Abstract
An active digital electronic tuner (AET) uses a digital PIN diode electronic tuner, an adjustable directional coupler, two circulators and a power amplifier to create a compact load pull tuner device able of generating octave frequency band virtual reflection factors |Gamma|1 at milli-second tuning speed.
Claims
1. An active electronic impedance tuner comprising an adjustable coupling module and an active tuning section, wherein the active tuning section comprises two circulators C1 and C2, each having three ports #1, #2 and #3, and a remotely controlled electronic tuner module, and an amplifier having input and output port; and wherein the adjustable coupling module comprises a slotted airline (slabline) having an input and an output port and a center conductor between the ports, and a directional coupler (wave-probe) remotely insertable into and sliding along the slabline and coupled to the center conductor, said wave-probe having a coupled and an isolated port; whereby the coupled port is connected to port #1 of C1 and the isolated port is terminated with characteristic impedance, and whereby port #2 of C1 is connected to the electronic tuner module and port #3 of C1 is connected to the input port of the amplifier; and whereby the output port of the amplifier is connected to port #1 of C2, port #2 of C2 is connected to the output port of the slabline and port #3 of C2 is connected to a load; whereby signal flow in the circulators is from port #1 to port #2, from port #2 to port #3 and from port #3 to port #1.
2. The tuner of claim 1, Whereby the electronic module comprises N (N>4) PIN diodes mounted along a microstrip transmission line and remotely switchable ON and OFF, thus creating a multitude of tuning states M=2.sup.N.
3. The tuner of claim 1, whereby the wave-probe is attached to the remotely controlled vertical axis of a mobile carriage, said carriage sliding, remotely controlled, along the axis of the slabline.
4. The tuner of claim 1, whereby the wave-probe, the slabline, the circulators and the amplifier operate in the same frequency band.
5. The tuner as in claim 1, whereby a band pass filter is inserted in the active tuning section before the amplifier.
6. The tuner as in claim 1, whereby a band pass filter is inserted in the active tuning section between the coupled port and C1.
7. The tuner as in claim 1, whereby the circulator C2 is replaced by an Isolator.
Description
BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS
(1) The invention and its mode of operation will be more clearly understood from the following detailed description when read with the appended drawings in which:
(2) FIG. 1 depicts prior art, a load pull test system.
(3) FIG. 2 depicts prior art, a compact signal coupler using a folded semi-rigid coaxial cable, (wave-probe).
(4) FIGS. 3A through 3B depict prior art, FIG. 3A depicts coupling factor, isolation and directivity data and FIG. 3B definitions of RF characteristics in a wave-probe coupler.
(5) FIG. 4 depicts prior art (see ref. 4), basic structure of electronic tuner using PIN diodes; item numbers in this figure are not used in the specification.
(6) FIG. 5 depicts prior art, variation of coupling factor of wave-probe when inserted into or retracted from the slabline.
(7) FIG. 6 depicts block diagram of Active Digital Electronic Tuner (AET) load pull tuner unit.
(8) FIG. 7 depicts detailed structure of AET.
(9) FIG. 8 depicts simplified signal flow in AET.
(10) FIG. 9 depicts the 1024 tuning states of electronic tuner using 10 PIN diodes (2.sup.10=1024 states).
(11) FIG. 10 depicts digital electronic tuner on microstrip using 12 PIN diodes and capable of creating 2.sup.12=4096 distinct tuner states.
DETAILED DESCRIPTION OF THE INVENTION
(12) The concept of the Active Electronic Tuner (AET) is shown in FIG. 6. A realistic implementation is shown in FIG. 7. It comprises a network of (a) Adjustable Coupler Module, (b) Digital Electronic Tuner and (c) Amplifier, joined using (d) two Circulators. The adjustable coupler module is mounted in a slotted airline (slabline) which has a center conductor, an input and an output port and reaches from the input port of the tuner to the second port of an output circulator, of which the third port is the output port of the tuner. The coupler and the digital tuner are remotely controlled by a control computer. The digital electronic tuner (70) is connected to the second port (71) of a circulator (72) of which the first port (73) receives the signal sampled by the coupler (74) and the third port (75) is connected to the input port of the (power) amplifier (76). The output port (77) of the amplifier (76) is connected to the first port (78) of a second circulator (79) of which the second port (701) is connected to the output port of the slabline (703) and the third port (702) is connected to an external load (not shown). The second circulator (79) can be replaced by an isolator (a circulator of which port #3 (702) is terminated with Zo (50); this isolator configuration can only be used if the outgoing and reflected signals from the DUT are sampled and measured using bidirectional couplers (10) and (11) inserted between the DUT and the tuner ((4) in FIG. 1, (706) in FIG. 7).
(13) The electronic tuner comprises a microstrip network in which a multitude (N>2, typically N=10 to 16) of PIN diodes (FIGS. 4 and 10) are incorporated and are controlled by an external electronic digital control board and a control computer controller (FIG. 6). The coupler (74) samples and couples energy from the center conductor (704) of the slabline (703) into the port #1 (73) of the circulator (72). The horizontal position of the coupler (74) is remotely controlled by electric stepper motor gear (705), (acme leading screw, belt or rack-and-pinion) drive. The distance of the coupling loop to the center conductor is remotely controlled by electric stepper motor driving a vertical axis.
(14) The coupling section comprises a wave probe (74) (FIG. 2). It is adjusted to provide a coupling factor S31 (FIG. 3B) at any given frequency (FIGS. 3A and 5). The coupling factor shown in FIG. 3A varies, in this case, between 25 and 15 dB (in linear meaning that between 0.3% and 3% of the signal power is coupled into the coupled port, and between 40 and 30 dB (0.1% and 0.3%) are coupled into the reverse coupled or isolated port). The directivity of 15 dB is necessary in order to reduce the risk of spurious oscillations of the active loop comprising the isolation-tuner-amplifier path.
(15) The signal injected into port #1 (73) of the first circulator is transferred to its second port (71). The signal is reflected at the tuner's (70) input port and is returned with modified amplitude and phase. The returned signal is transferred from port #2 (71) to port #3 (75) and injected into the input port of the amplifier (76). The amplified signal is fed (77) into the first port (78) of the second circulator and exits at the second port (701) and is injected back into the DUT through port (706), thus creating a virtual load for the DUT which is connected to port (706). Port (702) is terminated with characteristic impedance Zo (typically 50).
(16) A representation of the signal power wave flow in the system is shown in FIG. 8: Signal power wave <b> exits from the DUT port, enters the slabline and is coupled partly (coupling factor C<<1) into the active loop: <b*C>; then it is transferred from port #1 to port #2 of circulator (a), reflected at the tuner port by the reflection factor of the electronic tuner .sub.ET and transferred to port #3: <b*C*S.sub.31a*.sub.ET>. Hereby the scattering parameter (s-parameter) transfers from port #1 to port #2 (S.sub.21a) and from port #2 to port #3 (S.sub.32a) of the circulator (a) are combined into transfer factor S.sub.31a=S.sub.21a*S.sub.32a. In s-parameter nomenclature S.sub.xy describes the signal transfer from port y to port x in a 50 Ohm system (source and load impedances are 50 Ohm). If the source or load impedances change, s-parameters are duly transformed using existing relations. The amplified signal power wave <b*C*S.sub.31a*G*.sub.ET> is then transferred from port #1 to port #2 of circulator (b) and injected into the output port of the slabline in direction of the DUT: <a><b*C*S.sub.31a*G*.sub.ET*S.sub.21b>. This creates a virtual reflection factor of approximately .sub.LOAD=<a>/<b>C*S.sub.31a*G*.sub.ET*S.sub.21b. Assuming transmission factors between ports of the circulators are similar in size, then the previous relation can be approximated to .sub.LOADC*S.sub.21a.sup.3*G*.sub.ET. Transmission factor amplitudes are typically 0.1 dB or 0.99 and coupling factors are C0.01, in which case .sub.LOAD becomes equal to 1 for a gain G100 or 20 dB. This is an easily obtainable value for a power amplifier. It will, therefore, be relatively easy to manufacture, in praxis, active high-speed tuners using this method.
(17) The phase adjustability of the coupling section is beneficial in two ways: (i) in order to rotate and focus the tuning states close to and around the conjugate complex impedance of the DUT and (ii) in order to suppress spurious oscillations of the loop by changing the transmission phase of the loop. It is possible that spontaneous spurious oscillations occur at frequencies outside the scope of the investigation, starting out of background noise, and in-order to avoid this, a band-pass filter (BPF) can be inserted in the active loop between port #3 of circulator (a) and the amplifier or between the coupled port of the coupler and port #1 of circulator (a), (FIG. 8), without, otherwise, changing the basic operation and the scope of the invention.
(18) The tuning mechanism is shown in FIG. 9. It shows the tuner states (90) of the digital electronic tuner of FIG. 10. Each point on the Smith chart corresponds to a different ON/OFF digital combination of the PIN diodes in the tuner. If N diodes are used we have 2.sup.N combinations (N=8 results in 256 states, N=16 results in 65,536 states etc.). Such tuners typically use 12 diodes (4,096 states). However, since the distance between diodes is fixed, the reflection factors are not evenly distributed across the Smith chart, and, because diodes are not perfect short or open circuits when switched between ON and OFF states, there are always insertion losses, which reduce the maximum tuning range shown as a depleted area (91). The uneven impedance distribution creates the need to rotate the tuning area to match the DUT impedance. The active electronic tuner in this invention accomplishes this through the horizontal movement of the wave-probe as shown in FIG. 9. The size of the tuning range is controlled by the immersion of the wave-probe inside the slabline and the associated increasing coupling factor.
(19) Obvious alternative embodiments are imaginable but shall not impede on the originality of the idea of using slabline based phase and amplitude adjustable signal coupling structure to create a hybrid (active-passive) electronic load pull tuner.
