50-to-110-GHz high-performance millimeter-wave source modules

Hewlett-Packard Journal, April, 1991 by Mohamed M. Sayed, Giovonnae F. Anderson

State-of-the-art microcircuit technologies and development tools were employed to produce a W-band amplifier tripler, a V-band amplifier doubler, an R-band amplifier doubler, and a coupler detector for two new frequency multiplier modules.

THE MILLIMETER-WAVE PORTION of the electromagnetic spectrum lies between the microwave and far infrared regions. Generally, millimeter-wave frequencies are between 30 and 300 GHz (wavelengths from 10 to 1 mm). The main applications for millimeter-wave systems are in communications, radar, and spectroscopic observation.

Millimeter waves are attenuated by atmospheric constituents and gases at different rates for different frequencies (see Fig. 1). Frequencies where gaseous absorption is a minimum are called atmospheric windows. Regions of maximum absorption are called absorption bands. The main millimeter-wave atmospheric windows are centered at 3 5, 94, 140, and 220 GHz, and the main absorption band is around 60 GHz.

The bandwidths of the atmospheric windows are wide--and 16, 23, 26 GHz for the windows at 35, 94, and 140 GHz, respectively. In addition, millimeter-wave losses in these windows are low compared to infrared transmission in rain, fog, and smoke. These are advantages of millimeter-wave transmission. Other advantages are that millimeter-wave components are small, and a given antenna aperture yields a narrower beamwidth, higher precision, and better resolution than at microwave frequencies. For example, a 12-cm-diameter antenna produces a 1.8-degree beam width at 94 GHz, compared to 18 degrees at 10 GHz. Table I shows the key millimeter-wave characteristics for the windows at 35, 94, and 140 GHz.1

New Millimeter-Wave Sources

Millimeter-wave sources are essential instruments for developing almost all millimeter-wave systems and for extending the range of microwave systems. The requirements for these sources are high output power, full waveguide band coverage, low output harmonics, and compatibility with other HP microwave sources.

The HP 83557A and HP 83558A millimeter-wave source modules have been developed to complete the waveguide coverage of the millimeter-wave range up to 110 GHz. These source modules take the output of an HP microwave source, such as an HP 8360, and multiply it to millimeter-wave frequencies. They are members of the HP 8355xA series, which was originally introduced in May 1985.(2,3) Fig. 2 shows the two new source modules and the microwave sweep oscillators and synthesized signal generators with which they can be used. The HP 83557A covers the V-band range of 50 to 75 GHz and the HP 83558A covers the W-band range of 75 to 110 GHz. These two sources have high output power: 3 dBm for the HP 83557A and 0 dBm for the HP 83558A. Also available is the narrower-bandwidth HP 83558A Option H03, which supplies 3 dBm from 88 to 98 GHz. These new source modules can be used for either scalar or vector network analyzer applications.

The challenge in designing the new source modules was to supply state-of-the-art performance using the latest technologies and the features of the latest microwave sources such as the HP 8360 family (see article, page 6), without sacrificing backward compatibility with HP microwave sources introduced before 1985.

Design Philosophy

Design goals for the two new modules were:

* Higher output power than other sources on the market

* Frequency coverage of an entire waveguide band

* Low output harmonic content for use in scalar applications

* Use of the millimeter-wave source interface already defined for the rest of the HP 8355xA family before 1985

* Use of the same mechanical package as the rest of the HP 8355xA family

* Leveled output power with specifications equal to or better than other HP 8355xA modules

* Use of many of the user interface features offered by the HP 8360 family of sources.

The input frequencies for these two source modules were to be supplied by an HP 83550A millimeter-wave driver or other HP microwave sources along with an HP 8349B microwave power amplifier, which has a bandwidth less than 20 GHz. Thus the multiplier number was determined to be 4 for the Hp 83557A and 6 for the HP 83558A, as shown in Fig. 3.

Two alternatives were then available: multiply by 4 or 6 directly or multiply by two and then amplify and multiply by two for V band and by three for W band. Output power, input dc power, and harmonics are very different for the two alternatives. Table II compares these two alternatives for V-band and W-band source modules. For example, to obtain 3 dBm output power in W band by multiplying by 6 directly, an input dc power of over 33 dBm or 2W is performance output power leveling. This coupler has superior directivity and therefore a superior source match is achieved. Higher unleveled output power can be obtained by removing the external coupler detector.

For use with the new HP 8360 synthesized sweepers (see article, page 6), a nonvolatile RAM containing calibration data is included in the source modules. This can be read directly by the HP 8360 family to improve the leveling flatness of the system (see "Flatness Correction," page 59).