Browsing by Subject "Phased array"

Now showing 1 - 7 of 7

Open Access
A 94-GHz phase inverter-variable gain amplifier in SiGe BiCMOS
(2017-07) Aydoğan, Yiğit
Phased array radar systems are capable of steering the beam of radio waves electronically by adjusting the gain and phase of each antenna element as desired. In order to achieve that, each element has to have gain/phase control and these parameters have to be controlled separately. In W-Band designs, constant gain- 360 phase control is di cult to achieve due to parasitic e ects of high frequencies which may quickly di er across di erent settings. Dividing the phase control task into di erent blocks in system eases the design di culties. A well developed WBand technology SiGe BiCMOS is also crucial to achieve high frequencies and system control. In this thesis, a 94-GHz SiGe BiCMOS phase inverter with variable gain ampli- er is developed. Single bit-180 phase inversion enables to use multiple bit-180 phase shifter which is easier to design in W-Band. In addition to that, variable gain ampli er allows to use this circuit in phased array systems for amplitude tapering to achieve desired beam forming.
Open Access
ADMM based mainlobe power constrained phase-only sidelobe supression
(IEEE, 2014) Alp, Yaşar Kemal; Arıkan, Orhan
A novel sidelobe suppression technique is proposed for phased arrays, where only the phases of the array elements are adjusted to suppress the gain in the direction of interest while keeping the mainlobe power at a certain level. Mainlobe power constrained sidelobe suppression is formulated as a convex RSDP (Relaxed Semidefinite Program). Solution to resultant RSDP is obtained by ADMM (Alternating Direction Method of Multipliers) technique, which can handle designs for arrays with number of elements is significantly larger than that can be handled by other convex solvers such as CVX. In addition, although the available convex solvers can not provide a rank-1 solution matrix, a rank-1 solution matrix is obtained by modifying the ADMM iterations. In the conducted experiments, it is observed that proposed ADMM based method can achieve more than 10dB improvement in sidelobe levels compared to alternative techniques.
Open Access
Efficient analysis of large phased arrays using iterative MoM with DFT-based acceleration algorithm
(John Wiley & Sons, Inc., 2003) Ertürk, V. B.; Chou, H-T.
A discrete Fourier transform (DFT)-based iterative method of moments (IMoM) algorithm is developed to provide an O(Ntot) computational complexity and memory storages for the efficient analysis of electromagnetic radiation/scattering from large phased arrays. Here, Ntot is the total number of unknowns. Numerical results for both printed and free-standing dipole arrays are presented to validate the algorithm's efficiency and accuracy.
Open Access
Enhanced phase-sensitive SSFP reconstruction for fat-water separation in phased-array acquisitions
(John Wiley and Sons Inc., 2016) Yılmaz, Özgür; Sarıtaş, Emine Ülkü; Çukur, Tolga
Purpose: To propose and assess a method to improve the reliability of phase-sensitive fat–water separation for phased-array balanced steady-state free precession (bSSFP) acquisitions. Phase-sensitive steady-state free precession (PS-SSFP) is an efficient fat–water separation technique that detects the phase difference between neighboring bands in the bSSFP magnetization profile. However, large spatial variations in the sensitivity profiles of phased-array coils can lead to noisy phase estimates away from the coil centers, compromising tissue classification. Materials and Methods: We first perform region-growing phase correction in individual coil images via unsupervised selection of a fat-voxel seed near the peak of each coil's sensitivity profile. We then use an optimal linear combination of phase-corrected images to segregate fat and water signals. The proposed method was demonstrated on noncontrast-enhanced SSFP angiograms of the thigh, lower leg, and foot acquired at 1.5T using an 8-channel coil. Individual coil PS-SSFP with a common seed selection for all coils, individual coil PS-SSFP with coil-wise seed selection, PS-SSFP after coil combination, and IDEAL reconstructions were also performed. Water images reconstructed via PS-SSFP methods were compared in terms of the level of fat suppression and the similarity to reference IDEAL images (signed-rank test). Results: While tissue misclassification was broadly evident across regular PS-SSFP images, the proposed method achieved significantly higher levels of fat suppression (P < 0.005) and increased similarity to reference IDEAL images (P < 0.005). Conclusion: The proposed method enhances fat–water separation in phased-array acquisitions by producing improved phase estimates across the imaging volume. J. Magn. Reson. Imaging 2016;44:148–157. © 2015 Wiley Periodicals, Inc.
Open Access
Faz-MIMO sistemlerinde geliş açısı kestirim performansı karşılaştırması
(IEEE, 2021-07-19) Bahçeci, M. Umut; Güngör, Alper; Çetintepe, Çağrı; Tuncer, T. Engin
Bu çalışmada, literatürde yer alan Fazlı Çoklu Giriş-Çoklu Çıkış (Fazlı-MIMO) dizi konsepti ile Sıkıştırılmış Algılama (SA) teknikleri ilk defa birlikte ele alınarak bir radar sisteminde çoklu hedefler için geliş açısı kestirim (GAK) problemi özgün olarak ele alınmıştır. Göndermeç tarafında ortalama güç kıstasları gözetilerek farklı altdizi sayıları için geleneksel huzme şekillendirme ve rasgele fazlı ağırlıklı tasarım yöntemleri incelenmi ş; almaç tarafında ise huzme şekillendirme, ayrık SA ve grup SA olmak üzere üç farklı geri çatım yöntemi ile çoklu hedefler için GAK başarımı araştırılmıştır. Anılan her senaryo için farklı Sinyal-Gürültü-Oranları (SGO) altında gerçekleştirilen parametrik Monte Carlo benzetimleri ile hedef başına hata sonuçları elde edilmiştir. Düşük SGO durumunda, Fazlı-MIMO ve SA teknikleri birlikte kullanılarak GAK başarımının artırılabileceği gösterilmiştir. Ayrıca grup seyreklik çözümü ile ayrık çözüme kıyasla kestirim hatasında 3 kata kadar bir azalma sağlanmıştır.
Open Access
Phase-sensitive reconstruction for fat-water separation in multi-coil acquisitions
(IEEE, 2016) Yılmaz, Özgür; Sarıtaş, Emine Ülkü; Çukur, Tolga
Phase-sensitive steady-state free precession (PS-SSFP) is an effective technique for separating fat and water tissues, based on the phase difference between balanced steady-state free precession (bSSFP) bands. However, in phased-array coils, spatial sensitivity variations lead to noisy data away from coil centers and thereby degrade tissue classification. In this paper, we propose a new method to improve robustness of phase-sensitive fat-water separation against sensitivity variations.
Open Access
Phased-array MRI of canine prostate using endorectal and endourethral coils
(John Wiley & Sons, Inc., 2003) Yung, A. C.; Oner, A. Y.; Serfaty, J-M.; Feneley, M.; Yang, X.; Atalar, Ergin
A four-channel phased array consisting of one surface coil, two endorectal coils, and one flexible endourethral loop coil was designed for MRI of the canine prostate. The endorectal coils provide high signal in the posterior region of the prostate, while the endourethral and surface coils are sensitive to the central and anterior regions of the prostate. Gel phantom experiments indicate that the proposed phased-array configuration generates 15 times more signal-to-noise ratio (SNR) than a combination of two surface coils and one endorectal coil within the posterior region of the prostate; the performance of the two configurations is comparable near the anterior prostate surface. Ultimate intrinsic SNR (UISNR) analysis was used to compare the proposed phased array's performance to the best possible SNR for external coils. This analysis showed that the proposed phased array outperforms the best-case external coil within the posterior and central regions of the prostate by up to 20 times. In canine experiments in vivo, high-resolution fast spin-echo (FSE) images of the prostate were obtained with a pixel size of 230 μm obtained in 3 min 12 s. The proposed phased-array design potentially can be used to increase the accuracy of prostate cancer staging and the feasibility of MR-guided prostate interventions. © 2003 Wiley-Liss, Inc.