Two constructions of quaternary Legendre pairs of even length

We give the first general constructions of even length quaternary Legendre pairs: there is a quaternary Legendre pair of length $(q-1)/2$ for every prime power $q$ congruent to $1$ modulo $4$, and there is a quaternary Legendre pair of length $2p$ for every odd prime $p$ for which $2p-1$ is a prime power.