An active whip antenna that will be located at a long distance from its connected radio receiver needs to be designed. The receiver consists of an SDR (Software Defined Radio) USB dongle, a computer and application-specific software.
The input impedance of the receiver equals 50$\Omega$. A 50$\Omega$ coax cable with SMA connectors at both ends, will be used to connect the active antenna with the receiver.
The active antenne is intended to be used for the reception of radio signals in outdoor environments. The operating temperature of the active antenna should range from $-25\cdots+70^{o}$C.
The power supply for the antenna will be located nearby the receiver. The power consumtion of the antenna should be less than 0.25W. A small interface box is used to combine the supply power and the signal in such a way that both the signal and the supply power can be transported over the 50$\Omega$ coax cable, while zero DC bias voltage is maintained at the input of the receiver. This interface box is located at a short distance of the receiver.
The -3dB frequency range of the active antenna should equal 10kHz to 80MHz. The 1dB compression level at the output of the amplifier, measured at the input of the receiver should be above +0dBm (0dBm =1mW in 50$\Omega$). At the antenna input, this should be equivalent with an electrical field strength of 0.45V$_{\text{RMS}}$m$^{-1}$.
Limits for the antenna-referred equivalent noise spectral density depend on frequency; they have been listed in the table below. For other frequencies, these limits can be obtained by linear interpolation from the given values.
| Frequency | E-field noise density limit |
|---|---|
| 10kHz | 160nVm$^{-1}$Hz$^{-\frac{1}{2}}$ |
| 100kHz | 16nVm$^{-1}$Hz$^{-\frac{1}{2}}$ |
| 1MHz | 8nVm$^{-1}$Hz$^{-\frac{1}{2}}$ |
| 100MHz | 8nVm$^{-1}$Hz$^{-\frac{1}{2}}$ |
At the location of the antenna, interference signals may be present. The RMS value of the electrical field of interference signals at the mains frequency (50Hz or 60Hz) may be as large as 20Vm$^{-1}$, while at frequencies above 800MHz, their field strength can be as large as 50Vm$^{-1}$.
Intermodulation products in the frequency band of interest should be below -50dBm, measured at the input of the receiver.
The electronics for the active antenna, should realized in 1.8V CMOS18 technology or with surface mount devices and a power supplyof maximally 5V.
The active antenna should be protected against electrostatic discharge (ESD).
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