The Khatam al-Anbiya Headquarters is the branch of the regular Armed Forces (Artesh) responsible for providing strategic and operational-level air defense over the country, as well as much of the tactical air defense for other branches. 
For brevity's sake, the HQ is hereafter referred to by its infrequently-used Persian acronym, PADAJA ("پدجا "). It is more commonly referred to, especially in English-language media, by the acronym for the Islamic Republic of Iran Air Defense Force (IRIADF).
The headquarters was first formed in 1992 to coordinate the respective air defense efforts of the Artesh and IRGC. In August 2008 the HQ was promoted to its current status as an independent branch and given full command over the relevant units and their equipment, including the Artesh Air Force's radars, SAMs, and AAA. 
Today, the PADAJA is organized geographically. Operational control at the national-level is provided by a hardened air defense operations command (ADOC) at an unknown location. Control at the regional level is provided by nine regional commands, each headquartered in a sector operations center (SOC). These are sometimes referred to as divisions.  Each region has authority over a number of air defense groups – each equivalent to a brigade – and independent sites for radars and other equipment.
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Staff / Personnel:
As of April 2016 the PADAJA is commanded by Brigadier General Farzad Esmaeli.  He has held the position since December 2010. Before his appointment Esmaili commanded the force's Central Region HQ. Before this he served in a handful of groups on the western border. His positions included both technical and staff positions including radar operator, training officer, and operations deputy. 
The PADAJA's deputy commander is BG Ali-Reza Sabahi-Fard.  One of the more notable staff appointments is Coordination Deputy BG2 Mousa Bakhtiari, who is an IRGC officer, rather than Artesh. 
One point of uncertainty surrounds the position currently held by BG2 Abolfazl Shahri-Rad, which translates approximately as "executive deputy", or "administrative deputy". However, the precise meaning is unclear. The wording suggests a role equivalent to a chief-of-staff, but this role is traditionally associated with the coordination deputy.
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Air Defense Regions:
1) Northern Region:
Headquartered in Tehran, the northern region spans part or all of the Tehran, Alborz, and Mazandaran provinces (full extent unknown). 
As of September 2015 this region is commanded by BG2 Saeed Saeedi. 
2) Central Region:
Headquartered in Isfahan, the central region spans part or all of the Isfahan, Qom, and Markazi provinces (full extent unknown).  Its command is co-located with the Air Force's 8th Tactical Airbase
As of April 2016 this region is commanded by BG2 Abazar Jukar. 
3) Northwest Region:
Headquartered in Tabriz, the northwest region spans East and West Azerbaijan, Ardebil, Zanjan, and part of Kurdistan province.  It is suspected that the command is co-located with the Air Force's 2nd Tactical Airbase.
As of February 2016 this region is commanded by BG2 Malik-Ali Asadi-Fard. 
4) Western Region:
Headquartered in Hamedan, the western region spans part of Kurdistan and Markazi provinces, as well as Hamedan, Kermanshah, Ilam, and Lorestan (full extent unknown). Its command is co-located with the Air Force's 3rd Tactical Airbase. 
As of August 2015 this region is commanded by Col./BG2 Bijan Saadi. 
5) Southwest Region:
Headquartered at an unknown location – likely co-located with the Air Force's existing bases at Omidiyeh or Dezful – the southwest region spans the Khuzestan province and part of nearby Kohgiluyeh va Boyer Ahmed. It includes at least four groups (Ahvaz, Dezful, Omidiyeh, Behbahan). 
As of August 2015 this region is commanded by BG2 Mahmoud Ahmadi. 
It is infrequently referred to as the "4th Air Defense Region". 
6) Southern Region:
Headquartered in Bandar Bushehr, the southern region spans the Bushehr and Shiraz provinces, as well as Khark Island. 
As of September 2015 this region is commanded by BG2 Gholam-Abbas Esmail-Zadeh. 
7) Southeast Region:
Headquartered in Bandar Abbas, the southeast region spans the Hormozgan province, and part of Sistan va Baluchistan, as well as – almost certainly – the Strait of Hormuz and surrounding islands. 
As of January 2016 this region is commanded by BG2 Mohammed Farzan. 
It is infrequently referred to as the "6th Air Defense Region". 
8) Eastern Region:
Headquartered in Birjand, the eastern region spans South Khorasan, parts of Sistan va Baluchistan and Razavi Khorasan, and some or all of theYazd and Kerman provinces.  
As of April 2016 this region is commanded by BG2 Fardin Nisaen. 
9) Northeast Region:
Headquartered in Mashhad, the northeast region spans the Razavi and North Khorasan provinces, as well as part of Golestan.  Its command is located at the Air Force's now-vacant 14th Tactical Airbase.
As of September 2015 this region is commanded by BG2 Abdullah Rashad. 
 The branch is sometimes described as a "base" in English media. This arises from a mistranslation of the Persian word for "headquarters", which can either mean an abstract command body, or its physical garrison (ie base). This shows up in another acronym – KAAB – which is infrequently used by Iran's English-language media to refer to the "Khatam al-Anbiya Base". For example: (Mehr, 04/05/2016).
 History of [PADAJA]. AJA. Undated.
 Air Defense Has the Ability to Identify Any Enemy Movement. IRNA. 08/31/2013.
 KAAB ‘bolstered by indigenous knowledge, capabilities’. Mehr. 04/05/2016.
 Familiarization with Air Defense Commanders After the Revolution. AJA. Undated.
 Protection of Key Sites, Air Defense’s Main Duty: Iranian Commander. Tasnim. 01/18/2015.
 Youth Soldier Festival. Basij Press. 03/06/2016.
[7.5] Farewell & Introduction Ceremony for [PADAJA's ... Deputy] Held. YJC. 08/10/2015.
 BG2 Saaedi is first mentioned in 2013, when he is described as the region's commander. (AJA, 09/23/2013) A later article describes him as a one of the region's group commanders. (Defa Press, 09/05/2015)
 [title unclear]. MNA. 01/02/2013.
 Artesh Biggest Protector of Security After the Revolution. MNA. 04/05/2016.
 eg Markazi province (Youtube, 09/01/2014).
 [title unclear]. Tabriz-e Man. 02/06/2016.
 Skies of the Northwest Are Completely Covered. MNA. 09/02/2015.
 Col. Saadi Became Commander of Western Air Defense Region. FNA. 08/13/2015.
 Pars Namad Data, 01/12/2012
 Skies of Iran Safest in Region. Khouz News. 08/27/2015.
 [Image Gallery] Nowrooz Rahin-e Noor Caravan. 04/12/2014. AJA
 ibid Khouz News, 08/2015.
 [Air] Defense in the South of the Country Equipped Best. 01/12/2011. Fars News.
 Air Defense Completely Prepared to Proect Borders. 09/05/2015. Tabnak.
 Air Defense and Nat'l Security. Undated. AJA.
 Air Defense Monitors Possible Threats Deep in Neighboring Countries. 01/13/2016. ISNA.
 Parade imagery, Rooz-e Artesh 2009 & 2015.
 (Khorasan News, 09/03/2013)
 Air Defense Does Not Secure the Country's Skies with Anyone / ... . DANA. 04/15/2016.
 ibid DANA, 04/2016.
 Iran's Air Defense Monitors Spy Aircraft to an Altitude of 60,000 feet. 08/31/2015. IRNA
 ibid IRNA, 08/31/2015.