Excalibur is an all-rounded warframe and as one it doesn't excells in anything particularly, except for his facinating look of [Exalted Blade] ability. I love it, and for that I am building [Excalibur] for more sustainability using his ultimate skill.

• [Steel Charge]
  Even though [Exalted Blade] emits waves of energy that are considered as a ranged attack the initial slash is considered as a melee attack, and the damage from [Steel Charge] will be transferred from the melee damage instance to the waves.
  
• [Sure Footed]
  The time you take to get up after a knockdown is enough for the enemies to take half of your hit points. Resisting knockdowns will help to survibability.
  
• Vitality | Redirection | Flow
  These three are a must-have for survivability. While [Vitality] and [Redirection] are obvious, [Flow] can help to open more options for action. Some may use Fiber Steel instead of [Redirection] but [Excalibur]'s armor is not high anough to sustain damage. It should have at least 300 armor.
  
• [Chromatic Blade]
  This augmentation is a splendid change which converts damage into pure elemental damage depending on [Excalibur]'s energy color. The fan of combinations is wider now, you can play with that.
  
• [Intensify] | [Energy Conversion]
  [Chromatic Blade]'s status chance is 50% and is directly affected by ability strength. Status chance increases by 0.50% for every 1% of ability strength, so having 180% of ability strength will increase status chance to 100%. These two mods will do just right. Remember that for [Energy Conversion] to be effective you have to pick up an energy orb, so untill that moment you will only have 130% ability strength.
  
• Fleting Expertise
  To sustain the energy drain from [Exalted Blade] I chose [Fleeting Expertise]. The energy drain of this ebility will go down from 2.50 to 1.25 per second. But your ability duration will suffer a decrease of 50%.
  

• [Primed Continuity]
  That's why I cover the duration loss from [Fleeting Expertise] with this mod. Duration is important for crowd control and 15 seconds from Radial Blind is just enough.

• Arcane [Fury]
  This arcane provides a chance to increase Melee Damage upon delivering a critical hit. Depending of how you build [Exalted Blade] you will be having 120% more melee damage almost everytime.
  

• Arcane Barrier
  This, in turn, provides a chance to instantly restore shields whenever damage is received. Sometimes [Redirection] is not enough along with [Vitality] so for added survibability I chose a chance of restoring shields. Arcane Grace which grants a chance to restore a portion of health whenver damage is received can be a good substitute.