Conduct experimental research into VHF band was appear that an errors existed in a case of amplitude and phase unbalance of symmetrical transformers characteristics DF antenna array.
Often a function of DF errors depend on structure and technical characteristics of symmetrical transformers.
Wide band symmetrical transformers has amplitude and phase unbalance.
Value of polarization errors is proportional: , – asymmetry voltage, – antenna cur-rent; – pair aerials capacitance in dipole; – angular frequency.
Equivalent circuit of connections symmetrical antenna by transformers and transmissions line to DF unit (Figure 1).
As to Kirchhoff law total current-burning voltage in circuits is zero.
Therefore (1) currents, induced in top and bottom circuits are (2):
where, – is the sum secondary isolated circuits current, – out of phase voltage, induced from antenna; – in-phase voltage, induced from antenna, – antenna impedance; – primary transformer impedance; – mutual induction coefficient; .
, where, – input antenna feeder line voltage, – secondary symmetrical transfor-mers impedance, – primary transformers currents.
Equations can be reformulated with:
– out of phase gain;
– in-phase gain;
– coupling coefficient.
Input feed line voltage with ABCD parameters:
where – input current and voltage direction finder.
Equation (5) can reformulated with coefficient ABCD parameters as to un losses feed line:
Sum input direction finder voltage is:
If in-phase voltage is adding to out phase antenna voltage that out feed line voltage is:
Magnitude input direction finder sum voltage is:
In case and . With this assumption, it is easy to modify the equation (7) for max gain ( ) amplitude of unincluded feed line losses.
In case of direction-of-arrival with amplitude method four element circular antenna array bearing is:
, and systematic errors are: .
Errors due to the data sheet symmetrical transformers characteristics of DF antenna array:
, где , – gain antenna-feeder channel with symmetrical transfor-mers of four element circular antenna array.
Manufactured symmetrical transformers (center-tapped transformers) have amplitude and phase unbalance which is a function of insertion loss and frequency bandwidth (1dB, 2dB, 3dB).
Typical amplitude unbalance: 0.1dB over 1dB frequency range; 0.5dB over entire frequency range and phase unbal-ance:1over 1dB frequency range; 5 over entire frequency range.
Figures 2-4 shows error due to unbalance plotted against total balance symmetrical transformers for four element circular antenna array.
• The investigation symmetrical transformers characteristics with feed line of DF antenna array on accuracy. In-crease DF errors due to unbalance symmetrical transformers less than 0.1дБ over 1dB frequency range is not more than 2% at relation aperture to wave length for four element circular antenna array . Increase unbalance magnitude of symmetrical transformers to 0.5dB over entire frequency range involve increasing DF errors to 10%.