Low Profile ATSC Digital Television Fractal Antennas


Abstract

Without low profile fractal antennas designed for reliable reception of ATSC 8VSB Digital Television (Widescreen HDTV) millions of people in metropolitan (and rural) regions in North America will continue to be without a reliable television service.

With the exception of some households that have been able to recycle their Yagi-Uda antennas (VHF, UHF or Dual-band types) for reception of ATSC -- most North American households will continue to have television reception quality far below what the 8VSB signal transmission system is capable of achieving.

Historically : NTSC, PAL or SECAM fadeout events generally are "long duration" events due to the continuous wave nature of the traditional TV transmission signal. These fadeout events were tolerable (or at least interesting) to the traditional analogue television viewer.

ATSC 8VSB fadeout events in the digital television era are generally catastrophic and random. These fadeout events alienate less technically inclined television viewers, as the cause of reception failure is often not obvious. Viewers in general expect digital television (regardless of how it is transmitted) to be more reliable than analogue television. This reliability has not yet been achieved.

Most 8VSB set top box decoders (as of the mid to late 2010s) only possess "2nd generation" adaptive reception chipsets. These chipsets [and their associated receiver subsystems] have on average only adequate sensitivity to weak signals. These receivers possess only a limited ability to cope with instantaneous fade out events. Longer duration fade out events are at best "coped with" generally with variable degrees of success.

The most up to date 3rd and 4th generation 8VSB adaptive reception chipsets often do not perform as optimally as their designers originally hoped. There are a myriad of subtle (and gross) design and transmission issues that these receivers must cope with that are beyond the ability of a laboratory to simulate adequately.
Currently the ATSC HDTV viewer is left only with ongoing frustration. Most 8VSB decoders uniformly fail to tell the viewer that the received signal is unhealthy before a link loss event. Long duration fade events (as with analogue television) don't really happen with 8VSB as the digital television transmitters use 2/3rds to 1/3rd less power than their previous analogue relative.

Essentially, fractal antennas are the only way to make 8VSB HDTV reception reliable again, at the lowest possible cost to all parties involved.
If the antennas are designed properly, the need for antenna amplifiers (for a large number of users) may also be mitigated.



Why the current ATSC antennas are 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 data rates 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.

Ultimately 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 available

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 (not organized for content)


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 height
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.

Illustrated above :

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 for optimal broadband performance (as TV antennas mainly operate below 1.0 GHz), it can be broadly agreed upon that fractal antennas [that are designed to operate in the VHF & UHF TV bands] should be patentable.

This "patentability context" should only apply to getting multiple types of fractal antennas integrated (and optimized) onto a planar surface, with applicable control mechanisms to reduce consumer annoyance with the antenna system.

However, for fractal antennas operating from 90 MHz to 900 MHz


Entities with "Fractal Antenna Patents"


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. This is not only to keep costs down for the consumer, but to allow for innovation in design. In some nations, artistic designs are copyrightable -- but this should legal context should not be abused by antenna designers to artificially create a design monopoly.

As fractal antennas only mere imitations of nature, there needs to be a limit the extent that any fractal antenna can be patented or copyrighted.

Further technical reading

General DTV transmission technologies
Transmission systems
Fractals general information
Fractal antennas
Antenna system issues

Television bands

Antenna mounting areas

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



 Created by
Initial idea
Document created
Last revised
Version
Revision State

Max Power
15 June 2007
25 June 2008
23 March 2014 (Spelling)
0.95b
Final