What is the most difficult antenna problem you had to deal with?

Probably more a funny story rather than a difficult problem/design...  When I was a grad student in college we needed an antenna to receive the 10MHz WWVH signal reflected off the ionosphere.  We had just moved into a new engineering building and we built a simple half wave dipole on the roof.  Construction was straightforward but somewhat awkward because of the 15 meter span.  The only scary part was that we were 4 floors up and working next to an atrium that was open all the way to the ground.

The antenna worked well when we initially tested it,  but after a few weeks we started experiencing severe overloading of the receiver.  It took a while to figure out, but there was a project in the Geophysics building across campus that was communicating  with a ship offshore and the line of sight of their transmission was directly across our antenna.

I guess the moral of the story is be aware of your environment and the effect on your design, but with RF communication that's not so easy to do.  I'm amazed sometimes that things work at all...

also a school story: in the last year we had to make a project. One of my classmates made a HF morse code sender. Another one a programmable incubator for eggs. When the HAM guy pushed his morse key, the UV lights in the incubator would switch on

Well, I've had quite a bit of fun with antennas of all sorts - from DIY dipoles and Yagis for amateur/satellite applications, to compact antennas for digitally modulated silicon radios (Wi-Fi, Bluetooth, Zigbee, LoRa, LTE), to broadcast FM radio/TV and satellite. Meeting all the requirements is not easy - microwave work is still considered a "dark art" to me.

That being said, I guess my antenna story would be to do with the changeover to digital TV which required higher-frequency coverage than most already-installed antennas. The log-periodic was a natural choice, as they were compact and wide-bandwdth. Just one problem - the tapering elements, reducing in thickness didn't seem to please the local wildlife, so our magpies and crows started bending them and picking them off. That was not fun to replace!

I did some work servicing an amateur radio ground-station crossed-yagi on a rotator. That was pretty cool, except for the fact it was a giant construct and would be prone to jamming the rotator when the winds got too strong. Getting into satellite TV, truing up a dish to make sure it was properly focused and properly aligning the LNB in terms of position and skew is always a bit of a challenge. Pointing is the easy bit, even though even that can be tricky when your dish isn't all that big and you're trying to catch a buried feed that's intended for a much larger dish. In the past, I've had fun chasing analog weather satellite (APT) transmissions with a homebuilt QFA and chasing AMSAT AO-51 Echo similar amateur "easysats". But unfortunately, time is perhaps the more limiting factor.

More recently, I've been working on a few smaller projects involving LoRa - finding antennas that perform well but are compact can be difficult depending on the band and the radiation pattern + gain requirements. Unfortunately, when it comes to designing PCB-based antennas, almost anything can affect its tuning, to the material in use and the consistency of the manufacturing. It's hard to know we have an optimal solution, so usually we settle for "it works well enough." Otherwise, we stuff a connector onto it and use a commercial antenna ...

- Gough

I found the most difficult problem to deal with is determining realistic transmit ranges before actual purchase and testing of transceivers/transmitters/receiver.

Here's a classic example: https://cpc.farnell.com/rf-solutions/alpha-tx433s/rf-transmitter-module-fm-433mhz/dp/RF00476

Here the headline states that this transmitter module can provide transmit distances up to 300 metres. Good luck with that. With a poor/basic antenna you'll probably will get 30 metres line of sight and with a lot of work tuning and testing probably 100m, or slightly more, line of site in the real world. As others mentioned it depends on the environment. It takes a good deal of work and knowledge to stretch this distance and the antenna plays a significant but not sole role in achieving this improved performance.

Great story!

The most diffcult antenna problem I had was trying to read an NFC tag in a ball placed on a table. The orientation of the ball was critical. I ended up testing a multiplexed antenna array but couldn't quite manage the combination of orientation and distance considering the ball could only sit in a small depression on the table. (I know NFC antennas aren't strictly speaking antennas. The final solution used an active 2.4GHz solution.)

The final result was used for this - the balls were a "seed" that identified the user as the travelled round the exhibit.

...(If you have an antenna horror story, we think we'd all like to hear about it.)...

Getting a 10' diameter parabolic antenna (in two halves) into a building, up six flights of winding stairs, through two labs and out a fire escape, in order to get it onto the roof of the building. All whilst trying to look confident that it would actually work and that this was a perfectly normal and everyday sort of thing to do... Was actually going surprisingly well up until the point my belt buckle got latched into one of the cut-out holes on the back of the supporting rim. I must admit that it's pretty difficult to keep up the creditability after losing one's trousers in public...

This isn't really a horror story .... well maybe it was to my wife - to me it was more like my first successful antenna design. Way back before I could afford cable TV, I built a big Yagi antenna for my TV by taping Yagi elements to the ceiling in my living room - the antenna was aimed at the mountain where all the TV stations located their broadcast antennas, so the orientation never needed to change. We were renovating that house at the time, but the ceiling reno "had" to wait until we could afford cable TV.

I have a masters in antenna design. I will list out all the difficulties I faced throughout my master's. I have designed around 5-6 different antennas all of them are reconfigurable. The first problem is to match the results of the simulated antenna and the fabricated antenna. Often due to the fabrication tolerances, the connectors, solder as well as material parameters (dielectric const), the experimental results of the antenna do not match the simulated one. Another problem that I faced was the reconfigurability, the reconfiguration in antennas is done by using an active element, such as an RF switch (pin diode, FET, etc). The RF switch needs to be properly modeled to get accurate results, as well as the biasing circuit, needs to be proper for the freq. of operation. These RF devices are often very expensive and difficult to procure. In the below image you can see all my published papers to date on antennas as we all FSS.