Chapter Questions
Discuss the relative merits and drawbacks of using antennas, waveguides, and transmission lines as the media for a communications link.
Provide a broad definition of a waveguide. What is normally meant by the term waveguide?
Explain the basic difference between propagation in a waveguide versus a transmission line.
Explain why the different mode configurations are termed transverse electric or transverse magnetic.
What are the modes of operation for a waveguide? Explain the subscript notation for TE and TM modes.
What is the dominant mode in rectangular waveguides? What property does it have that makes it dominant? Show a sketch of the electric field at the mouth of a rectangular waveguide carrying this mode.
Describe the significance of the cutoff wavelength.
A rectangular waveguide is $1 \mathrm{~cm}$ by $2 \mathrm{~cm}$. Calculate its cutoff frequency, $f_{c e}(7.5 \mathrm{GHz})$
How does energy propagate down a waveguide? Explain what determines the angle this energy makes with respect to the guide's sidewalls.
For $\mathrm{TE}_{10}, a=\lambda / 2$. What is $a$ for $\mathrm{TE}_{20}$ ? (Assume a rectangular waveguide.)
Why is the velocity of energy propagation usually significantly less in a waveguide than in free space? Calculate this velocity $\left(V_g\right)$ for an $\mathrm{X}$-band waveguide for a $10-\mathrm{GHz}$ signal. Calculate guide wavelength $\left(\lambda_g\right)$ and phase velocity $\left(V_p\right)$ for these conditions. $\left(2.26 \times 10^8 \mathrm{~m} / \mathrm{s}, 3.98 \mathrm{~cm}\right.$, $3.98 \times 10^8 \mathrm{~m} / \mathrm{s}$ )
Why are free-space wavelength $(\lambda)$ and guide wavelength $\left(\lambda_g\right)$ different? Explain the significance of this difference with respect to Smith chart calculations.
Why are rectangular cross-sectional waveguides generally used in preference to circular crosssectional waveguides?
Why are circular waveguides used much less than rectangular ones? Explain the application of a circular rotating joint.
Describe the advantages and disadvantages of a ridged waveguide.
Describe the physical construction of a flexible waveguide, and list some of its applications.
Describe some advantages a ridged waveguide has over a rectangular waveguide.
List some of the causes of waveguide attenuation. Explain their much greater power handling capability as compared to coaxial cable of similar size.
Describe briefly the construction and purpose of a waveguide. What precautions should be taken in the installation and maintenance of a waveguide to ensure proper operation?
Why are waveguide bend and twist sections constructed to alter the direction of propagated energy gradually?
Describe the characteristics of shunt and series tee sections. Explain the operation of a hybrid tee when it is used as a TR switch.
Discuss several types of waveguide tuners in terms of function and application.
Verify the characteristic wave impedance of $405 \Omega$ for the data given in Problem 59 .
Calculate the characteristic wave impedance for an $X$-band waveguide operating at 8,10, and $12 \mathrm{GHz}$. $(663 \Omega, 501 \Omega, 450 \Omega)$
Explain various ways of terminating a waveguide to minimize and maximize reflections.
Describe the action of flap and vane attenuators.
Describe in detail the operation of a directional coupler. Include a sketch with your description. What are some applications for a directional coupler? Define the coupling of a directional coupler.
Calculate the coupling of a directional coupler that has $70 \mathrm{~mW}$ into the main guide and $0.35 \mathrm{~mW}$ out the secondary guide, $(23 \mathrm{~dB})$
Explain the basics of capacitively coupling energy into a waveguide.
Explain the basics of inductively coupling energy into a waveguide.
What is slot coupling? Describe the effect of varying the position of the slot.
Discuss the following with respect to waveguides:(a) Relationship between frequency and size.(b) Modes of operation.(c) Coupling of energy into the waveguide.(d) General principles of operation.
What is a cavity resonator? In what ways is it similar to an LC tank circuit? How is it dissimilar?
Explain the operating principles of a cavity resonator.
What are waveguides?
Describe a means whereby a cavity resonator can be used as a waveguide frequency meter.
Explain three methods of tuning a cavity resonator.
Explain briefly the principle of operation for a radar system.
Why are waveguides used in preference to coaxial lines for the transmission of microwave energy in radar installations?
With respect to a radar system, explain the following terms:(a) Target.(b) Echo.(c) Pulse repetition rate.(d) Pulse repetition time.(e) Pulse width.(f) Rest time.(g) Range.
Calculate the range in miles and meters for a target when $\Delta t$ is found to be $167 \mu \mathrm{s}$. (13.5 mi, $25,050 \mathrm{~m}$ )
What is the distance in nautical miles to a target if it takes $123 \mu$ s for a radar pulse to travel from the radar antenna to the target and back to the antenna, and be displayed on the pulseposition-indicator (PPI) scope? (10 mi)
What are double range echoes?
Why does a radar system have a minimum range? Calculate the minimum range for a system with a pulse width of $0.5 \mu \mathrm{s}$.
In detail, discuss the various implications of duty cycle for a radar system.
What is the peak power of a radar pulse if the pulse width is $1 \mu \mathrm{s}$, the pulse repetition rate is 900 , and the average power is $18 \mathrm{~W}$ ? What is the duty cycle? $(20 \mathrm{~kW}, 0.09 \%)$
For the radar block diagram in Figure 15-26, explain the function of each section.
A police radar speed trap functions at a frequency of $1.024 \mathrm{GHz}$ in direct line with your car. The reflected energy from your car is shifted $275 \mathrm{~Hz}$ in frequency. Calculate your speed in miles per hour. Are you going to get a ticket? ( $90 \mathrm{mph}$, yes!)
What is the Doppler effect? What are some other possible uses for it other than police speed traps?
Why is a Doppler radar often called a CW radar?
Using sketches, explain the physical construction of stripline, single-conductor microstrip, and parallel-coupled microstrip. Discuss their relative merits, and also compare them to transmission lines and waveguides.
What is a dielectric waveguide? Discuss its advantages and disadvantages with respect to regular waveguides.
Calculate $Z_0$ for stripline constructed using a circuit board with a dielectric constant of 2.1 , $b=0.1 \mathrm{in}$, $c=0.006 \mathrm{in}$, and $h=0.08 \mathrm{in}$. The conductor is spaced equally from the top and bottom ground planes. $(50 \Omega$ )
Make a sketch of a single-conductor microstrip that simulates an inductor to ground followed by a series capacitance.
Describe the proper procedure for troubleshooting waveguides.
Explain how to prevent arcs.
Explain where problems are most likely to occur with waveguides and describe a process to prevent these problems.
Describe how to test a waveguide.
A 9-GHz signal is operating in the dominant mode in a rectangular waveguide $3 \mathrm{by} 4.5 \mathrm{~cm}$. The characteristic (wave) impedance is $405 \Omega$. Provide a report that includes the $\lambda_R, \lambda, V_g$, and $V_p$ for this system; the SWR that would be caused by a hom antenna load of $350 \Omega+j 100 \Omega$; and the impedance in the guide $4 \mathrm{~cm}$ from the antenna load. Include a Smith chart analysis with the report.
Can a hybrid tee be used to feed the first stage of a microwave receiver (the mixer - no RF stage) with the antenna signal and local oscillator signal without any local oscillator radiation off the receiving antenna? Provide a sketch to illustrate.
Analyze the relationship between multiple targets and maximum range. Use the calculated maximum unambiguous range for a radar system with PRT equal to $400 \mu$ s to illustrate.
You must use a directional coupler to measure VSWR and to determine the loss introduced by a device in a waveguide system. Describe the tests you will use and how they differ from each other.