Search

EP-4740301-A1 - DIFFERENTIAL INPUT, SINGLE-ENDED OUTPUT QUADRATURE HYBRID COUPLER

EP4740301A1EP 4740301 A1EP4740301 A1EP 4740301A1EP-4740301-A1

Abstract

A Differential Input, Single-ended Output Quadrature Hybrid Coupler (DISO-QHC) is based on baluns, one or two phase shifters, and a Wilkinson combiner. The DISO-QHC is configured to receive two differential, quadrature RF signals from differential PAs and output a combined, single-ended RF signal to drive an antenna element or subarray. Impedance matching transformers configured as baluns perform the differential-to-single-ended conversion and PA output impedance matching, without any requirement on coupling factor. One or two phase shifting circuits align the single-ended, quadrature RF signals in phase. A Wilkinson combiner circuit combines the power of the outputs of the phase shifting circuits. Area and losses are reduced by combining components from the phase shifting circuits with the baluns, and with the Wilkinson combiner circuit (which is implemented with lumped-reactance components rather than transmission lines). The DISO-QHC does not have a specific isolation port, but the isolation resistor within the Wilkinson combiner dissipates the differential and reflected signal from the PAs resulting from the incoming wave reflected from the antenna. The DISO-QHC is compatible with a LMBA functionality. By injecting a current at the center point of the isolation resistor in the Wilkinson combiner, the impedance at PA ports can be modulated.

Inventors

  • FRITZIN, Jonas
  • MESQUITA, Fabien
  • ÖZEN, Mustafa

Assignees

  • Telefonaktiebolaget LM Ericsson (publ)

Dates

Publication Date
20260513
Application Date
20230706

Claims (20)

  1. 1. A Differential Input, Single-ended Output, DISO, Quadrature Hybrid Coupler, QHC (10), configured to receive two differential, quadrature Radio Frequency, RF, signals and output a combined, single-ended RF signal having substantially constant current under dynamically varying load impedance, characterized by: two output impedance matching transformers (12, 14), each receiving one of the differential, quadrature RF signals, and each configured as a balun outputting a single-ended RF signal; at least one output phase shifting circuit (18, 20) connected to a balun (12, 14) output and configured to impart a total of 90° of phase difference between the single- ended RF signals; an output power combiner circuit (22) configured to combine the outputs of the at least one phase shifting circuit (18, 20) and output the combined, single-ended RF signal.
  2. 2. The DISO-QHC (10) of claim 1 wherein the at least one output phase shifting circuit (18, 20) comprises one phase shifting circuit of +/- 90°.
  3. 3. The DISO-QHC (10) of claim 1 wherein the at least one output phase shifting circuit (18, 20) comprises two phase shifting circuits, one connected to each balun output, that sum to +/- 90° of phase difference.
  4. 4. The DISO-QHC (10) of any preceding claim wherein an inductance of a secondary winding of a balun (12, 14) is combined with a phase shifting circuit (18, 20) to reduce component count.
  5. 5. The DISO-QHC (10) of any preceding claim wherein the output power combiner (22) is a Wilkinson Combiner.
  6. 6. The DISO-QHC (10) of claim 5 wherein the Wilkinson Combiner (22) comprises lumped reactive components.
  7. 7. The DISO-QHC (10) of claim 6 wherein inductances or capacitances in the Wilkinson Combiner (22) are combined with inductances or capacitances of one or more output phase shifting circuits (18, 20) to reduce component count.
  8. 8. The DISO-QHC (10) of any preceding claim wherein the DISO-QHC (10) consists of two transformers (12, 14) and corresponding tuning capacitors, one or two inductors, one resistor and four capacitors.
  9. 9. The DISO-QHC (10) of any preceding claim wherein RF signal components reflected from a load into the output are substantially cancelled.
  10. 10. The DISO-QHC (10) of any preceding claim wherein the two differential, quadrature RF signals are generated by two differential Power Amplifiers (PA1 , PA2), and further comprising: an input power combiner circuit (24), configured as a splitter operative to receive a single-ended RF input signal and output two single-ended RF input signals; at least one input phase shifting circuit (26, 28) connected to an output of the input power splitter circuit (24) and configured to impart a total of 90° of phase difference between the two single-ended RF input signals; and two input impedance matching circuits (30, 32), each receiving a single-ended RF signal, and each configured as a balun generating a differential RF signal, wherein the differential balun outputs are connected to the inputs of the two differential Power Amplifiers (PA1 , PA2).
  11. 11. The DISO-QHC (50) of any of claims 5-10, wherein a resistor of the Wilkinson combiner circuit (52) comprises two resistors connected in series, and further comprising: a current source (54) connected between the two resistors of the Wilkinson combiner circuit (52), whereby the load impedances seen by Power Amplifiers (PA1 , PA2) generating the two differential, quadrature RF signals are modulated by controlling the frequency, phase, and amplitude of current output by the current source (54).
  12. 12. A method (100) of converting two differential, quadrature Radio Frequency, RF, signals into a combined single-ended RF signal having substantially constant current under dynamically varying load impedance, characterized by: converting the two differential, quadrature RF signals into two single-ended, quadrature RF signals in two output impedance matching transformers (12, 14) configured as baluns; imparting a total of 90° of phase difference between the two single-ended, quadrature RF signals by at least one output phase shifting circuit (18, 20) connected to a balun (12, 14) output; and combining the outputs of the at least one phase shifting circuit (18, 20) into one single- ended RF signal in an output power combiner circuit (22).
  13. 13. The method (100) of claim 12 wherein imparting a total of 90° of phase difference between the two single-ended, quadrature RF signals comprises imparting Qi° of phase shift to one RF signal and Qi+90° of phase shift to the other RF signal.
  14. 14. The method (100) of claim 13 wherein Qi=0°.
  15. 15. The method (100) of any of claims 12-14 further comprising reducing component count by combining an inductance of a secondary winding of a balun (12, 14) with a phase shifting circuit (18, 20).
  16. 16. The method (100) of any of claims 12-15 wherein the output power combiner (22) is a Wilkinson Combiner comprising lumped reactive components.
  17. 17. The method (100) of claim 16 further comprising reducing component count by combining inductances or capacitances in the Wilkinson Combiner (22) with inductances or capacitances of one or more output phase shifting circuits (18, 20).
  18. 18. The method (100) of any of claims 12-17 further comprising substantially cancelling RF signal components reflected from a load into the output.
  19. 19. The method (100) of any of claims 12-18 wherein the two differential, quadrature RF signals are generated by two differential Power Amplifiers (PA1 , PA2), and further comprising: converting a single-ended RF input signal into two single-ended RF input signals in an input power combiner circuit (24) configured as a splitter; imparting a total of 90° of phase difference between the two single-ended RF input signals in at least one input phase shifting circuit (26, 28) connected to an output of the input power splitter circuit (24); and converting the two single-ended, quadrature RF signals into differential quadrature RF signals in two input impedance matching circuits (30, 32); and inputting the differential quadrature RF signals to the two differential Power Amplifiers (PA1 , PA2).
  20. 20. The method (100) of claim 19 wherein the two input impedance matching circuits (30, 32) comprise impedance matching transformers, each configured as a balun generating a differential output signal from a single-ended input signal.

Description

DIFFERENTIAL INPUT, SINGLE-ENDED OUTPUT QUADRATURE HYBRID COUPLER TECHNICAL FIELD The present disclosure relates generally to wireless communications, and in particular to a Quadrature Hybrid Coupler conjured to convert a differential Radio Frequency (RF) input to a single-ended RF output having substantially constant current under dynamically varying load impedance. BACKGROUND Wireless communication networks are ubiquitous in many parts of the world. These networks continue to grow in capacity and sophistication. To accommodate more users, different types of devices, and different use cases, the technical standards governing the operation of wireless communication networks continue to evolve. The fourth generation (4G) of network standards has been deployed, the fifth generation (5G) is in development and early deployment, and the sixth generation (6G) is in design. With each generation, technological advances improve the capacity and spectral efficiency of the wireless communication system. For example, 5G added new frequency bands, and applied beamforming. This trend is expected to continue in 6G by exploiting additional frequency bands, and applying more advanced beamforming. 5G added a second frequency range, FR2. This provided significant new available spectrum in the range 24.25-52.6 GHz. At these high frequencies, wavelengths are small. This is advantageous, as antenna elements are also small, allowing for antenna arrays with hundreds, or even thousands, of antenna elements. However, carriers at these high frequencies suffer higher path loss, and hence have limited range, compared to conventional wireless telecom operating frequencies. Beamforming is one technique featured in 5G and 6G, to improve both coverage and capacity. Beamforming refers to the use of antennas having increased and controllable directionality, whereby an RF transmission (or reception sensitivity) is narrow, and is “aimed” in a specific direction. This is enabled by transmitting or receiving signals with controlled relative phase and gain in the antenna elements (or subarrays of antenna elements). The relative phases of, e.g., transmit signals sent to each antenna element are controlled to create constructive or destructive interference, thus amplifying the signal in some directions, and attenuating it in others, and hence controlling the direction in which the beam is transmitted. Similar phase manipulation of signals from antenna elements (or subarrays) in a receive antenna can also result in beamforming the sensitivity of an antenna array in receiving signals. Also, multiple orthogonal beams can be formed and aimed in different directions, thus simultaneously addressing multiple wireless devices, also known as User Equipment (UE). To form robust beams, antenna elements are normally placed tightly together. For example, a distance of A/2 is commonly used (where A is the RF wavelength), to form arbitrary beams without folding. However, the tight antenna spacing causes high electromagnetic coupling between the antennas, and additionally signals leak in between the antennas. The beamsteering, combined with the antenna coupling, makes the impedance seen by each power amplifier (PA) driving the antenna elements (or subarrays) deviate from a designed impedance. The PA is designed assuming a nominal load impedance for optimal output power, linearity, and efficiency. The PA amplifies and delivers electrical power to the antenna element/subarray, which converts it to an electromagnetic signal. However, if the load impedance seen by the PA diverges from its designed (optimum) value, there is an impedance mismatch, which degrades PA performance. To direct a beam to a desired direction, a phase shift is required between signals sent to different antenna elements (or subarrays). The same signal, except for the phase shift, is present at all antenna elements, and electromagnetic energy of the signal leaks between them. This is seen by the PAs as a mismatch from an optimal (matched) impedance, which is not present when no phase shifts are introduced to steer the beam. The designed impedance seen by the PA is referred to as the impedance in the boresight direction (/.e., where the RF signal is radiated normal to the plane of the antenna element). When coupling is present between the antenna elements (due to spacing), and the same signal is sent on all antennas, but with different phases, this is experienced by the PA as load impedance variation and mismatch, even though it originates from antenna leakage and to the delay introduced by the phase shifter (/.e., the mismatch typically grows higher as the beam-angle increases, since the relative phase shift between antennas increases). Because the impedance mismatch causes a partial reflection of the RF signal from the antenna element (or subarray) back toward the PA, a standing wave is generated along the transmission line connecting the two. This is quantified in the art as an antenna impeda