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The investigation symmetrical transformers characteristics of DF antenna array


V. M. Balyukov

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%.

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