By employing varactor diodes in a metasurface, the resonance frequency of a high-impedance surface (HIS) can be changed by a bias voltage. To modulate the frequency of the reflected wave from such surfaces, a phase variation of more than 360° is required. To overcome the phase variation limitation (<360°) in a conventional active metasurface, we fabricated a metasurface with two resonances and manipulated both poles simultaneously to achieve a phase variation exceeding 360° for smooth modulation of the reflection frequency. Because of this wide variation in the reflection phase, it is possible to modulate a broad range of frequencies between 2.75 and 3.25 GHz with up to 1-MHz variation in the modulation frequency. The best spurious-free dynamic range (SFDR) for this frequency range is 20.7 dBc at 3.25 GHz.

This article presents the design and implementation of a built-in fault detection technique for an active phased array antenna. The proposed method employs a current monitoring circuit integrated into the power protection board of the transmit-receive unit (TRU). This circuit consists of a current sense amplifier and an operational amplifier, which detect the drain current of the high-power amplifier within the transmit-receive module (TRM) and compare it against a predefined detection threshold. To facilitate channel control and status reporting of individual TRMs, a built-in test function was implemented in the field-programmable gate array within both the antenna controller and the TRU control board. The test logic monitors the pulse output of the current monitoring circuit and requires four pulse transmissions to confirm a fault. The effectiveness of the proposed technique was evaluated through an initial test using a TRU with an intentionally damaged TRM. Further validation was conducted at both the antenna and radar system levels. The results demonstrated that the antenna can accurately detect and isolate failed TRMs, thereby confirming the reliability of the proposed fault detection method.

This article presents a diagnostic method for transmit–receive modules (TRMs) in an airborne active phased array antenna (APAA). Given the spatial constraints of airborne radar systems, the diagnostic functionality was implemented using the peripheral probe method. To minimize the space, cost, and time required for modifications to the existing APAA, the side-lobe blanking (SLB) channel was employed as the probe. To prevent TRM saturation and to determine the fault detection threshold, an APAA-level test was performed using a movable anechoic chamber. The coupling level between the SLB antenna and TRM was maintained between −70 dB and −20 dB. With the result of the APAA-level test, a budget analysis on the signal path was performed, and the input attenuation level was determined. The received signal power was estimated at −40 dBm to −20 dBm. Based on the estimation, the detection threshold was determined as −50 dBm. For the operation of the diagnostic function, simple detection logic and associated control timing is implemented in the radar processor. The effectiveness of the proposed diagnostic method was validated by several test activities, including an anechoic chamber, a rooflab facility, and an actual fighter. The test result shows good agreement with the expectations.