Technical advice regarding Yagi Stack Arrays
Two or more Yagis can be stacked (Vertical) or bayed (Horizontal) in varying configurations to achieve increased gain or a particular signal formation. The centre to centre stacking distance of two antennas should be such that their respective capture areas do not overlap one another. Under these conditions the stacking of two antennas will produce a theoretical gain increase of 3dB over a single antenna, whilst stacking four antennas will produce a theoretical gain increase of 6dB.
Theoretical stacking gain of 3dB for doubling of array size is not necessarily realised in practice and allowance should be made for a realised stacking gain reduced in line with published research.
Viezbike, (Yagi antenna design, NSB Tech. note 688), obtained these figures for a pair of stacked 7 element yagis.
|Measured increase over single antenna (dB)
Powlishen, “Stacking Yagis is a science” (Ham radio) suggested 2.5 dB as a maximum stacking gain realised for a pair of stacked Yagis.
Alignment of antennas within the array is critical, with any misalignment being a potential cause of reduced gain and formation of unwanted side-lobes. The feed harness or power divider must provide signal to each antenna exactly in phase, unless beam tilt is a design feature.
Closer spacing other than the optimum, will result in less than ideal gain increase and could cause main beam distortion. It should be remembered that stacking antennas only reduces the beamwidth of the radiation in the plane of the array. This should be considered when choosing between a four stack array and a two bay two stack array.
Power dividers and phasing harnesses
Our PDY series of cable harnesses to suit base station applications are fully listed in our catalogue along with power dividers for FM Radio, DAB Radio and TV broadcast applications. Please contact the ZCG sales team for more information.
Advice to customers
It is established that theoretical stacking gain is not generally realised in practice. Establishment and maintenance of any stacking gain will require a totally stable electrical and mechanical environment. Specifically, the imbalance in mutual interaction in vertical four stacks will make gain and pattern formation vary considerably from that expected.
ZCG Scalar therefore offers the preceding advice on stacking on a general advisory basis only. No specific indication of expected gain or pattern formation resulting from stacking is offered. Increased gain may often best be achieved by using a single antenna of higher gain. Often the cheapest and most effective way to increase gain is to
reduce system losses, particularly in the transmission cables.
The table below shows the recommended stacking distance in the E and H planes for a few ZCG Scalar Yagis.
|E & H beam widths in degrees
|Stacking distance E plane in mm
|Stacking H plane in mm.
ZCG Scalar. and the author retain the rights to all intellectual property contained herein. This information should be used as a guideline only to help you in the appropriate selection of an antenna.