Abstract: A system utilizing bandpass sampling for converting an analog input signal A.multidot.sin ((.omega..sub.o +.omega..sub.s)t+.phi.)) into (I) in-phase and a (Q) quadrature-phase digital signals for digital signal processing, in which image rejection is enhanced. .omega..sub.s is the baseband frequency, .omega..sub.o is the IF center frequency, and .phi. is the phase of the analog input signal. A sequence of digital signal samples obtained by bandpass sampling is processed to derive either the I digital signal or the Q digital signal as a first digital output signal from a first series of alternate samples and to derive the other of the I and Q digital signals as a second digital output signal by computing the average of the absolute values of alternate samples that immediately precede and follow the samples of the first series. In accordance with this processing scheme, there is no phase error, but instead an amplitude error in each I/Q pair equal to the value of cos .omega..sub.s .tau.

Abstract: Insertion loss measurement at microwave frequencies is achieved using an improved IF substitution technique wherein the IF test signal is applied to a feedback loop which generates a feedback signal to null out the test signal. A precision calibrated attenuator in the path of the feedback signal is adjusted to achieve the null, and the difference between attenuator settings with the device under test in and out of the microwave test signal path is a measure of the insertion loss of the device under test. In one embodiment the difference signal between the IF test signal and the fed back null signal is divided into amplitude and phase components which are integrated and used to control the attenuation and phase shift, respectively, of a reference signal at the IF test signal frequency, the controlled reference signal comprising the fed back null signal. In another embodiment the amplitude and phase components are filtered at d.c., restored to IF, and recombined before being fed back as the null signal.

Abstract: Step attenuators wherein a number of individual attenuators are connected in series, with a switch across each individual attenuator, are well known. By opening and closing particular combinations of the switches, any one of a number of different values of attenuation may be selected. Each individual attenuator has in the past, as well as in the present invention, had a characteristic impedance equal to the impedance of both the signal generator (which feeds the input of the step attenuator) and the load (connected across the output of the step attenuator). However, the switches for selecting the individual attenuators may have substantial resistance especially where solid state switching diodes or mercury wetted reed relays are employed. The latter type switches display resistances caused by skin effect at highter frequencies. This causes inaccuracies of the attenuation steps due to mismatch, in prior art systems of the type described above.

Abstract: A device for testing the accuracy of an attenuator, over a range of frequencies from 1 to 18 GHz, for example, and having a first variable frequency signal generator which passes its output through the attenuator. The resulting output signal, and a local oscillator/mixer combination produce an IF signal (Hereinafter, "first signal"). A second signal source, at the IF frequency, passes its output through a variable attenuator and a step attenuator to produce a "second signal". The "first" and "second" signals are fed to a closed loop which includes an integrator that controls the variable attenuator to tend to keep the first and second signals at the same amplitude. A branch circuit, controls a second step attenuator; and includes means to produce an output level the value of which represents the value of signal level of the "first signal". The bandwidth of the closed loop is automatically narrowed when the amplitude of said first signal is low to give an optimum signal to noise ratio, under all conditions.

Abstract: A swept-frequency VSWR measurement system for slotted lines is disclosed in which the measurement values are rapidly produced as a graph of VSWR versus frequency over a range of 2-18 GHz, in which the VSWR is given directly by the height of the ordinate at any frequency without requiring subtraction of two values derived from graph measurements as previously done. In addition, a "slope" correction is continuously made for errors introduced by physical imperfections of the slotted line, simultaneously with the taking of the swept frequency measurement.