One of the useful properties of the binary XNOR is the fact that it is true only when both inputs are true and is otherwise false. The ternary XNOR does not share this property. A related gate does demonstrate this property and is called the Consensus Gate. The consensus gate is + when both inputs are +, is - when both inputs are -, and is 0 in all other conditions. Dr. Jones indicates that this gate is very useful in certain balanced ternary arithmetic circuits. In fact, the Consensus truth table is also the truth table of the carry-out when adding two ternary numbers. If you add two -'s you get a - carried to the next column over. If you add two +'s, you get a + carried over. Because of its usefulness in the future I'm glad it was a very simple one to build. It consists of a Min gate and a gate composed of two monadic C's OR'd together. Based on my earlier naming scheme, this two-C's-OR'd-together gate would be designated a "CDD gate" based on it's truth table. I simply took the outputs of each and OR'd the results together.

The CDD Gate, composed of two monadic C's OR'd together.

The Min Gate, composed of two monadic P's AND'ed together.

The final Consensus Gate, from OR'ing the above two gates together.

Here is the schematic.