Doubler/Amplifier Building Block for CW-Radar

MA-Thesis / Master von Manar Bakro

Abstract:

For the measurement of velocity of, e.g., cars on the street or objects in industrial fabrication scenarios we use microwave radiation from so-called CW-Radar systems. The CW-Radar measures the Doppler-frequency of the microwave radiation: A wave of fixed frequency (Continuous Wave, CW) is radiated through a high-gain antenna onto a moving target where it is reflected and the reflected wave is received by the radar antenna again. The reflected wave exhibits a frequency shift (Doppler-frequency) which is proportional to the radial velocity of the target and proportional to the frequency of the transmitted wave.

This wave has frequency 24GHz, generated in the transmitter and after that there are some of parts. The thesis task is to build one part of a radar system which operates at 24 GHz, namely the building block that takes-in the 12 GHz oscillator signal to double the frequency to 24 GHz and amplify it as a driver signal for the transmit amplifier.

This circuit uses RT/Duroid 5870 substrate with 0.25 mm thickness. The measured resonance frequency occurs at 24 GHz. To reduce the effects and the losses in the high frequency, the spacing between the microstrip lines can be increased, where a thinner RT/Duroid 5870 substrate of 0.25 mm is correspondingly used.

And most of the connectors are tested for 24GHz, and the best way to have high performance and low losses between changing from the coaxial cable to the microstrip, where there the most of the losses in the circuits for very high frequency. And there are a radiation in the space, can be considered also.

	INTRODUCTION	9
1	Continuous-Wave (CW) Radar	9
2	Microwave elements and simulation tools	13
2.1	Microstrip	13
2.2	Analysis Electromagnetic Simulation Tools	16
2.3	Microstrip radial stub:	19
2.4	Interdigital Capacitors :	21
2.5	Test Equipment and Techniques:	23
2.5.1	Connectors:	23
2.5.2	Normal connectors(SMA):	27
3	Doubler Frequency :	29
3.1	Balanced Doubler :	29
3.2	With Nonlinear effects:	37
4	Amplifier 24 GHz:	41
4.1	Amplifier Characterization:	41
4.1.1	Power Gain:	41
4.1.2	Stability:	44
4.2	Power Adjustment:	47
5	The Fabrication and Measurement
5.1	Doubler frequency:	50
5.2	The 24 GHz Amplifier	55
5.3	Measurement for all system	58
6	Conclusions	53
	Appendix A	60
	Appendix B	63
	Appendix C	66
	Appendix D	70
	Appendix E	72
	REFERENCE	75

Text Sample:

Chapter 2.5, Test Equipment and Techniques:

An Agilent 8722 network analyzer was used for most of the published measurements.

Today’s automatic network analyzers are generally built with test ports as perfect as possible. The rationale for doing this is that the impedance of the network analyzer test port should match the impedance of the calibration standards in order to avoid unwanted propagation modes at the test port interface. Supposedly, if unwanted modes exist at the test port interface then it cannot be assured that they remain constant with the connection of the various calibration devices.

Thus a calibration and subsequent measurement error will result due to the presence of these uncontrollable modes. However, it is recognized that unwanted modes can exist elsewhere in the network analyzer as long as they remain constant and are sufficiently attenuated at the test port.

A general rule of thumb is that higher order modes propagating down a coaxial transmission line are attenuated by 30 dB after travelling a distance d, where d is the diameter of the outer conductor of the coaxial line. It is generally desirable to have unwanted modes attenuated by more than 60 dB relative to the fundamental TEM mode at the test port interface. The test port connectors used were SMA connectors and the frequency range for all measurements was 23.8 to 24.2 GHz. Calibration was for this rang. All of the data was taken from the same calibration.

2.5.1, Connectors:

A fundamental problem in the construction of the packages for MICs is the requirement for low loss and low reflection coefficient of the transitions between the microstrip circuit on the substrate and the coaxial connector.

The problem has both electrical and mechanical aspects: the transition must be electrically optimized to reduce field discontinuities and machining tolerances, differing thermal expansion of substrate and housing, minimum current paths, and accounting for reliable contacts. These are relevant to the contacts between the strip conductor on the substrate and the coaxial inner conductor, and between the substrate’s ground metallization and the coaxial outer conductor. For very high frequency is better to use special connector, to assure maximum performance. Allow a low VSWR, low return loss, launch to 50 GHz to a board with only 2 through holes added to the board. They are recommended for multi-layer boards with coplanar waveguide or single layer microstrip circuit boards.