Q1 The incident electric field strength at an antenna aperture is 10mV/m. Given that the received signal power is 1 picoWatt the antenna effective aperture is:
a 10-7 m2
b 3.8 m2
c 0.01 m2
d 107 m2
e 1 m2
Q2 A 10GHz antenna has a physical aperture of 1 metre x 10cm. The antenna gain will be approximately:
a 31.4 dBd
b 42
c 31.4 dBi
d 62.8 dB
e 30 dBd
Q3 An antenna has a horizontal beamwidth of 10o and a vertical beamwidth of 20o , the antenna directivity is approximately:
a 206
b 0.06
c 0dB
d 46dB
e 16.7
Q4 A certain monopole antenna provides a system gain of 3 dB in service and is 90% efficient. What is its directivity?
a 2
b 5.1 dB
c 3.5 dB
d 3 dBd
e 3.2
Q5 An antenna radiates 100 watts and has a directivity of 10dB. The power received at a range of 1km in free space is 1 milliwatt. The antenna used to receive the signal has an effective aperture of:
a 12.6 m2
b 5 m2
c 126 m2
d 1.26 m2
e 10 m2
Q6 Each element in a linear array of two isotropic antennas is fed with the same signal, given that the element spacing is l, the resulting radiation pattern will:
a be a broadside pattern
b be an endfire pattern
c contain a radiation null along the axis of the array
d contain a main lobe in both endfire and broadside directions
e contain a main lobe at 45o to broadside
Q7 The element spacing in an array is
a determined solely on the grounds of element size
b required to be less than l/2 if the beam is to be steered
c limited to l if the beam is to be steered
d determined by the necessary input impedance
e is determined by the required beam steering angle
Q8 A 25 watt 900MHz basestation transmitter uses a half wave dipole antenna.
a the antenna feed current will be 0.59 A
b the transmitter output voltage will be approximately 1.8 kV
c the safe radius from the antenna will be 10m
d the antenna gain will be 5.1 dB
e the transmitter output voltage will be approximately 30 V
Q9 A helical antenna:
a provides a radiation pattern similar to a l/4 monopole
b will operate in the normal mode if its circumference is more than l
c will operate in the axial mode if its circumference is less than l
d will produce an endfire pattern when the circumference is more than l
e will always give more gain than a l/4 monopole
Q10 A parabolic dish antenna with diameter 1.5m operates at 30GHz, the distance to the far field is approximately:
a 450m
b 225m
c 1mm
d 10mm
e 0.1mm
Q11 An antenna with maximum dimension 2cm operates at 150MHz. The distance to the far field is approximately:
a 0.4mm
b 0.2mm
c 20cm
d 1m
e 10m
Q12 An antenna with gain 10 dB at 900 MHz delivers 1mW to a matched load from an off air signal. The power density at the antenna aperture is:
a 100mW/m2
b 8.8mW/m2
c 44.9mW/m2
d 6mW/m2
e 11.3mW/m2
Q13 A system transmits a 1 microwatt signal using an antenna with gain 10dB, the free space loss to the receiver is 100dB and the receiver antenna provides no additional gain. The signal to noise ratio at the output of the receiver low noise amplifier is 0dB and the system is thermal noise limited. Given that the noise figure for the low noise amplifier is negligible and its gain is 20dB, the receiver bandwidth is:
a 250 kHz
b 500 Hz
c 25 MHz
d 2.5 MHz
e 25 kHz
Q14 A 5 element linear array antenna has an element spacing of l/4 along the axis of the array. If all the elements are fed in phase,
a The radiation pattern would be end-fire.
b The radiation pattern would contain nulls in the end-fire direction
c The radiation pattern would contain grating lobes
d The radiation pattern would be broadside
e The antenna input impedance would be reactive
Q15 A 5 element linear array antenna has an element spacing of l/4 along the axis of the array. If the progressive phase shift across the array is 90o, the beam will be steered to:
a endfire
b 45o
c broadside
d -45o
e 90o
Q16 A vertical slot will give:
a horizontal polarisation
b vertical polarisation
c a radiation pattern similar to a horizontal dipole
d a radiation pattern similar to a vertical loop
e a low input impedance
Q17 A short horizontal loop will give a radiation pattern:
a like a short horizontal dipole
b like a short horizontal slot
c like a short horizontal slot but with opposite polarisation
d exactly like a short vertical dipole
e exactly like a short vertical slot
Q18 A linear array is constructed with the maximum possible spacing between elements which can be used with beam steering. The phase shift required between each element to steer the beam through 20o is:
a 0.53 radians
b 0.53 degrees
c 15 degrees
d 1.07 radians
e 30 degrees
Q19 A microstrip rectangular patch antenna is constructed using a substrate with er = 4. The length of the patch for operation at 3.4 GHz is approximately:
a 22 mm
b 44 mm
c 11 mm
d 88 mm
e 100 mm
Q20 The directivity of an antenna
a is not the same on transmit and receive
b is a measure of its in service gain
c is given by gain multiplied by efficiency
d is purely a measure of the focussing in the radiation pattern
e is lower on transmit than receive.
时间: 2005-3-14 01:54
作者: 固定无线接入
很有兴趣，请贴完全部3部分和相关答案，给你加个精华鼓励鼓励吧，嘿嘿
时间: 2005-3-14 02:07
作者: 固定无线接入
能不能把解题的公式写出来啊，多谢了
时间: 2005-3-14 09:44
作者: sinca
Transmission lines
Choose the best answer in each case:
Q1. The characteristic impedance of a line is:
(a) The ratio of voltage to current at any point on the line
(b) The input impedance of the line
(c) The ratio of incident voltage to incident current at any point on the line
(d) The ratio of incident voltage to reflected current at any point on the line
(e) The ratio of voltage to current at the line input
Q2. The reflection coefficient of a short circuit load is:
(a) 0 because the voltage falls to zero
(b) +1 because the current is high
(c) -1 because the energy in the magnetic field falls to zero whilst that in the electric field doubles
(d) 0 because the current falls to zero
(e) -1 because the voltage falls to zero
Q3. A 50W line is connected to a 30W load, the power reflected at the load is:
(a) 25% of the incident power
(b) 6.25% of the incident power
(c) 4 x the incident power
(d) 16 x the incident power
(e) all of the incident power
Q4. A line has R=0 W/m, G=0.1 S/m, L=250nH/m, C=100pF/m. The characteristic impedance is:
(a) 50W
(b) (50+j10)W
(c) 75 W
(d) (75+j1) W
(e) (50-j0.1)W
Q5. The range of possible values for the VSWR caused by a passive load is:
(a) 0 < VSWR < 1
(b) 0 < VSWR < ¥
(c) 1 < VSWR < ¥
(d) -¥ dB < VSWR < 0 dB
(e) -¥ dB < VSWR < +¥ dB
Q6. The range of possible values for reflection coefficient of a passive load is:
(a) -1 < g < +1
(b) 0 < g < +1
(c) 0 dB < g < ¥ dB
(d) -¥ dB < g < +¥ dB
(e) 0 < g < ¥
Q7. The return loss for a matched load is:
(a) 0 dB
(b) 0%
(c) 1
(d) ¥ dB
(e) -¥ dB
Q8. The input impedance of a lossless line terminated in a short circuit is:
(a) Purely reactive
(b) Purely real
(c) Zero
(d) Inductive
(e) always low
Q9. The input impedance of a lossless l/4 line terminated in an open circuit is:
(a) capacitive
(b) Infinite
(c) -jZo W
(d) Inductive
(e) A short circuit
Q10. The attenuation coefficient of a line is 0.01 Nepers/m. The attenuation over 100m of the line is:
(a) 1dB
(b) 0.0001 dB
(c) 8.686 dB
(d) -8.686 dB
(e) 0.0868 dB
Q11. A line has L=200nH/m and C=100pF/m. The phase velocity on the line is:
(a) 223 x 106 m/s
(b) 3 x 108 m/s
(c) 2 x 108 m/s
(d) 223 x 108 m/s
(e) 4 x 108 m/s
Q12. A line has L=250nH/m and C=100pF/m. The phase coefficient for the line at 100MHz is:
(a) p radians/m
(b) 3 radians/m
(c) 1.5 radians/m
(d) 90o/m
(e) 360o/m
Q13. A low loss 75W line has a resistance of 0.1 W/m. The loss over 10 metres of line is:
(a) 6.7 x 10-3
(b) 0.1 dB
(c) 1dB
(d) 0.058 dB
(e) 0.01 dB
Q14. A transmission line is:
(a) A co-axial cable
(b) An optical fibre
(c) Any structure that transfers a signal from one point to another
(d) A two conductor structure
(e) A metal waveguide
Q15. A 50W line is terminated in a 48W load. The reflection coefficient is:
(a) +0.02
(b) 0
(c) 1.98
(d) -0.9
(e) -0.02
Q16. A 50W line is terminated in a 75W load. The reflection coefficient is:
(a) 1.8
(b) -0.2
(c) +0.2
(d) +5
(e) 0.67
Q17. A 5 volt DC voltage source with internal resistance 10W is connected to a 75W line at t=0. The delay over the line from source to load is 20nS. The line is terminated with a resistance of 10W. What is the voltage at the source at t=20nS?
(a) 4.4 volts
(b) 0.67 volts
(c) 2.5 volts
(d) 1.03 volts
(e) 5 volts
Q18. A transmission line has a characteristic impedance of 75W and introduces a delay of 5 ns/m. The inductance and capacitance per metre are:
(a) 250nH/m, 44pF/m
(b) 375nH/m, 150pF/m
(c) 375nH/m, 67pF/m
(d) 250nH/m, 100pF/m
(e) 100nH/m, 250pF/m
Q19. A 75W transmission line introduces a loss of 0.1dB/m. The resistance per loop metre is:
(a) 0.012 W
(b) 1.73 W
(c) 0.12 W
(d) 75 W
(e) 150 W
Q20. A load has a return loss of 20dB when connected to a 75W line. The VSWR is:
(a) 1.22
(b) 0.82
(c) 0.01
(d) 10
(e) 100
Q21. A load has a quoted return loss of 10dB. If power delivered to the load is 1 Watt, the reflected power is:
(a) 0.1W
(b) 10W
(c) 0.9W
(d) 0.3W
(e) 1W
Q22. A load has a quoted return loss of 7dB. If the power delivered to the load is 10Watts, the reflected power is:
(a) 2W
(b) 2.5W
(c) 0.5W
(d) 0.4W
(e) 3W
时间: 2005-3-14 09:48
作者: sinca
Modulation Quiz
Q1. The baseband bandwidth of music for a broadcast FM signal is 15kHz, the deviation ratio is 5. The RF bandwidth is:
(a) 75kHz
(b) 150kHz
(c) 35kHz
(d) 180kHz
Q2. The information capacity of a channel is given by:
(a) bits/sec
(b) bits/sec
(c) dB
(d) dB
Q3. The theoretical maximum spectral efficiency of a simple binary transmission is:
(a) 1 bit/sec/Hz
(b) 1 bit/Hz
(c) 2 bits/sec/Hz
(d) 1 bit/sec/Hz
Q4. A PAM scheme employs 8 amplitude levels, the spectral efficiency is:
(a) 3 bits/sec
(b) 6 bits/sec/Hz
(c) 6 bits/Hz
(d) 3 bits/sec/Hz
Q5. A PCM scheme for hi fidelity audio with baseband bandwidth 20kHz employs a 16 bit code for each transmitted sample, the spectral efficiency of the scheme is
(a) 2 bits/sec/Hz
(b) 20k bits/sec/Hz
(c) 320 kbits/sec
(d) 640 kbits/sec/Hz
Q6. A PCM scheme for hi fidelity audio with baseband bandwidth 20kHz employs a 16 bit code for each transmitted sample, the minimum transmission bandwidth required is:
(a) 20kHz
(b) 40kHz
(c) 320kHz
(d) 640kHz
Q7. The data rate for the PCM scheme of Q 6 is:
(a) 640kbits/sec
(b) 320kbits/sec
(c) 640kbits/sec/Hz
(d) 40kbits/sec
Q8. A modulation system has Eb/No = 10dB with a signal to noise ratio of 13dB. The spectral efficiency is:
(a) 2 bits/sec
(b) 2 bits/sec/Hz
(c) 0.5 bits/sec
(d) 0.5 bits/sec/Hz
Q9. Pulse shaping is employed in digital transmission to:
(a) Minimise ISI
(b) Maximise signal speed
(c) Prevent inter-modulation
(d) Remove sharp edges
Q10. The peak frequency deviation for an FM system with a 1 MHz sinusoidal modulation is 100kHz. The peak phase deviation is:
(a) 0.1 radian
(b) 0.1o
(c) 10 radians
(d) 10o
Q11. An analogue telephone speech signal is to be used to modulate a carrier for transmission over a channel. The required channel bandwidth for:
(a) AM is 3.4kHz
(b) FM with peak frequency deviation 8.5 kHz is 20.4kHz
(c) 8 bit QPSK is 32kHz
(d) Conversion to 32kbit/sec ADPCM and then MSK is 32kHz.
Q12. A broadcast FM high fidelity audio signal is transmitted at 88.1MHz with a deviation ratio of 5. The required transmission bandwidth is:
(a) 200kHz
(b) 150kHz
(c) 88.1MHz
(d) 180kHz
Q14. MSK is:
(a) equivalent to QPSK
(b) binary FSK with the minimum distance between the two transmission frequencies
(c) FSK with Gaussian pulse shaping
(d) PSK with Gaussian pulse shaping
Q15. AM is
(a) An efficient modulation scheme in power terms.
(b) Very wasteful in power terms but easy to demodulate
(c) Inefficient and difficult to demodulate
(d) Spectrally inefficient but easy to demodulate
Q16. The signal spectrum for a 2Mbits/sec QPSK signal is:
(a) (b)
(c) (d)
Q17. The spectral efficiency of n-level PAM is:
(a) n bits/sec
(b) 2n bits/sec/Hz
(c) n bits/sec/Hz
(d) 2n bits/Hz
Q18. A 2kbits/sec digital signal is transmitted using PRK, the spectrum is:
(a) (b)
(b) (d)
Q19. A 2Mbits/sec binary FSK signal with peak deviation = 10MHz has a spectrum:
(a) (b)
(b) (d)
Q20. A channel has a bandwidth of 1MHz. The signal to noise ratio required to allow error free communication at an information rate of 2 MBits/sec is:
(a) 2
(b) 3dB
(c) 4.8dB
(d) 2dB
Q21. FM is:
(a) a linear modulation scheme
(b) a non-linear modulation scheme
(c) wasteful of signal power
(d) spectrally efficient
Q22. AM is:
(a) a linear modulation scheme
(b) a non-linear modulation scheme
(c) spectrally inefficient
(d) power efficient
Q23. The peak frequency deviation for an MSK system with data rate 56kbits/sec is:
(a) 56kHz
(b) 28kHz
(c) 224Hz
(d) 14kHz
Q24. The Signal to noise ratio for a certain system is 10dB. The maximum information rate over the channel for error free communications is found to be 1Mbit/sec. the transmission bandwidth is:
(a) 289kHz
(b) 1MHz
(c) 0.5MHz
(d) 2MHz
Q25. OOK is:
(a) More power efficient than AM
(b) Less power efficient than AM
(c) The same as AM
(d) More spectrally efficient than AM
