U.T. Ahmed

In-phase power divider using three parallel coupled lines for medium power applications

The design of a compact high power in-phase power divider with planar structure is presented. The proposed device utilizes a stepped impedance T-junction of microstrip line and a pair of three parallel coupled microstrip lines. To realize the required tight coupling for wideband performance, each of the side coupled lines are shorted to the ground. Moreover, one resistor is connected between the two-pair of three-line coupled structure to improve isolation property between the output ports of the device. Both the equivalent circuit and simulation results indicate that the proposed device operates from 1 GHz to 3 GHz with more than 15 dB isolation, 10 dB return loss and less than 0.5 dB of additional insertion loss.

Modified gysel power divider for hyperthermia using microstrip to slotline transitions

An in-phase power divider with high power handling capability is presented. The proposed design is a modified structure of the traditional Gysel design. The modification includes using microstrip to slotline transitions to connect the input port to the two output ports with the aim to match the ports across wide band. As with the conventional design, the device uses an external isolation resistor, and thus it is suitable for high power microwave based applications. The proposed structure provides 53% fractional bandwidth (1.5-2.6 GHz) based on 15 dB of isolation as the reference. The simulated results show equal power division with 1 dB additional insertion loss, more than 15 dB of return loss at the input, 10 dB at the output ports, and 15 dB isolation while maintaining less than 10° phase imbalance between the output ports.

Wideband in-phase power divider using cascaded parallel coupled microstrip lines

A compact wideband in-phase power divider is presented. The proposed device utilizes parallel coupled microstrip lines, connected in cascaded configurations, and a stepped impedance T-junction of microstrip line. To achieve tight coupling for wideband performance, a slotted ground is utilized under each of the parallel coupled lines. Moreover, chip capacitors are connected between the coupled lines to enhance the coupling. To improve isolation between the output ports, an isolation resistor is added between the microstrip lines that are connected to the output ports just before the coupled lines. The proposed structure provides 100% fractional bandwidth based on 15 dB isolation as the reference. The simulated results of the proposed divider show equal power division with less than 0.5 dB additional insertion loss and more than 13 dB return loss at all the ports with less than 1° phase imbalance across the band 1-3 GHz.

In-phase power divider with three octaves band using microstrip to slotline transitions and loosely coupled microstrip lines

The design of an in-phase planar power divider operating over a wide frequency band is presented. The proposed device uses a modified single section Wilkinson structure. The main feature of the proposed device is a broadside coupled microstrip/slotline configuration instead of using T-junction at the input port of the traditional design. Moreover, a pair of loosely coupled microstrip lines with two isolation resistors is used to enhance the matching of the output ports. The proposed structure provides 140% fractional bandwidth based on 15 dB isolation reference. The equivalent overall size of the structure is 0.25 λg × 0.25 λg, where λg is the guided wavelength at the lowest operating frequency. The simulated results of the proposed divider show equal power division with less than 0.5 dB additional insertion loss, more than 15 dB isolation and more than 10 dB return loss over the band 1.4 GHz-8 GHz. The device has equal power division between the two output ports with less than 0.5 dB amplitude imbalances and less than 2° phase imbalance across the band 1-8 GHz.

Wideband out-of-phase power divider using coupled lines and microstrip to slotline transitions

The configuration and design method of a compact broadband out of phase power divider employing a microstrip/slot technology is presented. To make it easy for integration with other devices, the proposed device employs a single substrate. A T-junction of microstrip-slotline-microstrip transitions at the input port and coupled microstrip lines with shunt open-ended stubs at the output ports of the top layer are used to achieve an out of phase signal division over a large frequency range. Moreover, a proper chip resistor is employed across a dumbbell-shaped slot underneath the coupled lines to improve the isolation between the output ports. The overall size of the structure is 0.18 λg × 0.31 λg, where λg is the guided wavelength at the lowest operating frequency. Following a proper theoretical method based on the even-odd mode approach and slotline design guidelines, the proposed structure is designed to operate across the band 1-4 GHz. The achieved simulated results show 123% fractional bandwidth assuming 15 dB of isolation as the reference. The proposed device has equal power division between the two output ports with less than 0.2 dB amplitude imbalance and less than 1° phase imbalance across the whole band.

Unidirectional antenna with planar reflector for heart failure detection systems

A broadband monopole antenna with unidirectional radiation is presented. The antenna is specifically designed for microwave systems aimed at the detection of heart failure. A reflector is added to the ground plane of the antenna to both enhance the bandwidth and directivity of the antenna. By the carful design of the radiator and reflector, the antenna achieves a broad operating bandwidth of 35.5% over the operating frequency of 684-980 MHz, which is used for the microwave-based imaging system for heart failure detection. The antenna has a compact size of 0.22 λ × 0.22 λ (where λ is the wavelength of the first resonance of the antenna). It provides a maximum gain of 4.9 dBi at 980 MHz, a stable and unidirectional radiation pattern.

Convex optimization approach for stroke detection in microwave head imaging

Convex optimization provides a method of minimization of a convex objective function subject to a convex domain imposed upon it by the problem. For microwave imaging in medical applications, such as head imaging, this technique is seldom investigated. In this paper, a microwave-based head imaging method based on convex optimization is presented. Convex optimization is used to successfully estimate the distribution of relative permittivity of the imaged objects at different directions and thus to improve the quality of the obtained microwave image. The obtained results using 32 antennas surrounding a realistic head model compare favorably with the images from using the traditional microwave head imaging algorithm, which assumes a certain fixed average permittivity for the whole imaged head. The results show that the target representing a bleeding inside the head is properly recovered using the proposed optimization despite using wide range of initial average permittivity values. However, the quality of images produced using the traditional approach depends strongly on the assumed average permittivity.