15m Asymmetrical Antenna by G3EFY
This mono-band antenna that can be constructed with either with a 1 wavelength (44ft) or 1½ wavelength (66ft) top section. In either case the feedpoint is 11ft from one end.
https://rsars.files.wordpress.com/2013/01/15m-asymmetrical-antenna-g3efy-iss-1-31.pdf

21,28MHz shortened dipole antenna (pipe type) by JA1HWO
Since the total length of the antenna is less than 5m, the thickness of the pipe is 16mm, and a 13mm pipe is inserted inside to resonate at 28.7MHz.
http://mk1502.web.fc2.com/ahf1/218dp_p.htm

21,28MHz shortened dipole antenna (wire type) by JA1HWO
Occasionally, we will introduce a dipole antenna that is perfect for those who want to go to the 21MHz or 28MHz band! It's easy because it is made up of few parts.
http://mk1502.web.fc2.com/ahf1/218dp_w.htm

21MHz Hentena by JA1HWO
This antenna was built around 1994, and later in 1997 we came up with an improved version of Hentena, "SKYDOOR" (see that for details), and currently use SKYDOOR.
http://mk1502.web.fc2.com/ahf1/21hente.htm

21MHz small space 2EL YAGI by JA1HWO
The 2EL Yagi antenna is currently not used much. I decided to make this antenna because the PC software said, "If you make it small, the gain does not change much with HB9CV or YAGI."
http://mk1502.web.fc2.com/ahf1/15yagi_s.htm

21MHz squalo antenna by JA1HWO
I wanted to make this antenna because it can be made small because it is a modification of dipole antenna.I made it up at 50MHz before, so I scaled up the antenna and it was 1.7m square, so it didn't get too big.
http://mk1502.web.fc2.com/ahf1/15sqalo.htm

3 Half Wave 15 Meter Doublet (in phase) by KC8AON
For a good multiband ( 10 thru 40 meters ) antenna, try a 3 half waves in phase doublet for 15 meters.
It is derived by using the formula for the G5RV, but substituting 21 Mhz in place of the usual 14 Mhz.
http://fpqrp.org/15mdub.htm

A Light and Sturdy Quad for 10 and 15 meters by KA3PDM & W3/CE3VU
Fishin' for DX? A few fishin' poles and a hank of wire can help you snag the Big One!
http://www.arrl.org/files/file/Technology/tis/info/pdf/9107030.pdf
 

A Small Transmitting Loop Antenna for 14MHz and 21MHz by VK5BR
By definition, the small transmitting loop has a circumference less than one quarter of a wavelength. Because of its small size, it is possibly an attractive proposition for someone with inadequate space to erect a larger aerial.
http://www.i1wqrlinkradio.com/antype/ch9/chiave1069.htm

The 10/15/20 Meter Trap Vertical Antenna by KGØZZ
This antenna project came out very nice. It's a rugged homebrew multi-band trap vertical antenna that works the 10, 15, and 20 meter amateur radio bands. The antenna can be mounted on the ground or on a mast.
http://www.amateurradio.bz/10_15_20_trap_vertical_antenna.html

The Cylinder Dipole by PA1B
The cylinder dipole has proven to be a very small indoor HF-antenna. The cylinder dipole with two Monster energy drink cans and a coil is easy to build and is working fine on 15 m.
https://a29.veron.nl/hams/pa1b/cylinder-dipole/

The HF Satellite Antenna by W4SAT
This is a no compromise dual band antenna. Instead of using traps, this design interlaces two separate antennas on one boom. This is a full size, four element beam on 10, and three elements on 15 meters!
http://www.qsl.net/w4sat/hfsat.htm

Ultra-short whip antenna for 2 bands by JA1HWO
Once I made short antennas at 6m, 2m and 430MHz, and also made 24 and 28MHz.
This time, I wanted to make something a little different, so I decided to try a matching hat with a capacity hat (capacity return, hereafter referred to as CH ) .
http://mk1502.web.fc2.com/ahf1/218_tanhp.htm

Zippiro Vortex by IZ7DJR
 
https://www.qsl.net/iz7djr/vortex15.htm