Sayan_1987 wrote:Though he had had success broadcasting his controversial radio program on highly regulated terrestrial airwaves, Howard Stern opted out of terrestrial broadcasting in favor of the less regulated satellite radio medium.
1.Though he had had
2.Though he has had
3.Even though he had
4.Having had
5.Having achieved

[spoiler]OA : 1[/spoiler]
[spoiler]While I understand that a past perfect tense is necessary here, but unable to understand how 'had had' can be a past perfect tense, it sounds odd I guess .[/spoiler]

It does sound odd indeed, but it is grammatically correct. Remember the past perfect is Sub + Had + Past Participle. The past participle of have is had. So saying he had had success is just fine.

I had a blue car -> Simple past
I had had a blue car -> Past Perfect.

Sayan_1987 wrote:Though he had had success broadcasting his controversial radio program on highly regulated terrestrial airwaves, Howard Stern opted out of terrestrial broadcasting in favor of the less regulated satellite radio medium.
1.Though he had had
2.Though he has had
3.Even though he had
4.Having had
5.Having achieved

[spoiler]OA : 1[/spoiler]
[spoiler]While I understand that a past perfect tense is necessary here, but unable to understand how 'had had' can be a past perfect tense, it sounds odd I guess .[/spoiler]

had had construction is absolutely correct.infact,in this case it is neccessary.
three correct constructions are-
1.had had
2.have had
3.has had

wrong constructions would be-
had have
had has
have have
has has
has have

so coming back to your question-
i had a pen. ===== i went to the store( both the sentences are in simple past)
i had had a pen ===== i had gone to the store.(both the sentences are in past perfect)
i have a pen(simple present)
i had a pen(simple past)
i have had a pen(present perfect)
i had had a pen(past perfect)

...hope it helps....