The QRPer Board

the antenna is similar to the one described here

https://qrper.com/2023/11/a-portable-ob ... -2-meters/

the calc formulas (in meters) are

Lambda=300/MHz
perimeter=Lambda*1.05

semip=perimeter/2

shortside=semip/3
longside=semip-shortside

the antenna offers low takeoff angle and a gain over 8dBi if the lower short side (horizontal) is placed at 0.66 Lambda from ground ( or ground plane), the size is manageable down to the 15m band and btw the antenna works fine at V/UHF

The impedance is an almost perfect match to 50 Ohm so it can be fed with a simple 1:1 BalUn (a w2du choke/balun will do fine at V/U, elsewhere a voltage balun will be ok for this antenna, see attached image)

getting back to the antenna here is an example for 29.000MHz

Lambda=300/29.000=10.34 meters
Perimeter=Lambda*1.05=10.86

the remaining calcs give us a semi perimeter of 5.43 meters which in turn gives us a short side of 1.81 which results in a quite manageable antenna plus, the bidirectional pattern the low takeoff angle and the gain over 8dBi will allow some nice DX and squeeze out the most from QRP power

the voltage balun below, will "float" the loop keeping it w/o a direct DC reference to ground the balun can be built using a binocular core

some more infos

https://reflector.sota.org.uk/t/oblong-for-10m/34523

and here's a reduced space antennna offering surprising performances, almost 2MHz bandwidth and a gain near 8 dBi

it's a dipole, and it's suitable for the HF bands, as an exanple, to setup a 20m dipole in limited space, the only relevant factor is the height and that's neeeded to achieve good gain (almost 8dBi at 0.6 wave); in practice, with respect to a full size horizontal dipole, the overall span is reduced by 40%, the formulas give results in metric units, the calculated lenghts are in the ballpark although it will be a good idea keeping the stubs a bit longer and trimming them after installing the antenna, the two calc factors lngfac and spcfac affect the resonance and the impedance match, and may need some adjustment if changing design frequency and wire gauge