UWB design for a hexagonal fractal microstrip NE antenna, or be careful
In the past few years, I regularly face challenges in developing UWB (ultra-wideband) microwave modules and functional units. And no matter how sad it is for me to talk about it, but I draw almost all the information on the topic from foreign sources. However, some time ago, in search of the information I needed, I came across a very interesting article that promised a solution to all my problems. About how the solution to the 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 should have a set of specific properties. Among these properties, the following can be distinguished:
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 there is a problem to drop in frequency below 1 GHz. In general, I got the impression that the 1 GHz frequency has some kind of mystical power - it can be approached, but it is very difficult to overcome, because this violates another requirement for the antenna, namely
2. Compactness. After all, it is no secret to anyone that now few people need a waveguide horn antenna of enormous size. Everyone wants the antenna to be small, light and compact, so that it can be pushed into the body of a portable device. But when compacting the antenna, it becomes very difficult to comply with paragraph 1 of the requirements for the antenna, because The minimum operating frequency 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 permittivity ... And it will be right, but this contradicts the next paragraph of our list, which states that
3. The antenna should be as cheap as possible and be made on the basis of the most affordable and inexpensive materials (for example, FR-4). Because no one wants to pay a lot, a lot of money for the antenna, even if it is three times brilliant. Everyone wants the cost of the antenna to zero at the stage of manufacturing the printed circuit board. For such is our world ...
4. There is one more requirement that arises when solving various problems related, for example, to short-range location, as well as the creation of various sensors using UWB technology (here it must be clarified that we are talking about low-power applications, where each dBm on the account). And this requirement says that the radiation pattern of the designed antenna should be formed in only one hemisphere. What is it for? In order for the antenna to "shine" in only one direction, without dissipating precious power into the "return". It also helps to improve a 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 is faced with a lot of restrictions and prohibitions that he needs to overcome heroically or witty.
And suddenly, as a revelation, the article “UWB Hexagonal Fractal Microstrip Antenna Design” appears , which promises a solution to all of the above problems (as well as those that were not mentioned). Reading this article causes a slight sense of euphoria. Although the full realization of what was written does not happen the first time, the magic word “fractal” sounds very promising, because Euclidean geometry has already exhausted its arguments.
We take it easy and feed the structure proposed by the author of the article, the simulator. The simulator growls in the womb of a computer cooler, chewing gigabytes of numbers, and spits out the overcooked result ... Looking at the simulation results, you feel like a little cheated boy. Tears come to my eyes, because again your childhood air 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 there is nothing similar.
There is still a timid hope that you didn’t understand something, did something wrong ... The search for the connection point, various variations with the topology begin, but all in vain - it is dead!
The saddest thing in this situation is that until the last moment you are looking for the reason for the failure in yourself. Thanks to the fellow workers whoexplained that everything is correct - it should not work.
PS I hope that my Friday post made you smile.
The moral of this exposition is this: be vigilant!
(And I really wanted to write an ANTI-article on this subject, because I was deceived).