In this study, the angle ambiguity of a single baseline is analyzed to design an antenna baseline for an interferometric radar altimeter (IRA). To overcome the shortcoming of a single baseline in which angle ambiguity occurs during every phase period, the IRA adopts multiple baselines for its antenna and estimates the target angle by employing the phase comparison monopulse algorithm. However, the problem with multiple baselines is that an angle ambiguity that is difficult to solve by signal processing occurs when the phase error is large. To minimize this problem at the antenna design stage, the angle ambiguity is analyzed according to the phase error and the baseline spacing. The analysis is performed by conducting a parameter study based on the Monte Carlo simulation, and the validity of the analysis is verified from the test data.

BackgroundIn this study, we investigate the utility of geometric orifice area (GOA) on cardiac computed tomography (CT) and differences from effective orifice area (EOA) on Doppler echocardiography in patients with bicuspid aortic stenosis (AS).MethodsA total of 163 patients (age 64 ± 10 years, 56.4% men) with symptomatic bicuspid AS who were referred for surgery and underwent both cardiac CT and echocardiography within 3 months were studied. To calculate the aortic valve area, GOACT was measured by multiplanar CT planimetry, and EOAEcho was calculated by the continuity equation with Doppler echocardiography. The relationships between GOACT and EOAEcho and patient symptom scale, biomarkers, and left ventricular (LV) functional variables were analyzed.ResultsThere was a significant but modest correlation between EOAEcho and GOACT (r = 0.604, p < 0.001). Both EOAEcho and GOACT revealed significant correlations with mean pressure gradient and peak transaortic velocity, and the coefficients were higher in EOAEcho than in GOACT. EOAEcho of 1.05 cm2 and GOACT of 1.25 cm2 corresponds to hemodynamic cutoff values for diagnosing severe AS. EOAEcho was well correlated with the patient symptom scale and log NT-pro BNP, but GOACT was not. In addition, EOAEcho had a higher correlation coefficient with estimated LV filling pressure and LV global longitudinal strain than GOACT.ConclusionGOACT can be used to evaluate the severity of bicuspid AS. The threshold for GOACT for diagnosing severe AS should be higher than that for EOAEcho. However, EOAEcho is still the method of choice because EOAEcho showed better correlations with clinical and functional variables than GOACT.