The investigation symmetrical transformers characteristics of DF antenna array

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.

(1)

Therefore (1) currents, induced in top and bottom circuits are (2):

(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.

(4)

Equations can be reformulated with:

? out of phase gain;

? in-phase gain;

? coupling coefficient.

Input feed line voltage with ABCD parameters:

; (5)

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:

. (6)

Magnitude input direction finder sum voltage is:

(7)

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:1over 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%.