. Someone will say that you can make an antenna on a dielectric with a high value of relative dielectric constant ... And it will be right, but this contradicts the next item on our list, which says that

3. The antenna should be as cheap as possible and manufactured on the basis of the most affordable and inexpensive materials (for example, FR-4). Because no one wants to pay a lot of money for an antenna, even if it is three times brilliant. Everyone wants the cost of the antenna at the manufacturing stage of the printed circuit board to go to zero. For such is our world ...

4. There is another requirement that arises when solving various tasks related, for example, with short-range location, as well as with the creation of various sensors using UWB technology (here it is necessary to clarify that we are talking about low-power applications, where each dBm counts). And this requirement states that the radiation pattern (NF) of the projected antenna should be formed only in one hemisphere. What is it for? To ensure that the antenna "lights" in only one direction, without dissipating the precious power in the "return". It also helps to improve the number of indicators of the system in which such an antenna is used.

Why am I writing all this ..? In order for the inquisitive reader to understand that the developer of such an antenna faces a lot of restrictions and prohibitions that he needs to heroically or ingeniously overcome.

And suddenly, as a revelation, the article “UWB Hexagonal Fractal Microstrip Antenna Design” manifests itself, which promises a solution to all the above mentioned problems (as well as those that were not mentioned). Reading this article causes a slight feeling of euphoria. Although from the first time the full awareness of the written does not occur, but the magic word “fractal” sounds very promising, because Euclidean geometry has already exhausted its arguments.



We take up the task boldly and feed the structure proposed by the author of the article to the simulator. The simulator growls the computer cooler, chewing on gigabytes of numbers, and spits out the digested result ... Looking at the simulation results, you feel like a little deceived boy. Tears come to my eyes, because again your children's airy dreams came across a cast-iron ... reality. There is no agreement in the frequency range 0.1 GHz - 24 GHz. Even in the range of 0.5 GHz - 5 GHz, nothing like that.



There still remains a timid hope that you did not understand something, did something wrong ... The search for the inclusion point begins, various variations with the topology, but all is in vain - it is dead!

The saddest thing in this situation is that until the last moment you are looking for the cause of failure in yourself. Thanks to the shopmates, who explained that everything is correct - it should not work.

PS I hope that my Friday post made you smile.
The moral of this statement is: be vigilant!
(And I really wanted to write about this anti-article, because deceived).