You might as well post some additional detail requirements such as:

Receive, transmit, both?
Desired beamwidth versus gain?
Application (UHF TV?)

How about a microstrip printed monopole, or half size bowtie, as long as you have a groundplane edge.
Add some size restrictions. Normally 9/4 bandwidth would require antennas at least 1/4 wavelength at 0.4 ghz, or 2.5/4 feet in length or 7.5 inches (if you have a groundplane). Depending on gain and VSWR spec's you may be able to push that down to 5 or 6 inches length, x 4 inches wide.

There's no easy magic to shrinking a wide bandwidth antenna, only narrow band shrinkage is common.


kch

For VE1BLL :
It`s for digital tv reception

For Higgler :
sorry...I don`t understand the "half size bowtie"  and
"have a groundplane edge".....

TV antennas work best if installed high on a mast with good (clear) line of sight to the transmitter site. Once up high on a mast, there tends to be lots of room for a full size antenna (at UHF).

Do you really need it to be small?

A remote preamplifier can be of significant help.

Stay away from those small round antennas. Based on personal experience and multiple reports, they don't work very well (except as unintended oscillators).

Have you confirmed the frequencies of your local channels? Do you really need the whole range?

Are all the channels you want being broadcast from the same relative direction?

I have a notch antenna design for digital TV for a cable equipment manufacturer Sonora Design of Ventura using a notch antenna.

Gain is +5 dBi across the band, and could be higher if needed. Size is 10"x10"x0.060".

Is this for home use, or a commercial product?

You haven't said what size restrictions you have. Your bowtie is too large. This 10"x10" dimension mentioned above is nearly the bare minimum (possibly get that down to 8"x8"), and to get +5 dBi at 400 Mhz, you need 1/2 wave reflector radials (just wires or printed wires) added to that dimension in the aft location of the notch antenna.

kch

Hmm.....the size restriction is just as small as we can....

http://0rz.net/a61BZ

In this ppt ,although it is for mobile phone application
the antenna used in this ppt is possible used for only
digital TV application??  If it is possible...I think the size is really small....

Threads would be more efficient if such requirements had been high-lighted at the outset.

Your link: I like the part where they want the reception to work even when driving at 150 kmh. Great...

I wonder why they didn't start with the possibility of simply sharing one (specially-designed) antenna to two functions?

58 dB isolation is foolish and can't be achieved just between antennas on a cell phone in a real life environment. You'll need to get that antenna to antenna isolation requirement down to around 30 dB for most locations, and preferably 20 dB while inside a car.

I've worked alot of isolation issues, from 44-115 dB requirements and 58 dB with the hand touching the phone while sitting in a car is not a realistic number (unless you're at 94 GHz).

Plus, picture having great isolation, say 60 dB, now put you and the antenna in a metal cage we call a car. antenna to antenna coupling inside a car roughly reduces any isolation by a factor of two (in dB).
Example; take a push on GPO connector adapter, isolation is measured at 100 dB in air (2-18 ghz), place it in a can and you measure 50 dB isolation due to all the energy radiated by one part staying in the volume and not escaping.
You'll need to get 40 dB of filtering for use inside a car.
I'd suggest adding a clever connector port to move the antennas away from each other. Still the car is a problem. Needs an external antenna.


http://www.mobiletv.nokia.com/resources/files/white_paper_DVB-H.pdf, here is a good nokia site that gives some more detail.

kch