Design for an Extendable Melee Weapon?
Background
I've been working on a RolePlay setting, for me and friends. The setting mostly uses energy weapons, and at the higher levels, anti-energy shields (Beam deflecting shields, or laser reflective materials). This comes with a trade off, leaving energy shielded targets vulnerable to material weapons, such as bullets and melee weapons.
Which are far, far less common. Since one cannot dodge a laser, but can move away from a projectile impact.
The setting has power armor, and is fairly high-tech. Advanced enough for 'heat sabers' and 'vibrating sabers' which make mince-meat out... Most things, and 'Thunderhammers' jack hammers that explain blunt force trauma, in detail, to the those ignorant of it.
Since the average battle involves heavy firepower, ammunition can easily run out, having a melee weapon is a fairly good back up. Ignoring major problems, such as closing the distance, we reach the issue I'm having.
Volume.
How, exactly, do you compact a melee weapon IE; a halberd. Into a form that does not expose your silhouette to targeting programs and the like. Then somehow, extend back to fighting form when needed.
Basically
How to design weapons that are compact, capable of extending back into normal form?
(Being compact and capable of extension, are not required traits. If the solution still saves of on volume while being practical.)