AN/TPS-43E Tactical 3-D Air-Surveillance Radar

1. System overview and history

In briefThe AN/TPS-43 was a radar that could travel by truck or aircraft, built by Westinghouse for the U.S. Air Force to detect aircraft at long range and report their range, bearing and height [1]. The E model, the version I maintained, began service in 1977. The USAF bought 57 E sets, and most TPS-43s were later rebuilt as the AN/TPS-75 [1][2][4][28]. This section covers the program timeline, the model family and the users.

The AN/TPS-43 is a transportable S-band, three-dimensional (range, azimuth, height) air-surveillance radar designed by Westinghouse for the U.S. Air Force. It was meant to give the long range and 3-D performance of large fixed radars in a package that could be airlifted and set up quickly [1]. It measures height by comparing signal amplitudes across six stacked elevation beams [17]. For nearly two decades it was the Air Force's only tactical ground-based long-range search and warning radar, and most sets were later converted to the AN/TPS-75 configuration [28].

Program timeline

Production and model lineage

Users. The TPS-43E was a USAF system, used by active-duty tactical control units and the Air National Guard [18][19]. Radomes.org also records temporary TPS-43/TPS-43E use at ADC sites such as Makah AFS [29]. U.S. Marine Corps use of the TPS-43E: Not found. Every source found points to USAF/ANG and foreign users; the USMC fielded other radars such as the AN/TPS-32, TPS-59 and TPS-63 [3].

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1A. Unit context: the 726th Tactical Control Squadron, Homestead AFB

In briefI served with the 726th Tactical Control Squadron at Homestead AFB, Florida, from 1985 to 1989. Official Air Force lineage confirms that name for those years; the unit was renamed the 726th Air Control Squadron in November 1991 [41]. Little of its 1980s activity is documented online, so this section is deliberately short.

→ See my military service records (companion page: training certificates, Achievement Medal, letter of recommendation and discharge, with the Social Security number blacked out).

Official designation, 1985–1989. According to the AFHRA lineage, the unit was constituted as the 726 Tactical Control Squadron on 30 Aug 1950, activated 2 Sep 1950, inactivated 15 Jul 1958, and activated again on 15 Oct 1969. It was redesignated the 726 Air Control Squadron on 1 Nov 1991 [41] Confirmed. Throughout my 1985–1989 service it was therefore officially the 726th Tactical Control Squadron, as I remember it. The patch's "AIR CON SQDN" wording matches the post-November 1991 designation, so this particular patch was most likely made after the redesignation Inferred. The squadron emblem was approved on 27 Mar 1974 [41]. Whether an earlier "Tactical Control" version of this patch existed was Not found.

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2. Block diagram and signal flow

In briefThe radar comes in two packages: a shelter that holds the electronics and operators, and a rotating antenna on a pallet [1]. A precise low-power signal is generated in the shelter and amplified to megawatts, then sent out through the antenna. The echoes come back through six separate receive channels for processing and height calculation [1][2]. The diagram traces that path.

The E model has two packages: an operations/radar-electronics shelter and an antenna pallet [1]. The signal path is fully coherent. The frequency generator produces a phase-coded RF pulse on one of 16 frequencies in 2.9–3.1 GHz, together with the STALO, COHO and monitor signals [2]. A broadband TWT drives the Twystron final amplifier [1][2]. Its output goes through the rotary joint to a stacked-beam feed in front of the reflector [2][3]. On receive, the six beam channels are amplified and converted to IF at the antenna and passed down through slip rings [2]. In the shelter they are log-detected, pulse-compressed, MTI- and CFAR-processed, and height-computed [1][2].

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3. Transmitter in depth

In briefThe transmitter is the core of this document. It generates a precise low-power pulse and amplifies it in two stages: first a traveling-wave tube (TWT), then the large VA-145E Twystron [1][2][5]. The Twystron is powered by a modulator. The modulator stores energy in a pulse-forming network (PFN) and releases it through a switch and a step-up pulse transformer in an SF6 gas-insulated tank. The pulse then goes to the tube, which sits on an oil-filled socket tank and is surrounded by a focus coil [2][7][9]. Subsections 3.1–3.11 follow that chain step by step, including cooling, protection and later upgrades.

The transmitter is a master-oscillator/power-amplifier (MOPA) chain. A low-power, phase-coded, frequency-agile drive is amplified first by a broadband TWT and then by a Twystron (hybrid klystron/TWT) final amplifier [1][2]. The Twystron is pulsed by a line-type modulator: a pulse-forming network (PFN) is discharged by a switch into a step-up pulse transformer [2][9]. The E brochure notes that the "frequency agile transmitter … is accessible simply by loosening four screws on its door" [1].

3.1 Transmitter at a glance

3.2 The Twystron: centerpiece of the transmitter

How a Twystron works

Varian's LaRue and Rubert (1964) describe the S-band VA-145A and C-band VA-146A as multi-megawatt "hybrid TWT's", also called "traveling wave klystrons" or "Twystron hybrid TWT's". Their key feature is "the compatibility achieved between the broadband klystron RF driver input circuit and the TWT forward fundamental extended interaction RF output circuit, leading to … wide bandwidth, high gain, high power, high operating efficiency, and relative uniformity of operating characteristics" [14]. In the first section of the tube, a series of resonant klystron cavities velocity-modulates the electron beam so that it bunches. A plain klystron would take its output from a single final cavity. In a Twystron the bunched beam instead passes through a TWT-type coupled-cavity output section, where it transfers energy to a traveling wave over several cells [15]. Adding cavities narrows a high-power klystron's bandwidth, typically to under 10%, while a TWT is broadband but long. The hybrid is a compact tube with bandwidth up to about 15% [15].

Why a Twystron in this radar

• Instantaneous bandwidth for frequency agility. The E can transmit on any of 16 frequencies across 200 MHz, pulse to pulse or in MTI bursts [1][2], and JATS selects the least-jammed frequency for the next pulse [2]. That needs an amplifier covering the whole 6.7% band Calculated without retuning, which the Twystron's roughly 15% capability [15] provides. Twystrons were "quickly adopted by many radar designs in order to improve frequency agility and thereby improve performance against radar jamming" [15]. Westinghouse's own design rationale was not found, so the conclusion that this is why it was chosen is Inferred.
• Coherence for MTI and pulse compression. Westinghouse describes the transmitter as a "pulsed broadband coherent amplifier" [2]. The CPACS 13-bit phase code is created in the frequency generator and "amplified through the driver and final power amplifier" [2]. A power oscillator such as a magnetron could not carry an injected phase code or hold a COHO phase reference. That contrast is Inferred from the architecture in [2].
• Megawatt output with klystron-like gain. One tube delivers about 3 MW peak [1][2][3] with 45 dB gain Unverified[31], so a modest TWT driver is the only intermediate stage [1].

A documented Twystron problem: rotary-joint mismatch

Rome Laboratory built three extended-interaction klystrons (EIKs) as form/fit/function replacements for the VA-145E. All met specification on the factory test stand, but all were unstable in a simulated AN/TPS-43E system because "the rotary joint … has a severe mismatch near the operating frequency band." Later tubes with a modified output-resonator impedance were stable only at some rotary-joint angles, and the effort ended in 1992 [5]. The episode shows how sensitive a broadband high-power output circuit is to the load it sees.

3.3 RF drive chain and waveform

• Frequency generator: produces the phase-coded RF drive pulse plus the STALO, COHO and RF monitor signals [2]. In the DAR it also supplies four IF monitor pulses and one phase-coded RF monitor pulse for receiver gain balance, alignment and MDS checks [2].
• TWT driver: broadband TWT [1][2]. A vendor lists "Electron Tube, TWT", P/N 138C326H02, NSN 5960-00-594-0824, under AN/TPS-43 and TPS-70 [7]. Its power level is Not found.
• Agility and JATS: in each PRI, JATS samples received power on all 16 frequencies and picks the least-jammed one for the next transmission [2]. To keep MTI working during agility, the DAR sends 12 pulses on one frequency before hopping [2]. The E brochure lists an "MTI agility" mode [1].
• Staggered PRF removes MTI blind speeds [1].
• Multiple pulse widths: Not found. All E/TPS-75 sources give a single pulse width of about 6.4–6.8 µs [3][4], with CPACS coding inside the pulse [1][2].

3.4 Modulator chain: HV supply → PFN → switch

3.5 The SF6 tank

• Why SF6. The electric-power industry uses SF6 widely for its "dielectric and other physical and chemical properties related to its lack of reactivity" [23]; it is inert, stable and nonflammable [24]. General engineering background Inferred: SF6 is strongly electronegative, meaning it captures free electrons, and when pressurized its breakdown strength is several times that of air. That allows much smaller HV clearances and suppresses corona, which is why it is used to insulate compact pulse transformers. Westinghouse's own reasons for choosing it for the TPS-43 are Not found.
• Tank contents. Pulse transformer: Confirmed [9][2]. Pulse-transformer part numbers listed for AN/TPS-43 include 146C795A01 (NSN 5950-01-128-2721) and 149C795A01 [7]. The TPS-75 listing puts a charging inductor inside the SF-6 tank [7]. Other contents, such as the charging diode or de-spiking networks, are Not found.
• Step-up ratio, gas pressure and fill procedure: Not found. The vendor list does include pressure switches, pressure regulators, pressure indicators and a dial pressure gauge under AN/TPS-43 [7]. These could belong to the SF6 tank, the waveguide pressurization system, or the cooling system; which is which is Not found.
• Pulse carried to the tube. As I remember it, the pulse ran from the SF6 tank into the base (cathode/heater end) of the Twystron in the oil tank Firsthand. This matches the DAR arrangement: pulse-transformer tank → twystron "mounted on an oil filled socket tank" [2]. The design of the HV bushing between the gas and oil sections is Not found.
• Waveguide pressurization is a separate system. The C model introduced "improved waveguide pressurization" [3], and a "Compressor Dehydrator" (335D548H01, NSN 4440-00-568-1532) is listed under AN/TPS-43 [7]. A compressor-dehydrator normally supplies dry air, which suggests that the RF waveguide was pressurized with dry air rather than SF6 Inferred. The actual pressurizing medium and pressure are Not found.

3.6 The oil tank and Twystron socket

• What is in the oil. Tube base and cathode/heater connections: Confirmed (DAR) [2]. Heater (filament) transformer: Inferred. In a cathode-pulsed tube the cathode and heater both swing to the full beam voltage during every pulse. The usual solutions are a bifilar pulse-transformer secondary that carries heater current at cathode potential, or a heater transformer insulated for the full pulse voltage, placed in oil [25]. Several filament transformers (147A720H01, 139C373H01, 147A739H01, 602B883H01), a "Filament Interrupt" assembly (364D080G01) and a TPS-70 "Filament Interrupt & Relay Assy" are listed [7], but where they sit is Not found.
• Oil type. The listed item is "Isolating Oil", spec VV-I-530 [7]. VV-I-530 appears to be the U.S. federal specification for electrical insulating (transformer) oil Unverified. The oil insulates the tube base at pulse voltage and carries heat away from it Inferred.
• Maintenance and safety (Inferred, general HV practice; no TPS-43E TO text found): check oil level and look for leaks; test dielectric strength periodically, since moisture and carbon reduce it; discharge and ground every HV point with a grounding stick before touching anything, because PFN capacitors can hold charge; and observe X-ray hazards. High-power klystron-type tubes emit X-rays when operated at high voltage and depend on their shielding [26][27].

3.7 The focus coil

• Purpose Inferred (standard linear-beam tube physics): the solenoid's axial magnetic field keeps the electron beam confined as it travels through the cavities and output section. Without it, space-charge forces spread the beam and it hits the tube body. That produces body current, heat, and eventually tube failure.
• Power supply. "Focus Coil P.S. Assy" (342D520G01, NSN 6130-00-572-1597), "Focus Coil P.S." (360D123G01) and "Focus Coil/Power" (360D231G01, NSN 5950-01-143-8945) are listed under AN/TPS-43, and further focus-coil supply assemblies under TPS-70 [7]. The C model introduced an "improved focus coil power supply" [3]. Field strength, coil current and regulation are Not found.
• Interlocks Inferred: standard practice inhibits beam voltage unless focus current is present and within limits. The specific TPS-43E interlocks are Not found.
• Tube changes. The B model had a redesigned "TWT hoist" [3], which confirms that the Twystron assembly was lifted with a hoist. The procedure was Not found. The TPS-70 list also includes a "Vacuum Pump Power Supply" [7], which suggests an appendage ion pump for the tube Inferred.

3.8 Cooling

• Model history. On the A model the heat exchanger was relocated to a remote position; the B model received a new transmitter heat exchanger [3]. In the DAR the shelter carries its air conditioners and heat exchanger stowed inside for transport [2].
• What each unit cooled: Not found. Likely heat loads, based on the sources, are the Twystron collector and body (roughly 5 kW of average RF output [3][4], plus the beam power that is not converted to RF Calculated), the focus coil, the oil socket tank and the dummy load(s) Inferred.
• Interlocks: the listed flow switches, pressure switches, air-flow switch and fan current monitor [7] are the kind of sensors that inhibit HV when coolant or air flow fails Inferred. Set points and coolant mix are Not found. Routine maintenance would include coolant level and concentration, filters/strainers, leak checks and fan checks Inferred.

3.9 Protection, interlocks and safety

3.10 RF output path, maintenance and test

• Output path (DAR). Twystron → waveguide couplers and a waveguide filter → high-power section of the rotary joint → coupler and two waveguide power dividers → 13 waveguides, each with a circulator → feed horns [2]. The rotary joint also carries two low-power S-band channels, one for STALO and one for test/calibration injection [2]. Rotary-joint parts, including "S-Band Rotary Joint" and "Hi-Pwr Coupler, Rotary (W/G)", are listed [7].
• Dummy loads: "Dummy Load 5kw" (378A525G01) and others (128C611H02, 128D611H01) [7].
• Test equipment and monitoring. The USM-454 oscilloscope was "supplied as part of the TPS-43" [20]. The DAR has a built-in monitor oscilloscope with probes for "any test point in the radar shelter", rotary switches to select meters, monitor panels on each major assembly, and PC-board fault lights [2]. The frequency generator supplies monitor pulses for log-slope, gain-balance and MDS checks [2].
• Technical orders. For the 1980s USAF E model, AN/TPS-43E TOs are listed as 31P3-2TPS43-54 through -82 [33]. Only titles were found; the contents are Not found.

3.11 Later transmitter retrofits (after my era)

• Replacement tube attempt (1992): extended-interaction klystrons were built as VA-145E replacements and dropped because of rotary-joint instability [5].
• Solid-state modulators: Stangenes/Raytheon replaced the thyratron line-type modulator, including its SF6 pulse-transformer tank, with a solid-state unit (117 kV, 80 A, 7.1 µs) [9][10]. DTI offered AN/TPS-43/70/75 transmitter modernization kits [11][12][13].
• INVAP M-TPS (Argentina) keeps "the original Twistron or Klystron tube" [30].
• 2025: the USAF is still sourcing repair of the VA-145E for the TPS-75 [6].

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4. Antenna and 3-D height finding

In briefThe antenna is a large folding reflector with a vertical stack of feed horns in front of it [1][2]. It does not scan up and down. Instead it receives on six fixed beams, stacked in elevation, all at the same time. Comparing an echo's strength in neighboring beams gives the target's elevation angle, and elevation plus range gives height [2]. My recollection of 13 waveguides matches Westinghouse's description of the derivative DAR radar [2].

Transmit pattern and receive beams

On transmit, two waveguide power dividers split the Twystron output 13 ways and put "the highest power at low elevation angles for best long range detection". The in-phase sum of the horn outputs forms a single composite transmit pattern covering the whole elevation sector [2]. That pattern is in effect a shaped, cosecant-like fan Inferred, although the brochure does not call it cosecant. On receive, the matrix forms six simultaneous stacked beams. The DAR brochure stresses that each pulse covers the full elevation, so no time is spent scanning in elevation [2]. Wikipedia instead describes an "organ-pipe scanner" that scans a pencil beam vertically, later replaced by a stripline matrix [16]. That account conflicts with the Westinghouse description of simultaneous beams for the E/DAR Sources differ, and the Westinghouse description is preferred here.

Amplitude-comparison height finding

DAR description [2]: after log amplification and CPACS decoding, the six height channels are sampled when a detection occurs in a search channel. The beam-pair selector sums adjacent channels into five pair signals. The strongest pair gives a base angle (the crossover of that pair), and the beam subtracter interpolates how far the target lies above or below it. Because amplitudes are logarithmic, subtracting them gives the ratio of the two beam amplitudes Inferred. The height computer then combines several hits, rejects bad values in a height evaluator, and corrects for antenna tilt, earth curvature and site elevation [2]. Board names in the vendor list include "Beam Peak Selector" and "Beam Substractor" [sic] [7]. Height accuracy is ±457 m (±1500 ft) at 185 km (100 nmi) [1][4].

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5. Receiver and signal processing

In briefThe echoes from the six beams are amplified, converted to a lower intermediate frequency (IF), and processed to separate aircraft from clutter and jamming [1][2]. The main techniques are coded-pulse compression (CPACS), moving target indication (MTI), automatic thresholding (CFAR) and sidelobe blanking [1]. The table collects the documented receiver figures.

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6. IFF/SIF

In briefIFF/SIF is the "who are you?" system. The radar site sends a coded interrogation on 1030 MHz, and friendly aircraft transponders answer on 1090 MHz with identity codes and, in Mode C, their altitude [35][36]. The E model used an AN/UPX-23 interrogator and two AN/UPA-59A decoders, with the interrogator inside the shelter, as I remember [1][3].

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7. Operations shelter, displays and communications

In briefThe E-model shelter was a self-contained control site. It had two operator positions, each with a large round radar scope (a PPI), an IFF decoder, a digital height readout and radios [1]. The transmitter was in the same shelter [1].

The E shelter has two complete operator positions. Each has an AN/UPA-62 display console, an AN/UPA-59 active/passive IFF decoder, a digital height readout, and ground-to-air and ground-to-ground communications [1]. The transmitter sits in the same shelter, "accessible simply by loosening four screws on its door" [1]. A Westinghouse digital target extractor (DTE) could be installed to send plot messages over telephone or radio links [1].

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8. Transport, siting, installation and prime power

In briefThe whole radar was built to move. The shelter and antenna pallet could go by truck, helicopter or a single C-130, or be towed on wheeled transporters, and Westinghouse quoted about an hour to set up and 30 minutes to tear down [1]. This section covers transport, erection, siting and prime power, and ends with a gallery of my field photographs.

8.1 From the field: photo gallery (Rick Childers, personal collection)

These are my own photographs of the radar being transported, erected and sited. The captions describe only what is visible. Locations and dates were not supplied and are not assumed.

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9. Maintenance concept

In briefThe E model was designed so military technicians could maintain it in the field, with built-in test equipment, plug-in replacement boards and a documented MTBF (mean time between failures) of more than 200 hours [1]. Deeper repair relied on contractor and depot support [1].

• Reliability and availability. E model: MTBF of more than 200 h and operational availability above 95%, with built-in fault isolation and plug-in replacement so that "military technicians [can] maintain the radar without special site equipment" [1]. DAR: MTBF 400 h and MTTR 30 min [2]. TPS-75: MTBF 600–1,000 h, MTTR 0.5 h, availability above 99% [4].
• BITE and monitoring. The E added more BITE [3]. BITE boards (for example 364D114G01, a BITE microprocessor and an A-D BITE assembly) are listed [7]. DAR monitoring used a built-in scope, per-assembly monitor panels and board fault lights [2].
• Field test equipment: USM-454 oscilloscope [20]; an HP signal generator is listed [7].
• Depot and contractor support. Westinghouse offered integrated logistic support: training, manuals, spares and depots. It supported TPS-43s "at 54 locations in 8 countries" [1]. In later years the TPS-75 repair workload went to Tobyhanna Army Depot (see the image below).
• 1980s technical orders: 31P3-2TPS43 series, titles only [33].

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10. ULSA and conversion to AN/TPS-75

In briefIn the 1980s the USAF upgraded the TPS-43E with an ultra-low-sidelobe antenna (ULSA) and updated electronics. The result was the AN/TPS-75, first delivered in December 1987 [4]. The Twystron transmitter family continued into the TPS-75 [4][6].

The ninth upgrade began in 1980: the ultra-low-sidelobe antenna (ULSA) entered full-scale development in 1981 and production in November 1984. The first two TPS-75(V)s were delivered in December 1987, and about 67 TPS-43s were upgraded [4]. The TPS-75 adds the ULSA (a stripline-matrix beamformer; 1.1° receive beam; 20° elevation coverage), updated electronics, UYQ-509 color raster displays and GSQ-120 remoting, but keeps the Twystron transmitter family [4][6]. ECCM additions include precision jam-strobe triangulation, a "cool antenna" for reduced IR signature, and enhanced ARM resistance [4]. During my 1985–1989 service, first ULSA production and then TPS-75 deliveries were under way, so a mixed fleet at unit level is plausible Inferred. When the 726th converted is Not found.

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Glossary

In briefPlain-language definitions of the abbreviations and terms used in this document. The citations point to sources that use or explain each term.

Amplitude comparison (height finding)

Working out a target's elevation angle by comparing the strength of its echo in two adjacent stacked beams; the DAR interpolates between beam crossover angles. [2]

AN/TPS-75

The USAF upgrade of the TPS-43E, with an ultra-low-sidelobe antenna and new electronics; first delivered in 1987. [4]

Backswing

The reverse voltage left on a line-type modulator's network after a pulse, for example when the load is mismatched or the tube arcs; a "backswing overload" trip is listed for the TPS-43. [25][7]

BITE

Built-in test equipment: circuits and indicators inside the radar that help technicians find faults. [2][1]

CFAR

Constant false alarm rate: processing that adjusts the detection threshold automatically so noise, weather and jamming do not flood the display with false targets. [1]

COHO / STALO

Coherent oscillator and stable local oscillator: reference signals from the frequency generator that keep transmitter and receiver phase-locked, which MTI and pulse compression need. [2]

CPACS

Coded pulse anti-clutter system: the transmitted pulse carries a phase code (13-bit in the DAR), and the receiver compresses the long 6.5 µs pulse to 0.5 µs for better range resolution and clutter rejection. [1][2]

DAR

Defense Acquisition Radar: Westinghouse export derivative of the TPS-43E with a solid-state modulator. Several detailed descriptions in this document come from its brochure. [2]

Duty cycle

The fraction of time the transmitter is on: pulse width × PRF, about 0.0017–0.0018 here. [2][4]

Frequency agility

Changing the transmit frequency, as often as every pulse, among the 16 channels to resist jamming. [1][2]

IFF/SIF

Identification friend or foe / selective identification feature: a secondary radar that interrogates aircraft transponders on 1030 MHz and receives coded replies on 1090 MHz (modes 1, 2, 3/A, C; Mode 4 is the encrypted military mode). [35][36]

ISLS

Interrogator sidelobe suppression: an IFF technique that prevents replies to interrogations received through the antenna's sidelobes. [36][1]

JATS

Jamming analysis and transmission selection: the radar measures jamming on every channel and picks the least-jammed frequency for the next transmission. [1][2]

Klystron

A linear-beam microwave amplifier tube in which resonant cavities bunch an electron beam. Very high power and gain, but relatively narrow bandwidth. [15]

Mobilizer

A wheeled transporter set that lets a shelter or antenna pallet be towed. [1][2]

MOPA

Master-oscillator/power-amplifier: a precise low-power signal is generated first and then amplified, unlike a power oscillator such as a magnetron. The phase coding and coherent MTI depend on this architecture. [2]

MTBF / MTTR

Mean time between failures / mean time to repair: reliability and maintainability figures. [1][4]

MTI

Moving target indication: comparing successive echoes so that stationary clutter (ground, buildings) cancels and moving aircraft remain. [1]

NSN

National stock number: the 13-digit U.S. federal supply-catalog number for a part. [6][32]

PFN (pulse-forming network)

A ladder of capacitors and inductors that is charged slowly and then discharged through a switch, delivering a flat-topped pulse of fixed width. It is the core of a line-type modulator. [25][9]

PPI

Plan position indicator: the round radar map display with the radar at the center (AN/UPA-62 in the E model). [1][34]

PRF

Pulse repetition frequency: pulses transmitted per second (about 226–278 here). "Stagger" varies the PRF from pulse to pulse to remove MTI blind speeds. [1][3]

Pulse transformer

A transformer that steps the modulator's pulse up to the tube's beam voltage (about 117 kV in the family retrofit data). In the TPS-43 family it sat in a pressurized SF6 tank. [9][25]

Rotary joint

The rotating waveguide coupling that passes transmitter power (and low-power signals) to the turning antenna, together with slip rings for the IF channels. [2]

SF6

Sulfur hexafluoride: a dense, inert, nonflammable insulating gas. It displaces air in confined spaces, and arcing produces toxic byproducts. [23][24]

Sidelobe blanking

Suppressing echoes and jamming that arrive through the antenna's sidelobes, using a small reference antenna and receiver. [1][2]

Stacked beam

An antenna that forms several fixed beams, one above another in elevation, and receives on all of them at once. The TPS-43E has six, covering 0–20°. [1][2]

Thyratron

A gas-filled (hydrogen) switching tube that can switch very high currents quickly. It was used to discharge the PFN in the original TPS-43-family modulator. [9][39]

Thyristor (SCR)

A solid-state switch, used in later modulator retrofit kits. [12][13]

TO

Technical order: USAF maintenance and operation manual (the 31P3-2TPS43 series for this radar). [33]

TWT

Traveling-wave tube: a linear-beam amplifier in which the beam continuously interacts with a wave along a slow-wave circuit. Very broadband. [15]

Twystron

A hybrid linear-beam tube: klystron-type input and buncher cavities followed by a TWT-type coupled-cavity output section, giving klystron-class power and gain over a wider bandwidth. The TPS-43E used the Varian-designed VA-145E. [14][15][5]

ULSA

Ultra-low-sidelobe antenna: the 1980s replacement antenna that turned the TPS-43E into the TPS-75. [4]

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11. Gaps and unverified items

In briefThis section lists what could not be found or confirmed, so readers can see where the document relies on inference or on my memory.

• No AN/TPS-43E technical-order text was available; there are no depot-level schematics or component values.
• Modulator: DC supply voltage, PFN section count and impedance, pulse-transformer ratio, SF6 pressure, and the exact switch tube used in USAF E sets (thyratron types are listed for the family; "thyristor" wording appears in one vendor's later releases) Not found/Sources differ.
• Oil tank: whether the heater transformer is in the oil Inferred; bushing design Not found; oil spec meaning Unverified.
• Focus coil: weight (~400 lb is my recollection only), field strength, current Not found.
• Cooling: the two units and ethylene-glycol coolant are firsthand only; loop assignments, mix and set points Not found.
• Protection: arc, VSWR and body-current trips Not found. Only the backswing trip, flow and pressure switches, and filament interrupt are documented as parts.
• Antenna: horn-to-beam mapping, beam pointing angles, horn spacing, circular-polarization option Not found. Organ-pipe scanner (Wikipedia) versus simultaneous beams (Westinghouse) Sources differ.
• Transport: 5-ton truck (firsthand) versus M35 2½-ton (Forecast/Wikipedia) Sources differ; generator type and kW Not found.
• Several detailed statements come from the DAR or TPS-75, not the 1977–1980s USAF E; each is marked in the text.
• 726th TCS: exercise and deployment record for 1985–89 Not found; the date the 726th converted to the TPS-75 Not found.
• Peak power, pulse width, PRF, weights and gain differ between sources and are shown side by side.

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12. Firsthand-account cross-check (R. Childers)

In briefEach of my recollections next to what the documents say.

→ Have photos, documents, or stories about the AN/TPS-43E? Share them on the contribution page.

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13. Image credits

In briefCredits and licenses for every image in the document.

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14. References

In briefEvery source cited in the text, using the same numbers.

1. [1] Westinghouse Electric Corp., Defense & Electronic Systems Center, AN/TPS-43E Tactical Radar System (marketing brochure, c. late 1970s; incl. p.12 "AN/TPS-43 E Characteristics"). Scanned copy hosted by MobileRadar.org. http://www.mobileradar.org/Documents/43E_Tactical%20Radar%20System.pdf
2. [2] Westinghouse Defense and Electronic Systems Center, Command & Control Div., Defense Acquisition Radar (DAR) brochure (T. I. Powell, Marketing Manager; c. early–mid 1980s). DAR is described as "evolved from the highly successful TPS-43E". Scanned copy hosted by MobileRadar.org. http://www.mobileradar.org/Documents/DAR.pdf
3. [3] MobileRadar.org, "Radar Descriptions" (TPN–VPS series), entries TPS-43 (Basic) through TPS-43M/DAR, TPS-70, TPS-75. https://www.mobileradar.org/radar_descptn_3.html
4. [4] Forecast International, Radar Forecast: TPS-75(V), archived report, Sept. 2002 (archived 03/2003). https://www.forecastinternational.com/archive/disp_old_pdf.cfm?ARC_ID=1675
5. [5] Rome Laboratory (formerly RADC), Extended-Interaction Klystron for the AN/TPS-43-E Radar System, DTIC ADA253166, June 1992 (abstract via DTIC OAI record; full text not retrievable during research because DTIC was under maintenance). http://oai.dtic.mil/oai/oai?identifier=ADA253166&metadataPrefix=html&verb=getRecord
6. [6] Air Force Sustainment Center, Sources Sought Synopsis FA8250-25-SSS-0684, "Repair of NSN 5960-00-078-0684, Twystron, AN/TPS-75" (posted 12 May 2025), as mirrored by HigherGov. https://www.highergov.com/contract-opportunity/sources-sought-synopsis-repair-of-nsn5960-00-078-fa8250-25-s…
7. [7] Caliber Sales, AN/TPS-43/TPS-70/TPS-72/TPS-75 Capabilities List (repair-vendor parts list with part numbers and NSNs), June 2021. Commercial list; the vendor's system attributions are not broken out by letter model. https://img1.wsimg.com/blobby/go/7495e429-d171-4b12-b927-5f3269381dd1/downloads/Capability%20List%20TPS-43-…
8. [8] GlobalSecurity.org, "AN/TPS-75 Radar System". https://www.globalsecurity.org/military/systems/aircraft/systems/an-tps-75.htm
9. [9] S. Hitchcock, P. Holen, M. Stangenes, M. Garbi, C. Rivers, H. Anamkath, R. Ross, L. Runge (Stangenes Industries), A. Gardner, J. Terry (Raytheon Technical Services), "Ground based radar modulator solid-state upgrade," 2012 IEEE International Power Modulator and High Voltage Conference, doi:10.1109/IPMHVC.2012.6518749 (abstract; the radar is not named in the abstract, see §3.4). https://doi.org/10.1109/ipmhvc.2012.6518749
10. [10] Stangenes Industries, "TPS-75 Modulators" product page. https://stangenes.com/Item/high-voltage-pulse-modulators/tps-75-modulators/tps-75-modulators
11. [11] Diversified Technologies, Inc., press release, 23 Feb 2016, "Diversified Technologies Transportable Radar Upgrade Replaces Obsolete Parts With Solid-State" (EIN Presswire/Marketwired). https://www.einpresswire.com/article/313136088/diversified-technologies-transportable-radar-upgrade-replace…
12. [12] Diversified Technologies, Inc., press release, 5 Feb 2019, "New Radar Transmitter Upgrade Kit Replaces Obsolete Parts With a High Reliability System" (PRWeb). https://www.prweb.com/releases/Diversified_Technologies_Inc_New_Radar_Transmitter_Upgrade_Kit_Replaces_Obso…
13. [13] M. Kempkes, M. Munderville (Diversified Technologies), "AN/TPS-43/70/75 Transmitter Modernization Kits," 2017 IEEE Pulsed Power Conference, Brighton (abstract). https://indico.global/event/6853/contributions/61662/
14. [14] A. D. LaRue, R. R. Rubert (Varian), "Multi-megawatt hybrid TWT's at S-band and C-band," 1964 International Electron Devices Meeting, doi:10.1109/IEDM.1964.187444 (abstract). https://doi.org/10.1109/iedm.1964.187444
15. [15] Wikipedia, "Twystron" (secondary summary; primary: [14]). https://en.wikipedia.org/wiki/Twystron
16. [16] Wikipedia, "AN/TPS-43" (used as a lead; several statements there are tagged "citation needed"). https://en.wikipedia.org/wiki/AN/TPS-43
17. [17] C. Wolff, Radartutorial.eu, "AN/TPS-43". https://www.radartutorial.eu/19.kartei/11.ancient/en/karte020.en.html
18. [18] MobileRadar.org, "The 1970's Tactical Air Control System (TACS) (cont'd)". https://www.mobileradar.org/tacs_2.html
19. [19] USAF unit history compilation, "606 Tactical Control Squadron" (usafunithistory.com PDF). https://usafunithistory.com/PDF/0600/606%20TACTICAL%20CONTROL%20SQ.pdf
20. [20] MobileRadar.org, "Test Equipment" (USM-454 oscilloscope "supplied as part of the TPS-43"). https://www.mobileradar.org/Other_test_equip.html
21. [21] Federal logistics data, NSN 5950-00-023-8464, "Coil, Electrical" (P/N VA1525G, 335D502G01), via LogiQuest Lite (also nsnequipment.com). https://www.lqlite.com/NSN/5950-00-023-8464
22. [22] CDC/NIOSH, Pocket Guide to Chemical Hazards: Sulfur hexafluoride. https://www.cdc.gov/niosh/npg/npgd0576.html
23. [23] U.S. EPA, "Byproducts of Sulfur Hexafluoride (SF6) Use in the Electric Power Industry." https://www.epa.gov/system/files/documents/2022-05/sf6_byproducts.pdf
24. [24] Utility substation procedure EOP 430.51.4, "SF6 Handling" (hosted by U.S. EPA). https://www.epa.gov/sites/default/files/2016-02/documents/eop430_51_4sf6handling.pdf
25. [25] G. N. Glasoe, J. V. Lebacqz (eds.), Pulse Generators, MIT Radiation Laboratory Series Vol. 5, McGraw-Hill, 1948, Part III (pulse transformers), pp. 499–562. https://archive.org/details/mit-rad-lab-series-version-2
26. [26] Mullard, Electronic Tubes Book 2 Part 4c: High-Power Klystrons (1986), general safety notes (X-radiation). https://frank.pocnet.net/other/Mullard/Mullard_ElectronicTubes_Book2Part4C_HighPowerKlystrons_1986.pdf
27. [27] Health Physics Society, "X rays from high-voltage tubes," Ask the Experts Q4037. https://hps.org/publicinformation/ate/q4037/
28. [28] Federation of American Scientists, "AN/TPS-43". https://man.fas.org/dod-101/sys/ac/equip/an-tps-43.htm
29. [29] Radomes.org, "AN/TPS-43". https://www.radomes.org/museum/equip/tps-43.html
30. [30] INVAP S.E., M-TPS: Modernized TPS-43 brochure. https://www.invap.com.ar/wp-content/uploads/2021/02/0A10-INV-AGDS-MTPS-FP-GO-001-A-EN.pdf
31. [31] everythingRF, listing "VA-145E – Communications & Power Industries" (values read from the search-indexed listing; the page is behind a bot check and could not be opened directly). https://www.everythingrf.com/products/klystrons/communications-and-power-industries-llc/963-296-va-145e
32. [32] NSN Equipment, "5960-00-078-0684 | VA145E | Electron Tube". https://nsnequipment.com/en/catalog/electron-tubes-and-associated-hardware/5960000780684/va145e
33. [33] Newport Aero, Technical Order listing, 31P3-2TPS43-54 … -82 (AN/TPS-43E). http://www.newportaero.com/home/manuals/technical_orders/browse/___336749/to.html
34. [34] MobileRadar.org, "Ancillary Equipment" (AN/UPX-23, AN/UPA-59, AN/UPA-62 entries). https://www.mobileradar.org/Other_radar_ancillary.html
35. [35] U.S. Congress, Office of Technology Assessment, Who Goes There: Friend or Foe? (1993), chapter on cooperative question-and-answer IFF. http://www.princeton.edu/~ota/disk1/1993/9351/935106.PDF
36. [36] Wikipedia, "Secondary surveillance radar" (summarizing ICAO Annex 10 Vol. IV). https://en.wikipedia.org/wiki/Secondary_surveillance_radar
37. [37] M. I. Skolnik (ed.), Radar Handbook, 2nd ed., McGraw-Hill, 1990, Ch. 20 "Height-Finding and 3D Radar," Eqs. (20.3), (20.6).
38. [38] C. Wolff, Radartutorial.eu, "Height or Altitude." https://www.radartutorial.eu/01.basics/Calculation%20of%20height.en.html
39. [39] "TRS/2: Crossatron switch for thyratron replacement in line modulators," 1988 IEEE Power Modulator Symposium, doi:10.1109/MODSYM.1988.26259 (abstract; near-socket replacement for the Model 7390 thyratron in a radar line modulator). https://doi.org/10.1109/modsym.1988.26259
40. [40] Firsthand account, R. Childers, former AN/TPS-43E technician, 726th Tactical Control Squadron, Homestead AFB, 1985–1989 (recollections and personal photographs supplied Sept. 2026). Used only where labeled.
41. [41] Air Force Historical Research Agency (DAF Historical Support Division), fact sheet "726 Air Control Squadron (ACC)": lineage, assignments, stations and honors through 19 Oct 2011 (prepared by Patsy Robertson, reviewed by Daniel Haulman). https://www.dafhistory.af.mil/About-Us/Fact-Sheets/Display/Article/432101/726-air-control-squadron-acc/
42. [42] USAF unit history compilation, "726 Air Control Squadron" (usafunithistory.com PDF; mission-equipment list). https://usafunithistory.com/PDF/0700/726%20AIR%20CONTROL%20SQ.pdf
43. [43] MobileRadar.org, "Units 726–6483" (726th Tactical Control Squadron entry: call sign, equipment, deployments). https://mobileradar.org/unit_726_6483.html
44. [44] USAF unit history compilation, "72 Expeditionary Air Support Operations Squadron" (lineage of the 72nd Tactical Control Flight; created 10 May 2025, citing AFHRA). http://usafunithistory.com/PDF/50-74/72%20EXPEDITIONARY%20AIR%20SUPPORT%20OPERATIONS%20SQ.pdf

Written by Rick Childers, 25 September 2026, from open sources and firsthand experience. Not an official technical order; do not use for maintenance or safety procedures.