In this paper, the impact of amplitude and phase imbalance on a proposed dual differential fed patch antenna is analyzed in the context of system effective reflection coefficient and axial ratio (AR). A single square patch with four ports is used as a solo radiating element and provides absolute symmetry at radiating. An in-depth analysis will be presented to understand the impact of external RF chain components on the performance of the proposed antenna. When fully differential excitations and perfect symmetry can be achieved, all six polarization states exhibit identical system effective reflection coefficients with close to ideal AR for CP. When phase imbalance and amplitude imbalance only exist in between the two differential pairs, the antenna system matching performance is found to be unchanged. In the presence of the feed network, circular polarization (CP) achieves a measured maximum AR of 0.49dB along the antenna pointing angle, while linear polarization (LP) has a measured maximum cross polarization of −30dB. This work monitors the beamwidth over which the AR can be kept below 1dB (BW-AR−1dB). Based on the optimization of phase imbalance, a novel BW-AR−1dB enhancement technique is introduced. Compared to the case with better AR at the main beam location, an improvement of 14. beamwidth is measured without significant degradation of AR. Isolation better than 40dB across an operating frequency of 9.27 – 9.4 GHz has been experimentally demonstrated for the proposed dual differential fed technique. The resulting antenna is compact and low profile which is an appealing candidate for phased array applications.

A monolithically integrated optical receiver in InP for 10 Gb/s intensity modulation direct detect (IMDD) application is presented. The sensitivity at the bit error rate (BER) 10-3 is measured to be -27.1 dBm. An integrated PIN diode photodetector (PD) minimizes the parasitics caused by wire bonds between the PD and the transimpedance amplifier (TIA). For the first time, electronics and photonics are monolithically integrated into a single InP IC. The avalanche photodetector (APD) is replaced with PIN PD, exhibiting comparable sensitivity and requiring a simple 3.3 V supply voltage. A single transistor voltage-to-current convertor between two cascaded TIAs performs automatic gain control (AGC). A total dynamic gain control of 9 dB has been demonstrated with a dynamic range of more than 17 dB, employing only four transistors and dissipating 8.5 mW. Improved gain peaking extends the operating bandwidth and makes it suitable for higher-speed applications. The power supply rejection ratio (PSRR) exceeds 24 dB without needing on-chip bandgap references.

In this paper, a method to reduce mutual coupling between an E-plane and H-plane coupled microstrip patch antenna is presented. Two dual differentially fed square patches are designed in a 1 × 2 antenna array configuration. To minimize mutual coupling and its effects, coupled split-ring resonators (SRRs) are designed, characterized and positioned between the patches. Circular SRRs are designed and coupled to produce a band-stop response to suppress surface waves propagating within the dielectric substrate while enhancing isolation. Mutual coupling interactions and the suppression mechanism are discussed in relation to the patches and SRRs. The patch radiators are dual differentially fed to achieve polarization diversity. E- and H-planes decoupling is achieved between the two patches throughout their bandwidth while maintaining good antenna performance. A prototype of the antenna array and the SRR is fabricated and measured to validate the decoupling approach. With a separation distance of 0.49$\lambda$ between the patches, the measured S-parameters show an impedance bandwidth of |S11|≤−10 dB, covering 9.27–9.46 GHz, and −38 dB and −35 dB mutual coupling for E- and H-planes, respectively, are observed throughout the antenna operating bandwidth.

A monolithically integrated InP optical receiver for applications in 25 Gb/s intensity modulation direct detection (IMDD) is presented. A feedforward voltage-to-current converter-based automatic gain control (AGC) is numerically analyzed for a peaking capability without any on-chip inductor. The novel analysis yields a unique dual-mode noise suppression strategy: the proposed transimpedance amplifier (TIA) front-end exhibits third-order roll-off for superior out-of-band noise suppression, while the purposely enlarged feedback resistor provides an optimal in-band noise suppression. Moreover, the proposed AGC can be adapted for higher speeds by simple parameter scaling. Benefiting from the classic current multiplier, a factor of 2 is simulated to achieve an extra current gain of 6 dB with minimal speed reduction and power consumption. Furthermore, an unconventional dummy TIA topology is derived from the current multiplier. Both the tracking and fixed biasing dummy TIAs, combined with the proposed TIA front-end, are implemented in a monolithically integrated 25 Gb/s optical receiver employing only NPN HBTs. The measured sensitivity for the complete receiver at a bit error rate (BER) $\rm 10^{-2}$ is −24 dBm ( $4.63~\mu $ A ${}_{pp}$ ), with an overload of −6 dBm ( $291.94~\mu $ A ${}_{pp}$ ).