Faulty subarray module circuit boards are detected in a phased array antenna having many subarray module circuit boards while the antenna is fully assembled and operationally integrated with a radar system. A far field ratio frequency test source illuminates the antenna. Binary digital signals that control subarray steering bits are set to a reference setting. A particular subarray module circuit board that is under test has its 180.degree. main phase bit toggled between 0.degree. and 180.degree.. The radar selects the output of that particular subarray module by Doppler filter type of software filtering. The amplitude of the in-phase and quadrature phase signals from the radar is recorded. The binary digital signals that control subarray steering bits are set to a second setting. The 180.degree. main phase bit of the module under test is again toggled between 0.degree. and 180.degree.. The output of the module under test is again selected by Doppler filter type of software filtering. The amplitude of the in-phase and quadrature phase signals from the radar is recorded. The phase difference from the reference setting to the second setting is computed and compared with a predetermined threshold. If desired, the test source may have a multi-element feed including multiple dipoles, each dipole having a radiation pattern wide enough to cover two rows of subarray modules, the test source being switched to the particular one of the dipoles that illuminates the row including the module under test.

Techniques for simultaneous measurement of multiple array elements of an array antenna. The array is illuminated with a coherent signal source, and each array element phase shifter is cycled through a range of phase shifter settings at a unique rate. The phase shifted signals from each array element are combined to provide a composite signal. The composite signal is processed to extract the phase of the coherent source signal as received at each element. The phase information is used to determine the location of the elements relative to each other.

A frequency range gate closure circuit for use in synthetic aperture radars that incorporate a digital waveform generator or direct digital synthesizer that improves the mapping resolution of the radars. Range gate closure motion compensation is more accurately implemented using the present circuit. The digital waveform generator or direct digital synthesizer is clocked by a system clock, and processes control words corresponding to a desired slope of the stretch frequency modulation of transmitted radar signals, to generate frequency modulated pulse output signals. The range gate closure circuit includes a digital data accumulator for receiving an increment value and a pulse repetition frequency value of the radar. Logic circuitry is coupled to an output of the digital data accumulator and is coupled to receive a digital modulo threshold signal and output the increment value when it is less than the digital modulo threshold signal every pulse repetition interval. The difference between the digital modulo threshold signal and the increment value is coupled to the digital data accumulator to reset it when the increment value is less than the digital modulo threshold signal. A coarse time delay counter is coupled to the logic circuitry for counting desired coarse time delays needed by the circuit. The frequency range gate closure circuit decrements a frequency offset of a local oscillator frequency sweep by the increment value every pulse repetition interval until the frequency offset is less than the digital modulo threshold signal so that the frequency offset is equal to the expected Doppler frequency error.

Electronic Warfare (EW) systems aboard aircrafts are used to protect them from guided missile by denying threat radar systems the ability to track the aircrafts. In a typical operation, a threat radar system transmits RF signals aimed at the target aircraft. The surface of the target reflects a portion of the incident signal back towards the threat radar antenna where the reflected signal is detected, allowing the threat radar system to determine the target's range, angle and velocity. The present invention relates to EW systems that are dependent on measuring the RF phase of a signal transmitted by a target tracking threat radar. The use of the invented technique will make it possible to implement a robust Electronic Counter-Measures (ECM) technique, known as Cross-Eye, using two airborne platforms. The technique is very effective in preventing a threat radar from tracking a target aircraft and guiding a launched missile to the target aircraft.

A system and method for calibrating a phase array antenna using a near-field probe and focused null and a signal coherent with the beam received or transmitted at the null location of the probe. In the transmit mode, a base-band phase comparator circuit is established by locating the first probe at the angular location of the null and the first probe measures the field at the null while an offset phase reference probe, or second probe, measures the field at one of the sum peaks of the difference lobes as the reference. In the transmit mode, the method uses the pattern characteristics of the difference pattern to allow direct measurement of the phase reference by the second probe that is located at one of the sum peaks of the difference pattern. In the receive mode, the signal source provides the reference and the second probe is not necessary.