Jeff Liebermann wrote:


The bad news is that if Apple stabilizes the rx front end, and
eliminates the oscillation or regeneration, my guess(tm) is that the
resultant phone is going to have a serious rx sensitivity problem. If
you look at the cellular antenna in the iPhone 3G and other internal
antenna cell phones, they're not very simple looking devices. Lots of
strange lumps, traces, pads, and oddities, all designed to optimize
performance in the 800/900 and 1800/1900 MHz bands. Getting them to
look like 50 ohms for minimum VSWR is also important. Lots of
articles in the IEEE Antenna and Prop proceedings on the topic of
cramming a dual band antenna in the smallest possible package.

On the other foot, the iPhone 4 antenna is crude. As far as I can
tell from here, it's a crude monopole (single wire) antenna. There's
no matching circuit for VSWR reduction, and no attempt to optimize
performance in the desired bands. I might have missed something in
the dissection, but all I can see is an end fed monopole, without a
counterpoise or underlying ground. Such an antenna is going to have
resonances at odd frequencies, and miserable antenna efficiency.


I doubt they're using regeneration or some such similar scheme (too hard
to control for manufacturing variability)..

However,
the idea of self interference is interesting... (e.g. your finger
couples the WiFi to the cellular front end, which blocks)

It could even be as dumb as a dc bias shift thing (save a penny by
leaving out the capacitor, oops, that removed the DC block)


As far as match goes, in very compact systems, the idea of matching 50
ohms goes out the door unless one of your components happens to be 50
ohm impedance.. It's not like they're stringing together building blocks
with SMA connectors inside there. Lots of these RF circuits are
implemented with differential in and out these days, and the Z is
whatever it happens to be.