1. Jacob M. Ramey EGRE 307: Integrated Circuits 5/6/2015
Final Lab – Individual Report
Jacob M. Ramey
EGRE 307 – Integrated Circuits
Electrical Engineering
Virginia Commonwealth University
Abstract and Theory- This lab report details
the design of the Antenna and Impedance
matching network and how important the
antenna design was to the overall function of
a communications system
The design of an Antenna for the purpose of
sending a sound wave (music) over the air and
receiving it on the other end to be played. There
are two main elements of the communications
system - each containing several important
parts that make up the Transmitter and the
Receiver. Inside each of these are filters,
amplifiers, modulators, buffers, and impedance
matching networks. Even if all these parts are
working flawlessly without a good antenna
design the signal will have too much
attenuation to propagate notable distances.
Antenna's are essentially just stubs that are
(normally) comparable to the electrical length
of the frequency which they are designed to
emit the most power at. For this labs design
specification, the frequency of transmission is
from 600k-620kHz. This corresponds to a
wavelength given by
𝑐 = 𝑓𝜆
𝜆 =
3 ∗ 108
[600𝑘: 620𝑘]
= [483.87: 500] (𝑚)
The wavelength of the signal is very important
because it determines the length that the
antenna needs to be.
Though an electrically short antenna may be
used and can be very effective, a very well
made impedance matching network is
necessary and it also needs to work over a wide
band. This is a limitation when working with L-
network matching because these are normally
made to work around a single frequency and
not a range of frequency. Because of this, there
is distortion in the signal because different
frequencies will attenuate at different rates.
The antenna design most familiar for my
group and I is the Quarter Wave Transformer
(QWT). The radiation spectrum gives by a QRT
is given by Figure 1
Figure 1: Grounding plane increases directivity of the
antenna.
As the name implies, it requires an electrical
length equal to a quarter of the wavelength, in
our case this corresponds to 410.1 ft of wire.
This is enormous for an antenna that needs to
be used inside at small distances. The solution
to this problem was using a concept called a
'loading coil'.
The idea of a loading coil came from the
early telecommunications field when engineers
needed to send signals a larger distance.

2. Jacob M. Ramey EGRE 307: Integrated Circuits 5/6/2015
The wire is wrapped around a core instead of
going straight up into the air - this allows us to
make an antenna that requires a length of 410ft
in a physical height of the solenoid of around
3ft. The wrapping of the wires enable us to
keep the size of the antenna down and also
contribute to the inductive effect of the wire
being wrapped around the solenoid core. This is
a good thing for us because naturally the wire
of such a length will have a capacitance that
negatively impacts the performance of the
antenna by lessening the power it would
receive. Such lost power would be absorbed by
the antenna and sent back towards to generator.
The last thing we want is to lose power that
would otherwise be used to send out signal at a
further distance with less distance at the final
output. Amplification of a weak signal works
but also it amplifies the noise of the signal as
well.
The inductive effect of the wrapping of the
wires can be found by integrating Amperes law
over a cylinder[1]. The resulting equation is a
function of the radius of the solenoid, the
length, and the number of turns. It is given by
With this effect accounted for and the length
of the wire being a quarter wavelength
electrically, the matching of the network would
be as simple as putting a capacitor in parallel
with the antenna that matches its impedance
with the input to deliver the maximum power to
the load. This value was calculated and in order
to account for the error in our build and
calculations, we used a variable capacitor in
parallel that was within the range of the value
we needed. The matching of the network
worked well and after adding the capacitor we
increased around range for receiving the signal
from ~1ft to ~12ft.
The only problem was that the antenna emitted
the greatest power at a frequency other than the
one we had designed it for. The solution for this
was a processed dubbed 'wire tapping'.
Instead of connecting the source to the
antenna at the base, several other points on the
antenna were attached to the source and tested.
Placing the source at one point gave a different
response than the other in terms of frequency
and amplitude. After testing many places on the
antenna line we found the best place to emit our
frequency and the amplitude of the signal was
also much larger than the first location. This
difference was 1 order of magnitude and gave
us a much clearer signal on the other side since
we did not have to amplify it as much.
Conclusion:
The use of the QWT proved to be effective at
transmitting a signal at our design frequency
enough to have it heard audibly from the other
side of the room after demodulation. The most
difficult part of designing the antenna was the
impedance matching part because I had little
experience with it until later in the semester in
EGRE 310: Microwave and Photonics
Engineering. After working with my team,
other classmates, and the TA I found a much
easier was to accomplish this.
References:
[1] Fitzpatrick, R. (2006) Self-Inductance [Online]
Available http://farside.ph.utexas.edu
/teaching//lectures/node82.html
[2] Weaver, R. (2009) Radio Theory [Online] Available
http://electronbunker.ca
/Radio_Theory.html
[3] Pozar, D. Impedance Matching and Tuning in
Microwave Engineering 2nd ed. New York: John Wiley
and Sons,1998