Background/General Answer:
The German High Command fell for the deception of Operation Bodyguard, the ally operation that used American General George S. Patton as a decoy. The Germans had a high respect for Patton and he was the only “cowboy” they really feared. They were certain that Patton would be the one leading the invasion of Europe so Ike set up Patton with a phantom army set to attack at Calais. (Note: Pau de Calais is 300km by air from where the actual landing at Normandy took place.) This was in part because of German fear/respect for Patton and also as reprimand for Patton slapping a soldier that was too scared to fight in Sicily.
The Allies also called in every double-agent and denial & deception tactic in their book to sell Operation Fortitude, the sub-operation to Bodyguard involving Patton and a fictional invasion of Norway. Hitler was certain that the invasion would come at Calais (Fortitude South) and Norway (Fortitude North) and Patton would lead the attack on Calais. Now whether or not the German Generals unanimously bought this is debatable, but Hitler clearly did. This was coming just after Operation Valkyrie failed and very few military men were prepared to argue with their Fuhrer at this point.
Normandy was relatively light staffed using conscripts that weren’t German. Normandy didn’t seem like the ideal invasion point because it was farther away from the Rhine, father from Britain than Calais, and wasn’t near a deep water port. Calais was the closest location on Europe to Britain, well within range of the big artillery guns and air support. So, defenses were prepared at Calais.
Fortifications/Preparations:
Defending the entire coastline of a continent from invasion is terribly difficult and having been pushed back very hard on the Eastern Front Germany did not have the capability to prepare a repelling force for all potential landing areas. This is where, in 1942, the Atlantic Wall came in. Germany conscripted almost a million French workers to build it. Land-able beaches were mined, fitted with barbed wire, vehicle obstacles, gun towers, bunkers, and a still formidably sized German or conscript force. Natural terrain was used greatly to the German advantage. Towers were built atop of the sheer cliffs (which is why casualties were so high on Utah beach).
Calais was the strongest point on the Atlantic Wall.
Batterie Waldam at Calais had over a mile of bunkers, tank traps, barriers, machine gun emplacements, and other defenses. Defense-in-depth was used here as Rommel planned for a series of buildings to defend at various distances.
Batterie Todt was a set of four gun casemates with ammunition storage and fire support. The four casemates used 12,000 cubic meters of concrete and 3,200 tons of steel. This gun emplacement shelled Dover regularly during the Battle of Britain. It wasn’t until September 1944 that Britain finally defeated this emplacement with giant guns you may recognize named Winnie and Pooh. (Note: Winnie was named after Winston Churchill and Winnie the Pooh was named after Winnipeg, a bear at a zoo in London. The gun “Pooh” was then in turn named after Winne the Pooh to complement the existing Winnie gun.) These gun emplacements were massive turrets that still exist today.
Batterie Oldenburg had 255mm and 240mm guns staggered across their location to provide a wider range of fire. This location was also called “Le Moulin Rouge”.
Batterie La Coupole was a V-2 bunker near Calais that fired the rockets into Britain that killed more civilians than British soldiers were dying in battle at the time.
Calais was augmented with 7,500 German soldiers and possibly more conscripts. Dunkirk, a mere 30km away with a major road connecting them, had another 12,000. 30km in the other direction at Boulogne was another 10,000 Germans.
Needless to say, with the difficulty we had taking the beaches on Normandy, had we actually attacked Calais where the Germans thought we would – we would almost definitely have lost.
"Hitler couldn't rid himself of the fear that the British and the Americans might attempt to reduce pressure on the Soviets by launching a limited invasion of Norway of France, the the Soviet government repeatedly demanded such a "second front".
Hitlers fears where not entirely unfounded. From his perspective, which his army commanders rarely understood, especially in the East was that any attack in the West would pose a much more immediate threat to the core German Reich than an equivalent enemy advance in Russia because of the relative distances involved.
Therefore at a March 28th conference on the upcoming Blau campaign, Hitler insisted that several high-priority units remain in the West as a strategic reserve."
Now although this book focuses on the Eastern Front & Stalingrad before during and after the Blau campaign, I thought this passage was important to include in my answering of your question.
Hitler absolutely did know an invasion was coming eventually. On 23 March 1942 Hitler issued Führer Directive No. 40, which called for the creation of the Atlantic Wall, which was to protect the Coast line of the Occupied counties Norway all the way to France from said invasion.
By 1944 The German High command expected an Allied invasion of France was imminent. Erwin Rommel was put in charge of Army Group B with responsibility for defending the French coast against the long anticipated Allied invasion. When he arrived he found that the fortifications where vastly uncompleted and undermanned. He built them up over months in order to adequately defend the coast for the coming invasion. Including placing millions of mines, laid thousands of tank traps and obstacles set up on the beaches and throughout the countryside, including in fields suitable for glider aircraft landings, the so-called Rommel's asparagus.
Hitler himself expected a Normandy invasion for a while, Rommel and most Army commanders in France believed there would be two invasions, with the main invasion coming at the Pas-de-Calais. Even after the Normandy invasion has begun the German high command still believed the main invasion would come at the Pas-de-Calais.
So in short, the answer to your question is Yes, he did expect an invasion, except they didn't know when or exactly where, but decided to put up defenses along the entire coast line from Britain in order to defend against it.
