Mobile wireless communications device with reduced harmonics resulting from metal shield coupling

A mobile wireless communications device, comprising:

• an antenna;
• radio frequency (RF) circuitry operative with the antenna;
• a transmission line and a power amplifier connected to the antenna;
• an antenna switch connected to said antenna and RF circuitry;
• and
• an RF shield surrounding said power amplifier and antenna switch for isolating said power amplifier and antenna switch from said antenna and RF circuitry, and further comprising a low pass filter within the transmission line connected to said power amplifier and to said antenna switch, said low pass filter further comprising a capacitor and first resistor in series and an inductor and second resistor in parallel and having resistance, inductance, and capacitance values such that at a fundamental frequency the impedance of the capacitor is higher than the first resistor and the impedance of the inductor is lower than the second resistor and at higher harmonic frequencies the impedance of the capacitor is reduced and the first resistor becomes a dominant element.

A method of operating a mobile wireless communications device, which comprises:

• providing an antenna and radio frequency (RF) circuitry operative with the antenna and a transmission line and power amplifier;
• switching between receiving and transmitting RF signals through the antenna using an antenna switch;
• and
• isolating the power amplifier and antenna switch from the antenna and RF circuitry by surrounding the power amplifier and antenna switch with an RF shield and reducing any RF coupling of Voltage Standing Waves of upper harmonic frequencies from the power amplifier into the antenna switch through the RF shield using a low pass filter positioned within the transmission line and formed from a resistor, inductor and capacitor wherein at a fundamental frequency, the impedance of the capacitor is higher than a first predetermined resistance and the impedance of the inductor is lower than a second predetermined resistance, and at higher harmonic frequencies, the impedance of the capacitor is reduced.