to 110 GHz. As shown in the lower part sion loss, with an intermediate-fre- tech for NASA’s Jet Propulsion Labora- of Figure 2, the phase difference intro- quency bandwidth of 25 GHz, at input tory. duced by the switch remained within frequencies from 78 to 110 GHz. This This invention is owned by NASA, and a ±10° of the desired value of 180° over all mixer performance is comparable to patent application has been filed. Inquiries con- but a small lower-edge portion of the fre- that of commercially available wave- cerning nonexclusive or exclusive license for its quency band from 90 to 110 GHz. guide mixers, which, unlike this circuit, commercial development should be addressed to In a test of its performance as a bal- are not compatible with MMICs. the Patent Counsel, NASA Management Of- anced fundamental-frequency mixer, This work was done by Todd Gaier, fice–JPL. For more information, contact iaof- the circuit operated at a 12-dB conver- Mary Wells, and Douglas Dawson of Cal- [email protected]. Refer to NPO-30916. Generating Ka-Band Signals Using an X-Band Vector Modulator Advanced modulations can be selected by programming an FPGA. NASA’s Jet Propulsion Laboratory, Pasadena, California A breadboard version of a transmitter greater than those of older, simpler modulation is selected or changed by for radio communication at a carrier fre- modulation schemes. programming the FPGA accordingly. quency of 32 GHz (which is in the Ka The transmitter architecture (see fig- Programming is controlled by use of an band) utilizes a vector modulator oper- ure) was chosen not only to enable gen- external computer connected to the ating at a carrier frequency of 8 GHz eration of the required modulations at FPGA via a universal serial bus. (the low end of the X band) to generate 32 GHz but also to reduce the number The 24-GHz output of the frequency- any of a number of advanced modula- of components needed to implement multiplier path and the 8-GHz output of tions that could include amplitude the transmitter. Instead of incorporating the modulator path are combined in a and/or phase modulation components. an 8-GHz signal source, the transmitter mixer to obtain the desired modulated The 8-GHz modulated signal is mixed utilizes an 8-GHz signal generated by a 32-GHz signal. The performance of the with a 24-GHz signal generated by an up- voltage-controlled oscillator that is part mixer is improved by including an isola- converter to obtain the desired 32-GHz of an X-band transponder with which tor in its output path. The isolator out- modulated output. the fully developed version of this trans- put is coupled through a 32-GHz band- The transmitter is being developed as mitter would be used in the original in- pass filter to an output amplifier. a prototype of downlink transmitters for tended spacecraft application. The oscil- The transmitter performed well in ini- transmission of data from spacecraft to lator power is divided onto two paths, tial tests, demonstrating capability for Earth at high rates (>100 Mb/s). The one of which goes through the vector transmitting data at rates >100 Mb/s. In transmitter design could also be adapted modulator, the other through amplifiers particular, data rates from 650 kb/s to to terrestrial and Earth/satellite commu- and a ×3 frequency multiplier. Band-pass 130 Mb/s were demonstrated using nication links. The advanced modula- filters are included downstream of the quadrature (quaternary) PSK and 16- tions (which can include M-ary phase- frequency multiplier to suppress un- QAM. shift keying (M-PSK), offset phase-shift wanted harmonics. This work was done by Scott Smith, keying (OPSK), and M-ary quadrature The in-phase (I) and quadrature (Q) Narayan Mysoor, James Lux, Brian Cook, amplitude modulation (M-QAM). These components of the modulation are gen- and Biren Shah of Caltech for NASA’s Jet modulations are needed because for a erated by use of a field-programmable Propulsion Laboratory. For further informa- given amount of signal bandwidth, they gate array (FPGA) and fed through driv- tion, contact [email protected]. enable transmission of data at rates ers to the vector modulator. The desired NPO-42995 32-GHz 32-GHz Band-Pass Filter Band-Pass Filter Mixer 8-GHz 32 GHz Voltage-Controlled X3 Oscillator 24 GHz Power 8 GHz Divider Vector Modulator I Driver FPGA Q Driver To Obtain a 32-GHz Modulated Signal, an 8-GHz signal is multiplied in frequency to 24 GHz along one path and modulated along another path, then the outputs of the two paths are combined in a mixer. NASA Tech Briefs, January 2009 11.