As there has been a lot of discussion about antennas lately, I'm wondering if anyone has played around with an inverted F antenna? I notice in the wikipedia article that there's one used in DECT phones that looks pretty simple and relatively small:
Since DECT phones run around 900Mhz, it would seem to be extremely relevant to those of us running at 915Mhz. DECT 6.0 is a different frequency altogether (1.9Ghz)
There are also inverted F antenna's that can be traced on PCB, with the advantage being that they're a bit more compact (as in Figure B below) than just straight traces:
[Edit #1: here's a simplified guide I found on how to do a trace antenna:
http://colinkarpfinger.com/blog/2010/the-dropouts-guide-to-antenna-design/Unfortunately, his example is for 2.4Ghz, so it would have to be adapted somewhat. It does seem to indicate, though, that I would need a network analyzer, which I can't really cost justify: I could buy a lifetime supply of splatch antennas for the cost of one of one network analyzer.
]
[Edit #2: On the other hand, TI does have a Design Nuide for how to do a 915Mhz Inverted F-antenna:
http://www.ti.com/lit/an/swra228c/swra228c.pdfand so perhaps that can be more readily adapted. In fact, it gives the exact dimensions of the antenna trace that would be needed. Further, it states in the conclusion, "Measurements of reflection show that the center frequency is easily adjusted by trimming the antenna length." The part that I'm puzzled over though is exactly what all those little discrete components need to be, and their values, between the radio and the antenna. Is there a similar way to wing it when it comes to those?]
[Edit #3: If all else fails, I'm guessing that some kind of folded monopole or meandering monopole antenna should be possible (as briefly outlined in
http://www.atmel.com/Images/Atmel-42332-ISM-Band-Antenna-Reference-Design_Application-Note_AT09567.pdf) by making the trace longer than it needs to be and then shortening it a bit at a time until the sweet spot is reached. It may not be perfect, but perhaps it would work good enough (?). ]
[Edit #4: I just found a Design Note for a chip antenna, and on its face it sounds quite good:
PCB footprint is just 8mm x 6mm in size:
http://www.ti.com/lit/an/swra160b/swra160b.pdf915Mhz Johanson chip atennas cost $0.92 each on Digikey in quantity 1. On the other hand, a uSplatch antenna is 9.14mm x 12.7mm but apparently can be mounted vertically if so desired to help keep a small footprint. The regular splatch antenna is 13.7mm x 27.94mm.
Is a chip antenna the smallest antenna that still performs reasonably well?]