4. SITING LOSSES

Television reception using indoor antennas will be
affected by all normal propagation phenomena plus building
attenuation. Limited building attenuation data are
available. An excellent review of pertinent literature
prior to 1975 is given by Wells, et al., (1975). Wells and
Tryon (1976) report 6.3 dB average attenuation measured in
single family homes at 860 MHz using ATS-6 as the source of
site illumination. Snider (1965) reported median losses of
5.5 dB at 180 MHz and 7.8 dB at 750 MHz in buildings on the
University of Colorado and Colorado School of Mines
campuses. An average value of 6.6 dB building attenuation
for VHF/UHF television is probably a good assumption based
upon the cited data. This loss is offset somewhat by the
loss in the transmission line to an outside antenna. These
losses average 0.3 dB at the low end of the VHF band to
1.1 4B in the UHF band for 10 m of new, dry transmission
line according to Swinyard (1960). The net loss caused by
indoor antenna siting rather than outdoor siting is about
6.3 dB at VHF and 5.5 dB at UHF.

The field strength at the indoor antenna may be less
than that at an outdoor antenna because of the antenna
height over ground. Typically an outdoor antenna may be 6m
to 12 m above ground while the indoor antenna may be 2 m to
6 m above ground depending upon the height of the building
and antenna location.

To obtain realistic field strengths as a function of
antenna height, the Institute for Telecommunication
Sciences, Radio Propagation Over Irregular Terrain, Version
5.00 (9/8/77), computer program was used to calculate field
strengths at 70 MHz and 700 MHz for randomly sited receiving
antennas 10 km to 50 km from a 7.85 dB gain transmitting
antenna, 450 m above average terrain, with an input power of
100 kW. Three different terrain roughness factors, AH, were
used to indicate rolling plains, AH = 40 m; hills,

AH = 80 m; and mountains, AH = 160 m. Other propagation
parameters were chosen to match those of the Aurora,
Colorado area where AH happens to be 83 m. These calculated
data are presented in Table 2, where the field strengths are
expressed in decibels relative to l microvolt per meter, or
dBu.

14


ure 4. (a) Reference dipole gain pattern normalized to the

-15 dB plot level (5 dB per amplitude increment)

measured at 653 MHz. Reference level is circled.

(b) Double bow-tie array gain pattern measured at 653 MHz.
8


From these power budget data it is apparent that
adequate indoor antenna gain is available to make signal
levels delivered to the television receiver comparable at
VHF and UHF for the particular conditions assumed in these
power budget equations.

Outdoor antenna power budget data for 9 m antenna
heights are at least 13.1 dB greater than corresponding
indoor data. A significant factor in the difference is the
6.6 GB building attenuation. To overcome 6 dB of this
attenuation, the size of the double bow-tie array would have
to be doubled in width and height. That is, an eight
element bow-tie array in front of a 65 cm square reflector
might have a gain of 14.4 dB versus 8.4 dB for the double
bow-tie array.

6. REFERENCES

Cottony, H.V. (1958), Techniques for accurate measurement of
antenna gain, NBS Circular 598, December.

FitzGerrell, R.G. (1967), The gain of a horizontal half-wave
dipole over ground, IEEE Trans. Ant. and Prop., 15, No.
4, July, pp. 569-571.

FitzGerrell, R.G., R.D. Jennings, J.R. Juroshek (1979),
Television receiving antenna system component
measurements, NTIA Report 79-22, June.

Snider, J.B. (1965), A statistical approach to measurement
of RF attenuation by building materials, NBS Report
8863, July.

Swinyard, W.O. (1960), VHF and UHF television receiving
equipment, Proc. IRE, 48, No.6, June, pp. 1066-1080.

Wells, P.I., D.A. Hill, A.G. Longley, R.G. FitzGerrell,
L.L. Haidle, and D.V. Glen (1975), An equipment design
for the measurement of building attenuation.
Unpublished technical memorandum.

Wells, P.I., and P.V. Tryon (1976), The attenuation of UHF
radio signals by houses, OT Report 76-98, August.

18


Table l.
Table 2.

Table 3.

LIST OF TABLES

PAGE
VSWR vs. Mismatch Loss 2
Field strength, dBu 15
Calculated Power Flow Values for the 16

50 km path with AH = 80 m in Table 2.


Also presented in Table 2 are the field strength
differences between the 2 m and 9 m receiving antenna
heights at 70 MHz, A or and at 700 MHz, 470 - The overall
average of A 0 is 6.4 dB with a range of baty 2.2 dB. The
overall average of 4700 is 5.2 dB with a range of 10.9 dB.

The relative loss incurred by siting a VHF antenna
indoors at a 2 m height rather than outdoors at a 9 m height
is about 12.7 dB as a result of a net loss of 6.3 dB for
building attenuation and 6.4 dB for the decrease in field
strength with height. This relative loss is 10.7 dB at UHF
as a result of a net loss of 5.5 dB for building attenuation
and 5.2 dB for the decrease in field strength with height.

TABLE 2. Field Strength (FS), dBu,

For AH = 80m

Receive Antenna Receive Antenna A769 4700
Height = 2m height = 9m aB
Distance Frequency, MHz Frequency, MHz FS @ 9m FS @ 9m
km 70 700 70 700 -FS @ 2m -FS @ 2m
10 99.9 102.7 106.1 102.7 6.2 0.0
20 88.4 96.5 95.6 96.5 7.2 0.0
30 80.5 92.9 88.0 92.9 7.5 0.0
40 74.2 90.3 81.5 90.4 7.3 0.1
50 68.7 82.8 75.8 87.1 7.1 4.3

For AH = 80m

10 97.4 102.4 102.7 102.4 5.3 0.0
20 86.9 96.3 92.5 96.3 5.6 0.0
30 79.4 91.9 85.2 92.7 5.8 0.8
40 73.1 84.2 79.0 90.2 5.9 6.0
50 67.6 77.1 73.5 83.2 5.9 6.1

For AH = 160m

10 94.2 97.9 98.2 102.2 5.8 4.3
20 82.4 87.3 88.5 96.1 6.1 8.8
30 75.2 79.2 81.5 90.1 6.3 10.9
40 69.1 72.1 75.5 82.8 6.4 10.7
50 63.6 65.7 70.2 76.1 6.6 10.4

15




POWER BUDGET

Indoor Antennas, 2m Above Ground

Frequency, MHz 70 700

Power Flow, 2

aB rel to 1W/m - 72.7 - 61.6
Antenna Constant,

dB + 3.8 - 16.2
Range of measured

gain from Fig 5,

dB - 4.8, -2.5 - 5.0, + 8.4
Building

attenuation, dB - 6.6 - 6.6
Transmission line

loss, dB 0 0
Range of

Power received, dBW - 80.3, -78.0 89.4, -76.0
Outdoor Antennas, 9m Above Ground

Frequency, MHz 70 700

Power flow, 2

dB rel to 1 W/m - 66.8 - 55.6
Antenna constant,

dB + 3.8 - 16.2
Measured gain

from Fig 5, dB + 3.6 + 10.0
Building

attenuation, dB 0 0 ‘
Transmission

line loss dB - 0.3 - 1.1
Power received, dBW - 59.7 - 62.9

17


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Measured length and loss data versus frequency for an
extensible reference dipole is shown in Figure 2. A minimum
VSWR is obtained at 177 MHz with a length of 81 cm. This
reference dipole is attached to the out-of-phase ports of a
hybrid junction with two equal length, 50 ohm, coaxial
cables. Measured insertion loss of the hybrid junction used
as a balanced-to-unbalanced line transformer, or balun, is
0.74 dB. Measured mismatch loss of the antenna at the balun
input port is 0.18 dB caused by a VSWR of 1.5 giving a total
correction due to losses of 0.92 dB to add to the dipole
gain, yielding an actual tuned dipole gain of 0 dB. In the
actual data processing, this correction is subtracted from
measured test antenna gain because a relative gain
measurement technique is employed. This correction is
important because a lossless half-wave dipole is the
standard of reference and uncorrected losses will make the
relative gain of the antenna being tested greater by an
amount equal to the correction factor.

All but one of the indoor antennas measured for this
report had balanced transmission line terminals, thus
requiring the use of a commercial television balun to
connect them to the receiving system. Corrections to the
test antenna gain data were made for losses in this balun as
was the case for the reference dipole. Balun insertion loss
and mismatch loss, with a 300 ohm resistor between the
balanced line terminals, were measured using a 75 ohm
bridge. The sum of these losses is plotted versus frequency
in Figure 3. Insertion loss predominates and increases with
frequency to relative maximums of 0.9 dB at 195 MHz and 2 dB
at 750 MHz; it decreases to 1.2 dB at 900 MHz. Mismatch
loss increases uniformly with frequency to 0.45 dB at
900 MHz; it is less than 0.1 dB below 650 MHz.

The calculated data in Figure 1 show that a 1.3 wave-
length dipole (88 cm at 450 MHz) may have 3 dB more
directivity than a tuned half-wave dipole. Therefore, a
dipole type of television antenna may have a gain of 3 dB if
some method of reducing mismatch loss is used in its design.
For single element antennas the shape and length are changed
from those of a linear half-wave dipole to those of a loop,
which is a circular folded dipole, and those of a bow-tie,
which is a triangular dipole. Various arrays of simple
antenna elements are used to obtain antenna gains greater
than 3 dB.


Indoor Television Antenna Performance
R.G. FitzGerrell*

The ability of a television receiving antenna to
deliver adequate signal power to the terminals of its
receiver is determined by its gain relative to a lossless
half-wave dipole antenna. This report presents measured
gain data for indoor television receiving antennas in the
VHF and UHF bands and discusses the effects of building
attenuation and height gain on a power budget used to
compare antenna performance.

1. INTRODUCTION

Antenna performance is generally characterized by
antenna gain and input voltage standing-wave ratio, VSWR.
Gain is a measure of both the directional properties of the
antenna radiation pattern, called directivity, and the
radiation efficiency. This efficiency is a measure of
dissipative losses in the antenna elements, which are
negligible for antennas fabricated with good dielectrics and
conductors with dimensions on the order of one-eighth
wavelength or larger. A result of television receiving
antenna dimensions being on the order of one-half wavelength
or larger is that their gain is basically due to
directivity.

When antenna gain is measured relative to that of a
tuned half-wave dipole antenna, mismatch loss becomes part
of the measured gain. The term "tuned" implies that these
losses are essentially eliminated from the reference dipole
by adjusting its dimensions to obtain an input impedance
providing a conjugate match to that of the transmission line
to the test system receiver. This receiver is assumed to be
perfectly matched to the transmission line. Conventional
television receiving antennas are not tuned at all channel
frequencies, and the resulting decrease in antenna gain
caused by mismatch loss is minimized by the antenna design

*The author is with the U.S. Department of Commerce,
National Telecommunications and Information Administration,
Institute for Telecommunication Sciences, Boulder, CO 80303.





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Tuned 'Y. Dipole Gain

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S
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50 700 200 400 600-600 1000
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Figure l. Gain, directivity, and mismatch loss

for a dipole 84 cm long, 1 cm diameter

connected to a 100 ohm balanced
transmission line.


FORM OT-29
(3-73)

BIBLIOGRAPHIC DATA SHEET

U.S. DEPARTMENT OF COMMERCE
OFFICE OF TELECOMMUNICATIONS

1. PUBLICATION OR REPORT NO.
NTIA Report 79-28

2. Gov't Accession No.

3. Recipient's Accession No,

4, TITLE AND SUBTITLE

Indoor Television Antenna Performance

5, Publication Date

October 1979

6. Performing Organization Code

ITS/NTIA

7. AUTHOR(S)
R.G. FitzGerrell

8. PERFORMING ORGANIZATION NAME AND ADDRESS
U.S.Department of Commerce

Institute for Telecommunication Sciences
National Telecommunication & Information Admin,
325 Broadway, Boulder, Colorado 80303

9 Project/Task/Work Unit No.

9104386

10, Contract/Grant No.

11. Sponsoring Organization Name and Address

Federal Communications Commission

12. Type of Report and Period Covered

14. SUPPLEMENTARY NOTES.

15, ABSTRACT (A 200-word or less factual summary of most significant information. If document includes a significant

bibliography ot literature survey, mention it here. )

The ability of a television receiving antenna to deliver
adequate signal power to the terminals of its receiver is
measured by its gain relative to that of a lossless half-wave

dipole antenna. This report presents measured

gain data for

indoor television receiving antennas in the VHF and UHF bands
and discusses the effects of building attenuation and height

gain on a power budget used to compare antenna

performance.

16. Key Words (Alphabetical order, separated by semicolons)

17. AVAILABILITY STATEMENT

#34} UNLIMITED.

18. Security Class (This report)

Unclassified

20, Number of pages

18

(J) FOR OFFICIAL DISTRIBUTION.

19. Security Class (This page)

Unclassified

21, Price:

W U.S, GOVERNMENT PRINTING OFFICE 1979-0-682-173/163

USCOMM-DC 29716-P73



NTIA-REPORT-79-28

Indoor Television Antenna Performance

R.G. FitzGerrell

U.S. DEPARTMENT OF COMMERCE
Juanita M. Kreps, Secretary

Henry Geller, Assistant Secretary
for Communications and Information

October 1979



Mismatch Loss + Balun Insertion Loss, dB

Figure 3.

24

2.2

2.0-

0.6,-

oa

0.2

poi t 1 a es ee ee

50

400 200 400 600 800-1000
Frequency, MHz

Measured test antenna balun mismatch
loss plus insertion loss.



2807-77 | T T ee en ee

260

240 2

220+ length

Dipole Length, cm

Mean Mismatch Loss + Balun Insertion Loss, dB

0 1 oj J 4 | 1 1 1 i {oj 1 i Jo
50 100 200 400 600 800 1000

Frequency, MHz

Figure 2. Measured reference half-wave dipole
length and mismatch loss plus balun
loss.


as much as possible. The optimum design has minimum
mismatch loss and maximum directivity over the frequency
band of interest.

Unless a frequency independent antenna design is
employed, such as a log-periodic dipole array, television
receiving antenna gain usually peaks near the middle of the
frequency bands of interest. At this peak, the directivity
and mismatch are nearly optimum. Below this peak, the
antenna becomes electrically smaller, the directivity
approaches that of a dipole, and mismatch losses tend to
increase. Above this peak, the antenna becomes electrically
larger, the main beam of the radiation pattern may become
multilobed, and mismatch loss may increase.

Antenna VSWR is generally used in performance specifi-
cations rather than mismatch loss because it is an easily
measured scalar quantity. The VSWR is related to mismatch
loss by the following equation:

2
Mismatch Loss (dB) = 10 logyg {1- (yan)

when the antenna is attached to a receiver with an input
VSWR = 1. Table 1 relates a range of mismatch loss and VSWR.

TABLE 1. VSWR vs. Mismatch Loss

VSWR Mismatch Loss dB

The directivity and mismatch loss can be calculated for
a linear dipole antenna in free space (FitzGerrell, 1967).
The sum of these quantities is antenna gain and, as used in
this report, is relative to that of a lossless half-wave
dipole. Data plotted in Figure 1 illustrate the relation
between these quantities versus frequency for a dipole one-
half wavelength long at 177 MHz, the middle of Channel 7,
with a l cm diameter. The data show that a gain of 0 dB at
177 MHz could be realized by tuning the dipole to the
100 ohm balanced transmssion line assumed in these
calculations. A lossless tuning device would be required to

eliminate the 0.4 dB mismatch loss resulting from a VSWR of
1.8 at 177 MHz.


5.

DISCUSSION AND CONCLUSIONS

Power budget equations relating the power flow in the
plane-wave field incident on an antenna to the power
available at the receiver terminals are useful for comparing
antenna system performance at different frequencies. The
only component of power budget equations for simple antenna,
transmission line, receiver systems not discussed so far is
the antenna constant which is equal to the ratio of power
available at the terminals of a properly oriented half-wave
dipole antenna to the power flow per unit area in the
incident field (FitzGerrell, et al., 1979). 2
constants at 70 MHz and 700 MHz for a power flow of 1 W/m

at the antenna are +3.8 dB and -16.2 dB.

The antenna

The calculated

field strengths at the receiving antenna for a middle value
path in Table 2, AH = 80 m and distance = 40 km, are

converted to power flow relative to 1 W/m
that, for this path, 49
are close to the average values.

TABLE 3.

= 5.9 dB and 4500 =

in Table 3. Note
6.0 dB which

Calculated Power Flow Values for the
40 km Path With AH = 80 m in Table 2.

Antenna Height, Frequency Field Strength, Power Flow, 2
m MHZ dBu dB rel to 1W/m
2 70 73.1 - 72.7
9 70 79.0 - 66.8
2 700 84.2 - 61.6
9 700 90.2 - 55.6

Power budget equations for power at the receiver

terminals in dB relative to 1 W, dBW,

using the power flow data from Table 3.

16

can now be written





Figure l.

Figure 2.

Figure 3.

Figure 4.

Figure 5.

Figure 6(a).

Figure 6(b).

LIST OF FIGURES

Gain, directivity, and mismatch loss
for a dipole 84 cm long, 1 cm diameter
connected to a 100 ohm balanced
transmission line.

Measured reference half-wave dipole
length and mismatch loss plus balun
loss.

Measured test antenna balun mismatch
loss plus insertion loss.

(a) Reference dipole gain pattern
normalized to the -15 dB plot level

(5 dB per amplitude increment)
measured at 653 MHz. Reference level
is circled. (b) Double bow-tie array
gain pattern measured at 653 MHz.

Measured gain versus frequency of the
eight antennas.

Measured VHF antenna VSWR for the VHF/UHF
indoor antenna, solid line, and the
rabbit ears, dashed line. Note the solid
line is the minimum VSWR envelope for
twelve tuning switch positions.

Measured UHF antenna VSWR. The VHF/UHF

indoor antenna was measured for three
different coupling loop orientations.

iv

PAGE

11

12

13


3. INDOOR ANTENNAS AND MEASURED GAIN

Six indoor antennas purchased for this gain measurement
effort are listed below.

A.

A conventional VHF extensible "rabbit ears"
antenna measured with both elements fully extended
to their 110 cm length and oriented in the
vertical plane 45 deg above horizontal.

A VHF/UHF indoor antenna consisting of extensible
VHF "rabbit ears", with a VHF 12 position tuning
switch, combined with a UHF loop and rotatable
coupling loop. The VHF elements were fully
extended to their 115 cm length and oriented in
the vertical plane 45 deg above horizontal. The
tuning switch was adjusted for maximum received
signal level, corresponding to minimum mismatch
loss, at each test frequency. The UHF gain was
measured with the VHF elements at their shortest
length. The UHF pattern changed somewhat with
rotation of the coupling loop, but the gain
remained essentially constant.

A monopole antenna consisting of a portable
television replacement rod assembly mounted on a
wire grid model of a receiver. This element was
extended 44 cm and oriented 45 deg above
horizontal. This length minimized mismatch loss
over the UHF band.

An original equipment UHF loop, with a 17.5 cm
diameter, supplied with portable television
receivers.

An original equipment clip-on UHF bow-tie dipole
33.5 cm long.

A bow-tie array consisting of two UHF bow-tie
dipoles arrayed vertically 21.5 cm apart and 5 cm
in front of a 32 cm square reflector grid.

A combination VHF/UHF antenna for use as a secondary
reference antenna for field measurements was fabricated
using a 4-bay UHF bow-tie array and a modified, VHF, log-
periodic dipole array. The UHF array has a 42 cm by 91 cm
reflector and the VHF array has a 160 cm boom length. A
61 cm spacing between these antennas results in a modest

sized,

lightweight antenna, on a single supporting mast.



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Figure 5. Measured gain versus frequency of the

eight antennas.

11


TABLE

LIST OF FIGURES.......

LIST OF TABLES...

ABSTRACT. cece eccccece

INTRODUCTION......

OF CONTENTS

THE GAIN MEASUREMENT TECHNIQUE.....

INDOOR ANTENNAS AND MEASURED GAIN..

SITING LOSSES... .eeeeeececccceveeee

DISCUSSION AND CONCLUSIONS.........

REFERENCES. ce ecscccccccccesccceeeees

iii

PAGE

iv

14
16

18






2. THE GAIN MEASUREMENT TECHNIQUE

The Table Mountain antenna test range consists of a
large turntable, flush with test range ground, illuminated
by a VHF/UHF television antenna erected 6 m above ground
about 700 m away. A frequency synthesized signal generator
provides a CW signal to the illuminating antenna. A refer-
ence dipole antenna is placed on a tripod, centered on the
turntable, at heights on the order of 2 m to 4 manda
reference signal level is measured. This level is entered
in the receiving system computer and a radiation pattern is
measured to check for proper dipole pattern and for maximum
gain at the -15 dB plot amplitude - a result of a computer
normalization based on the reference signal level. The
reference dipole is replaced by a test antenna and another
radiation pattern is produced with receiving system gain
levels unchanged. The gain of the test antenna relative to
that of a lossless half-wave dipole at the same height is
the decibel level on the plot above (+) or below (-) the
reference level minus the dipole loss correction from
Figure 2 plus the balun loss correction from Figure 3.
Note, the balun is not used for the UHF monopole or the
secondary reference antennas discussed later.

According to Cottony (1958), the resulting gain is
numerically equal to free-space gain if the test antenna
radiation pattern is symmetrical in the vertical plane, the
plane of symmetry passes through the base of the illumina-
ting antenna, and the terrain at the test site is smooth and
flat. It is assumed that these conditions prevail at the
Table Mountain test site and that the accuracy of the main
beam gain data presented in this report are on the order of
+ 0.5 dB.

Figure 4a is a plot of the reference dipole radiation
pattern and 4b is a plot of the gain pattern, relative to
that of the dipole maximum gain, for a double bow-tie
antenna at 653 MHz. For this particular example, the
relative gain is 7.1 dB, the reference dipole correction is
-0.88 dB, and the balun correction is +1.72 dB, thus giving
a gain relative to a lossless half-wave dipole of 7.9 dB.


The antennas are electrically connected to a single 50-ohm
coaxial cable with a VHF/UHF splitter and balun combined in
a small weatherproof box. Gain of the outdoor antenna
provides a useful comparison for judging the gains of the
indoor antennas.

Figure 5 is a plot of measured antenna gains versus
frequency and Figures 6a and 6b are plots of measured
antenna VSWR versus frequency. As discussed in Part l,
mismatch loss caused by VSWR values greater than unity are
an intrinsic part of gain as defined in this report.

Indoor VHF antennas with a 90 deg angle between the
elements in the vertical plane are quandrant antennas. The
antennas have gain for both vertically and horizontally
polarized field components thus reducing their gain below
that expected of a purely horizontally polarized dipole.
The VHF tuning on the VHF/UHF indoor antenna does reduce
mismatch loss by improving the VSWR as shown in Figure 6.
The gain of the indoor VHF antennas is 4 dB to 10 dB below
that of the combination VHF/UHF outdoor antenna.

The UHF monopole and UHF portion of the VHF/UHF indoor
antenna have similar gains 2 dB to 20 dB below that of the
combination VHF/UHF outdoor antenna. Loop antenna gain
appears to have been sacrificed for the ability to steer the
ill-defined radiation pattern of the VHF/UHF indoor antenna.
Low monopole gain is also due to an ill-defined radiation
pattern and the fact that this antenna should have a
substantial amount of gain for verticaly polarized field
components.

The indoor UHF loop and clip-on bow-tie have similar
gains over a relatively broad frequency band for such simple
antennas. Their maximum gains are comparable with that of
the maximum dipole directivity shown in Figure l.

The double bow-tie indoor UHF antenna has a maximum
gain 6 dB greater than that of the single bow-tie antenna,
which is exactly the value simple array theory would predict
if the reflector grid behind the dipoles was very large. An
infinitely large reflector places all of the radiation
pattern into one hemisphere, thus resulting in a 3 dB
increase in directivity. Doubling the number of elements
also doubles the directivity, approximately, giving another
3 dB increase. The same reasoning should result in a 4-bay
bow-tie antenna gain 3 dB greater than that of the double
bow-tie array. Measurements indicate 1.6 dB greater gain
because the balun and splitter, which are an integral part
of the outdoor VHF/UHF combination antenna, have an
insertion loss on the order of 1.5 dB.

10