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The Use of HP ME in the WBand Tripler Design

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The use o' drafting tables oencils and paper for design and drafting at HP is rapidly disappearing and being replaced by computers, displays, and keyboards The primary mechanical design software is HP ME 10 for two-dimensional work and HP ME 30 for solids modeling

The package for the W-band tripler microcircuit described in the accompanying article was designed using ME 10 The required views were constructed with exact geometry so that other areas involved in documentation and manufacturing would see the correct configuration This Tile was then electronically transferred to the model shop for the fabrication of prototype parts. Since this package is relatively complex, consisting of four machined pans, it was translated into an ME 30 solid body for better visualization The tapered waveguide equation, developed using the HP Microwave Design System (MDS), was also sent to the model shop, routed through a translator, and entered into the ME 30 solid body

All of the ME 30 information was routed through another translator and then the prototype packages were machined using a computer-controlled machine lool. Once necessary revisions or corrections to the package were implemented the file was transferred to the drafting area, where a simple command in ME 30 generated all six views of a part and the part was formally dimensioned and formatted for manufacturing specifications. The production machining area was also able to import these files into its own system with very little time tor production programming restructuring. Fig 1 showstheflowchartoftheprocedureused.

Reference

1 S. LDCknart. Changing Worn Markets Itie CA1P Mandate a! HP1 Innovation Vol 8. no 2. Spilng.'Summer 1989. po 20-29

Roy Marciulionis

Development Engineer Network. Measurements Division

Fig. 1. Flow chart of the process leading trom ME 10 design to final drafting and production.

methods of suppressing these modes are: changing the substrate to a lower-dielectric material, changing the substrate thickness, and reducing the height of the waveguide to push the cutoff frequency above-band.

This problem is overcome by changing the substrate from 0.010-inch sapphire (er = 9.fiJ to 0.010-inch fused silica (er = 3.2) and reducing the height of the waveguide. The choice of material and substrate thickness is a compromise between the need to suppress the LSE modes, the impedance requirements for achieving the proper input match to the diodes, and the feasibility of fabricating the thin-film capacitors necessary for diode biasing. The waveguide height is reduced from 0.074 inch to 0.070 inch to ensure that the cutoff frequency is above-band. The doubling device for both the R-band and the V-band doublers is a 40-fiiir Schottky diode on an n + + liquid phase epitaxy layer on a GaAs substrate.

Placing the dielectric circuit into the waveguide is mechanically difficult. For this reason, a split block approach is employed. As shown in Fig. 14. the waveguide housing is in two parts, and one part includes machined cavities above and below the waveguide. These cavities are one quarter wavelength (at midband) from the waveguide and filled with polyiron. The polyiron ensures that no modes can exist in the cavities. The cavities themselves presenl an open circuit, which transforms to a short circuit at the edge of the waveguide.

R-Band Amplifier Doubter

The input signal of 12.5 GHz to 18.75 GHz (maximum input power - 15 dBm) is first amplified by an MM1C (microwave monolithic integrated circuit) amplifier. This amplifier is a reactively matched two-stage MESFET amplifier designed to give 22-dHm output power from 12 GHz to 20 GHz. The amplifier roll-off below 12 GHz provides rejection for the lower harmonics coming from the source, bike many amplifiers, this one had a tendency tu oscillate if the input and bias leads were of any significant length. Therefore, several large monoblock capacitors were added around the circuit to keep it from oscillating The multiplier operates on the previously discussed frequency

Fig. 14. Split block design of the finhne-to-waveguide transition of the V-band amplifier doubler

Fig. 15. Slotline-to-microstnp transition of the R-band amplifier doubter with circuit model

Fig. 15. Slotline-to-microstnp transition of the R-band amplifier doubter with circuit model doubling principle. The circuit is realized on a 0.010-inch sapphire substrate. The frequency-doubled signal propagates down the slotline and through a transition (transformer) into microstrip line. The slotline-to-microstrip transition and its model are shown in Fig. 15, It is formed hv overlapping the slotline and the microstrip line.

Amplifier Multiplier Performance

Typical output power performance data for the W-band amplifier tripler, the V-band amplifier doubler, and the R-band amplifier doubler is shown in Fig. 16. The different technologies, devices, and thin-film parameters used in

50 52 54 55 58 60 62 64 66 68 70 72 74 V Band Frequency (GHz)

75 80 85 90 95 100 105 110 w Band Frequency (GHz)

Fig. 16, Typical output power of the W-band amplifier tripler. the V-band amplifier doubler. and the R-band amplifier doubler component development for the HP 83557A and HP 83558A millimeter-wave source modules are shown in Table HI.

Table Ml

Technology Used for Components of the HP 83557A and HP 83558A Source Modules

Component Devices

Coupler detector

W-band amplifier tripler

V-band amplifier doubler

R-band amplifier doubler

Beam-lead diode

Beam-lead diode. GaAs FET

Beam-lead diode, GaAs FET

Beam-lead diode,

MMIC

Thin-Film

0.005-inch sapphire, integrated capacitors

0.005-inch sapphire, integrated capacitors,

0.010-inch fused silica

0.010-inch sapphire

ME 10/30

mechanical design

MDS, ME 10/30 mechanical design

ME 10/30 mechanical design, MDS

ME 10/30 mechanical design. MDS

Source Module System Evaluation

Once the individual components were developed and met their specifications, the source module was assembled with the component bias board and the source interface board, A few challenging issues were discovered and resolved by the project team for the source and the system to meet specifications.

Dynamic Range. The V-band source module is specified to deliver leveled output power between +3 dBm and -2 dBm. The maximum output power, +3 dBm. determines the required minimum input power to the source module. For the HP 83624A and HP83550A sources, the minimum

12.5

13 13.5 14 14.5 15 15.5 15 16.S 17 17.5 W-Band Source Input Frequency (GHz)

12.5 13 13.5 14 14.5 15 15.5 16 16.5 17 17.5 IB 18.5 V-Band Source Input Frequency (GHz)

Fig. 17. Input power for - 2-dBm output power for the V-band source module and for - 5-dBm output power for the W-band source module.

12.5

13 13.5 14 14.5 15 15.5 15 16.S 17 17.5 W-Band Source Input Frequency (GHz)

Flatness Correction

Among the many features ot the HP 8360 farm yol synthesized sweep oscillators, the flatness correction capability offers the m.i ¡meter-wave source module user better oulpul power flainess through the module's own internal tiatness correction data and an HP 8360 user-definable flatness calibration routine.

The digital flatness correction 'or the mi-¡meter-wave source modules works in much the same manner as the internal flatness correction that is standard In ail HP 8360 series synthesized sweepers The flatness correction array is stored in nonvolatile RAM in each millimeter-wave module. It contains offset factors n cB to compensate for the unfitness of the module's coupler and detector These numbers are stored at frequency Intervals corresponding to the module's multiplication factor times 100 MHz (nominal). The V-band module, for example, is a x 4 module and carries offset data every 400 MHz. The W-band module Is x6 and has correction data every 600 MH2 This array is read into the HP 8360'S memory whenever a millimeter module is connected and an instrument preset Is executed. The module flatness correction then resides In a special array in the Instrument The HP 8360 uses this information to correct the module s coupler and detector flatness at a finite number of frequencies across the millimeter waveguide band Linear interpolation is performed in the HP 8360 for frequencies between each flatness correction point, resulting in some flatness errors typically on the order ol 0.2 dB. Another source of fiatness error is Ihe nonllnearlty of the detector and logger The flatness correction data is stored at the specified maximum leveled oulpul power As the power is lowered, small flatness errors occur, with approximately 0.2 dB error at the minimum specified output power However, all flatness errors over the power level ana frequency ranges are less than 0.5 dB, leaving only the uncertainty of the power measurement in question

If better flatness than this is required either across the entire waveguide band or over a smaller subsel of frequencies one can choose to implement Ihe user flatness correction. The user flatness capability allows the operator to set the user correction array start/stop frequencies with up to 505 frequency points The user flatness correction is performed at the current output power selling, allowing the operator the choice of outpui power leve! With an HP 437B power meter connected to the HP 8360 over the HP-iB interface and the power sensor connected to the oulpul of the millimeter-wave module, the HP 8360 can measure the power and store the flatness offset data into its user flamess array automatically Alternatively, a user-wrltlen calibration program and any power meter can be used Once ihe calibration Is complete the operator can choose any subset of frequencies within Ihe user flatness correction array and continue to use thai portion of the user correction array

Lon Dear den

Development Engineer Network Measurements Division power is +17 dBm at 18.75 GHz. For other sources that deliver lower power than + 17 dBm al 18.75 GHz, the HP 8349B amplifier is recommended. The minimum output power, -2 dBm, determines the required minimum set-table power to be delivered by the source. This power is — 5 dB m for the HP 83550A, HP 83595C. and HP 83592G without the attenuator option. Therefore, the source mod ule is tested with + 15-dBm input power la deliver output power of +4.25 dBm from 50 to 75 GHz, taking into consideration the leveling loss and the measurement uncertainty. The source module is also tested for - 2-dBm output power with the minimum settahie power from the source of -5 dBm from 12.50 to 18.75 GHz. The module's gain and gain flatness are adjusted to meet the specification. The typical input power to the source module to meet its — 2-dBm specification is shown in Fig. 17. A similar test is performed for the W-band source module. Leveling Sensitivity. The V-band source module can be configured with HP 8360, HP 8673C/D. HP 83550A, HP 8340/ 41B, and HP 8359x sources. The conversion efficiency of the YIG-tuned multiplier of each of these sources is linear in the normal operating output power range. However, at very low output power, it can become nonlinear, which can cause ALG peaking and leveling loop oscillations. Oscillations can also occur if the conversion efficiencies of the R-band amplifier doubler and the V-band amplifier doubler change rapidly with output power variations. Therefore, the V-band source module w:as also tested with a sample of all applicable sources to verify its ALG stability. The output frequencies were varied and the input power variation was monitored. The worst-case output frequency is used to test every source module to guarantee source system stability. Typical leveling sensitivity of the V-band source module is shown in Fig. 18, which is for 62.5 GHz, The 0,5V/GHz tuning voltage is used to adjust the source module gain and gain shape to meet the required system parameters for stability. A similar lest is also performed for the W-band source module.

Harmonic Analysis. The output harmonic content of the V-band source module is generated hy the 3/4. 5/4, and 6/4 harmonics as shown in Table U. The desired 6/4 or 3/2 harmonic is generated within the V-band doubler and can be measured and adjusted separately on the subassembly level. The analysis for the 3/4 and 5/4 harmonics is shown in Fig. 19. The desired multiplied signal from the R-band doubler is f, and the unwanted signal is 3/2 f, or i2. Both signals are amplified and doubled again to generate the wanted signal ta. However, two unw-anted signals are generated within the V-band doubler and propagated to the output. The upper portion of f2 (50 to 56.25 GHz) is 3/4 fQ.

Fig. 18. Leveling sensitivity of the V-band source module

Fig. 18. Leveling sensitivity of the V-band source module

Since the multiplier is a very efficient mixer, f, and fz mix with each other and with the wanted output signal to generate 5/4 f„. The 3/4 f(1 product is easily eliminated since the amplifier portion of the V-band amplifier doubler has high attenuation in that frequency range. The 5/4 f,, signal is directly related to the third harmonic of the input frequency or and can also be adjusted by tuning the R-band amplifier doubler. This is a major advantage of the 2A2 scheme of multiplying over the straight x 4 scheme.

For the W-band source module, the unwanted output signals are 5/6 f0, 7'6 f„, and 8/6 fQ as shown in Fig. 20. The 8/6 f,j or 4/3 ifl product is generated within the W-band tripler and can be measured and adjusted separately at the subassembly level. Again, because the tripler is an efficient mixer, it adds and subtracts the ft and f-a signals to produce 5/6 f,j and 7/6 fl;i The 5/6 fn product is proportional to the gain of the amplifier portion of the W-band amplifier tripler. Since this gain is really an attenuation at 50 to 55 GHz, the 5/6 f„ product is less than -40 dBc, However, the 7/6 f„ product is proportional to the amplifier gain at 25 and 37.5 GHz, which is high. Thus the R-band amplifier doubler is adjusted to reduce the fs signal output, which in turn reduces the 7/6 f0 output.

Output Power Level Flatness. The output power can vary by about + 3 (IB without any correction. Thus an eight-breakpoint scheme is used to correct for the output power flatness. For better than + 1-dB flatness, nonvolatile RAM inside the source module contains corrections for level flatness and can be read by the HP 8360 synthesized sweeper

62.5

Fig. 19. Harmonic analysis for the V-band source module

f. + t,

0 0