Experiment No. 1: Study of Microwave cables, connectors, adapters, wave-guides, components & passive devices.

Transcription

1 Bangladesh University of Engineering and Technology, Dhaka Department of Electrical & Electronic Engineering (EEE) EEE 434: Microwave Engineering Sessional Experiment No. 1: Study of Microwave cables, connectors, adapters, wave-guides, components & passive devices. Objective: The objective of this experiment is to get acquainted with all sorts of microwave cables, connectors, adapters, waveguiedes, components and other passive devices. Mainly we will get familiarized with the microwave components that are available in our laboratory. Microwave components to be examined: 1. Coaxial cables: Flexible semirigid. 2. Connectors: GR Type-N BNC SMA APC 3. Adapters: GR female to SMA male SMA male to load BNC male to SMA male SMA male to SMA male APC-7 to Type-N female APC-7 to Type-N male APC-7 to SMA male 4. Waveguides 5. Microwave power divider 6. Directional Coupler

2 7. Microwave training kit (LRL 550B-SS): Oscillators: Klystron Tube Mount Solid State Oscillator Slotted line Tuning probe Thermistor mount Detector mount Waveguide Junction or Tees: E-plane Tee H-Plane Tee Magic Tee Attenuator: Fixed attenuator Variable flap attenuator Waveguide to coaxial transition Power Supply, Thermistor Bridge and Amplifier Directional Coupler Horn Antenna, Termination and Shorting plate Report: 1. Write short notes on all the components listed above. 2. Draw the isometric view of all the components.

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9 Reference: 1. Microwave Devices and Circuits, 3 rd Edition, Samuel Y. Liao 2. LRL MODEL 550B-SS MICROWAVE TRAINER KIT OBSERVED MICROWAVE COMPONENTS: Coaxial Cables: Coaxial cable is an electrical cable consisting of a round conducting wire, surrounded by an insulating spacer, surrounded by a cylindrical conducting sheath, usually surrounded by a final insulating layer. It is used as a high-frequency transmission line to carry a highfrequency or broadband signal. Sometimes DC power (called bias) is added to the signal to supply the equipment at the other end, as in direct broadcast satellite receivers. Because the electromagnetic field carrying the signal exists (ideally) only in the space between the inner and outer conductors, it cannot interfere with or suffer interference from external electromagnetic fields. Coaxial cables may be rigid or flexible. Rigid types have a solid sheath, while flexible types have a braided sheath, both usually of thin copper wire. The inner insulator, also called the dielectric, has a significant effect on the cable's properties, such as its characteristic impedance and its attenuation. The dielectric may be solid or perforated with air spaces. Connections to the ends of coaxial cables are usually made with RF connectors. Radio-grade flexible coaxial cable. A: outer plastic sheath B: copper screen C: inner dielectric insulator D: copper core Semi-rigid cable is a coaxial form using a solid copper outer sheath. This type of coax offers superior screening compared to cables with a braided outer conductor, especially at higher frequencies. The major disadvantage is that the cable, as its name implies, is not very flexible, and is not intended to be flexed after initial forming.

10 Coaxial cable connectors Coax cable connectors, often called RF connectors are in widespread use. Wherever radio frequency or RF connections need to be made there is the possibility of using coaxial connectors. It is also important that RF coaxial cable connectors have a characteristic impedance that matches that of the cable. If not, a discontinuity is introduced and losses may result. There is a variety of connectors that are used for RF applications. Impedance, frequency range, power handling, physical size and a number of other parameters including cost will determine the best type for a given applications. UHF connector The UHF connector, also sometimes known as the Amphenol coaxial connector was designed in the 1930s by a designer in the Amphenol company for use in the radio industry.these coaxial connectors have a threaded coupling, and this prevents them from being removed accidentally. It also enables them to be tightened sufficiently to enable a good low resistance connection to be made between the two halves. UHF Male UHF Female N-type connector The N(Navy)-type connector is a high performance RF coaxial connector used in many RF applications. This coax connector was designed by Paul Neill of Bell Laboratories, and it gained its name from the first letter of his surname.this RF connector has a threaded coupling interface to ensure that it mates correctly. It is available in either 50 ohm or 75 ohm versions. The connector able to withstand relatively high powers when compared to the BNC or TNC connectors. The standard versions are specified for operation up to 11 GHz, although precision versions are available for operation to 18GHz. N-Male N-Female The N-type coaxial connector is used for many radio frequency applications including broadcast and communications equipment where its power handling capability enables it to be used for medium power transmitters, however it is also used for many receivers and general RF applications. BNC connector The BNC(Bayonat Navy Connector) coax connector is widely used in professional circles being used on most oscilloscopes and many other laboratory instruments. The BNC connector has a bayonet fixing to prevent accidental disconnection while being easy to disconnect when necessary. This RF connector was developed in the late 1940s and it gains its name from a combination of the fact that it has a bayonet fixing and from the names of the designers, the letters BNC standing for Bayonet Neill Concelman. In fact the BNC

11 connector is essentially a miniature version of the C connector which was a bayonet version of the N-type connector. BNC Male BNC Famale Electrically the BNC coax cable connector is designed to present a constant impedance and it is most common in its 50 ohm version, although 75 ohm ones can be obtained. It is recommended for operation at frequencies up to 4 GHz and it can be used up to 10 GHz provided the special top quality versions specified to that frequency are used. TNC connector The TNC connector is very similar to the BNC connector. The main difference is that it has a screw fitting instead of the bayonet one. The TNC connector was developed originally to overcome problems during vibration. As the bayonet fixing moved slightly there were small changes to the resistance of the connections and this introduced noise. TNC Male TNC Female Like the BNC connector, the TNC connector has a constant impedance, and in view of the threaded connection, its frequency limit can be extended. Most TNC connectors are specified to 11 GHz. SMA(Sub-Miniature A connector) connector This sub-miniature RF coaxial cable connector finds many applications for providing connectivity for RF assemblies within equipments. It is often used for providing RF connectivity between boards, and many microwave components including filters, attenuators, mixers and oscillators, use SMA connectors. SMA Male SMA Female

12 The connectors have a threaded outer coupling interface that has a hexagonal shape, allowing it to be tightened with a spanner. Special torque spanners are available to enable them to be tightened to the correct tightness, allowing a good connection to be made without over-tightening them. SMA connectors are regularly used for frequencies well into the microwave region, and some versions may be used at frequencies up to 26.5 GHz. For flexible cables, the frequency limit is normally determined by the cable and not the connector. SMB(Sub-Miniature B connector) connector It was developed as a result of the need for a connector that was able to connect and disconnect swiftly. It does not require nuts to be tightened when two connectors are mated. Instead the connectors are brought together and they snap fit together. Additionally the connector utilizes an inner contact and overlapping dielectric insulator structures to ensure good connectivity and a constant impedance. SMB SMB coaxial connectors perform well under moderate vibration only and the 50 ohm versions are often specified to 4 GHz. 75 ohm versions of the SMB coaxial connector are also available. SMC connector Sub Miniature C or SMC coaxial cable connector is similar to the SMB connector, but it uses a threaded coupling interface rather than the snap-on connection. This provides a far superior interface for the connection and as a result, SMC coaxial cable connectors are normally specified to operate at frequencies up to 10 GHz. APC-7 Connector :

13 The APC-7 (Amphenol Precision Connector - 7 mm) offers the lowest reflection coefficient and most repeatable measurement of all 18 GHz connectors. Development of this connector was a joint effort between HP and Amphenol which began in the early 1960s. This is a sexless (hermaphrodite) design and is the preferred connector for the most demanding applications, notably metrology and calibration. These connectors are designed to perform repeatably for thousands of interconnect cycles as long as the mating surfaces are kept clean. You will find these connectors on the front of some network analyzers APC-7 Connector sex: A common misconception is that the sex of a connector has something to do with the outer connector. WRONG! The sex of the connector refers only to the inner conductor. With the notable exception of the "sexless" 7 mm connector, connectors are come in matched pairs. The term "male" implies a connector where the center conductor protrudes, while the term "female" implies a connector where the center connector forms a sleeve around its male counterpart. Alternative terms are "plug" for male, and "jack" for female.

14 Elbow Connectors: The term "elbow" is another bit of connector slang, it means a right-angle bend connector or adapter. Rightangle connectors come in two types: 90 degree, and swept (see photo below). In general, the swept connectors are better at high frequencies, and the outer jackets are molded rather than machined. If you took apart a 90 degree elbow you'd see why. It's because the dielectric typically is not continuous at the 90 degree junction, so there is some parasitic inductance that screws up the VSWR. Elbow Connector Adapters: Within any connector family there are three adapters you can use. A male-to-male adapter refers to an adapter with two male ends. This is often referred to as a "barrel" adapter. A female-to-female adapter has two female ends; it is often referred to as a "bullet" adapter. An adapter with one male end and one female end is often referred to as a "connector saver". This is because this type of adapter is often screwed onto an expensive piece of test equipment or component that requires a lot of connect/disconnect cycles. If an incident occurs where one of the connectors is damaged, it is far

15 cheaper to throw away and replace the connector saver than to repair expensive equipment that it is protecting. Below is a picture of an SMA connector saver, barrel and bullet adapter. Waveguide Adapters Waveguides are metallic transmission lines that are used at microwave frequencies, typically to interconnect transmitters and receivers (transceivers) with antennaswaveguide has a number of advantages over coax, microstrip and stripline. It is completely shielded (excellent isolation between adjacent signals can be obtained), it can transmit extremely high peak powers and it has very low loss (often almost negligible) at microwave frequencies. Waveguide E-plane and H-plane Rule of Thumb: The E-plane bend is bent the "easy way", and the H-plane bend is bent the "hard way", which can be seen in the photo below. It is obvious to us what is meant by easy and hard way when we are bending a rectangular rod. H-plane bend and E-plane bend (WR-28) Waveguide Junctions or Tees: Below are some pictures of some waveguide splitters one may find in lab. Note that basic network theory, says that one can't make a three-port splitter that is lossless and matched at all three ports, so if one wants to split a

16 signal, his best bet is the magic tee, just feed the sum port, terminate the delta port and the outputs are the colinear ports. E-plane tee (WR-28) H-plane tee (WR-28)

17 Magic tee (WR-62) Flexible Waveguide : There are two primary types of flexible waveguide. One is flexible and twistable, the other is non-twistable. A picture of the latter type is shown here: Power Divider: Flexguide (non-twistable) Power dividers and combiners are used in microwave frequencies because of the different behavior of circuits. Therefore, power dividers in microwave frequencies are not just resistive power dividers as in the low frequency or DC model. In microwave frequency applications power can be reflected from the output ports. Then to avoid the reflected power expected power divider should satisfy the maximum power transfer theory, which says the impedance of the load should be the complex conjugate of the impedance seen from the load end when load is not connected. This is called "matching" of the ports. This leads to transferring maximum power to the. There are three types of dividers: 1-) WILKINSON 2-) T-JUNCTION 3-) SPLIT-TEE Female power divider: Male power divider: n_3way n_2way n_4way SMA 3 way SMA 2 way SMA 4 way

18 Directional Coupler : Below are two "cross-guide" couplers. One has a fifty-ohm termination built in. WR-42 cross-guide coupler with terminated port WR-42 cross-guide coupler Waveguide to coax adapter (WR-62 to type N) Between series adapter (WR-51 to WR-42) STANDARD DIGITAL ATTENUATORS Advanced Control Components offers a line of 4- through 6-bit PIN diode digital attenuators in either the 1-2GHz or 2-4GHz frequency range with up to 63dB of total attenuation. The attenuators are optimized for attenuation accuracy and flatness, low insertion loss and VSWR, fast switching speed and compact packaging. The attenuators feature TTLcompatible drivers and operate from a single +5V DC supply for simple system integration. Monotonicity is guaranteed for all models. All standard digital attenuators are available with hermetic seal and high-rel screening for mil and space qualified applications.

19 MPS-2100 Inline Optical Attenuator : The MPS-2100 Singlemode In-line Optical Attenuator is a fixed value attenuator that is integrated into a standard fiber optic jumper cable. MPS-2100 Singlemode In-line Optical Attenuators utilize Corning fiber and are offered in two different connector brands; Our Corning line is built using Corning connectors and our Value line uses quality connectors at a substantial discount. They are available in a single window or dual window format with an attenuation value up to 25 db. The In-Line Attenuator is available in fiber diameters of 250 micron, 900 micron or 3mm and comes integrated into any length jumper. It can be supplied with or without connectors, or as a pigtail version. Every assembly exceeds Telcordia standards and is tested for insertion and return loss. In addition, each attenuator is individually tested and is supplied with it s individual test record sheet. Applications : Telecommunication Systems Metropolitan Area Networks Local Area Networks CATV Systems EDFA Transmission Systems Flann Microwave Programmable Attenuator : Specification: High Speed Operation 0-60 db in 1.2 seconds. 0.1 db or 1 percent accuracy. Attenuation Range 0 to 60 db continuous variable.

20 Microwave OscillatorsOscillator is an electronic device used for the purpose of generating a signal. They are often found in computers, wireless receivers and transmitters, and audio-frequency equipment, and music synthesizers. They provide the signal source for all microwave systems, including both transmitters and receivers. They can generate a frequency source such as wave or square wave Microwave oscillators are useful in applications like audio signal generation, reference signals for different applications and in measurement applications. Square wave oscillators are most often used as clock sources for digital electronics circuits and similar applications. Microwave crystal oscillators have spectrum applications ranging military and aerospace applications in communication, electronic warfare, navigation, radar etc. in consumer electronics such as cable TV systems, Cellular and cordless, home computers, phones, pagers, VCR, video cameras etc. They are offered in parameters differing in oscillation frequency, total frequency stability, and RF connector type. Klystron Tube mount: Variable flap attenuator:

21 DISCUSSION: A microwave system normally consists of a transmitter subsystem, including a microwave oscillator, waveguides, and a transmitting antenna, and a receiver subsystem that includes a receiving antenna, transmission line or waveguide, a microwave amplifier, and a receiver. In order to design a microwave system and conduct proper test of it, an adequate knowledge of the components involved is essential.