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This paper presents the effect of different bias circuits configurations on the noise performance of GaAs HBT (heterojunction bipolar transistor) power amplifiers at the receiver band. Various bias circuits have been used for the power amplifier in an WCDMA (wideband code division multiple access) transmitter module including the output duplexer at PCS band (Tx: 1850 ∼ 1910 MHz, Rx: 1930 ∼ 1990. A bias circuit with cascode current mirrors for the 1 st and the 2 nd stages shows less than −180 dBm/Hz receiver band noise with −39 dBc of ACPR (adjacent channel power ratio) at 25.2 dBm antenna output power.

Magnetic sheet backing of the search coil is proposed to improve the detection range of a pulsed-induction (PI) metal detector (MD) system. A planar square spiral mono coil is printed on an FR-4 substrate, and layers of magnetic sheets are attached to the substrate. The coil geometry is modelled using the finite-element method, and the static magnetic field distributions are compared. With the magnetic sheet backing, the magnetic field is shown to increase in the target direction and to decrease in the opposite direction. The coils are fabricated and applied to a PI MD system. It is demonstrated that the proposed magnetic sheet-backed search coils have longer detection ranges than the coil without magnetic sheet backing.

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