Series AM84 LINAC Power Amplifier

The Series AM84 LINAC covers frequencies of 2.85 & 3GHz, and has a maximum output power of 1000 watts

Series AM84 LINAC Power Amplifier

The Series AM84 LINAC covers frequencies of 2.85 & 3GHz, and has a maximum output power of 1000 watts

Product Series: AM84 LINAC

Product Applications:

High Energy Physics

The AM84 is a Solid State High Power Amplifier (HPA), intended for use as drive amplifiers for Klystron tubes. The amplifier is a “Pulsed Class A” design. The duty cycle indicates the limits of the amplifier in terms of the maximum pulse width and repetition rate that can be supported.

High power GaAs (Gallium Arsenide) transistors are controlled via a TTL command line to switch the bias levels so that the amplifier will be in a class A state for the duration of the RF pulse, but otherwise in a standby state.

This design provides the superior performance possible from a class A design but without the disadvantages of high power consumption and heat generation, and offers significant advantages over conventional class C amplifiers as the amplitude variation and phase excursions caused by transistor junction heating are greatly reduced by the application of pre-pulse bias.

Specifications

Centre Frequency : 2.85Ghz (Model AM84-3S1-55-60R), 3GHz (Model AM84-3S2-55-60R)
Full Power Bandwidth : 40Mhz min
Peak Output Power : +59.5dBm min @ 5% duty
3dB Power Bandwidth : 200Mhz typ
Input Power for Rated Output : +5dBm nom, +10dBm max
Absolute max input Power : +20dBm
Duty Cycle : 5% max
Input Signal Characteristic : Pulsed
Input Pulse Width : 500uS max
Pulse Repetition Frequency : 10KHz max
RF Output Stability in Pulse : 0.1dB/10uS max, 0.5dB/500uS max @ peak O/P
RF Output Phase Stability in Pulse : 1 degree max
Non Harmonic Spurious Output : >100dBc
Input Return Loss : 14dB min
Output Return Loss : 18dB min
Noise Figure : 6dB typ
System Power Supply : Mains 230VAC 1-phase 3KvA peak max
Pulse control rise time (0-100% RF) : 5uS
Pulse control fall time (100-0% RF) : 5uS
RF Rise/Fall time : 75nS max
TTL Pulse Control Signal : TTL HIGH = amplifier biassed to class A
TTL Enable Signal : TTL HIGH = amplifier ACTIVE
Dimensions (LWH) : 19″ x 4U x 550mm rack mountable chassis
Weight : 25Kg nominal
Operating Temperature : 0 to 40C ambient
Storage Temperature : -20 to 85C

Notes

1. Duty Cycle

The amplifier duty cycle is limited to 5% at which the amplifier may be continuously operated. The pulse width and repetition frequency of the RF signal may be varied as required, but must not exceed the maximum rated duty. Built-in protection against excessive duty cycle in incorporated, which will automatically limit the RF output if this level is exceeded.

2. RF output Variation in Pulse

The above specifications apply when the amplifier is operated in saturation. Reduced RF output levels will result in correspondingly increased amplitude variation. It may be necessary to increase the TTL control to RF pulse delay to achieve optimum performance. Note that this will reduce the prf that is possible.

Typical amplitude variation during pulse

3. Power Consumption

The primary power input demand will be a function of the duty cycle. 110V and 230V versions are available – please specify when ordering.

4. Pulse Control Rise & Fall Time

This is the period of transition between standby & active states determined by measurement of the rise & fall time of a CW signal from 0-100% and from 100% to 0.

During the standby state the amplifier is disabled drawing minimal power, and can not amplify an RF signal.

In response to a TTL (high) command, the amplifier switches to an active state with full DC bias, and is able to amplify a pulse. The duration of this transition is the Pulse Control Rise Time.

At the end of the pulse the amplifier may be reverted to the standby state. The duration of this transition is the Pulse Control Fall Time. Note that the application of RF signals during these transitions will result in a distorted output.

5. RF Rise & Fall Time

The RF rise/fall times are for a pulsed RF signal, with the amplifier stabilised in class A in response to TTL pulse-control signal.

6. TTL Pulse Control Signal

The TTL pulse control line is AC coupled to prevent accidental application of CW RF input signals.

7. Test Data

Test data for operation under specific duty conditions (pulse width & frequency) can be provided on request.

Otherwise, test data under maximum duty conditions is provided.

Signal Interfaces

RF Input N type female panel jack
RF Output N type female panel jack
TTL Enable BNC female panel jack
TTL Pulse control BNC female panel jack
Safety Interlock D-type at back panel
Remote Status 15 way D-type at back panel

Mechanical

Dimensions (LWH) 19” x 4U x 550mm Rack mountable chassis
Weight 25Kg nominal

The front panel mountings should not be used to support the entire weight of the amplifier when mounted in a 19″ rack. The side extrusions accept M5 captive nuts, which should be located at the rear of the unit to provide additional support. Alternatively, the amplifier should be rested on a tray within the rack.

Front Panel Controls & Indicators

Main power keyswitch: Initialises unit & activates cooling system.
Mains power indicator: Yellow LED indicates AC power is applied.
PSU status indicator : Green LED indicates status of AC/DC convertors.
RF status indicator: Yellow LED indicates presence of RF at the output port
TTL status indicator: Yellow LED indicates TTL-high enable signal is applied
Reflected power indicator: Red LED indicates reflected power in excess of 200W
Over temperature indicator: Red LED indicates amplifier shut-down due to over temp.
Output Power Meter : 3.5 digit LED meter reading peak forward output power in watts. (Limited accuracy where prf <10Hz or PW <1uS)

Remote Status Interface

TTL RF On/Off, over temperature status, VSWR and PSU status reported to rear panel D-type connector.

TTL RF On/Off Status: High = ON
Over Temp Status: High = Alarm
VSWR Status: High = Alarm
PSU Status: High = OK

Analog voltage approx proportional to RF output level on rear panel D-type connector:

Forward Power Detector Output: +5V nom @ Peak RF O/P
Detector Dynamic Range: 15dB min

Protection Features

Output power limiter
Amplifier output is limited if average RF output power exceeds 5% duty.

Reverse Power Protection
Integral output isolator provides full power mismatch protection. Automatic shut down if reverse power exceeds 200w average.

Over temperature protection
Monitors power module temperature, with automatic over temp shut-down (with front panel indication) and auto reset.

Safety interlock contacts
A two-state output is provided in the form of a pair of normally-closed dry relay contacts. The output is conductive (20 mA maximum current ) when the internal conditions required for normal operation of the amplifier have been satisfied. Failure of any condition, or the activation of a self-protective feature (excess reverse RF power or over-temperature) causes the contacts to be open. The contacts are available at the rear panel D-type connector.

Environmental

Operating temperature range: 0 to 40C ambient
Storage temperature range: -20 to 85C

The amplifier should be operated in a clean environment.

Operation in sand/grit/dust environment may severely reduce the life of the internal cooling fans. The front (intake) and read (exhaust) of the amplifier should not be obstructed. On no account must the amplifier be subjected to water ingress.

Options

Manual Output Power Control

Provides 3dB output power range with minimal degradation of output pulse stability from the saturated level. Control is by front panel adjustment knob. It may be necessary to increase the pulse control TTL-RF pulse delay to 25uS for this feature to operate effectively.

Operation

As described in Section 2 note 4, an RF signal may be amplified only when a TTL command is applied at the pulse control connector. Full details of the operating procedure are detailed in the operating manual supplied with the equipment.

3.1 Amplifying a Pulsed RF Signal

It is necessary to synchronise the RF pulse with the TTL pulse control signal. This is accomplished using two square wave pulse generators capable of the desired PRF, one as master the other as slave. The slave is configured to trigger a pulse from an RF source, the master to output the TTL pulse control signal to the amplifier and after the required delay (pulse control rise time), trigger the slave.

Amplifying a Pulsed RF Signal

For SMR20 specifications & function refer to the operating manual or to online information at: http://www2.rohde-schwarz.com/file_3894/smr_20-40%20e03.pdf

Fig 1 - Using external pulse generators with an SMR20 Rohde & Schwarz source

NB. It is not necessary to program a delay between the end of the RF pulse and the TTL pulse control signal.

Fig 2. Typical pulse timing for 10uS RF pulse

Generating RF Pulses from a CW Input

RF pulses may be generated by using a pulse generator to apply TTL signals to the pulse control line. Note that since there will be no pre-pulse bias, the shape of the RF pulse will approximately follow the bias slope for a nominal 5uS (pulse control rise/fall time) at the leading and trailing edges, and show significant amplitude variations during rise & fall.

Fig 3. Typical Pulse Timing for 10uS pulse

Deliverables

Each amplifier is supplied packed in a purpose designed carton containing:

Pair of keys for front panel keyswitch. These are uncoded and factory replaceable.
Pair of front panel handles with fixing screws. These are removed for transit.
Mains power cable 2m.
Operating manual with test data.

Maintenance

No maintenance is required in normal operation and there are no user-serviceable parts within the amplifier. Each amplifier is factory tested and supplied with a set of test results. If degradation in performance to below the specified levels occurs, or a failure is suspected, then the complete unit should be returned to the manufacturer together with details of the fault.

Safety

The amplifier is subject of safety tests at the factory is supplied compliant with the LV and EMC Directives and bears the CE marking.

The amplifier is heavy and care should be taken when lifting. Carrying handles are provided at the front panel.

Hazardous voltages are present within this line-operated unit. Do not remove any panels.

The centre conductor of the RF output connector should not be touched whilst the unit is in operation. Up to 1000W RF power can be present which may cause skin burns.

Connection to the RF output port must not be made or broken whilst operating at high power levels. This may result in damage to or destruction of the output connector.

The amplifier MUST be grounded.

Line supply is filtered within the amplifier. A slow-blow fuse is located in the mains inlet. Should this repeatedly fail the amplifier should be returned to the factory for investigation.

Small objects and thin cables etc should be kept away from the rear panel cooling fans which are fitted with finger guards.

Warranty

Microwave Amplifiers Ltd warrants for two years from date of shipment that the goods supplied will be in fully compliance with the agreed specifications and will be free from defects in material and workmanship. Any and all other warranties (except of title) express or implied, relating to fitness for particular purpose, merchantable quality or otherwise are expressly disclaimed. Seller will not be responsible for special or consequential loss or damages. Liability shall be limited to the repair or replacement of defective products subject to the return of the product intact, and un-tampered with by the buyer.

AM84 LINAC