Satcom Transceiver Delivers Linear 13 W

Cover Story SATCOM TRANSCEIVER Satcom Transceiver Delivers Linear 13 W

This highly integrated microwave assembly employs ERICA AYCIN Member of the Technical Staff advanced SMT fabrication techniques to reduce size, Narda Microwave-East, 435 Moreland Rd., Hauppauge, NY 11747; (631) 231-1700, e-mail: [email protected]; weight, and power to previously unattainable levels. Internet: www.nardamicrowave.com.

Frequency upconverter/downconverter subsystems designed for satellite communications (satcom) terminals tend to be larger than the ever-shrinking units for terrestrial consumer wireless systems. Ruggedized equipment for military satcom systems is larger still. However, as demonstrated by the model 81000 satcom transceiver subsystem from Narda Microwave-East (www.nardamicrowave.com), innovative approaches to design and fabrication can dramatically reduce the size, weight, and power consumption of even military satellite terminals. In a housing measuring just 15 x 6.25 x 3.25 in., and weighing only 15 lb., the model 81000 not only packs frequency upconverter and downconverter subsystems, but a 13-W linear RF power amplifier, a power supply, control circuits, and Ethernet and RS-485 connectivity. Model 81000 (FFig. 1) is designed for use on platforms ranging from ffixed-wingixed-wing aaircrafti and helicopters to UAVs and ground vehicles to mman-portablean-po applications when operated from the integrated F bbattery pack. The design of the unit is based on a combination of Narda-developed advances in microwave- iintegrated-circuit (MIC) and surface-mount technologies tthat allow Integrated Microwave Assemblies (IMAs) tto surpass the mechanical and electrical capabilities of cconventional integrated assemblies. Model 81000 is an LL-band/Ku-band unit, with models covering X- and KKa-band satcom bands available as well. ThThee design of the assembly was based on a set of custom 1. Model 81000 is a satcom trans- specificationsf that encompassed performance, size, weight, power ceiver mounted in a rugged enclosure consumption, and ruggedness. Designers at Narda performed a system measuring 15 x 6.25 x 3.25 in., and flow-down analysis from which an architecture consisting of four func- weighing a manageable 15 lb. tional blocks emerged—a block upconverter (BUC), block downconverter (BDC), solid-state power amplifier (SSPA), and DC power and control subsystem. Each functional block was assigned performance specifications based upon the system flow-down analysis, designed and developed independently and finally integrated at the top system-level assembly. The BUC, BDC, SSPA, control circuits, and power supply are shown in Fig. 2.

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The upconverter and downconverter modules 2. The transceiver is constructed of four in the L-band/Ku-band model 81000 were largely modules: two converters, a 13-W linear designed and fabricated using what the company RF power amplifier, and a module con- calls its “Ultimate SMT” technology, which has been taining control and a DC/DC converter. successfully utilized at frequencies through 31 GHz. This technology has several advantages. There is no housing of the type typically associated with SSPA MIC construction but rather a single multilayer board formed of various microwave laminates. Block upconverter Higher-frequency components are on the top side of the board (Fig. 3), with lower-frequency devices and control and digital circuits on the bottom side (Fig. 4). Blind and through vias achieve grounding and interconnections between layers. Voltage The use of controlled-depth, machined pockets conditioning on the top side of the board between metallized layer 1 (RF signal) and layer 2 (RF ground) helps Block downconverter optimize performance. The controlled-depth rout- ing process ensures that the machined pockets do not protrude into the ground layer by more than 10 to 20 μin. Standard MIC-type components, such as bare die and alumina filters, are inserted into the pockets. Layer 2 can be considered the ground plane of a conventional single-layer assem- The Model 81000 transceiver at a glance. bly, which the technique mimics. A microstrip line on the top layer is wire-bonded directly to RECEIVE BLOCK UPCONVERTER the component in the pocket and then back to Input frequency range (GHz) 11.45 to 12.75 the microstrip line on the other end, maintaining (10.95 to 12.75) Output frequency range (MHz) 950 to 1450 single-layer ground connectivity. (950 to 1700) With conventional SMT techniques, signal and Downconversion bands (GHz) 11.45 to 11.95 ground paths must transition to and from the (others available) 11.8 to 12.3 device using vias, which introduce discontinuities 12.25 to 12.75 and reduce the level of achievable performance, Gain, minimum (dB) 35 especially at higher frequencies. By eliminating Input power (dBm) -95 to -30 these transitions, designers can exert more control over performance, which in the case of a filter is Noise figure (dB) 15 essential as transitions and their inevitable dis- Frequency reference (MHz) 10, internal or external continuities affect the filter’s rejection and return Transmit block upconverter loss characteristics. This technique allows the Input frequency range (MHz) 950 to 1700 designer the flexibility to utilize both MIC and Output frequency range (GHz) 13.75 to 14.5 SMT simultaneously, taking advantage of the Gain, minimum (dB) 58 benefits that each technology offers. The bottom side of the BUC and BDC boards Noise figure (dB) 20 (7 optional) contains the reference oscillator section, the lower- SOLID-STATE RF POWER AMPLIFIER frequency portion of the synthesizer, including Linear RF output power at -26 dBc spectral +41.14, 13 regrowth, one symbol offset from carrier the main and offset loops, and DC and control (dBm, W) circuits. The output of the main loop is fed to the top side of the board using a through-board OTHER SPECIFICATIONS transition, after which it is multiplied to the DC input power (VDC) +48 desired higher-frequency range, filtered to reduce DC input current, maximum (ADC) 4.0 at Plin spurious content, amplified, and applied to the Communications interfaces Ethernet, RS-485 LO port of the respective mixer. Dimensions (in.) 15 x 6.25 x 3.25 The top side of the board incorporates ground Weight (lb.) 15 via “fencing” strategically placed in a pattern to o isolate areas that either create or are sensitive Operating temperature range ( C) -30 to +55

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3. The block downconverter is implemented on a two-side multilayer circuit board. The high-frequency side shown here includes via fencing that isolates areas that radiate or are sensitive to high-frequency energy and interconnects layer 1 and 2 ground plane metallization. A form-in-place gasket shown on the cover provides EMI shielding.

to radiated emissions. The vias determine its spectral regrowth accomplished using several interconnect the layer 1 and and 1-dB compression perfor- novel techniques. A combination layer 2 ground plane metalliza- mance versus quiescent drain of digitally controlled potenti- tion and mate with a channel- current. The bias point that ometers, HEXFET switches for ized cover containing a conduc- optimized each of these criti- independent drain voltage on/ tive form-in-place (FIP) gasket cal parameters was used in the off control, and built-in drain that is compressed between the system. current monitoring circuitry, body of the module and the The devices are mounted into are incorporated to set the bias cover to provide a high level of the SSPA housing using a sol- points of each output device. EMI shielding (Fig. 3). The cover dering approach to minimize During factory alignment, each acts as a heat-transfer surface to the electrical discontinuities output device is turned on indi- pull heat from the board to the between the device package vidually and its digital potenti- cover where it is dissipated via a and the input/output microstrip ometer is adjusted through use heat sink. Earlier designs did not transmission lines. The solder of automated test equipment to use an FIP gasket and required also provides a good thermal establish optimal bias points. a large number of screws to interface between the device The automatic alignment is secure the cover. Eliminating and the housing, lowering junc- repeated at multiple temper- the screws and replacing them tion temperature and increasing atures, the result of which is with vias and EMI compression reliability. stored in a calibration look-up gasketing reduced size by at least Surface-mount MMIC devic- table in the RF amplifier mod- 40 percent, weight by about 30 es are employed as gain stages, ule. At run time, the microcon- percent, and simplified assembly and temperature-sensitive atten- troller reads the temperature as well. uator pads are used to provide a and calibration data from the The four-stage, 13-W linear degree of temperature compen- power amplifier and adjusts the (20-W output power at 1-dB sation. However, system-level digital potentiometers accord- compression) SSPA (Fig. 5) uses temperature compensation is ingly. This unique biasing tech- internally matched GaAs MES- accomplished by microproces- nique eliminates the more con- FETs in Class AB operation for sor-controlled voltage-variable ventional process of manually balance among power output at attenuators (VVAs) in the BUC measuring drain current and 1-dB compression, maximum and BDC modules. Printed- adjusting a potentiometer or linear power (defined as the circuit filters are also included iteratively replacing select-at- power at which the spectral to provide harmonic and local test resistors to establish proper regrowth, measured at a one oscillator rejection. Finally, a biasing. As a result, the power symbol rate offset, reaches a diode detector after the final amplifier can be aligned in less predetermined maximum), and output stage of the SSPA offers time, with better precision, and DC power consumption. During precise power level detection with more consistent perfor- the design phase, each internally capability. mance over temperature. The matched device was evaluated to Bias control in the SSPA is microcontroller and power

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5. TheThe 13-W llinearinear RF power amplifieramplifier is mated with a control board that provides microcontroller I/O, gate bias, temperature monitoring, power detection, regulation, and filtering functions.

4. This view shows the downconverter’s low- frequency, control, and power functions.

distribution board responds to calibration look-up tables that not moisture to pass through commands from a host comput- are resident in all three RF mod- the unit. er, incorporates self-protection ules and adjusts the VVAs in Model 81000 is available in functionality, reports health and each RF module. Temperature the standard configuration with status information to the host and calibration data are com- the performance shown in the computer, provides temperature- bined with host system com- table, or in X-band and Ka-band compensated gain control for mand data to provide adjustable configurations to serve these each RF module, and in the Ka- gain and maintain constant gain other satcom bands. Construc- band version, adjusts the power over temperature. In addition tion in the case of the Ka-band amplifier’s operating points as a to providing control functions, converter employs Narda “Ulti- function of temperature. the microcontroller and power mate MIC” approaches, which Power supply voltages, syn- distribution board convert the are similar in many respects to thesizer lock detect outputs, “raw” +48-VDC input power the Ultimate SMT techniques power amplifier drain currents, into regulated and filtered +12 described above but contain a and detected RF power output and +6.5 VDC supply voltages higher degree of MIC content. are all continuously monitored. required by the RF modules. If either synthesizer goes into The four-module assembly Narda Microwave-East, 435 an out-of-lock condition, the has a finned heat sink and two Moreland Rd., Hauppauge, NY transmitter is taken off the air to fans for cooling. The SSPA is 11747; (631) 231-1700, e-mail: prevent interference with other mounted to the “cool” side of [email protected]; users. If the drain current of any the heat sink furthest from the Internet: output device exceeds a safe level, fans. Fan speed is controlled www.nardamicrowave.com or if an attempt is made to drive automatically, although it can the SSPA power output beyond a be reprogrammed for specific safe level, the transmitter is shut applications. The assembly has down to prevent damage. an environmental seal between The microcontroller reads the cover and the housing and a the temperature sensors and Gore-Tex vent to allow air but

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