VSWR tolerant tunable hybrid duplexer

The disclosure describes a dual hybrid duplexer including two hybrid couplers, two intra-filters, a tunable isolation load, and a phase shifter. The phase shifter may be located at the isolation port. The phase shifter may be located at the antenna port. In one embodiment, a dual hybrid duplexer includes two hybrid couplers, two intra-filters, a tunable isolation load, a first phase shifter located at the isolation port, and a second phase shifter located at the antenna port. The first and second phase shifters have a difference of 90 degrees (plus or minus 10 degrees).

FIELD OF THE DISCLOSURE

This disclosure is in the field of tunable duplexer architecture for multiband communications. Specifically, conventional switches and duplexers may be replaced by tunable duplexers including 90 degree hybrid couplers or including quadrature couplers.

BACKGROUND

FIG. 1. Conventional radio cellular systems include many switches and many individual (non-tunable) duplexers.FIG. 1illustrates a conventional multi-band system with amplifiers, band switches, duplexers, an antenna T/R (Transmit Receive) switch, and an antenna.

In conventional radio cellular systems that operate in multi-modes and multi-bands (such as 3G, 4G, and/or 5G systems), there are many duplexer related components. These components include T/R (transmit/receive) switches such as PA (power amplifier) band switches and antenna band switches. These components are growing in numbers and undesirably increasing the total solution cost and size.

Specifically,FIG. 1illustrates a conventional system including: amplifiers (AMP2and AMP4); band switches (SW2and SW4); duplexers module (DMOD) including duplexers (D17, D8, D5, D13, D2, D1, and D4); an antenna T/R (Transmit/Receive) switch SW6; and a main antenna ANT. For the sake of clarity and conciseness, many other elements (such as a diversity antenna and related circuitry) are not shown inFIG. 1. Also, the wiring for received signals exiting the duplexer is not shown.

Beginning with low band elements, low-band amplifier AMP2receives a voltage VA2IN and then outputs an amplified voltage VA2OUT. Low-band switch SW2receives VA2OUT, and selectively outputs one of: V17, V8, V5, and V13.

High-band amplifier AMP4receives a voltage VA4IN and outputs an amplified voltage VA4OUT. High-band switch SW4receives VA4OUT and then selectively outputs one of: V2, V1, and V4.

Remaining in transmit mode, antenna T/R (transmit/receive) switch SW6receives one or more duplexed voltages (VD17, VD8, VD5, VD13, VD2, VD1, or VD4), selects one of these received duplexed voltages, and outputs the selected voltage as VANT to main antenna ANT.

In a receive mode, signals flow from right to left. Main antenna ANT receives a signal as VANT, antenna T/R switch selectively outputs VANT as one of VD17, VD8, VD5, VD13, VD2, VD1, or VD4towards a corresponding duplexer (D17, D8, D5, D13, D2, D1, or D4respectively). For example, if duplexer D17is selected, then the received signal VANT is transmitted through antenna T/R switch SW6and then towards duplexer D17as VD17. Duplexer D17receives the received signal VD17, and then outputs a duplexed received signal (not shown). The duplexer generally performs filtering that is specific for the band in which the duplexer is operating.

FIG. 2(a).FIG. 2(a) is a conventional dual hybrid tunable duplexer with intra-filters that reflect RX signals and pass TX signals, illustrating the paths from a power amplifier to an antenna. The hybrid structures inFIG. 2(a) are 90 degree hybrid structures with a −3 dB power split on the quadrature ports. These hybrids are also known as 90 degree Hybrid couplers or Quadrature Couplers.

Specifically,FIG. 2(a) illustrates power amplifier AMP6outputting signal V20for transmission. Hybrid HYB2receives signal V20and splits this signal into two “half power” signals: V22exiting the top right with no phase shift (an “in-phase output”), and V23exiting the bottom right with 90 degree phase shift (a “quadrature component”). Thus, hybrid HYB2simultaneously provides a 3 dB power split into two signals (half power to the upper right, and half power to the lower right), and a 90 degree phase shift to one of the signals (to the lower right).

Tunable filter TF2receives V22(the upper signal, or “in-phase output”), and transmits almost all of this signal as V24(due to low reflectivity Γ in the TX band, and high reflectivity Γ outside of the TX band). For example, Tunable filter TF2may be a band pass filter centered at the transmit frequency.

Tunable filter TF4receives V23, and transmits almost all of this signal as V25(due to low reflectivity Γ in the TX band). In one embodiment, tunable filters TF2and TF4are identical.

Hybrid HYB4receives V24, shifts it 90 degrees, and send it out the antenna port Port2to the antenna ANT. Additionally, HYB4receives V25, and sends it out Port2without any additional shifting. Now, these two half power signals have each been shifted 90 degrees, and they will add (not cancel) at Port2. Thus, the antenna ANT receives combined signal VANT substantially equivalent to the entire V20shifted 90 degrees, and with out of band portions of the signal having been filtered or reflected (high Γ RX) out.

In summary, HYB2splits the TX signal into two halves, while shifting the lower half by 90 degrees. The second hybrid HYB4combines the split signals, while shifting the upper half by 90 degrees. Overall, the antenna ANT receives combined signal VANT that is substantially equivalent to the entire V20shifted 90 degrees. Additionally, tunable RX filter TRXF2and isolator ISO2are discussed below.

During transmission, hybrid or “quadrature” coupler HYB4typically provides 20 to 30 dB of isolation between receiving RX port3and transmitting antenna port2.

FIG. 2(b).FIG. 2(b) illustrates isolation at the receiver port caused by the second hybrid coupler. Specifically, as discussed above, hybrid HYB4receives signal V24(a half power, un-shifted, filtered, transmission signal). V24is transmitted directly to V26without any additional shifting.

Additionally, hybrid HYB4receives signal V25(a half power, 90 degree shifted, filtered transmission signal). V25is transmitted to V26with an additional 90 degree shift, creating a half power, 180 degree shifted, filtered transmission signal. Thus, V26combines a half powered, un-shifted, filtered transmission signal with a half power, 180 degree shifted, filtered transmission signal, and these two signals ideally cancel out because they are equivalent in magnitude but 180 degrees out of phase. Thus, V26is near zero, illustrating very high isolation between the transmitted output VANT and any signal leaking out as V26. In practice, these combined signals do not perfectly cancel (due to mismatching), but they do provide approximately 20 dB to 30 dB of cancellation (20 to 30 dB lower power than the transmission signal VANT).

FIG. 2(c).FIG. 2(c) illustrates reflections from the tunable filters directed towards the isolation port. Tunable filter TF2reflects (leftward) any out of band portions of the received half power un-shifted transmission signal V22(due to high Γ RX). Hybrid HYB2shifts this upper reflected signal by 90 degrees and sends the shifted reflected signal (downward and to the left) to the isolation port Port4.

Tunable filter TF4reflects (leftward) any out of band portions of the received half power 90 degree shifted transmission signal V23(due to high Γ RX). Hybrid HYB2does not shift this lower reflected signal any more, while sending this reflected signal (to the left) to the isolation port Port4.

Isolation port resistor ISO4absorbs both of these (out of band, undesired) reflected signals, in order to avoid these reflected signals being problematically reflected back into the hybrids.

FIG. 2(d).FIG. 2(d) illustrates receiving an un-tuned signal. An un-tuned signal RX is received at antenna ANT, and accepted by hybrid HYB4at Port2. A half power 90 degree shifted un-tuned signal RX is output (upper left) towards filter TF2. Simultaneously, a half power un-shifted un-tuned signal RX is output (lower left) towards filter TF4.

FIG. 2(e).FIG. 2(e) illustrates reflecting and tuning the received signal. Filter TF2reflects the half power, 90 degree shifted un-tuned signal RX to the upper left of hybrid HYB4. HYB4passes this signal (without additional shifting) towards tunable RX filter TRXF2.

Further, filter TF4reflects the half power, un-shifted, un-tuned signal RX to the lower left of hybrid HYB4. Hybrid HYB4passes this signal (while adding a 90 degrees shift) towards tunable RX filter TRXF2.

Exiting the top right of hybrid HYB4, these two half power signals (now each shifted 90 degrees) are combined into a whole power signal shifted 90 degrees V26. Tunable filter TRXF2may be tuned to a specific band, and thus may pass VRXOUT in a selected specific band, while filtering out portions of the received signal that are in other bands.

FIG. 3(a).FIG. 3(a) is a second type of conventional dual hybrid tunable duplexer, with intra-filters that pass RX signals and reflect TX signals, illustrating the paths from a power amplifier to the intra-filters.

Specifically,FIG. 3(a) is a different configuration of the same elements shown inFIG. 2(a), except that the intra-filters (the tunable filters located between the hybrids) now pass (instead of reflect) RX signals, and reflect (instead of pass) TX signals. Power amplifier AMP8sends a transmission signal TX to Port1of hybrid HYB8. Hybrid HYB8sends a half-power, un-shifted TX signal to tunable filter TF6, and sends a half-power, 90 degree shifted TX signal to tunable filter TF8. In one embodiment, tunable filters TF6and TF8are identical.

FIG. 3(b).FIG. 3(b) reflects transmission signals by the “intra-filters” located between the hybrids. The split signals from the previous figure are each reflected. Specifically, the half power, un-shifted signal is reflected by tunable filter TF6(due to high Γ TX). Any out of band portions of this signal are passed by the tunable filter. In other words, the reflected signal has been filtered to be in a selected transmission band. Hybrid HYB8receives this reflected signal at the upper left, and sends it towards the antenna while shifting 90 degrees (resulting in a half power, 90 degree shifted, filtered signal at Port2).

Tunable filter TF8receives a half-power, 90 degree shifted, unfiltered signal from hybrid HYB8, and reflects a filtered portion of this signal back towards hybrid HYB8(due to high Γ TX). Hybrid HYB8passes (receives at the lower left port and sends out the lower right port of the hybrid) this reflected signal (without any additional phase shift) towards the antenna ANT at Port2.

These two half-power, 90 degree shifted, filtered signals are combined at Port2to create a full-power, 90 degree shifted, filtered signal TXOUT.

FIG. 3(c).FIG. 3(c) illustrates that the RX noise is cancelled. Tunable filters TF6and TF8passes (low Γ RX) portions of TXIN that are outside of a selected TX band. These transmitted noise signals pass through hybrid HYB6. The lower noise signal is shifted 90 degrees (for a second time) by HYB6, resulting in 180 degree shifted signal exiting at Port3. The upper signal is passed by HYB6without any shifting to Port3. These two noise signals effectively cancel at Port3(RXOUT equals about zero) because one of the noise signals has been shifted 180 degrees, and the other has not been shifted.

Somewhat similar to the above discussion ofFIGS. 2(a)-(e),FIGS. 3(a)-(c) provide substantial isolation between full power, 90 degree shifted, filtered output TXOUT relative to noise RXOUT. Isolation resistor ISO4performs a function (terminating reflections) similar to isolation resistor ISO2inFIG. 2, as discussed above.

The above conventional architectures suffer because the isolation from the transmit port Port1relative to the receive port Port3is a function of antenna load changes. The antenna load changes may be characterized by an antenna VSWR (Voltage Standing Wave Ratio). Thus, conventional architectures suffer from degraded isolation whenever VSWR changes, and an antenna load can often change by a factor of 10 (up to 10:1 VSWR).

Additionally, if the antenna is not almost perfectly matched, then the performance of the conventional architectures degrades. For example, if the dual hybrid has an impedance of 50 ohms, and if the antenna does not have an impedance of 50 ohms, then the antenna is mismatched at the antennal port Port2of the dual hybrid. Further, antenna load changes may change the impedance of the antenna during operation. Conventional architectures cannot solve these problems.

SUMMARY

The present disclosure relates to a tunable duplexer architecture that addresses the need to reduce system cost and system size.

In one embodiment, a dual hybrid duplexer includes two hybrids, two intra-filters, a tunable isolation load, and a phase shifter. The phase shifter may be located at the isolation port. The phase shifter may be located at the antenna port.

In one embodiment, a dual hybrid duplexer includes two hybrids, two intra-filters, a tunable isolation load, a first phase shifter, and a second phase shifter. The first phase shifter is located at the isolation port. The second phase shifter is located at the antenna port. The first and second phase shifters have a difference of 90 degrees (plus or minus 10 degrees).

The dual hybrid duplexer may further include an impedance tuner at the antenna port.

DETAILED DESCRIPTION

FIG. 4.FIG. 4illustrates a dual hybrid architecture including a 90 degree phase shifter and a tunable isolator load at the isolation port, and intra-filters that reflect RX (have high Γ RX).

FIG. 4is similar toFIG. 3, with the following modifications: the isolation load ISO6is tunable; a phase shifter PS2is inserted between the isolation load ISO6and Port4of hybrid HYB2, and an antenna impedance tuner AIT2is inserted between Port2of hybrid HYB4and the antenna ANT. These modifications create desired cancellations when the antenna ANT is mismatched.

FIG. 5.FIG. 5illustrates a dual hybrid architecture including a 90 degree phase shifter and a tunable isolator load at the isolation port, and intra-filters that reflect TX (have high Γ TX).

FIG. 5is similar toFIG. 4, with the following modifications: the isolation load ISO6is tunable; a phase shifter PS2is inserted between the isolation load ISO6and Port4of hybrid HYB6, and an antenna impedance tuner AIT4is inserted between Port2of hybrid HYB8and the antenna ANT. These modifications create desired cancellations when the antenna ANT is mismatched.

FIGS. 6(a) through6(h) illustrate the flows resulting from a transmit signal TX injected at the transmit port Port1. These figures are similar toFIG. 5, but with additional details regarding signal flows. The intra-filters inFIGS. 6(a) through6(h) are highly TX reflective (high Γ TX).

FIG. 6(a).FIG. 6(a) illustrates a transmit signal TX received from a power amplifier not shown) and injected into the transmit port Port1of hybrid HYB10. As a result, HYB10sends a 90 degree shifted signal TX90towards tunable filter TF8, and sends an un-shifted signal TX0towards tunable filter TF10. In one embodiment, tunable filters TF8and TF10are identical.

Tunable filters TF8and TF10may be band pass filters centered at a receiving frequency RX, thus having a low Γ (low reflection) at RX and having a high Γ (high reflection) at TX. Thus TF8and TF10will pass at the receiving frequency RX, and will reflect at the transmitting frequency TX. The reflection coefficient Γ equals (1-x), wherein x is the transmission coefficient. Each tunable filter will pass a portion of the received signal (seeFIG. 6(b)), and will reflect a portion of the received signal (seeFIG. 6(c)).

As a result, hybrid HYB12sends 2*x*TX90(a combination of x*TX90and x*TX90) out of Port4towards phase shifter PS6. Hybrid HB12also sends x*TX0and x*TX180out of Port3and towards RXOUT (these two signals are 180 degrees out of phase, so they cancel each other out, as desired).

The signal2*x*TX90(a combination of x*TX90and x*TX90) out of Port4towards phase shifter PS6is a relatively small signal, because x (transmission factor for TX) is very small for filters TF8and TF10(high Γ TX and low Γ RX, which is equivalent to low x TX and high x RX).

Therefore PS6and ISO10can be small or moderately sized, relative to conventional tunable circuits that may have to deal with power levels of perhaps 20 or 30 dB greater power.

FIG. 6(c).FIG. 6(c) illustrates reflections from tunable filters TF8and TF10, occurring at the same time as the transmissions from these tunable filters discussed above inFIG. 6(b).

Tunable filter TF8reflects a portion (1-x) of the received signal TX90(received inFIG. 6(a)), thus reflecting (1-x)*TX90to the left towards HYB10. Similarly, tunable filter TF10reflects a portion (1-x) of the received signal TX0, thus reflecting (1-x)*TX0) to the left towards HYB10.

Hybrid HYB10receives these two reflected signals, and sends a transmission signal2*(1-x)*TX90(a combined (1-x)*TX90and (1-x)*TX90) towards antenna ANT. This transmission signal is similar to the transmission signal inFIG. 3discussed above, wherein the initial transmission signal TXIN from power amplifier AMP8is split by hybrid HYB8, the split signals are effectively filtered (or tuned) by reflection (high Γ TX) by tunable filters TF6and TF8, and finally combined by hybrid HYB8at port Port2on the way to the antenna ANT.

FIG. 6(d).FIG. 6(d) illustrates a reflected signal from the antenna ANT. As discussed inFIG. 6(c), hybrid HYB10sends signal2*(1-x)*TX90to the antenna ANT. The antenna ANT might not be perfectly matched with the dual hybrid circuit, and thus might reflect some of this signal back to the hybrid HYB10, with a reflection coefficient of ΓL. Thus, the reflected signal is ΓL*2*(1-x)*TX90towards hybrid HYB10.

Hybrid HYB10receives this reflected signal and sends part of it as ΓL*(1-x)*TX90towards tunable filter TF8, and sends part of it (after shifting 90 degrees) as ΓL*(1-x)*TX180towards tunable filter TF10.

Tunable filter TF8passes ΓL*x*(1-x)*TX90towards the top left of hybrid HYB12. Tunable filter TF10passes ΓL*x*(1-x)*TX180towards the bottom left of hybrid HYB12.

Hybrid HYB10shifts the received upper signal by 90 degrees and outputs it at Port3as ΓL*x*(1-x)*TX180. Hybrid HYB10receives the lower signal and outputs it (un-shifted) at Port3as ΓL*x*(1-x)*TX180.

FIG. 6(e).FIG. 6(e) illustrates a reflected signal from tunable isoload ISO10. As previously discussed inFIG. 6(b), hybrid HYB12sends a signal2*xTX90towards phase shifter PS6. Phase shifter PS6shifts this signal90degrees as it passes towards tunable isoload ISO10(signal2*x*TX180, not shown) towards tunable isoload ISO10. Tunable isoload ISO10has a reflection coefficient of Γiso, such that the reflected signal is Γiso*2*x*TX180(not shown). This reflected signal passes back through phase shifter PS6, is shifted an additional 90 degrees, resulting in Γiso*2*x*TX270(not shown), which is equivalent to −Γiso*2*x*TX90as shown.

−Γiso*2*x*TX90enters the upper right part of hybrid HYB12. A portion is directed left (without additional shifting) towards tunable filter TF8as −Γiso*x*TX90. Another portion is directed downwards and to the left (with an additional 90 degrees of shifting) towards tunable filter TF10as −Γiso*x*TX180.

FIG. 6(f).FIG. 6(f) continues tracking the signals fromFIG. 6(e). Tunable filter TF8receives −Γiso*x*TX90(not shown) and reflects −Γiso*x*(1-x)*TX90towards the upper left of hybrid HYB12. Hybrid HYB12receives this signal, phase shifts it 90 degrees, and outputs it at port3Port3as −Γiso*x*(1-x)*TX180.

Further, tunable filter TF10receives −Γiso*x*TX180(not shown) and reflects −Γiso*x*(1-x)*TX180towards the lower right of hybrid HYB12. Hybrid HYB12receives this signal, does not shift it, and then outputs it at port3Port3as −Γiso*x*(1-x)*TX180.

FIG. 6(g).FIG. 6(g) simultaneously illustrates all of the signals fromFIGS. 6(a) through6(f) discussed above. Six signals are outputted at port3Port3as RXOUT. The first two (x*TX0and x*TX180) cancel as previously discussed. The next four signals cancel only if and when ΓL (the reflection coefficient of the antenna ANT) equals Γiso (the reflection coefficient of the tunable isoload ISO10.

Expressed as an equation: ΓL=Γiso causes cancellation of all of the reflected signals at port3.

As discussed above, the reflection coefficient ΓL of the antenna ANT may vary as VSWR varies. If the reflection coefficient Γiso of the tunable isoload ISO10is variable, then the reflective coefficient Γiso may be varied such that it is equal to the reflective coefficient ΓL of the antenna. In this case, at port3, all of the signals shown inFIG. 6(g) will cancel.

As discussed in detail above, the 90 degree phase shift on the isolation port and the matching of the impedance on the isolation port relative to the antenna port causes the reflected TX signals at any frequency (i.e. at TX and RX frequencies) to cancel at the RXout, thus maintaining a good isolation of the tunable duplexer under mismatched antenna conditions.

One major benefit of this embodiment is that the tunable network can be located at the isolation port, thus it will not see the TX large signal power because the isolation port is already isolated from the TX signal by at least 10-20 dB due to the intra-band filter. Thus, the tuner at the isolation port can be a lossy tuner and/or can be a small size tuner because it is not required to handle large signal power (unlike a tuner at the antenna port).

If a tuner already exists on the antenna port, then the antenna port tuner would provide a coarse tuning (e.g. retune from 10:1 to 2:1 resolution) and the tuner on the isolation port would provide a fine tuning (e.g. tune from 2:1 to 1.05:1 resolution) to get the target TX-RX isolation of the duplexer.

FIG. 7.FIG. 7illustrates only the outputs signals at RXOUT at Port3for the circuit ofFIG. 6(a). As discussed above, ΓL=Γiso causes cancellation of all of the reflected signals at Port3.

FIG. 8.FIG. 8illustrates the results of a simulation of a dual hybrid based on a fisher hybrid network with VSWR1:1 (indicating that the antenna is matched). The TX reflective filter is a shunt filter that has a series resonance at TX frequency and parallel resonance at RX frequency. The TX and RX frequencies correspond to band2 duplexer settings (the TX is set to 1850 MHz and the RX is set to 1930 MHz). The Q settings are around 60.

In the case of VSWR1:1, the isolation at TX frequency is about −1.5 dB (see m3) and at RX frequency is about −1.6 dB (m4), while the isolation TX-RX is about −44 to −49 dB at TX (m5) and RX (m6) frequency respectively.

Thus, the curve with m3is the transmit frequency curve. The curve with m4is the receive frequency curve. The curve with m5and m6is the isolation curve indicting isolation between TX and RX. Thus, m5indicates that that the transmit frequency at the receive port (Port3) is lowered by 44 dB.

FIG. 9.FIG. 9illustrates the results of a simulation of a dual hybrid based on a fisher hybrid network with VSWR of 4:1 at the antenna port (indicating that the antenna is not matched), and the isolation port is not tuned. In this case, the isolation at TX frequency is about −3.4 dB at m3and at RX frequency is about −3.5 dB at m4, while the isolation TX-RX is about −21.8 dB at TX (m5) and −21.4 dB at RX (m6). Thus, if the antenna is not matched, and the isolation port is not tuned, the isolation has degraded from −44 dB to −21 dB.

FIG. 10.FIG. 10illustrates the results of a simulation of a dual hybrid based on a fisher hybrid network with VSWR of 4:1 at the antenna port (indicating that the antenna is not matched), and the isolation port is tuned. In this case, the isolation at TX frequency is about −3.4 dB (m3) and at RX frequency is about −3.5 dB (m4), while the isolation TX is about −42 dB at TX (m5) and RX is about −51 dB (m6). InFIG. 10, the isolation port is tuned to match the antenna port impedance, and the isolation has improved to 42 dB at TX and 51 dB at RX.

FIG. 11.FIG. 11illustrates the results of a simulation with VSWR 4:1, Q=60, with tuning on the isolation port of 4:1, and 0 degrees phase shift at the isolation port (instead of the desired 90 degrees phase shift fromFIG. 6(a)). The isolation is degraded relative to a 90 degree phase shift.

Some conventional duplexers use tuning at the isolation port (not shown). However, conventional duplexers do not use phase shifters.

In the embodiment ofFIG. 6(a), the phase shift may be −90 degrees and generate similar cancellation. In practice, the phase shift may be within 10 degrees of 90 degrees (from 80 degrees to 100 degrees) or within ten degrees of −90 degrees (from −100 degrees to −80 degrees) to generate substantial cancellation of undesired signals.

Further, fast tuning of the isolation port (relative to changes in the antenna load changes, or relative to an antenna port mismatch algorithm) is preferable. This fast tuning may be performed by a control portion located on the duplexer, or by a separately located control portion that is in communication with the duplexer.

FIG. 12.FIG. 12illustrates isolation and VSWR 1:1 with a quality factor Q of 80. The isolation at TX frequency is about −1 dB (m3) and at RX frequency is about −1 dB (m4), while the isolation TX is about −46 dB at TX (m5) and RX is about −49 dB (m6).

FIG. 13.FIG. 13illustrates isolation for VSWR 1:1 with quality Q=90 at the upper edge of band 2 frequencies. The isolation at TX frequency is about −1.2 dB (m3) and at RX frequency is about −1.2 dB (m4), while the isolation TX-RX is about −46 dB at TX (m5) and −44 dB at RX (m6).

FIG. 14A.FIG. 14Aillustrates placing a phase shifter at the antenna port of the duplexer, using high Γ RX intra-filters.FIG. 14Ais similar toFIG. 4, except that the phase shifter PS8is now located between hybrid HYB4and antenna impedance tuner AIT2.

FIG. 14B.FIG. 14Billustrates placing a phase shifter at the antenna port of the duplexer, using high Γ TX intra-filters.FIG. 14Bis similar toFIG. 5, except that the phase shifter PS10is now located between hybrid HYB8and antenna impedance tuner AIT4.

FIG. 15.FIG. 15illustrates isolation for VSWR 4:1 (0=90), at the upper edge of band2 frequencies, with a 90 degree phase shifter on the antenna port.

The isolation at TX frequency is about −3/1 dB (see m3) and at RX frequency is about −3.2 dB (m4), while the isolation TX-RX is about −45 dB at TX (m5) and −47 dB at RX (m6). Similar results can be obtained by placing a 90 degree phase shifter on the isolation port.

In general, a first phase shifter may be placed on the isolation port and a second phase shifter may be placed on the antenna port such that the difference between the two phase shifters is 90 degrees or −90 degrees. Substantial cancellation occurs when the difference is between 80 degrees and 100 degrees, or between −100 degrees and −80 degrees. SeeFIGS. 16A and 16Bbelow.

FIG. 16A.FIG. 16Aillustrates using two phase shifters having a difference of 90 degrees, with intra-filters having high Γ RX.FIG. 16Ais similar toFIG. 14A, except that the shifting function has been distributed over two locations.

The first phase shifter is in a first location between hybrid HYB4and antenna impedance tuner AIT2, and shifts 45 degrees. The second phase shifter is in a second location between hybrid HYB2and tunable isoload ISO6, and shifts −45 degrees.

FIG. 16B.FIG. 16Billustrates using two phase shifters having a difference of 90 degrees, with intra-filters having high Γ TX.FIG. 16Bis similar toFIG. 14B, except that the shifting function has been distributed over two locations.

The first phase shifter is in a first location between hybrid HYB4and antenna impedance tuner AIT2, and shifts 45 degrees. The second phase shifter is in a second location between hybrid HYB2and tunable isoload ISO6, and shifts −45 degrees.FIGS. 16A and 16Bare the most general embodiment, wherein the phase shifting may be performed at two distinct locations.