Communication System

TX/RX, Single Antenna (Circulator), Dual Stage Conversion

A full duplex communication transceiver architecture that uses a ferrite circulator to share a single antenna between the transmit and receive paths. Both TX and RX employ dual-stage frequency conversion for improved image rejection and selectivity.

Component Descriptions

Signal Chain Walkthrough

Antenna

A single antenna serves both transmit and receive functions. Typically a horn, parabolic reflector, or phased array element matched to the operating frequency band. The antenna connects to the circulator's common port.

Circulator (3-Port)

A ferrite circulator provides simultaneous TX/RX operation through a single antenna. Port 1 connects to the antenna, port 2 routes receive signals to the LNA, and port 3 accepts transmit signals from the PA. Typical isolation between TX and RX ports is 20-30 dB, with insertion loss of 0.3-0.8 dB.

LNA (Low Noise Amplifier)

The first active stage in the receive chain sets the system noise figure. A GaAs or InP pHEMT MMIC LNA provides 15-25 dB gain with noise figures of 0.5-3.0 dB depending on frequency. Placed immediately after the circulator to minimize front-end losses.

Bandpass Filter (BPF)

An RF bandpass filter after the LNA rejects out-of-band interference, image frequencies, and LO leakage. Waveguide or suspended stripline construction for low insertion loss at microwave frequencies.

Mixer 1 (1st Downconversion)

The first mixer translates the RF signal to the first intermediate frequency (IF1) by mixing with Local Oscillator 1 (LO1). Dual-stage conversion places IF1 at a frequency high enough to provide adequate image rejection without requiring extremely selective RF filtering.

IF Amplifier + Filter

Provides gain at the first IF frequency and additional channel selectivity. The IF filter defines the receiver's noise bandwidth and adjacent channel rejection.

Mixer 2 (2nd Downconversion)

The second mixer converts IF1 down to the final baseband or second IF frequency (IF2) using LO2. This second conversion stage enables fine frequency tuning and additional selectivity.

Transmit Path (PA, Driver, Upconverters)

The TX path mirrors the RX path in reverse: baseband input is upconverted in two stages using the same LO frequencies, filtered, amplified by a driver amplifier, and delivered to the PA (power amplifier). The PA output connects to the circulator's TX port for radiation through the shared antenna.