Abstract: A new sampling technique for waveform measuring instruments (including methods and circuits for implementing same) comprises the step of processing a series of digital signal samples through a decimator to extract a decimated sample value from each decimated sample interval in a series of decimated sample intervals. The series of digital signal samples is simultaneously processed through a digital peak detector to extract maximum and minimum values (peak detect sample values) from each decimated sample interval. For a given decimated sample interval, a difference between the maximum and minimum sample values for the interval is calculated. If the difference exceeds a glitch detect threshold value, the maximum and minimum sample values for the given decimated sample interval are transferred to a video sample memory. If not, the decimated sample value for the given decimated sample interval is transferred to the video sample memory.

Abstract: A filtering apparatus permits alias-free frequency domain measurement in any of a plurality of measurement bandwidths. The input signal is first passed through one of a plurality of low-pass filters. The appropriate filter is selected by a controller to provide a cut-off frequency at least as great as the selected measurement bandwidth. An analog-to-digital convertor ("ADC") samples the filtered input signal at a sample rate (f.sub.s) set by the controller to be at least twice the measurement bandwidth. The digitized samples are then processed by a digital low-pass filter (i.e. a finite impulse response filter) to further reduce the bandwidth of the input signal to the measurement bandwidth. Operation of the digital filter is controlled by a number of filter coefficients provided by the controller as a function of the desired measurement bandwidth. A memory is provided between the ADC and the digital filter.

Abstract: A microstrip patch antenna assembly (20, 52, 106) is formed of a patch radiator (24, 58) and a feed structure (26, 64) of microstrip feed elements (48, 50, 66, 68) disposed on opposite sides of a ground-plane element (22, 54) and spaced apart therefrom by layers (28, 30, 72, 74) of dielectric material. A single slot (108) or a pair of orthogonally positioned slots (44, 46, 82, 84) within the ground-plane element couples linearly or circularly polarized microwave power from the feed structure to the patch radiator. Additional radiators (60, 62) may be stacked above the foregoing radiator, the radiators being separated by further layers (76, 78) of dielectric material. A plurality of square-shaped raidators (58, 60, 62) may be employed for multiple-frequency operation in which case the radiator size and the thickness of dielectric material between the radiator and the ground-plane element establish a resonant frequency.