I work for a sat phone company and we’ve had a lot of antennas on one particular model phone come up bad, which is a royal pain because finding replacements is getting to be well nigh impossible (seems a lot of people with names beginning with Captain, Major, etc. are needing the phones in a hurry) and we’re winding up with a lot of perfectly good phones, except for the fact that the antenna’s bad. So I pry one of the antenna’s apart (don’t tell my boss!) and its like nothing I’ve ever seen. Instead of being a coil of wires around an iron core its this plastic thing that looks almost like a barber pole except that instead of the red stripes there’s metal bands and the wire that goes from the connector that plugs into the back of the phone terminates into a tulip shaped piece of metal that sits inside of this plastic tube. No where does the flower part touch the metal bands (they’re on the outside of the tube). How in the heck does this thing work? The phones operate, I think, in the L-band range (at least that’s what my boss says). Anybody know of a better design I could fabricate? If you need detailed specs, I can scrounge them up for you. Also, any guesses as to what could be causing them to conk out on us? Thanks.
It sounds like the antenna is capacitively coupled to the rest of the circuit. The tulip-shaped piece of metal forms one “plate” of the capacitor, and the metal bands form the other “plate”. At L-band frequencies (1.15-1.73 GHz) it doesn’t take much capacitance to create a low impedance path.
I’m not sure what could actually fail on the antenna- it sounds like it’s just some metal and plastic. Maybe the “tulip” gets deformed? At those frequencies, it would be easy to detune something if you mess with it.
Arjuna34
Arjuna34, there’s not really much room for that “tulip” to move around in and get deformed. Of course, I’ve only torn apart a bad antenna, it might look somewhat different in a working one (but if it is, I bet you can’t tell by using the naked eye). The phones have two antenna’s, the other one, which never breaks, is one that’s about an inch in diameter and looks like a small stop sign. (You stick it on the phone and slap it on the roof of a car.) Any idea of how it’s put together? Its in a solid piece and I can’t tear into it without damaging the insides.
In my community we have had more microwave tech startups than any other area in the US over the last 5 years and I have sold and leased industrial facilites to several of them. There are some excellent design and fabrication houses here that do design and fab work for Motorola and other manufacturers and could probably duplicate your antenna fairly quickly and in quantity.
Drop me an email if you would like their telephone #'s.