Completed Master Thesis
Hilmi Kayhan Yılmaz (January 2019)- now RF Design Engineer at Roketsan
MSc Thesis Title: Improvement of Image Rejection for Hartley Image Reject Receivers
Summary: In this thesis, a tunable amplitude compensation method is presented for Hartley image-reject topology which eliminates amplitude errors causing degradation in image rejection performances.
Firstly, different types of receiver topologies and solutions of these topologies for image signal problem are investigated as background knowledge. Especially, methods that need to be applied in these topologies to obtain sufficient image rejection ratios are studied for broadband systems. The presented solution of Hartley image reject topology for image signal problem is proven by mathematical expressions and supported by simulation results. The amplitude and phase errors of components used in the topology are identified. Also, the effects of these errors on image rejection ratios are investigated. In addition to the tunable amplitude compensation method for obtaining improvements of image rejection values, a non-tunable phase compensation method is also applied to the proposed design. The effects of the proposed tunable amplitude compensation method are measured on the designed receiver which covers 950-1450 MHz band. Improvement of image rejection values is presented. It is also shown that the necessity of filter banks could be eliminated by the proposed method.
Besides, the frequency synthesizer is another critical part of the receiver design. Tunable reference clock frequency method is presented as a spur reduction method for spurious signals which are caused by using fractional-PLL in frequency synthesizer design. It is shown that tunable reference clock frequency is applicable for frequency spread spectrum systems which have 200 us guard time. Up to 40 dB spur reduction is achieved for LO signals which are required for 950-1450 MHz receiver. Superior results are obtained when considering the communication standards requirements in terms of phase noise and spurious power response. Measurement performed using both proposed methods are evaluated by a comparison with the literature and similar commercial products.
Ozgur Bostan (February 2014)- now PhD. Student at Bogazici University, Electronics Eng. Program; co-founder of RFTEK (www.rftek.com.tr)
MSc Thesis Title: Design and implementation of a low-cost, Compact and Long Range monostatic UHF RFiD reader with Read Point Extension
Summary: The designed hardware is a low-cost, compact and long-range Gen2 compliant UHF RFiD reader with extended read point capability. The reader has up to 30 dBm (1 Watt) output RF power at two selectable antenna ports. The reader has an antenna tuning circuit, a novel feature, to reduce reflected RF power from antennas. This is achieved by tuning output impedance of the reader to the impedance of antenna. The reader can also tune the antenna impedance during operation in case the environment of the antenna changes. A power detector is used to control and limit the output power to regulatory requirements. While designing the hardware, several technical
skills within a wide spectrum of disciplines were used like PCB design in high frequency, radio frequency, physics of RF, digital and analog design.
Extended read point capability is provided with another hardware design called RF multiplexer circuit. This product has been designed in order to increase the number of antenna output ports of UHF RFiD reader to reduce the system implementation cost in dense antenna applications.
This hardware design is also a part of another Research & Development project funded by the Ministry of Science, Industry and Technology of Turkey. As a part of this project and this thesis, the UHF RFiD reader has been designed as a domestic product to lower the cost of manufacture.
As a result of this project, all the objectives have been achieved and a prototype of UHF RFiD reader, which has a control unit and a graphical user interface, and an RF multiplexer have been manufactured to be used in any desired UHF RFiD application
Hakkı Toran (July 2012), now Network Engineer at Huawei
MSc Thesis Title: Compact Size Ultra-Wideband Metamaterial Antenna
Summary: In this thesis, fundamental concepts of metamaterials and electromagnetic wave propagation in metamaterial medium, brief theory of transmission lines, and CRLH transmission line approach to metamaterials are introduced. Using the concept of CRLH metamaterial, compact size ultra-wideband metamaterial antennas are designed and implemented Antennas are excited by a coaxial feed. The shape of the antenna is tapered to provide impedance matching over a wider band. Furthermore ring slot is opened on the radiating part of the antenna; however spurious resonances emerged within the frequency band of the metamaterial antenna. Using rectangular split-ring slots instead of rectangular ring slots eliminated those unwanted resonances and improved the voltage standing wave ratio (VSWR) frequency bandwidth and gain of the antenna. The final antenna, compact size ultra-wideband antenna with split-ring slot, has VSWR value<2 from 3.8GHz to 16.4GHz according to simulation results, 4GHz to 17.5GHz according to measurement results. Although the designed and realized antennas have very compact sizes overall dimensions of the antenna are just 18mm x 26.2mm, they can successfully cover a large spectrum. The final antenna has an omni-directional radiation pattern. During design a commercial 3D electromagnetic solver program FEKO was used to simulate the antenna and obtain antenna evaluate the results. Metamaterial antennas designed and simulated using FEKO, are fabricated on a FR4 substrate with dielectric constant 4.3 and thickness 1mm. Voltage standing wave ratio and input impedance of the fabricated antennas are measured using a network analyzer. The results obtained from measurement and simulation are in good agreement with each other.
Gökmen Işık (July 2012), now studying at Canada
MSc Thesis Title: Heart Shape Ultra Wideband Antenna
Summary: In this thesis, ultra wide band antenna is designed and
realized. To overcome the narrow band characteristics of patch antenna, the
structure of the radiation is designed with elliptical and rectangular patch.
Also triangular patches are used edge of the antenna to enhance the VSWR and
gain. In addition, presented antenna ground plane is consisting of rectangular
and elliptical patch which is modified with a small segment of arc at the
Antenna performance is specified in terms of system gain not only at azimuth, but also at low elevation angles, and the Voltage standing wave ratio (VSWR) over a prescribed frequency band. Numerical simulation show that the antenna has a bandwith ratio of 5:1 within the frequency range of 4-19.1 GHz with compact dimensions of 25 x 26 mm^2. It is printed on substrate having 0.5 mm thickness. However, measured values were slightly higher than the simulated ones in a small frequency range. Even with that discrepancy, ultra wide band antenna performance is observed. Since we did not have the ability to measure system gain, we relied on simulated values which were higher than 0dBi over the target frequency band.
A. Zeynep Saylan (January 2011)* now Senior Integration Engineer at Alcatel-Lucent
MSc Thesis Title: RFiD System Design
*now with Alcatel-Lucent as Senior Technical Support Engineer
She received her BS degree from Electrical and Electronics Engineering Department of Gebze Institute of Technology, Gebze in 2007. Her current research topics are microwave antenna and circuit design. She has written an MSc. thesis with the title ” RFiD System Design”.
Summary: RFID systems have become very popular in recent years due
to their wide area of usage. RFID systems are used in supply chain, security related
areas, logistics, and so on. By using RFID system, human based errors can be
eliminated so the costs can be reduced. The RFID systems are composed of four
main components; namely the reader, the antenna, the tag and the computer.
In this master thesis, a linear polarized UHF RFID antenna and a multiplexer are designed and fabricated to reduce RFID equipment costs. Wide reading range can be achieved using a multiplexer instead of multiple RFID reader. The designed antenna is cheaper than the antennas in the industry while presenting similar operational parameters.
The designed UHF RFID antenna is simulated from 850 MHz to 880 MHz. Return loss of the antenna is lower than -10dB in the range of 855 MHz to 875 MHz. The fabricated antenna has an input impedance of , a return loss of -18.57 dB, a relatively high gain of 5.4 dBi and a read range of 8 meters at 2 Watt reader power. The fabrication cost of a single antenna is around 15 $ which is fairly cheap. The operation parameters are similar to the antennas in the industry, since conventional materials and components are used. Cost reduction can be achieved by using the presented antenna.
A multiplexer is designed and fabricated to multiplex the RFID reader port to two ports and extend the read range of the RFID reader. The main contribution in this design is the usage of pin diodes which are very cheap and easy to find. This in return reduces the fabrication costs. The designed circuit has only a few components, thus a relatively low complexity. It is easy to replace any component in case of a failure. The multiplexer is controlled by a PIC which allows the user to determine the read times of each RFID reader antenna. This innovative design allows a cheap solution to wide area applications of RFID where multiple antenna usage is necessary to read every tag in the reading zone.