Aleš Maršálek: Multi-frequency reflector feed with circular polarization for a small parabolic antenna (2002) [pdf] in Czech 4255 k

Abstract: In this thesis, a multi-frequency reflector feed of a parabolic antenna is designed. For the construction to a microstrip antenna was used. A disk of rotary symmetry with f/D in the interval 0.4 to 0.5 was given. Operating frequencies of the reflector feed are 1270 MHz and 2400 MHz. Right-handed circular polarization in both bands is used. The reflector feed should be matched to the input impedance 50 W. Signals in both bands have to be well isolated and simultaneous operation has to be possible. Requirements for the primary radiator were given in the first chapter. Generally over view of microstrip antennas is provided in the second chapter. Properties of a rectangular patch and a circular one are compared in third chapter. The circular patch with air dielectric is chosen. One patch is designed for each band. The fourth chapter describes possibilities of the achievement of the circular polarization. Perturbation segments we used to accomplish this task. The fifth chapter discusses a adjustment of both patches. The patches are configured into stacked orientations with individual feeding. The sixth chapter describes matching of the input impedance and feeding technique. In the seventh chapter computer simulations are described. The simulations were used to finalize the design of the reflector feed. In the last chapter, realization of the antenna, experimental results and the final adjustment of the antenna are described. Impedance of both patches and the signal isolation were measured. Then directivity pattern and axial ratio of circular polarization were measured. According, to the experimental results, the final adjustment of the reflector feed was done. The presented reflector feed of parabolic antenna satisfies all requirements.


Petr Kutín: Local Oscillator for 24 GHz Downconverter (2002) [pdf] in Czech 1166 k

(recognized by the Czech IEEE MTT/AP/ED Committee)

Abstract: This thesis deals about design and construction of a local oscillator for converter of receiver working in 24GHz band. In receiver is applied the chip CHR2295 (United Monolithic Semiconductor), which contains frequency doubler of local oscillator. Local oscillator is designed in two parts. First one is a oscillator which generates signal at frequency 24,104MHz. The oscillator is designed like a crystal oscillator. It’s output signal is multiplied and amplified in a second part. This one includes five multipliers and two stage amplifier. The whole chain is designed and realized on a PTFE substrate with the thickness 0,5mm. Multipliers and amplifier was modelled and simulated by Serenade 8.5. The oscillator layout was made by Eagle layout editor 4.01.



Pavel Hanák: L-band Linear Power Amplifier (2004) [pdf] in Czech 759 k

(recognized by the Czech IEEE MTT/AP/ED Committee)

Abstract: The objective was to design and construct a linear power amplifier with following parameters: Central frequency 1269 MHz, output power 40 W and linear power gain at least 13 dB at supply voltage of 13,8 V. Two 50 W N-type RF connectors were required as input and output of the amplifier. Two RF power amplifier modules Mitsubishi M57762 were purchased to achieve this goal (see datasheet at the end of the thesis). Each module is capable of delivering up to 20 W of power in frequency band between 1,24 and 1,3 GHz. The two modules were coupled by microstrip branchline couplers to work in parallel into common load. Thus required output power of 40 W was achieved. After completion of design of all mechanical parts, the amplifier was constructed and some basic measurements were done. Linear power gain of the finished amplifier is around 16 dB in the entire band of the modules. Therefore, requirements stated above were met. Intermodulation distortion of 3rd order is -20 dBc at the central frequency of 1269 MHz. Second part of this thesis discusses the possibility of creating the amplifier using Motorola RF LDMOS transistor MRF9210. Doing so would not be without issues, as the transistor is designed for band of 880 MHz only. Nevertheless, a viable solution was found. The finished amplifier with M57762 modules is currently used in communication system for experimental satellite P3D.


Petr Vágner: Local Oscillator for 24 GHz Downconverter (2005) [pdf] in Czech 2246 k

(recognized by the Czech IEEE MTT/AP/ED Committee)

Abstract: This work contains a description of low phase noise frequency synthesizer working in microwave X-band. Design and realization of the PLL synthesizer is included. The synthesizer will serve as local oscillator for frequency conversion so it is designed for fixed frequency 11,952 GHz. The phase locked loop works at half frequency (i.e. 5,976 GHz) and it is designed using MMICs by Hittite Microwave Corporation. 5,5 GHz to 6,1 GHz voltage controlled oscillator HMC431 and low noise phase frequency detector HMC439 are used. The signal from output of the VCO goes through directional coupler. Coupled signal is divided by one divide-by-2 prescaler followed by two divide-by-5 prescalers. Total division ratio is 50 so resulting frequency is 119,52 MHz. Reference 119,52 MHz signal is generated by external overtone crystal oscillator. Output of the phase frequency detector drives an active loop filter with wide bandwidth to minimize phase noise. The VCO frequency is doubled to 11,952 GHz by active frequency doubler using GaAsFET transistor. Signal is filtered by bandpass filter and finally amplified to 8,6 dBm by single stage amplifier.





Jaromír Marek: Feed for dish antenna and low noise amplifier on Ka Band (2006) [pdf] in Czech 1270 k 

(recognized by the Czech IEEE MTT/AP/ED Committee)

Abstract: This work deals with design of a receiving system front end for satellite communication on the frequency 24,048 GHz. The first part of the project is optimal feed system for parabolic dish with ratio f/D = 0,4. Because of the minimal system noise temperature, which could be achieved in receiving satellite signal, low side-lobes of the parabolic dish are required. The feed is designed for circular polarization. In this work, the circular polarization is generated by using the dielectric slab. The advantage of this method is simple changing the direction of circular polarization wave. The second part of the project is the low noise amplifier (LNA) with high associated gain. The basic point of the design is choice of the active device. In the present time, the ultra low noise transistors based on the GaAs with high mobility electron are available. Commercial available amplifiers, which use this devices provide gain more than 20 dB and noise figure 1,5 dB. In this work two amplifiers are designed. The design with device NEC NE350184C is described. The alternative  amplifier uses device Agilent ATF-36077. Both amplifiers use two stage circuit.