Filters will definity help, but so will polarzation, distance and the directional nature of the antennas you use.
Polarization is simple, turn one antenna 90 degrees from the other. Distance is simple as well, move them as far apart as possible and get as much "structure" as you can between them, say opposite side of a house. Directional Antennas will also improve things but are limited to point to point applications.
I usually try these first, then make up the difference with a Filter. This way you won't pay for more filter than you need. For example, I seldom need more than a simple two or three pole filter after doing this and usually none at all.
If you do need a filter try the lower band (400MHz) first. You can find some good Lowpass designs in the ARRL books if you care to build it yourself. I think I saw a 1Ghz High pass on one of the ham sites, but don't remember where right now. It was coaxial and they made the coupling cap (dielectric rod) from plastic so it's inexpensive. Another was a PCB type.
I agree with what you have written, just one thing screening if directional types are used can further add to the isolation achievable. I using omni directional types then you have said it all. Putting them at different levels can also help. Here in the UK we use aerials, antennae are found on insects. seems the original has it that antenna was the yardarm of a ship. The use of the term describing protrusions coming out of insects heads was first coined in the 17th century. Thanks to T. plant of Birmingham UK. See Practical Wireless letters April 2007 Also on the web. A great read for all radio persons.
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Isolation Between Antennas
Re: Isolation Between Antennas
