The Low Profile ATSC 8VSB DTV Fractal Antenna


Abstract

Without low profile fractal antennas reliable reception of ATSC 8VSB DTV (and Widescreen HDTV) will not be possible in metropolitan areas for substantial segments of the population in North America. A substantial percentage of 8VSB fadeout events are generally catastrophic and random. Most 8VSB set top box decoders only have 2nd generation adaptive reception chipsets. Even the most up to date 3rd and 4th generation 8VSB adaptive reception chipsets often do not perform in the real world as optimally as their designers originally hoped for.

NTSC, PAL or SECAM fadeout events have long run temporal variations that make them tolerable (or at least interesting) to the viewer. However, the HDTV viewer is left only with frustration as most decoders uniformly fail to tell the viewer that the received signal is unhealthy before a link loss event. Essentially, fractal antennas are the only way to save 8VSB HDTV reception at the lowest possible cost.

If the antennas are designed properly, the need for antenna amplifiers (for a large number of users) will be mitigated.

Why the current arrangement is not working
The 8VSB waveform is a "single carrier waveform" that is systemically subject to the vagaries of Single Side Band (SSB) fading. SSB is the analog waveform it is most closely related to 8VSB. SSB is used by PAL, SECAM and NTSC -- the three existing TV broadcasting systems that have been around for some 50 years.

Options that need to be considered
Why these options need to be considered
Recovering a clock signal in order to decode a received waveform has always been a tricky proposition in digital RF communications. If we derive the receiver clock from the recovered data, we have a sort of "chicken and egg" dilemma. The data must be sampled by the receiver clock in order to be accurately recovered. The receiver clock itself must be generated from accurately recovered data. The resulting clocking system quickly "crashes" when the noise or interference level rises to a point that significant data errors are received.

When NTSC (and PAL) were invented, the need was recognized to have a powerful sync pulse that rose above the rest of the RF modulation envelope. In this way, the receiver synchronization circuits could still "home in" on the sync pulses and maintain the correct picture framing -- even if the contents of the picture were a bit snowy. NTSC (and PAL) also benefited from a large residual visual carrier (caused by the DC component of the modulating video). This residual carrier helped TV receiver tuners zero in on the transmitted carrier center frequency.

The 8VSB transmission system employs a similar strategy of sync pulses and residual carriers that allows the receiver to "lock" onto the incoming signal and begin decoding, even in the presence of heavy ghosting and high noise levels. The first "helper" signal is the ATSC pilot. Just before modulation, a small DC shift is applied to the 8VSB baseband signal (which was previously centered about zero volts with no DC component). This causes a small residual carrier to appear at the zero frequency point of the resulting modulated spectrum. This is the ATSC pilot. This gives the RF PLL circuits in the 8VSB receiver something to lock onto that is independent of the data being transmitted.

Although similar in nature, the ATSC pilot is much smaller than the NTSC visual carrier, consuming only 0.3 dB or 7 percent of the transmitted power. With NTSC, PAL and SECAM on average 50% of the transmitter power went into transmitting sync pulses.

For DVB-T and ISDB transmission technologies, there is no need to use a fractal antenna
DVB-T and ISDB are both multicarrier waveforms, thus there is no need to use a fractal antenna to receive them. Also, both have configurable error correction and configurable datarates that allow the bandwidth to be matched precisely to the content that needs to be transmitted -- in a way that is most error resilient.

Thus there is no need [at this point in time] for European Union (or more specifically European Broadcasting Union), ASEAN or Japanese (or Brazilian) consumers to get new TV antennas.

Ultimatly it is up to the consumer to use a better antenna
While most businesses (and more commonly home owners) can install Log Periodic "LP " antennas (typically in Horizontal polarization, in the Yagi-Uda family of antennas), many apartment dwellers as well as condo dwellers don't have access to mounting an outside antenna for legal or space reasons.

It must be noted that the LP antenna type itself a kind of lesser fractal, so one could in essence argue that fractal antennas have proven themselves in the television reception area for some 50 years.

A low profile antenna is needed that can fit inside people's flats that itself is not visible, but can provide link margins similar to the existing LP antennas used on people's rooftops. So another kind of fractal antenna must therefore be used. Any kind of fractal antenna would probably be better than the standard dipoles (and "rabbit ears" antennas for UHF) that are associated with current TV sets in North America.

Catastrophic 8VSB fading events are caused by the loss of "carrier lock" coupled with a loss of the inserted "DC" component (mandatory at 7%, by specification) causing a partial or total loss of the PLL lock on the datastream.

Fractal antennas needed here as no other workable solution is avalable
In order to compensate against the loss of "carrier lock" (and the DC component lock), your antenna must get bigger -- classical antenna theory for all practical purposes dictates this for single carrier wave reception.

A large antenna surface area (and an antenna that is multiply resonant) seems to be the only viable way to achieve reliable SSB or 8VSB reception. Fractal antennas (even some the smallest ones) have relatively large surface areas by default. Fractal antennas also can have the ability to intercept polarized electromagnetic waves in a superior manner to the dipoles that are in common use, at least when it comes to concentrating and channeling incoming electromagnetic energy.

Important design considerations drawn from fractal antenna research


Ideally this kind of fractal antenna should be mountable on a vertical Venetian track blind. A window blind is a window covering composed of long strips of fabric or rigid material. Examples include shutters, Venetian blinds, roller shades and curtain-like track blinds. A blind limits outside observation and thus “blinds” the observer to the view. The main types are slat blinds which can be opened in two ways and solid blinds.
Suggested structure ("Concatenated Horizontal H trees")
















each antenna replicated vertically equal 150 cm hight
each subunit being about 6 cm2
each antenna sub element minimum size should be 0.8 mm
each antenna sub element minimum size should be 1.6 mm
each antenna sub element increment step should be 0.2 mm













How fratal iteration affects behavior in the microwave range








Experimental setup needed to create fractal antennas for DTV reception, more than one kind of fractal should be used in these antennas.



Manufactured fractal antennas with target fractal dimension ~1.58 compared with the size of 10 euro cents. All antennas are assumed to be tapped at the bottom vertex or valley of the "V".

From Left to Right and by columns:

Delta-Wired Sierpinski monopoles (DWS); Y-Wired Sierpinski monopoles (YWS); Sierpinski Arrowhead monopoles (SA); and Koch-1 Sierpinski monopoles (K1S).

Note: Each step down each column is the next fractal antenna iteration, from 1 to 5.



Intellectual property issues
Because of the complexity of fine tuning antennas to operate above 1.0 Ghz, it can be broadly agreed upon that fractal antennas that are designed to operate in this range should be patentable. However, for fractal antennas operating from 900 kHz to 900 MHz this rule should not apply unless there is a profound issue of miniaturization involved (an antenna size reduction of at least 1000:1, per wavelength) -- where the antenna is also optimized for wide bandwidth performance (40 MHz below 50 MHz, 400 MHz above 50 MHz).

People do have the right to take existing fractal antenna designs and create their own distinct designs -- providing that the design shows either distinct intellectual or  artistic effort. As fractal antennas only mere imitations of nature, there needs to be a limit the extent that any fractal antenna can be patented. There most importantly of all be a full as possible disclosure of the antenna's bandwidth, gain, selectivity and efficiency to the consumer.

Further technical reading (where applicable cite this document in Wikipedia)

General DTV transmission technologies
Transmission systems
Fractal antennas
Antenna system issues

ATSC standard documents
Regulators (North America, where ATSC 8VSB HDTV has been adopted)
Companies that produce fractal antennas


 Created by
Max Power, CEO
Power Broadcasting
Initial idea
15 June 2007
Document created
25 June 2008
Last modified
12  August 2010
Appearance, organization