No it is in fact a fully functional second receiver. It is used for signal diversity and redundancy to avoid shadowing.
It really helps to keep at least one of the receivers with a direct line to the transmitter. Since 2.4GHz has the short antenna's you can imagine that a big engine or battery or muffler MIGHT have the ability to block the signal. So this was a way around that.
Many don't use this due to the cost and have since done receivers with whiskers that allow the same. Futaba is a good example of that.
Signal boost - can only be done at the Transmitter - the receiver only gets the signal. It can't do anything to boost the power of the signal.
The way I understand it is the "satellite rx" is a 2nd rx that is looking for the same signal from your tx. Redundancy would be a good term here. Positioning the satellite rx away from and perpendicular to the the main rx (particularly the antenna). I use this type of rx in my sailplane. I use the other small rx's in parkflyer craft.
Some receivers with a satellite port can be used without a satellite, and some can not.
I have used my Orange 6 ch rx's without and never had a problem, but they are in parkflyers, They have 1 satellite port.
I have a Orange 9 ch in a large trainer, I have 2 satellites plugged into it, when I do a ground range check, I have about 3 times normal range check (with the range check button pushed in). 1 ant. at leading edge, 1 at trailing edge, 1 at hinge line of elevator.
The AR7000 receiver must be used with a satellite RX, mine would sometimes work in my hobby room without one and sometimes not, so I sent it in to HH.
They told me that it must be used with a satellite, that is why one came with it, same for AR9000. On Spektrums, if it comes with a satellite port, use it.
I tested a Spektrum AR7000 rx with a Orange satellite rx, it didn't work. I had heard they would but it did not work for me,
Small, remote receiver attached to antenna provides signal path diversity
4-Channel – throttle, elevator, aileron and rudder channels for park flyers, trainers and most sport planes
Flight log and telemetry compatible
The full-range Spektrum AR400 is easily one of the best receiver values in RC. Giving pilots the speed and precision of the genuine DSMX control plus the signal security of an active amplified antenna. This antenna features a small, integrated remote receiver that enables the AR400 to “see around” reflective materials on a model and avoid antenna polarization blind spots. It allows the AR400 to pick out its transmitter’s signal with remarkable clarity in the noisiest 2.4GHz environments.