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Milimetre dalga boyunda yüzgeç hat karıştırıcı tasarımı

Balanced finline mixer design in millimeter wawe band

  1. Tez No: 46269
  2. Yazar: DEMET SEVİL ARMAĞAN
  3. Danışmanlar: PROF.DR. OSMAN PALAMUTÇUOĞLU
  4. Tez Türü: Yüksek Lisans
  5. Konular: Elektrik ve Elektronik Mühendisliği, Electrical and Electronics Engineering
  6. Anahtar Kelimeler: Belirtilmemiş.
  7. Yıl: 1995
  8. Dil: Türkçe
  9. Üniversite: İstanbul Teknik Üniversitesi
  10. Enstitü: Fen Bilimleri Enstitüsü
  11. Ana Bilim Dalı: Belirtilmemiş.
  12. Bilim Dalı: Belirtilmemiş.
  13. Sayfa Sayısı: 74

Özet

ÖZET Radar, radyometre ve haberleşme sistemleri için milimetre dalga frekanslarmdaki uygulamalar son yıllarda oldukça önem kazanmıştır. Bu karıştırıcı tasarım çalışması, pasif bir algılayıcı olan radyometre gerçeklenmesinde kullanılmak üzere yapılmıştır. Bahsedilen 8 mm dalga boyundaki radyometre ile bitki örtüsünü incelemek amaçlanmaktadır. Tasarlanacak karıştırıcının işaret frekansı 34 GHz ve ara frekansı 2.5 GHz olarak belirlenmiştir. Milimetre dalgaboyunda çalışan ve oldukça zayıf işaretleri algılaması gereken bir karıştırıcının duyarlılığının çok yüksek olması gerekir. Ancak milimetre dalgaboyunda çalışan devrelerde saçılım, zayıflama, süreksizlikler ve kavislerden kaynaklanan kayıplar, küçük boyut zorunluluğu ve bundan kaynaklanan mekanik problemler tasarımcıyı zorlar. Radyometrenin önkatmda kullanılacak bu karıştırıcı için yapılan etüd çalışmalarında yüzgeç hatları (finline) ile tek dengeli karıştırıcı tasarımı yapmanın en uygun çözüm olduğu görülmüştür. Diyot olarak GaAs Beam Lead Schottky Barrier diyotlar kullanılmıştır. Karıştırıcının RF ve LO girişleri yüzgeç hatlarla yapılmış; IF çıkışı için mikroşerit alt geçiren süzgeç tasarlanmıştır.Tasarlanan devrenin maskesi, dielektrik malzeme (Dufoid-5880) üzerine pozlandırılmış daha sonra metal kılıfı hazırlanmıştır. Yapılan incelemelerden bu karıştırıcı topolojisinin 110 GHz'e kadar kullanılabileceği görülmüştür.

Özet (Çeviri)

SUMMARY BALANCED FİNLİNE MIXER DESIGN IN MILLIMETER WAVE BAND Rapidly expanding activities in millimeter-wave hardware developments have created an urgent need for broad-band mixers for the receivers used in remote sensing, radio astronomy, ecology, electronic warfare, surveillance, meteorology, radiometer, and communication systems. During the past decade, significant improvements have been made in millimeter-wave mixers. Most of this, however, have been limited to narrow-band applications. Recently, several broad-band mixers have been built in waveguide circuits. The use of GaAs beam-lead Schottky diodes in integrated circuit mixers provides low noise performance and avoids a mechanical diode contact in whisker-contacted mixers and therefore has better reliability and needs less assembly. Integrated circuit technologies provide the advantages of low cost, light weight, and small size. These also have the potential of direct translation into monolithic circuits and even large-scale integration. For a transmission structure to be suitable as a circuits, one of the principal requirements is that the structure should be“planar”in configuration. A planar geometry implies that the characteristics of the element can be determined from the dimensions in a single plane. Various forms of planar transmission lines have been developed for use in millimeter wave integrated circuits (MWICs). The microstrip line, inverted microstrip line, slot line, coplanar waveguide and coplanar strip line are representative planar transmission lines. The circuits realized using any one of VIthe aforementioned transmission lines or combinations of them have distinctadvantages such as light weight, small size, improved performance, better reliability and reproducibility, and low cost. They are also compatible with solid state chip devices. Integrated circuits employing these structures at microwave frequencies have been widely discussed in the literature. When a slot line is placed in a waveguide bridging the broad walls, the structure is popularly known as a finline. Finlines are frequently used in MWICs because of their favorable properties, such as low dispersion, broad single mode bandwidth, moderate attenuation, and compatibility with solid state chip devices. As is evident, finline structures are quasi-planar as compared to microstrip-like structures. Since the substrate of the finline lies in the E plane of the rectangular waveguide, such lines are also called E-plane transmission lines. E-plane circuits can also be realized using microstrip, coplanar lines, and suspended microstrip. It is evaluated that approximately 110 GHz is the upper frequency limit for utility of the above-mentioned transmission media in MWICs. This limitation results from the combination of techniques required for meeting fabrication tolerances and handling fragility and mode suppression. Losses in this structures at higher frequencies also become significant. Radiation losses from bends, discontinuities, and surface waves pose a serious problem in the case open structures. However, this problem can be partly alleviated by using metallic shielding. This mixer design study is a part of the 8 mm wavelength radiometer. It is aimed to investigate the vegetation canopy using this radiometer. Mixer is the first device for the passive sensors like radiometer, radiotelescope, etc. So there VIIare a lot of studies to improve the mixer performance. It was decided to design Dicke type radiometry and it has the two IF stage. Designed mixer is the first stage of the radiometer and its characteristics defined as RF frequency 34 GHz, IF frequency 2.5 GHz and bandwidth 600 MHz. For this millimeter wavelength mixer design, firstly mixer theory has been examined carefully. Then it was decided to use a online configuration and GaAs beam-lead Schottky barrier diodes in a single balanced mixer. Single balanced mixer can be obtained by combining two single ended mixers. The two diodes are driven in opposite phase. Various hybrids and baluns are used to supply the RF and LO power to the two mixer diodes. In this study, RF and LO power are splayed via finline structure (See Fig.l). To employ the diodes in opposite phase, coplanar waveguide is used. On the otherhand, it is necessary to take IF signal from a diode. IF signal is at 2.5 GHz frequency and it can be used microstrip line for this port. That's means we have to use special balun to combine the coplanar waveguide, finline and microstrip. This balun LOCAL OSCILLATOR Figure 1. Balanced Finline Mixer at 8 mm VIII(like a Marchand balun) have been discussed in the literature [22]. The other problem for this millimeter wave mixer conjuration is waveguide to finline transition. Quarter-wave matching transformer is used for this transition [19]. A fundamental limitation on the sensitivity of a microwave receiver employing a diode mixer arises from the fact that in the frequency conversion process only a fraction of the available RF signal power is converted into power at the intermediate frequency. Some RF signal is also converted to the usually unwanted image frequency and other harmonics, too. This 'overall' loss is dependent primarily on the diode junction properties, and secondarily on the diode's packages parasitics(i.e., mismatch of signal power by Rg, G) and on the match at the input and output ports of the mixer. Any impedance mismatch at the signal and LO frequencies not only results in signal loss due to reflection but also affects the IF impedance at the IF terminals of the mixer, an effect that becomes more serious for mixer diodes with low conversion loss. The IF impedance is the impedance seen looking into the IF port of a mixer. It is important to match this impedance to the IF amplifier input. The pertinent mixer diode IF impedance (ZIF) is that impedance at the output terminals of the mixer when the mixer diode is driven by a local oscillator. The IF impedance is a function of the local oscillator power level and also depends on the RF properties of the mixer and the circuits connected to the RF terminals of the mixer. In this study RF and IF impedance of the mixer is calculated. IF port is matched the IF output impedance, but RF port could not matched. IXLastly, IF filter was designed for this mixer. In the mixer, RF and LO signals produce nfRF±mfLO products. The desired IF output is either Irf+Ilo or ^RF'^LO (uPPer anc* lower sidebands) and the IF filter is usually selected to pass only one of these outputs. If it is desired fRf-fix) outPut> usually low-pass filter is designed at IF port. For this finline mixer, microstrip low-pass filter is designed at 2.8 GHz. Microwave filters can be design using low frequency prototype filter synthesis techniques. For this filter design insertion-loss method is used. Firstly, a prototype low-pass filter is designed selecting Chebyshev type filter. The element values are determined for 30dB attenuation, and O.ldB ripple at 2.8 GHz cutoff frequency. Then, this filter is designed with the microstrip line technology. A Duroid substrate is used with permittivity 2.2 and thickness 0.38mm. The ladder network of capacitors and inductors by using cascaded microstrip sections is implemented, and the performance of the filter is measured. After the configuration of the mixer is complete, print circuit diagram has been obtained by using Ledit computer program. Then the plane circuit is prepared. After the creating metallic shielding GaAs beam-lead Schottky diodes are located on the plane circuit, and performance of the mixer is measured. All the investigations on millimeter wave receivers show that this finline mixer configuration can be used until 110 GHz frequency. X

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