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Communication System

TX/RX, Single Antenna (SPDT), Single Stage Conversion

TX/RX SINGLE ANTENNA (SPDT) — SINGLE STAGE CONVERSION RECEIVE PATH ANTENNA SPDTSwitch RX LNALow Noise BPF MIXERDownconv LO IF AMP BASEBANDRX Output TRANSMIT PATH BASEBANDTX Input DRIVERAMP MIXERUpconv LO BPF PAPower Amp TX SINGLE CONVERSION: ONE MIXER STAGE PER PATH | SHARED LO BETWEEN TX AND RX
Component Descriptions

Signal Chain Walkthrough

The single-stage conversion architecture uses only one mixer in each direction, reducing complexity, cost, and DC power consumption compared to dual-stage designs.

Single Downconversion (RX)

The receive path uses a single mixer to translate the RF signal directly to the IF or baseband frequency. This is simpler but requires more selective RF filtering to reject image frequencies, since there is no second conversion stage to provide additional image rejection.

Shared Local Oscillator

A single LO source drives both the RX downconverter and TX upconverter. This ensures frequency coherence between transmit and receive, simplifying the frequency plan. The LO may be a synthesizer, PLL, or VCO depending on tuning requirements.

When to Use Single-Stage

Single-stage conversion is preferred when: the IF frequency is high enough for adequate image rejection with a single BPF; the system bandwidth is relatively narrow; power consumption must be minimized; or cost and complexity are primary constraints.

Typical Specifications

Component Specifications

ComponentParameterTypical Value
SPDT SwitchInsertion Loss0.5 - 1.5 dB
SPDT SwitchIsolation30 - 50 dB
LNANoise Figure0.5 - 3.0 dB
LNAGain15 - 25 dB
MixerConversion Loss5 - 8 dB
MixerLO Drive+7 to +13 dBm
PAOutput Power+20 to +37 dBm
Design Note: Single-stage conversion requires careful IF selection. The IF must be high enough that the image frequency falls outside the RF BPF passband. For example, with RF at 28 GHz and IF at 2 GHz, the image at 24 GHz must be rejected by the BPF. If the RF BPF cannot achieve sufficient image rejection, consider a dual-stage architecture instead.
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