A set of MMIC frequency multipliers and balanced mixers have been designed for the local oscillator system of the Atacama large millimeter array (ALMA). These millimeter-wave elements form a critical link in the active multiplier chains between the relatively low frequency microwave oscillators and the very high frequency submillimeter-wave, cooled multipliers of the LO subsystem. A complete chipset for four frequency bands is described, along with preliminary results on prototypes for two additional bands

Boyd, Tod

Bryerton, Eric

Cesarano, Patrick

Morgan, Matthew

Saini, Kamaljeet

Thacker, Dorsey

Weinreb, Sander

Crossref

A millimeter-wave diode-MMIC chipset for local oscillator generation in the ALMA telescope

Caltech Authors - Main

 
A Millimeter-Wave Diode-MMIC Chipset for Local Oscillator 
Generation in the ALMA Telescope 
Matthew Morgan1, Eric Bryerton1, Patrick Cesarano2, Tod Boyd1, Dorsey Thacker1, Kamaljeet Saini1, and 
Sander Weinreb3 
1National Radio Astronomy Observatory, Charlottesville, VA., 22903 
2L-3 Communications GSI, Chantilly, VA., 20151 
3California Institute of Technology, Pasadena, CA., 91125 
 
Abstract  —  A set of MMIC frequency multipliers and 
balanced mixers have been designed for the local oscillator 
system of the Atacama Large Millimeter Array (ALMA).  These 
millimeter-wave elements form a critical link in the active 
multiplier chains between the relatively low frequency microwave 
oscillators and the very high frequency submillimeter-wave, 
cooled multipliers of the LO subsystem.  A complete chipset for 
four frequency bands is described, along with preliminary results 
on prototypes for two additional bands. 
Index Terms  —  Millimeter-wave frequency converters, 
millimeter-wave mixers, MMICs, phase-locked loops, radio 
astronomy. 
I. INTRODUCTION 
The Atacama Large Millimeter Array (ALMA) is a 
millimeter-wavelength telescope currently under construction 
in the Chajnantor region of northern Chile.  Consisting of an 
array of antennas, each 12 m in diameter, with an upper 
frequency limit over 900 GHz, it will be the largest and most 
sensitive instrument in the world at millimeter and 
submillimeter wavelengths [1]. 
Implementing ALMA has presented engineers with 
numerous technological challenges to overcome, and 
innovations have been required in almost every subsystem.  
The local oscillator subsystem, for example, must provide 
sufficient pump power to SIS mixers up to nearly a THz, 
tunable over broad ranges, and phase-locked to a reference 
signal common to the whole array which in some 
configurations may span up to 10 km. 
Fig. 1 is a block diagram for the typical ALMA LO 
assembly present in each antenna for each frequency band.  
Specific details, such as the multiplication factors and number 
of gain stages, may vary depending on the components 
available and requirements for each band.  Generally 
speaking, however, the LO signal is generated by a phase-
locked loop that begins with a microwave YIG-tuned 
oscillator.  This is followed by one or two multipliers that 
scale the signal frequency up into the millimeter-wave range, 
where it is mixed with a common reference distributed to the 
array by optical fiber.  Following the PLL is a final stage of 
amplification and subsequent multiplication which brings the 
signal frequency up to the submillimeter-wave range required  
 
Fig. 1. Block diagram of a typical LO chain for ALMA.  The 
millimeter-wave components, which can be implemented as MMICs 
but are not available commercially, are described in this paper. 
 
TABLE I 
Current ALMA Frequency Bands 
Band # 
RF 
Frequency 
Final 
Mult. 
IF 
Range 
mm-Wave LO 
Frequency 
Band 1 31.3-45 GHz    
Band 2 67-90 GHz    
Band 3 84-116 GHz -- 8 GHz 92-108 GHz 
Band 4 125-163 GHz x2 8 GHz 66.5-77.5 GHz 
Band 5 163-211 GHz    
Band 6 211-275 GHz x3 12 GHz 74.3-87.7 GHz 
Band 7 275-373 GHz x3 8 GHz 94.3-121.7 GHz 
Band 8 385-500 GHz x5 8 GHz 78.6-98.4 GHz 
Band 9 
(original) 
602-720 GHz x5 8 GHz 122-142.4 GHz 
Band 9 
(modified) 
602-720 GHz x6 8 GHz 101.7-118.7 GHz 
Band 10 787-950 GHz    
 
by the receivers. 
Because amplifiers are not feasible at the final LO 
frequency for many of the ALMA bands using present 
transistor technology, the efficiency of the final stage of 
multiplication is paramount.  Cooled, Schottky-Diode 
multipliers are being provided for ALMA by Virginia Diodes, 
Inc.  Though some of these are implemented monolithically, 
the highest frequency band is for now composed of advanced 
planar Schottky diodes flip-chip mounted on a quartz substrate 
with integrated matching and idler circuitry.  This  
0-7803-8846-1/05/$20.00 (C) 2005 IEEE 1587
 
  
 (a) (b) 
 
   
 (c) (d) 
 
Fig. 2. Photographs of the MMIC triplers for (a) Band 4, (b) Band 
6, (c) Band 8, (d) Bands 3, 7, and 9-modified.  Chip dimensions are 
2.0 x 0.73 x 0.1 mm. 
 
high-performance component is more reliable and less 
expensive than classic whisker-contact diode multipliers, yet 
is capable of better efficiency and more power at high 
frequency than that of a fully-monolithic design in the 
submillimeter-wave range.  However, the goal of minimizing 
the global cost of the array drives us to selecting a MMIC 
approach for as many of the remaining elements of the LO 
subsystem as possible, so virtually every active component 
between the YIG oscillator and the final multiplier is a MMIC 
chip. 
The lower-frequency MMICs, including usually the first 
stages of amplification and multiplication, are available at low 
cost from commercial suppliers, but the millimeter-wave 
multipliers, mixers, and power amplifiers required custom 
designs.  Thus, the MMIC chipset described in this paper 
closes the gap between the relatively low frequency 
microwave oscillators, and the very high frequency, 
submillimeter-wave multipliers. 
II. ALMA BANDS 
Frequency coverage for the ALMA facility has been divided 
into 10 bands, as shown in Table I.  Bands 3, 6, 7, and 9 are 
scheduled to be delivered with the first antennas on the 
construction site, and complete chipsets for those bands have 
already been developed.  Chips for bands 4 and 8 are also 
under development for deployment in the near future.  Table I 
also shows how the millimeter-wave frequencies for the 
MMIC portions of the LO subsystem are derived, based on the 
multiplication factors that follow them and the IF frequency 
range of the front ends for those bands.  Not unexpectedly, the 
differing multiplication factors lead to a great deal of overlap 
between the required bands and the potential for chip reuse. 
It is worth noting that Band 9 was originally expected to use 
a quintupler following the last stage of amplification, and that 
chips were designed for the resulting 122-142.4 GHz 
frequency range.  However, the Band 9 schematic was 
eventually modified to incorporate a final multiplier of 6 
instead of 5, allowing us to take advantage of better power 
 
 
Fig. 3. Output power for the triplers in Bands 3, 6, 7, and 9-
modified.  Input power was 17.6 ±1.2 dBm. 
 
 
Fig. 4. Output power for the triplers in Band 4 (simulated) and 
Band 8 (measured).  Input power for the Band 8 tripler was 19 dBm. 
 
amplifiers that were available at the lower input frequency [2]-
[4]. 
III. MULTIPLIERS 
Broadband, Schottky-Diode MMIC triplers in W-Band have  
already been demonstrated [5]-[6].  Building upon this earlier 
work, several new triplers have been designed for the ALMA 
millimeter-wave LO frequency bands.  These generally 
correspond to the second stage of multiplication in Fig. 1.  
Photographs of these chips appear in Fig. 2. 
These chips were all fabricated by UMS in their BES 
Schottky-Diode MMIC process.  All the diodes in these high 
frequency designs have a contact area of 3 µm2.  The junction 
capacitance for these devices is nominally 6fF, with a parasitic 
series resistance of 7 Ω. 
Each of the triplers is composed of three basic sections.  
First is an input matching network with open-circuited stubs, 
which also serves to provide a third-harmonic ground-return.   
1588
 
   
 (a) (b) 
 
   
 (c) (d) 
 
Fig. 5. Photographs of the MMIC mixers for (a) Band 4, (b) Band 
6, (c) Band 3, 7, and 9-modified, and (d) Band 9-original.  Chip 
dimensions are 2.0 x 0.73-1.2 x 0.1 mm. 
 
Following this is an anti-parallel diode pair which efficiently 
generates the third harmonic while intrinsically suppressing all 
even-harmonic spurs.  Finally, the output matching network 
includes AC-grounded stubs which provide a ground-return 
path at the fundamental frequency, as well as a means of 
injecting DC-bias to the diodes, and a low-order bandpass 
filter that rejects higher-order spurious tones. 
Measurements of the output power versus frequency for the 
two triplers used in Bands 3, 6, 7, and 9 (the four bands that 
will be delivered with the first antennas) is shown in Fig. 3.  
The input power in both cases was approximately 18 dBm, 
though it varied over almost a 3 dB range due to limitations of 
the test setup.  This fluctuation of the input power can account 
for much of the ripple seen in Fig. 3, especially since the 
conversion loss is a relatively strong function of the input 
power.  Generally speaking, the triplers deliver about 1 mW of 
power over their design range with approximately 18 dB 
conversion loss. 
Band 8 will use a pre-existing design [5], the measurements 
for which are reproduced in Fig. 4.  The figure also shows 
simulated data for a newly developed Band 4 tripler that has 
not yet been tested.  Although historically the conversion loss 
has been about 2 dB higher than that predicted by our 
simulations, the agreement in terms of saturated output power 
and frequency response is usually good.  Harmonic rejection 
for these triplers is typically in excess of 20 dB. 
IV. MIXERS 
A number of custom millimeter-wave balanced mixers were 
also required to complete the phase-locked loops in the 
ALMA LO subsystem, and were made using the UMS BES 
Schottky diode MMIC process.  These circuits are shown in 
Fig. 5.  The RF and LO frequency ranges are those shown in 
the last column of Table I, with a common IF frequency range 
of DC-200 MHz.  There were two basic topologies used for 
the design of these mixers.  Those mixers shown in Fig. 5a  
 
Fig. 6. Measured conversion loss for the mixers used in Bands 3, 
6, 7, 9-original, and 9-modified, and simulated conversion loss for 
the mixer in Band 4.  LO power in all cases is 10 dBm. 
 
and Fig. 5c are single-balanced mixers that are loosely based 
on earlier broadband, millimeter-wave mixer designs [7].  This 
topology consists of a single balun, implemented here by a 
folded ring hybrid, which drives a pair of diodes in series.  
Short-circuited stubs provide RF matching and a ground-
return for the IF.  The IF signal is the extracted from between 
the two diodes through a low-pass non-reflective filter. 
The chips shown in Figs. 5b and 5d, however, are double-
balanced ring-mixers.  Ring hybrids are used in both cases to 
couple the LO and RF signals into the diode ring.  For the 
band 6 mixer, shown in Figure 5c, the hybrids are arranged in 
a convenient interlocking layout that encloses the diode ring 
and allows easy access to the differential ports for RF/LO 
injection, and to the common-mode ports for IF extraction and 
ground-return.  The same could not be done with the original 
Band 9 (122-142.4 GHz) mixer, because the resulting ring 
hybrids were too small to fit around the diodes.  Instead, the 
hybrids were folded adjacent to the diodes and connected to 
them with a differential matching network.  Both layouts were 
successful, and we believe these represent the first fully-
monolithic double-balanced mixers in this frequency range. 
Tests on early versions of these mixers revealed that the 
performance can be very sensitive to the impedance present on 
the IF port at the RF/LO frequency.  The IF port is connected 
to a PC-Board where the low-frequency PLL circuitry is 
implemented, so the exact impedance seen on this port at the 
much higher millimeter-wave frequencies is not easily 
predicted or controlled, but generally it is reactive and changes 
very rapidly as a function of frequency.  This was not 
originally considered important because the on-chip hybrids 
were meant to isolate the millimeter-wave frequencies from 
the IF port by placing a virtual short between the diodes where 
the output line is connected.  However, like the off-chip 
components, these hybrids also present a reactive impedance 
to the IF port at frequencies above and below the resonant 
center-frequency of the structure.  It is possible, then, for an 
1589
 
off-chip component in the IF path to resonate with the on-chip 
hybrid in the millimeter-wave band, which has the effect of 
decoupling the diodes from one of the input signals.  This is 
particularly problematic for the LO, since a small drop in the 
absorbed LO power can have a relatively large effect on the 
conversion loss of the mixer.  For this reason, some of our 
early mixers exhibited suckouts near the center of their 
intended band of operation when integrated with the rest of the 
system. 
We were able to solve this problem by placing a structure 
on the IF output line that was very lossy in the RF/LO band, 
but lossless in the low IF band.  Effectively, we put single-
order, non-reflective, bandstop filters on the chip after the 
mixer to prevent any possible resonance with off-chip 
components.  This effectively removed or at least greatly 
reduced the dip in the conversion loss at the center of the band 
without affecting the overall conversion loss everywhere else. 
The measured conversion loss for each of these mixers is 
shown in Fig. 6.  Although the original Band 9 mixer for 122 -
142.4 GHz is no longer needed for ALMA due to the new 
frequency plan, the initial design turned out very well and is 
worth reporting here. 
V. POWER AMPLIFIERS 
The final custom MMIC components required for many of 
the ALMA LO bands are power amplifiers.  Typically, at least 
20 mW is needed in the millimeter-wave bands to drive the 
final stage of multiplication in order to get enough LO power 
for the SIS mixers.  Some custom MMIC designs that were 
suitable for this application had already been developed for 
other projects [2]-[3], but additional circuits needed to be 
developed and the results are described in another publication 
[4]. 
VI. CONCLUSION 
We have described the development of a set of millimeter-
wave MMIC multipliers and balanced mixers for the ALMA 
radio telescope array.  These chips have been integrated with 
other commercial MMICs and components to form a compact, 
cost-effective local-oscillator system for driving 
submillimeter-wave SIS receivers.  Early tests on an 
integrated receiver system have shown that the noise 
contributed to the front-end by the LO assembly built with 
these chips is less than that of a Gunn Oscillator. 
ACKNOWLEDGEMENT 
The authors wish to thank United Monolithic 
Semiconductors for fabrication of the Schottly Diode MMIC 
chips described in this paper.  This work was carried out in 
part at the National Radio Astronomy Observatory, a facility 
of the National Science Foundation operated under 
cooperative agreement by Associated Universities, Inc. 
REFERENCES 
[1] A. Wooten, Ed., Science with the Atacama Large Millimeter 
Array.  San Francisco, CA: ASP, 2001, vol. 235. 
[2] L. Samoska and Y.C. Leong, "65-145 GHz InP MMIC HEMT 
medium power amplifiers," IEEE MTT-S Intl. Microwave Symp. 
Digest, pp. 1805-1808, Phoenix, AZ, 2001. 
[3] M. Morgan and S. Weinreb, "A W-Band monolithic medium 
power amplifier," IEEE MTT-S Intl. Microwave Symp. Digest, 
Philadelphia, PA, 2003. 
[4] L. Samoska, E. Bryerton, M. Morgan, T. Boyd, D. Pukala, A. 
Peralta, M. Hu, and A. Schmitz, "Medium power amplifiers 
covering 90-130 GHz for the ALMA Telescope Local 
Oscillators," submitted to the IEEE MTT-S Intl. Microwave 
Symp, Long Beach, CA, 2005. 
[5] M. Morgan and S. Weinreb, "A full waveguide band MMIC 
tripler for 75-110 GHz," IEEE MTT-S Intl. Microwave Symp. 
Digest, pp. 103-106, Phoenix, AZ, 2001. 
[6] K. Lin, H. Wang, M. Morgan, T. Gaier, and S. Weinreb, "A W-
Band GCPW MMIC diode tripler," 32nd European Microwave 
Conference, Milan, 2002. 
[7] M. Morgan and S. Weinreb, "A monolithic HEMT diode 
balanced mixer for 100-140 GHz," IEEE MTT-S Intl. 
Microwave Symp. Digest, pp. 99-102, Phoenix, AZ, 2001. 
 
 
 
1590


English

 A Millimeter-Wave Diode-MMIC Chipset for Local Oscillator 
Generation in the ALMA Telescope 
Matthew Morgan1, Eric Bryerton1, Patrick Cesarano2, Tod Boyd1, Dorsey Thacker1, Kamaljeet Saini1, and 
Sander Weinreb3 
1National Radio Astronomy Observatory, Charlottesville, VA., 22903 
2L-3 Communications GSI, Chantilly, VA., 20151 
3California Institute of Technology, Pasadena, CA., 91125 
 
Abstract  —  A set of MMIC frequency multipliers and 
balanced mixers have been designed for the local oscillator 
system of the Atacama Large Millimeter Array (ALMA).  These 
millimeter-wave elements form a critical link in the active 
multiplier chains between the relatively low frequency microwave 
oscillators and the very high frequency submillimeter-wave, 
cooled multipliers of the LO subsystem.  A complete chipset for 
four frequency bands is described, along with preliminary results 
on prototypes for two additional bands. 
Index Terms  —  Millimeter-wave frequency converters, 
millimeter-wave mixers, MMICs, phase-locked loops, radio 
astronomy. 
I. INTRODUCTION 
The Atacama Large Millimeter Array (ALMA) is a 
millimeter-wavelength telescope currently under construction 
in the Chajnantor region of northern Chile.  Consisting of an 
array of antennas, each 12 m in diameter, with an upper 
frequency limit over 900 GHz, it will be the largest and most 
sensitive instrument in the world at millimeter and 
submillimeter wavelengths [1]. 
Implementing ALMA has presented engineers with 
numerous technological challenges to overcome, and 
innovations have been required in almost every subsystem.  
The local oscillator subsystem, for example, must provide 
sufficient pump power to SIS mixers up to nearly a THz, 
tunable over broad ranges, and phase-locked to a reference 
signal common to the whole array which in some 
configurations may span up to 10 km. 
Fig. 1 is a block diagram for the typical ALMA LO 
assembly present in each antenna for each frequency band.  
Specific details, such as the multiplication factors and number 
of gain stages, may vary depending on the components 
available and requirements for each band.  Generally 
speaking, however, the LO signal is generated by a phase-
locked loop that begins with a microwave YIG-tuned 
oscillator.  This is followed by one or two multipliers that 
scale the signal frequency up into the millimeter-wave range, 
where it is mixed with a common reference distributed to the 
array by optical fiber.  Following the PLL is a final stage of 
amplification and subsequent multiplication which brings the 
signal frequency up to the submillimeter-wave range required  
 
Fig. 1. Block diagram of a typical LO chain for ALMA.  The 
millimeter-wave components, which can be implemented as MMICs 
but are not available commercially, are described in this paper. 
 
TABLE I 
Current ALMA Frequency Bands 
Band # 
RF 
Frequency 
Final 
Mult. 
IF 
Range 
mm-Wave LO 
Frequency 
Band 1 31.3-45 GHz    
Band 2 67-90 GHz    
Band 3 84-116 GHz -- 8 GHz 92-108 GHz 
Band 4 125-163 GHz x2 8 GHz 66.5-77.5 GHz 
Band 5 163-211 GHz    
Band 6 211-275 GHz x3 12 GHz 74.3-87.7 GHz 
Band 7 275-373 GHz x3 8 GHz 94.3-121.7 GHz 
Band 8 385-500 GHz x5 8 GHz 78.6-98.4 GHz 
Band 9 
(original) 
602-720 GHz x5 8 GHz 122-142.4 GHz 
Band 9 
(modified) 
602-720 GHz x6 8 GHz 101.7-118.7 GHz 
Band 10 787-950 GHz    
 
by the receivers. 
Because amplifiers are not feasible at the final LO 
frequency for many of the ALMA bands using present 
transistor technology, the efficiency of the final stage of 
multiplication is paramount.  Cooled, Schottky-Diode 
multipliers are being provided for ALMA by Virginia Diodes, 
Inc.  Though some of these are implemented monolithically, 
the highest frequency band is for now composed of advanced 
planar Schottky diodes flip-chip mounted on a quartz substrate 
with integrated matching and idler circuitry.  This  
0-7803-8846-1/05/$20.00 (C) 2005 IEEE 1587
   
 (a) (b) 
 
   
 (c) (d) 
 
Fig. 2. Photographs of the MMIC triplers for (a) Band 4, (b) Band 
6, (c) Band 8, (d) Bands 3, 7, and 9-modified.  Chip dimensions are 
2.0 x 0.73 x 0.1 mm. 
 
high-performance component is more reliable and less 
expensive than classic whisker-contact diode multipliers, yet 
is capable of better efficiency and more power at high 
frequency than that of a fully-monolithic design in the 
submillimeter-wave range.  However, the goal of minimizing 
the global cost of the array drives us to selecting a MMIC 
approach for as many of the remaining elements of the LO 
subsystem as possible, so virtually every active component 
between the YIG oscillator and the final multiplier is a MMIC 
chip. 
The lower-frequency MMICs, including usually the first 
stages of amplification and multiplication, are available at low 
cost from commercial suppliers, but the millimeter-wave 
multipliers, mixers, and power amplifiers required custom 
designs.  Thus, the MMIC chipset described in this paper 
closes the gap between the relatively low frequency 
microwave oscillators, and the very high frequency, 
submillimeter-wave multipliers. 
II. ALMA BANDS 
Frequency coverage for the ALMA facility has been divided 
into 10 bands, as shown in Table I.  Bands 3, 6, 7, and 9 are 
scheduled to be delivered with the first antennas on the 
construction site, and complete chipsets for those bands have 
already been developed.  Chips for bands 4 and 8 are also 
under development for deployment in the near future.  Table I 
also shows how the millimeter-wave frequencies for the 
MMIC portions of the LO subsystem are derived, based on the 
multiplication factors that follow them and the IF frequency 
range of the front ends for those bands.  Not unexpectedly, the 
differing multiplication factors lead to a great deal of overlap 
between the required bands and the potential for chip reuse. 
It is worth noting that Band 9 was originally expected to use 
a quintupler following the last stage of amplification, and that 
chips were designed for the resulting 122-142.4 GHz 
frequency range.  However, the Band 9 schematic was 
eventually modified to incorporate a final multiplier of 6 
instead of 5, allowing us to take advantage of better power 
 
 
Fig. 3. Output power for the triplers in Bands 3, 6, 7, and 9-
modified.  Input power was 17.6 ±1.2 dBm. 
 
 
Fig. 4. Output power for the triplers in Band 4 (simulated) and 
Band 8 (measured).  Input power for the Band 8 tripler was 19 dBm. 
 
amplifiers that were available at the lower input frequency [2]-
[4]. 
III. MULTIPLIERS 
Broadband, Schottky-Diode MMIC triplers in W-Band have  
already been demonstrated [5]-[6].  Building upon this earlier 
work, several new triplers have been designed for the ALMA 
millimeter-wave LO frequency bands.  These generally 
correspond to the second stage of multiplication in Fig. 1.  
Photographs of these chips appear in Fig. 2. 
These chips were all fabricated by UMS in their BES 
Schottky-Diode MMIC process.  All the diodes in these high 
frequency designs have a contact area of 3 µm2.  The junction 
capacitance for these devices is nominally 6fF, with a parasitic 
series resistance of 7 Ω. 
Each of the triplers is composed of three basic sections.  
First is an input matching network with open-circuited stubs, 
which also serves to provide a third-harmonic ground-return.   
1588
    
 (a) (b) 
 
   
 (c) (d) 
 
Fig. 5. Photographs of the MMIC mixers for (a) Band 4, (b) Band 
6, (c) Band 3, 7, and 9-modified, and (d) Band 9-original.  Chip 
dimensions are 2.0 x 0.73-1.2 x 0.1 mm. 
 
Following this is an anti-parallel diode pair which efficiently 
generates the third harmonic while intrinsically suppressing all 
even-harmonic spurs.  Finally, the output matching network 
includes AC-grounded stubs which provide a ground-return 
path at the fundamental frequency, as well as a means of 
injecting DC-bias to the diodes, and a low-order bandpass 
filter that rejects higher-order spurious tones. 
Measurements of the output power versus frequency for the 
two triplers used in Bands 3, 6, 7, and 9 (the four bands that 
will be delivered with the first antennas) is shown in Fig. 3.  
The input power in both cases was approximately 18 dBm, 
though it varied over almost a 3 dB range due to limitations of 
the test setup.  This fluctuation of the input power can account 
for much of the ripple seen in Fig. 3, especially since the 
conversion loss is a relatively strong function of the input 
power.  Generally speaking, the triplers deliver about 1 mW of 
power over their design range with approximately 18 dB 
conversion loss. 
Band 8 will use a pre-existing design [5], the measurements 
for which are reproduced in Fig. 4.  The figure also shows 
simulated data for a newly developed Band 4 tripler that has 
not yet been tested.  Although historically the conversion loss 
has been about 2 dB higher than that predicted by our 
simulations, the agreement in terms of saturated output power 
and frequency response is usually good.  Harmonic rejection 
for these triplers is typically in excess of 20 dB. 
IV. MIXERS 
A number of custom millimeter-wave balanced mixers were 
also required to complete the phase-locked loops in the 
ALMA LO subsystem, and were made using the UMS BES 
Schottky diode MMIC process.  These circuits are shown in 
Fig. 5.  The RF and LO frequency ranges are those shown in 
the last column of Table I, with a common IF frequency range 
of DC-200 MHz.  There were two basic topologies used for 
the design of these mixers.  Those mixers shown in Fig. 5a  
 
Fig. 6. Measured conversion loss for the mixers used in Bands 3, 
6, 7, 9-original, and 9-modified, and simulated conversion loss for 
the mixer in Band 4.  LO power in all cases is 10 dBm. 
 
and Fig. 5c are single-balanced mixers that are loosely based 
on earlier broadband, millimeter-wave mixer designs [7].  This 
topology consists of a single balun, implemented here by a 
folded ring hybrid, which drives a pair of diodes in series.  
Short-circuited stubs provide RF matching and a ground-
return for the IF.  The IF signal is the extracted from between 
the two diodes through a low-pass non-reflective filter. 
The chips shown in Figs. 5b and 5d, however, are double-
balanced ring-mixers.  Ring hybrids are used in both cases to 
couple the LO and RF signals into the diode ring.  For the 
band 6 mixer, shown in Figure 5c, the hybrids are arranged in 
a convenient interlocking layout that encloses the diode ring 
and allows easy access to the differential ports for RF/LO 
injection, and to the common-mode ports for IF extraction and 
ground-return.  The same could not be done with the original 
Band 9 (122-142.4 GHz) mixer, because the resulting ring 
hybrids were too small to fit around the diodes.  Instead, the 
hybrids were folded adjacent to the diodes and connected to 
them with a differential matching network.  Both layouts were 
successful, and we believe these represent the first fully-
monolithic double-balanced mixers in this frequency range. 
Tests on early versions of these mixers revealed that the 
performance can be very sensitive to the impedance present on 
the IF port at the RF/LO frequency.  The IF port is connected 
to a PC-Board where the low-frequency PLL circuitry is 
implemented, so the exact impedance seen on this port at the 
much higher millimeter-wave frequencies is not easily 
predicted or controlled, but generally it is reactive and changes 
very rapidly as a function of frequency.  This was not 
originally considered important because the on-chip hybrids 
were meant to isolate the millimeter-wave frequencies from 
the IF port by placing a virtual short between the diodes where 
the output line is connected.  However, like the off-chip 
components, these hybrids also present a reactive impedance 
to the IF port at frequencies above and below the resonant 
center-frequency of the structure.  It is possible, then, for an 
1589
 off-chip component in the IF path to resonate with the on-chip 
hybrid in the millimeter-wave band, which has the effect of 
decoupling the diodes from one of the input signals.  This is 
particularly problematic for the LO, since a small drop in the 
absorbed LO power can have a relatively large effect on the 
conversion loss of the mixer.  For this reason, some of our 
early mixers exhibited suckouts near the center of their 
intended band of operation when integrated with the rest of the 
system. 
We were able to solve this problem by placing a structure 
on the IF output line that was very lossy in the RF/LO band, 
but lossless in the low IF band.  Effectively, we put single-
order, non-reflective, bandstop filters on the chip after the 
mixer to prevent any possible resonance with off-chip 
components.  This effectively removed or at least greatly 
reduced the dip in the conversion loss at the center of the band 
without affecting the overall conversion loss everywhere else. 
The measured conversion loss for each of these mixers is 
shown in Fig. 6.  Although the original Band 9 mixer for 122 -
142.4 GHz is no longer needed for ALMA due to the new 
frequency plan, the initial design turned out very well and is 
worth reporting here. 
V. POWER AMPLIFIERS 
The final custom MMIC components required for many of 
the ALMA LO bands are power amplifiers.  Typically, at least 
20 mW is needed in the millimeter-wave bands to drive the 
final stage of multiplication in order to get enough LO power 
for the SIS mixers.  Some custom MMIC designs that were 
suitable for this application had already been developed for 
other projects [2]-[3], but additional circuits needed to be 
developed and the results are described in another publication 
[4]. 
VI. CONCLUSION 
We have described the development of a set of millimeter-
wave MMIC multipliers and balanced mixers for the ALMA 
radio telescope array.  These chips have been integrated with 
other commercial MMICs and components to form a compact, 
cost-effective local-oscillator system for driving 
submillimeter-wave SIS receivers.  Early tests on an 
integrated receiver system have shown that the noise 
contributed to the front-end by the LO assembly built with 
these chips is less than that of a Gunn Oscillator. 
ACKNOWLEDGEMENT 
The authors wish to thank United Monolithic 
Semiconductors for fabrication of the Schottly Diode MMIC 
chips described in this paper.  This work was carried out in 
part at the National Radio Astronomy Observatory, a facility 
of the National Science Foundation operated under 
cooperative agreement by Associated Universities, Inc. 
REFERENCES 
[1] A. Wooten, Ed., Science with the Atacama Large Millimeter 
Array.  San Francisco, CA: ASP, 2001, vol. 235. 
[2] L. Samoska and Y.C. Leong, "65-145 GHz InP MMIC HEMT 
medium power amplifiers," IEEE MTT-S Intl. Microwave Symp. 
Digest, pp. 1805-1808, Phoenix, AZ, 2001. 
[3] M. Morgan and S. Weinreb, "A W-Band monolithic medium 
power amplifier," IEEE MTT-S Intl. Microwave Symp. Digest, 
Philadelphia, PA, 2003. 
[4] L. Samoska, E. Bryerton, M. Morgan, T. Boyd, D. Pukala, A. 
Peralta, M. Hu, and A. Schmitz, "Medium power amplifiers 
covering 90-130 GHz for the ALMA Telescope Local 
Oscillators," submitted to the IEEE MTT-S Intl. Microwave 
Symp, Long Beach, CA, 2005. 
[5] M. Morgan and S. Weinreb, "A full waveguide band MMIC 
tripler for 75-110 GHz," IEEE MTT-S Intl. Microwave Symp. 
Digest, pp. 103-106, Phoenix, AZ, 2001. 
[6] K. Lin, H. Wang, M. Morgan, T. Gaier, and S. Weinreb, "A W-
Band GCPW MMIC diode tripler," 32nd European Microwave 
Conference, Milan, 2002. 
[7] M. Morgan and S. Weinreb, "A monolithic HEMT diode 
balanced mixer for 100-140 GHz," IEEE MTT-S Intl. 
Microwave Symp. Digest, pp. 99-102, Phoenix, AZ, 2001. 
 
 
 
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A millimeter-wave diode-MMIC chipset for local oscillator generation in the ALMA telescope

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