### I. Introduction

### II. Proposed LMBA Design

*Z-*parameters of the 3 dB coupler and the current from each branch [13, 14]. As shown in Fig. 1, the equal amplitude quadrature current signals of the balanced pair can be represented as follows:

*bI*

_{1}and

*bI*

_{2}, where

*b*is the current drive levels at the balanced pair while

*I*

_{1}and

*I*

_{2}represent the currents in the balanced pair. The current drive level indicates the drain current normalized to the peak drain current and ranges between 0 and 1. At the same time, current from the control device can be represented as

*cI*

_{3}, with c as the current drive level for the two-stage control auxiliary device.

*Z*

*Ω load (e.g., 50 Ω), the voltage–current relationship through the isolation port can be represented as below:*

_{o}*Z*-parameters of the 3 dB coupler are as follows:

*S*-parameters are then converted to

*Z*-parameters while including the respective voltage and current relationships for all four ports. Using the above current relations, the impedances seen by the balanced pairs are as follows:

*k*is a real value representing the indirect current drive level for the amplifier in the second stage. As such

*b*and

*c*are the current drive levels on the balanced pair and the two-stage control auxiliary devices, respectively.

*I*

*represents the peak drain current of the balanced pair. Similar to the conditions applied in [3], the output power can be computed inclusive of the two-stage control amplifier.*

_{pk}*β*is the turn-on current drive level for the two-stage control auxiliary device. The two-stage control auxiliary devices are biased in Class C, where they are OFF when 0<

*b*<

*β*and ON when

*β*≤

*b*≤1. By applying the condition (6) on expression (5), the output power can be expressed as follows:

*k*= 1, then the output power beyond the drive level

*β*is evaluated as

*k*= 1 condition models a conventional LMBA with a single control device, the drive level is fixed and the evaluated OBO and IBO vary as in [3], resulting in the inherent nonlinear property of the LMBA architecture. Conversely, with a two-stage control auxiliary device, the drive level in the control side can be controlled and there is a chance to improve the IBO and OBO relationship of the LMBA as shown in Eq. (8). This is because the value of

*k*, which represents the indirect current drive level of the second stage active device in the two-stage control amplifier, can be controlled effectively to adjust the IBO and OBO variation inherent in the LMBA architecture.

*R*

*value helpful in configuring the output matching networks. The obtained load-pull data of the transistor model display an optimal resistance of 25 Ω while considering the intrinsic parasitic components of the device. Cree’s CGH40006P gallium nitride (GaN) high electron mobility transistor (HEMT) model is used to perform the load-pull simulations.*

_{opt}1)Determine the design frequency band and target power requirements.

2)Based on (1), identify the appropriate devices for the balanced amplifier pair.

3)From load-pull analysis, find the optimum load impedances considering the intrinsic parasitic elements.

4)Design a 90° coupler for the target design frequency and the uneven Wilkinson power splitter for the target power split ratio.

5)Select devices for the two-stage control signal power.

6)Locate the optimal load for the two-stage control and design the interstage matching network.

7)Design the output matching networks according to the evaluated optimal impedances.

### III. Implementation and Measurements

*S*-parameter measured data are compared against the simulated data in Fig. 7.