Offset frequency converter for phase/amplitude data measurement receivers
First Claim
1. In or for a radio frequency apparatus, an intermediate frequency (IF) circuit for providing an IF output signal derived from a higher frequency input signal originating from a remote frequency source at a frequency coherent with a reference signal generated within said radio frequency apparatus, comprising:
- a local oscillator including a programmably variable digital frequency synthesizer, said local oscillator being independent of said remote frequency source, said local oscillator providing said reference signal;
offset frequency converter means responsive to frequency differences within a predetermined range of frequencies between said reference signal and said input signal, for providing a stable mixing signal; and
utilization means responsive to said input signal and said mixing signal to provide said IF output signal.
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Accused Products
Abstract
An offset frequency converter for the intermediate frequency (IF) stages of a multi-channel radio frequency (RF) phase/amplitude measurement receiver, particularly useful for measuring the performance characteristics of antennas. The converter allows use of noncoherent transmitter and receiver local oscillator sources which utilize digital frequency synthesizers and enables harmonic mixing to be employed when the tuning resolution of the receiver local oscillator is incremental. The converter samples an incoming first intermediate frequency signal IF1 in a reference channel, which typically is obtained by mixing an LO source in the receiver with an incoming signal from a reference antenna. The IF1 sample is then upconverted with an upconversion signal to a higher frequency, filtered, and the downconverted with a downconversion signal to an IF1 +IF2 signal offset from the IF1 sample by a lower second intermediate frequency IF2. The added frequency offset IF2 is derived from a time stabilized source independent of the transmitter but coherent with the receiver LO. The mixed IF1 +IF2 signal is heterodyned with signals in both the signal channel from the antenna under test and the reference channel to obtain coherent outputs at IF2 which differ by phase and magnitude corresponding to the characteristics of the antenna under test. The circuit exhibits high frequency agility and obviates the need for coherency between the receiver LO and transmitter LO.
133 Citations
53 Claims
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1. In or for a radio frequency apparatus, an intermediate frequency (IF) circuit for providing an IF output signal derived from a higher frequency input signal originating from a remote frequency source at a frequency coherent with a reference signal generated within said radio frequency apparatus, comprising:
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a local oscillator including a programmably variable digital frequency synthesizer, said local oscillator being independent of said remote frequency source, said local oscillator providing said reference signal; offset frequency converter means responsive to frequency differences within a predetermined range of frequencies between said reference signal and said input signal, for providing a stable mixing signal; and utilization means responsive to said input signal and said mixing signal to provide said IF output signal. - View Dependent Claims (2, 3, 4, 5, 6, 7, 8, 9, 10, 11, 12, 13, 14, 49, 50)
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15. In or for a radio frequency receiver including a local oscillator stage having a frequency synthesizer for generating a local oscillator signal at steps of predetermined frequency increments and a harmonic mixer for mixing said local oscillator signal with an incoming RF signal from a remote frequency source independent of said local oscillator to obtain a downconverted intermediate frequency (IF) output signal, an improved high agility frequency converter, comprising:
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means responsive to said local oscillator stage for mixing said local oscillator signal with said incoming signal to provide a first IF signal (IF1) means for sampling said IF1 signal to provide a reference IF1 signal; means for providing a stable clock reference signal at a predetermined second IF frequency signal (IF2); offset frequency converter means responsive to said reference IF1 signal and said second IF frequency signal for providing an IF1 +IF2 signal; and means for mixing said IF1 +IF2 signal with said first IF signal (IF1) to provide said IF output signal at said second IF frequency IF2, whereby said harmonic mixer may be utilized even when the receiver processes a signal from a transmitter which is non-coherent with respect to said local oscillator. - View Dependent Claims (16, 17, 18, 19, 20, 21, 22, 23, 24, 25)
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26. An intermediate frequency (IF) stage of a radio frequency (RF) antenna measurement receiver, said receiver being operative for measuring the characteristics of a test antenna which receives a transmitted signal at a first frequency derived from a remote frequency source, comprising:
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means for receiving a reference signal input from a reference antenna positioned to receive said transmitted signal; means for receiving a test signal input from an antenna under test positioned to receive said transmitted signal; a first reference channel IF means responsive to a receiver local oscillator signal derived from a receiver local oscillator independent of the remote frequency source, for downconverting said reference signal input into a first reference intermediate frequency (IF1REF) signal; a first test channel IF means responsive to said receiver local oscillator signal for downconverting said test signal input into a first signal intermediate frequency (IF1SIG) signal; sampling means for taking a sample of said IF1REF signal to provide an IF1REF sample signal; means for generating a second intermediate frequency reference signal (REF IF2); offset frequency converter means responsive to said IF1REF sample signal and said REF IF2 signal to provide a mixed IF1 +IF2 signal; means for splitting said IF1 +IF2 signal into two signal portions; means for mixing one portion of said IF1 +IF2 signal with said IF1REF signal to provide an intermediate frequency output signal associated with said reference signal input (IF2REF); and means for mixing the other portion of said mixed IF1 +IF2 signal with said IF1SIG signal to provide an intermediate frequency output signal (IF2SIG) associated with said test signal input, whereby said IF2REF signal and said IF2SIG signal are coherent in frequency notwithstanding a frequency difference between the receiver local oscillator signal from the receiver local oscillator and the transmitted signal from the remote frequency source. - View Dependent Claims (27, 28, 29, 30, 31, 32, 33, 34, 35, 36, 37, 38)
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39. An offset frequency converter responsive to an input (IF1REF) signal and a stable clock reference signal (REF IF2) to provide an offset output (IF1 +IF2) signal which is the sum of said input signal and said clock reference signal, comprising:
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means for providing a stable clock reference signal (REF IF2); an oscillator circuit for providing an upconversion LO signal and a downconversion LO signal, said downconversion LO signal being different in frequency from said upconversion LO signal by said clock reference signal; means in said oscillator circuit for controlling the difference between said upconversion LO signal and said downconversion LO signal to the frequency of said stable clock reference signal; and a frequency converter stage responsive to said upconversion LO signal, said downconversion LO signal, and said input signal to provide said offset output signal. - View Dependent Claims (40, 41, 42, 43, 44, 45, 46, 47, 48, 51, 52, 53)
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Specification