But how can we get the advantages of the 2-Element-Quad and can increase the gain? Let us take a look to the classic Quad (pic. 1). If you prefer a good F/B and greater bandwidth, the gain is 4,7 dBd and F/B is 25-30 dB with a high impedance of 110 Ω. Increasing the gain to 5,7 dBd means very low bandwidth, a bad F/B of 6-8 dB and a lower impedance of 40 Ω . With a good compromize we do not reach more than 5 dBd gain.  

The first step is a simple modification. The original single loop with a circumference of 1 λ and a side length of 0,25 λ has only a gain of 1,3 dBd and an impedance of 130 Ω. The Quad element is a stacked system, but the distance between the two parts is to low and the current maxima are to close together. We can increase the gain by changing the Quad to an "Oblong”. The stacking distance will be greater, but the radiating horizontal parts of the loop become smaller. The best compromize between the two influences and the bandwidth is a relation of 0,15 : 0,4 λ (pic. 2). The gain of this loop is now 2,6 dBd and the radiation resistance drops down to 35 Ω. This is the reason why the elements should not be wires with too much loss. See table 1.

Table 1: Data of 2-m-Oblongs with 6-mm-Elements, lengths in lambda

It is possible to add a second loop and a third reflector element. So we come to the Double-Quadlong (Pic. 5). The gain is 7,5 dBd and the impedance is 28 Ω, too.

A very good antenna is the 4x-Quadlong in Pic. 6 with 5 reflectors. The gain increased to 9,3 dBd the azimuth-angle is still 72° and an impedance of 50 Ω is easy to feed. These constructions are to high for the shortwave bands or 50 MHz, but for 2m you get excellent antennas.

The distance of the reflector element in all cases is 0,15 - 0,16 λ.

A comparison of all antenna parameters is listed in the table below. 

A description of the two antennas is on the page with the 2-m-Quadlongs