Fast tuning YIG frequency synthesizer

An apparatus for generating a synthesized output signal at any frequency in a predetermined range of microwave frequencies including at least the frequencies from 5 gigahertz to 10 gigahertz with the ability to change the frequency of said synthesized output signal in about 100 nanoseconds, comprising:

• a fixed frequency reference oscillator for generating a fundamental frequency reference signal, said fundamental frequency reference signal being at least 400 mHz at an offset of 100 kilohertz;
• a comb line generator having an input and an output, said input for receiving said fundamental frequency reference signal, said comb line generator for generating at said output a plurality of harmonics of said fundamental frequency reference signal, each one of said plurality of harmonics of said fundamental frequency reference signal having a frequency which is an integer multiple of said fundamental frequency reference signal;
• a first, fixed-tuned, switched, passband filter array having an input coupled to said output of said comb generator and having an output, comprising a plurality of fixed-tuned, permanent magnet biased YIG passband filters each of which has a signal input and a signal output and a different center frequency for its passband, said passband defining the frequencies of signals that can pass through said passband filter without substantial attenuation, said filter array including a first multiplexer means, said first multiplexer means for selectively coupling said fundamental frequency reference signal and said plurality of harmonics thereof appearing at said output of said comb line generator and said input of said first, fixed-tuned, switched, passband filter array to said signal input of a selectable one of said fixed-tuned, permanent magnet biased YIG passband filters and selectively coupling said signal output of the selected one of said fixed-tuned, permanent magnet biased YIG passband filters to said output of said first fixed-tuned, switched passband filter array, said first multiplexer means including gallium arsenide field effect transistor switching devices to perform high speed switching for selection of the appropriate one of said YIG passband filters, and further including a control signal input for receiving a signal which controls which of said plurality of fixed-tuned, permanent magnet biased YIG passband filters is selected for coupling to the output of said comb line generator by said first multiplexer means, each said fixed-tuned, permanent magnet biased YIG passband filters having the frequency of one of said plurality of harmonics within the passband thereof, said first fixed-tuned, switched, passband filter array for receiving said plurality of harmonics of said fundamental frequency reference signal and for filtering out all but a selected one of said plurality of harmonics, and for presenting the selected harmonic of said plurality of harmonics at said output of said first fixed-tuned, switched passband filter array;
• a variable frequency local oscillator in the form of a direct digital synthesizer hereafter referred to as a DDS, for generating a variable frequency output signal at an output, said output signal having a frequency which can be varied from a minimum frequency up to a maximum frequency with the frequency difference between said minimum frequency and said maximum frequency being equal to at least one-half the frequency of said fundamental frequency reference signal, said variable frequency local oscillator being capable of switching to a new output frequency in 100 nanoseconds or less;
• a mixer having an output and having a first input coupled to said output of said first fixed-tuned, switched passband filter array and having a second input coupled to said output of said variable frequency local oscillator so as to receive said variable frequency output signal, said mixer for mixing the output signal of said variable frequency local oscillator with said selected harmonic appearing at said first input and for generating an output signal at said output of said mixer which includes said selected harmonic as well as upper and lower sideband signals thereof having frequencies which are the sum and difference, respectively, of the frequency of said selected harmonic and the frequency of the output signal from said variable frequency local oscillator;
• a second fixed-tuned, switched, passband filter array having an input and an output, comprising a plurality of fixed-tuned, permanent magnet biased YIG passband filters each of which has a signal input and a signal output and each of which has a different center frequency for its passband, each said passband defining the range of frequencies which can pass through said fixed-tuned, permanent magnet biased YIG passband filter without substantial attenuation, each said passband having a center frequency and a bandwidth selected to encompass a selected range of possible output frequencies for one sideband of one of said plurality of harmonics of said reference signal at said fundamental frequency, said second fixed-tuned, switched, passband filter array coupled to receive the output signal from said mixer through a second multiplexer means, said second multiplexer means for selectively coupling said mixer output to said signal input of a selectable one of said fixed-tuned, permanent magnet biased YIG passband filters having a passband which encompasses the frequency of the desired synthesized output signal, and for coupling the signal output of said selected one of said fixed tuned, permanent magnet biased YIG passband filters of said second fixed-tuned, switched passband filter array to a synthesizer output, said second multiplexer means including gallium arsenide field effect transistors for performing high speed switching in selection of the appropriate one of said fixed-tuned, permanent magnet biased YIG passband filters.