I am designing a monopole antenna For 59MHz frequency . The lamda length is 5m. I tried for lamda/2 which is directly interfaced to sma connector. Couldn't get proper return loss.( According to prof. Girish kumar the antenna length should be lamda/2 for minimum ground plane. )
I'm pretty sure a half wavelength monopole is going to give you about the worst impedance you could have. Think of what you're trying to do at the feed point. You're trying to make a halfwave resonant structure where the current is zero at the far end (tip) AND at the feed point. What I suspect your professor stated was that this would RADIATE well, but not that you could feed it worth a darn!
The other thing to remember about not having a ground plane... The shield of the coax that feeds it becomes the opposite pole of your dipole. If you can make that shield electrically look the same length as the element, so that you're actually feeding the center of a dipole, then you can still radiate quite well and even have a good match. This is the concept behind a sleeve dipole.
Michael
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