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Cell Phone Adaptive Antenna Impedance matching with embedded traces in a printed circuit board

IP.com Disclosure Number: IPCOM000237078D
Publication Date: 2014-May-29
Document File: 5 page(s) / 123K

Publishing Venue

The IP.com Prior Art Database

Abstract

Disclosed is a cost-effective and reliable method for impedance matching for cellular phone adaptive antennas. The design provides an antenna impedance matching network with a printed circuit board (PCB) structure that incorporates switchable etches to achieve multiple selectable impedance options.

This text was extracted from a PDF file.
This is the abbreviated version, containing approximately 51% of the total text.

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Cell Phone Adaptive Antenna Impedance matching with embedded traces in a printed circuit board

An existing method and an associated apparatus can automatically adjust an antenna's impedance matching in a wireless transceiver employing phase amplitude modulation. However, with the existing method and apparatus, if a tuning device is absent, then "the antenna impedance observed by the transceiver circuits is a function of the operating frequency, and may also vary substantially depending upon the proximity of the antenna to the human body." [*]

Figure 1: Figure from existing method and apparatus [1]

The impedance matching network used is a Pi network composed of lump element capacitors, switches, and a transmission line that behaves as an inductor. (Figure 2)

Figure 2: Banks of capacitors (614 & 616) are located at the end of a transmission line (612) along with switches (618) such as relays, pin diodes, or Field Effect Transistors (FETs) to form a tunable Pi network.

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A problem with a Pi network, shown physically in figure 2 and electrically in Figure 3, is that the impedance is not constant or uniform from end to end. The lump capacitors that are located at the ends of the transmission line (612) are prone to act as alternating current (A/C) shorts that decrease the Pi network's overall impedance, especially for waveforms with fast transitions. An inductive transmission line is prone to raise the Pi network's impedance due to inductive kick.

Figure 3: Pi network electrical structure

Figure 4 illustrates a typical Pi network's TDR response and exhibits the non-linear characteristic impedance (Z0) response.

Figure 4: Pi network's TDR response

The novel contribution is a design that replaces the lump element Pi network (426) in

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Figure 1 with a printed circuit board (PCB) that incorporates a variable impedance transmission line. The solution provides an antenna impedance matching network with a PCB structure that incorporates switchable etches to achieve multiple selectable impedance options. Since this structure does not include lumped element capacitors attached to the ends of transmission line, this design can be a true distributive transmission line with uniform impedance from end to end. This antenna impedance matching network is cost effective, without lump element capacitors. In addition, it promises a lower failure rate with fewer components and lack of a capacitor's voltage stress.

In Figure 5, Conductor 0 is the trace path for the transmitted signal of the cell phone. Cond...