Browsing by Subject "Wideband"

Now showing 1 - 6 of 6

Open Access
A 6-18 GHz GaN power amplifier MMIC with high gain and high output power density
(IEEE, 2019) Sütbaş, Batuhan; Özipek, Ulaş; Gürdal, A.; Özbay, Ekmel
A three-stage reactively-matched 6-18 GHz power amplifier MMIC design is presented. The design effort is focused on obtaining a low-loss output matching network for a high output power density. Active unit cells consist of an 8×125 μm transistor stabilized with a symmetrical parallel RC circuit. The wideband amplifier is fabricated using our in-house 0.25 μm GaN on SiC HEMT process. The fabrication technology details and overall device performance are reported. Experimental results show that the MMIC has a minimum gain of 22 dB and a maximum gain of 26.5 dB across the operation band. An average output power density higher than 3.3W/mm with an associated average power-added efficiency of 22.5% is achieved. The MMIC demonstrates output power greater than 9.5 W at the center frequency. This design is distinguished from recent studies with its low-ripple high gain and high output power density.
Open Access
Accurate and process-tolerant resistive load
(IEEE, 2020) Sütbaş, Batuhan; Özbay, Ekmel; Atalar, Abdullah
Resistive terminations cannot preserve high-quality matching at high frequencies due to the parasitic effects of the nonideal resistor. Moreover, resistance values of the termination resistors in integrated circuits are subject to process variations. Therefore, it is difficult to obtain accurate and process-tolerant terminations that are crucial for high performance in microwave circuits. We propose a new resistive network that compensates for the high-frequency parasitic effects of the resistors to improve the bandwidth of the termination. In addition to maintaining accuracy, the presented network provides tolerance to variation in the resistor values. The accuracy and tolerance of the proposed structure is analytically shown and experimentally verified by three test structures at the X-band fabricated on a GaN technology. The experimental results show that a small size and wideband 50-Ω load with a return loss better than 25 dB can be obtained, while the resistor value changes ±30%.
Open Access
Accurate isolation networks in quadrature couplers and power dividers
(IEEE, 2021) Sütbaş, Batuhan; Özbay, Ekmel; Atalar, Abdullah
When quadrature couplers and power dividers are implemented in integrated circuits, accurate isolation networks can not be realized due to the nonideal resistors and the process variations. We present an isolation network design technique which cancels the resistor parasitic effects and also increases the tolerance to variations in the resistance values. A Lange coupler and a power divider are designed at Ka-band using the proposed accurate and process-tolerant isolation networks. The improvement is analytically shown and empirically verified with our in-house GaN-based microstrip MMIC process. For the coupler, the measured return losses and isolation are better than 20 dB from DC to 40 GHz. The power divider achieves 20 dB return losses and isolation in a fractional bandwidth of 50%. Both devices maintain 20 dB performance even when the variation in sheet resistance is as high as 30%.
Open Access
Design of a wideband and bi-directional transducer for underwater communications
(2007) Elmaslı, Işıl Ceren
A two ceramic layer stacked transducer structure for short range underwater communications at high frequencies is studied in this work. The structure has a wide bandwidth of one octave and operates at 350 kHz center frequency. Transducer structure inherently has two electrical and two acoustic ports. Ceramic layers are matched to water load through quarter wavelength thick matching layers on each radiating face. Using electrical ports separately to compensate for the large acoustic length of the structure in water is also investigated. It is shown that the wide bandwidth operation can be maintained. The beamwidth of the structure is narrow due to end - fire effect of two back – to – back radiating elements.
Open Access
The design of a wideband and widebeam piston transducer in a finite closed circular baffle
(2008-06-07) Şahin, Z.; Köymen, Hayrettin
The design of a high power piezoelectric underwater transducer operating at frequency range 40 kHz-80 kHz with acoustic power capability in excess of 250W is described. The transducer consists of two back-toback elements. Each element is formed by stacked PZT-4 ceramic rings, a matching and a steel backing layer, and placed in a finite rigid circular baffle. We investigate the dependence of bandwidth and beamwidth to the combination of piston and baffle radii, a and b, respectively. With ka of 2.45 (κ is the wave number) at resonance and a b/a ratio of 2, the transducer resonates at 60kHz with 67% bandwidth and has a beamwidth of 60° at each half space. We show that when two transducers are placed at right angles spatially and driven in parallel, we can obtain an omnidirectional beam pattern in the lower frequency band. The beam pattern exhibits two dips in each quadrant at the higher end of the frequency band, which are within 8 dB. We also investigated power handling capability of the transducer from thermal point of view using finite element analysis. The input impedance measurements agree well with the numerical results within the pass band.
Open Access
Spectrally selective imaging with wideband balanced steady-state free precession MRI
(John Wiley and Sons Inc., 2016) Çukur, Tolga
Purpose Unwanted, bright fat signals in balanced steady-state free precession sequences are commonly suppressed using spectral shaping. Here, a new spectral-shaping method is proposed to significantly improve the uniformity of stopband suppression without compromising the level of passband signals. Methods The proposed method combines binomial-pattern excitation pulses with a wideband balanced steady-state free precession sequence kernel. It thereby increases the frequency separation between the centers of pass and stopbands by π radians, enabling improved water-fat contrast. Simulations were performed to find the optimal flip angles and subpulse spacing for the binomial pulses that maximize contrast and signal efficiency. Results Comparisons with a conventional binomial balanced steady-state free precession sequence were performed in simulations as well as phantom and in vivo experiments at 1.5 T and 3 T. Enhanced fat suppression is demonstrated in vivo with an average improvement of 58% in blood-fat and 68% in muscle-fat contrast (P < 0.001, Wilcoxon signed-rank test). Conclusion The proposed binomial wideband balanced steady-state free precession method is a promising candidate for spectrally selective imaging with enhanced reliability against field inhomogeneities.