Electronic – Is it possible to bi-directionally route a 4G signal using a connected set of antennas only

When we talk about a digital representation of a signal it is implied that we can store this representation in memory, which requires that the amount of information (bits) is finite.

An analog signal has an unbounded amount of information, both in its level and in its variation in time. To make the amount of information finite you must quantize both.

Both 'single dimensional' quantizations you suggest can be done, but each transforms an analog signal into another analog signal, that must undergo further quantization before it can practically be converted to digital.

Brain mentioned an application of discrete-time continuous-value. A LED bar that indicates the loudness of your music is an example of an (in principle) continuous-time discrete-values system.

One could argue whether a continuous signal in either dimension exists at all. Charge is quantized (number of electrons) and according to modern theories time is so too, and practical circuits have limited speed anyway.

IR works well outdoors if excellent daylight blocking filters are used on receiver.

You need to measure range, azimuth for tracking then , altitude and centre offset error above bucket for dropping.

Amplitude will change with distance and offset to beam angle of each emitter as well as 'copter tilt, yaw and roll. You can also emit pulses at different frequencies with separate PLL optical receivers, spread apart from 30 to 50kHz. Clever might be one band for NS and another for EW, but avoid harmonic carriers like 24, 48 kHz. AGC is very effective but rate of tracking is uncertain, so tracking errors can be affected by rotation of moving copter. Time sequenced bursts to each emitter can also help determine location of each emitter using narrow vertical offset angles to help in centering before drop.

It is a geometry problem which can be solved using spacial and time resolution to very precise position if you need it. But I will let you figure this out.

As you know from recent history tracking one emitter with one antenna is ineffective.

If you can chose any method, you can make it beacon 2way with ground detected position error or 1way with bucket surrounded by a string of emitters with alternating wide angle and narrow angle , so you can compute tracking error from far and near field and overhead.

Photodiodes are very precise but amplifiers using single transistor have a wide spread in gain. Emitters can be calibrated to match by design but initially can vary widely 50%. Keep this in mind. Transconductance receivers have precise gain but suffer from wide bandwidth noise and thus filters are needed. Remote control receivers are cheap, accept a wide range of signal sources with AGC and PLL burst tracking filter but will only track the strongest signal, so several may be needed with synchronous time slots emitted for each frequency.